INORGANIC-BLENDED P-TYPE SEMICONDUCTOR AND METHOD OF PREPARATION THEREOF

Abstract

Inorganic semiconductors typically have limited p-type behavior due to the scarcity of holes and the localized valence band maximum, hindering the progress of complementary devices and circuits. In this work, we propose an inorganic blending strategy to activate the hole-transporting character in an inorganic semiconductor compound, namely tellurium-selenium-oxygen (TeSeO). By rationally combining intrinsic p-type semimetal, semiconductor, and wide-bandgap semiconductor into a single compound, the TeSeO system displays tunable bandgaps ranging from 0.7 to 2.2 eV. Wafer-scale ultrathin TeSeO films, which can be deposited at room temperature, display high hole field-effect mobility of 48.5 cm.sup.2/(Vs) and robust hole transport properties, facilitated by TeTe (Se) portions and OTeO portions, respectively.

Claims

1. A semiconductor composition comprising tellurium, selenium, and oxygen, wherein the semiconductor composition is substantially free of Se.sup.4+.

2. The semiconductor composition of claim 1, wherein the semiconductor composition comprises Te.sup.0, Se.sup.0, and Te.sup.4+, wherein regions comprising Te.sup.0 and Se.sup.0 are substantially crystalline or polycrystalline and regions comprising Te.sup.4+ are substantially amorphous.

3. The semiconductor composition of claim 1, wherein the semiconductor composition has a hole mobility between 23.1-65.6 cm.sup.2/(Vs) at room temperature.

4. The semiconductor composition of claim 1, wherein the semiconductor composition has a bandgap of 0.7 eV to 2.2 eV.

5. The semiconductor composition of claim 1, wherein the semiconductor composition is Te.sub.(1-x)Se.sub.xO.sub.y, wherein 0.1x0.9 and 0.04y0.98.

6. The semiconductor composition of claim 1, wherein the semiconductor composition is Te.sub.(1-x)Se.sub.xO.sub.y, wherein 0.1x0.3 and 0.59y0.98.

7. The semiconductor composition of claim 1, wherein the semiconductor composition is Te.sub.(1-x)Se.sub.xO.sub.y, wherein 0.1x0.3 and y0.01=1.18-1.95x.

8. The semiconductor composition of claim 1, wherein the semiconductor composition is Te.sub.(1-x)Se.sub.xO.sub.y, wherein 0.1x0.9 and 0.04y0.98; and the semiconductor composition has a bandgap of 0.7 eV to 2.2 eV.

9. The semiconductor composition of claim 8, wherein the semiconductor composition has a hole mobility between 23.1-65.6 cm.sup.2/(Vs).

10. The semiconductor composition of claim 1, wherein the semiconductor composition is Te.sub.(1-x)Se.sub.xO.sub.y, wherein 0.1x0.3 and 0.59y0.98; and the semiconductor composition has a bandgap of 0.7 eV to 2.2 eV.

11. The semiconductor composition of claim 10, wherein the semiconductor composition has a hole mobility between 23.1-65.6 cm.sup.2/(Vs).

12. The semiconductor composition of claim 1, wherein the semiconductor composition is selected from the group consisting of Te.sub.0.7Se.sub.0.3O.sub.0.59, Te.sub.0.8Se.sub.0.2O.sub.0.80, and Te.sub.0.9Se.sub.0.1O.sub.0.98.

13. A method for preparing the semiconductor composition of claim 1, the method comprising: combining tellurium (Te) powder and selenium (Se) powder thereby forming a TeSe mixture; depositing the TeSe mixture on a surface of a substrate by physical vapor deposition thereby forming a TeSe film; and contacting the TeSe film with oxygen plasma thereby forming the semiconductor composition.

14. The method of claim 13, wherein the Te powder and the Se powder are combined in a molar ratio of 1:9 to 9:1, respectively.

15. The method of claim 13, wherein the Te powder and the Se powder are combined in a molar ratio of 7:3 to 9:1, respectively.

16. The method of claim 13, wherein the oxygen plasma is generated at a power of 30-100 W under a pressure of 0.1-10 Torr.

17. A semiconductor device comprising the semiconductor composition of claim 1, wherein the semiconductor device is selected from the group consisting of a thin-film transistor, a photodetector, and a solar cell.

18. The semiconductor device of claim 17, wherein the semiconductor device is a thin-film transistor having a hole mobility between 23.1-65.6 cm.sup.2/(Vs) or a photodetector having a response speed of about 5 s.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and other objects and features of the present disclosure will become apparent from the following description of the disclosure, when taken in conjunction with the accompanying drawings.

[0029] FIG. 1. TeSeO synthesis and microstructure characterization. (a) Schematic of p-type TeSeO semiconducting system containing group 16 elements. (b) grazing incidence X-ray diffraction (GIXRD) patterns and (c) atomic force microscopy (AFM) images of TeSeO thin films with different compositions. Insets of (b) display the corresponding sample photographs. Inset of (c) shows the corresponding roughness values of TeSeO thin films based on root-mean-square deviation (R.sub.q) and arithmetic-mean deviation (R.sub.a). (d) Cross-sectional high-resolution transmission electron microscopy (HRTEM) image of Te.sub.0.7Se.sub.0.3O.sub.0.59 thin film. (e) Selected area electron diffraction (SAED) patterns of TeO.sub.1.16, Te.sub.0.7Se.sub.0.3O.sub.0.59, and Te.sub.0.5Se.sub.0.5O.sub.0.32 thin films.

[0030] FIG. 2. Chemical bonding and band structure of TeSeO. X-ray photoelectron spectroscopy (XPS) (a) Te 3d, (b) O 1s, and (c) Se 3d analysis of TeSeO thin films with different compositions. (d) Absorption spectra of the prepared films with different compositions. Ultraviolet photoelectron spectroscopy (UPS) spectra of TeSeO thin films at (e) secondary electron cut-off regions and (f) valence-band regions. (g) Energy band diagram of the TeSeO thin films with changing compositions.

[0031] FIG. 3. Transport properties and electrical robustness of TeSeO. Output curves of (a) Te.sub.0.7Se.sub.0.3O.sub.0.59, (b) Te.sub.0.8Se.sub.0.2O.sub.0.8, and (c) Te.sub.0.9Se.sub.0.1O.sub.0.98 TFTs. Inset of (a) shows the optical image of the device. Transfer curves and hole mobilities of (d) Te.sub.0.7Se.sub.0.3O.sub.0.59, (e) Te.sub.0.8Se.sub.0.2O.sub.0.8, and (f) Te.sub.0.9Se.sub.0.1O.sub.0.98 TFTs. (g) On/off switching measurements of Te.sub.0.8Se.sub.0.2O.sub.x and Te.sub.0.8Se.sub.0.2 TFTs and representative on/off switching cycles.

[0032] FIG. 4. Nanopatterned TeSeO and broadband photodetection. (a) SEM images of the nanosphere lithography process consisting of nanosphere assembly, size reduction, TeSeO deposition, and nanosphere lift-off. (b-f) Broadband UV-vis-SWIR operation of flexible nanopatterned TeSeO photodetectors with a chopped frequency of 0.2 Hz. (g) Optical responsivity of TeSeO with different compositions under various incident light wavelengths.

[0033] FIG. 5. Mechanical analysis of honeycomb TeSeO optoelectronics. (a) finite element analysis (FEA) simulation of the TeSeO layer/PI substrate model at a bending radius of 1.5 mm. (b) Top views of strain distribution on the bent TeSeO honeycomb layer and (c) representative area. (d) The device photocurrent under on/off switching light illumination (0.2 Hz) as a function of bending cycles. (e) Time-resolved photoresponse of Te.sub.0.7Se.sub.0.3O.sub.0.59 PDs measured at 1550 nm illumination with a chopped frequency of 10 kHz. Comparison of (f) photoresponse speed and (g) hole mobility of metal oxides, metal halides, perovskite halides, organic materials, TeSeO, etc.

[0034] FIG. 6. GIXRD patterns of TeSeO thin films with different compositions and XRD pattern of the -TeO.sub.2 powder. All the diffraction peaks agree with the typical hexagonal crystal system with P3.sub.121 [152] space group composed of chalcogen chains along the c axis. The diffraction peak positions shift slightly to higher angles with increasing Se content, indicating the decrease of the lattice constant. This finding could result from the Se substitution in Te sites, in which the Se atom has a relatively smaller radius of 0.14 nm than that of the Te atom (0.16 nm). At the same time, the increased full width at half-maximum of the diffraction peaks also reveals the suppressed material crystallinity.

[0035] FIG. 7. (a) Raman studies of TeSeO thin films with different compositions, where three first-order Raman active modes located at 90 cm.sup.1 (E.sub.1 transverse (TO) phonon mode), 118 cm.sup.1 (A.sub.1 mode), and 138 cm.sup.1 (E.sub.2 mode) were identified. (b) Schematic vibration patterns of the Raman modes of E.sub.1, A.sub.1, and E.sub.2 in chiral-chain Te or Se materials. The E.sub.1 and E.sub.2 modes represent bond-bending and bond-stretching with a larger admixture, respectively, whereas the A.sub.1 mode is caused by chain expansion in the basal plane.

[0036] FIG. 8. (a) Cross-sectional high-angle annular dark-field scanning transmission electron microscopy (STEM-HAADF) image and (b) energy-dispersive X-ray spectroscopy (EDS) mapping of the TeSeO film. The distributions of Te, Se, and O signals are relatively uniform without noticeable element segregation.

[0037] FIG. 9. XPS (a) Te 3d, (b) O 1s, and (c) Se 3d analysis of ten different positions of TeSeO thin films grown on a 4-inch SiO.sub.2/Si wafer.

[0038] FIG. 10. XPS Te 3d analysis of (a) TeO.sub.1.16, (b) Te.sub.0.7Se.sub.0.3O.sub.0.59, (c) Te.sub.0.5Se.sub.0.5O.sub.0.32, and (d) Te.sub.0.3Se.sub.0.7O.sub.0.15 thin films. (e) XPS Te 3d.sub.5/2 peak analysis of TeSeO thin films with different compositions. (f) Extracted Te.sup.4+/(Te.sup.0+Te.sup.4+) ratios of TeSeO thin films. The coexisted Te.sup.4+ and Te.sup.0 peaks are clearly distinguished at 572.8 eV and 576.0 eV, respectively, which means the partial oxidation of Te. With increasing Se content, the corresponding Te.sup.4+/(Te.sup.0+Te.sup.4+) ratios decrease from 58% (TeO.sub.1.16) to 25% (Te.sub.0.3Se.sub.0.7O.sub.0.59), revealing that the Se content can suppress the binding process between Te and O.

[0039] FIG. 11. XPS (a) Se 3d and (b) O 1s peak analysis of TeSeO thin films with different compositions. The distinct peaks observed around 530.2 eV in the O 1s spectra imply the O acts as lattice oxygen species OTeO. Generally, the adsorbed oxygen or hydroxyl group has higher binding energy, around 532 eV, which is not witnessed in our TeSeO films. At the same time, no Se.sup.4+ (typically around 60 eV) peak is found from Se 3d spectra, mainly owing to its larger electronegativity (2.55) than that of Te (2.1), which makes it difficult to react with oxygen molecules to form SeO.sub.2.

[0040] FIG. 12. Transfer characteristics of wafer-scale Te.sub.0.8Se.sub.0.2O.sub.0.8 TFT array (1010 array) using (a) linear y-coordinate and (b) logarithm y-coordinate. The corresponding performance distribution of (c) mobility and (d) V.sub.TH for wafer-scale Te.sub.0.8Se.sub.0.2O.sub.0.8 TFT array. The TFT array shows 100% device yield with hole mobility of 48.28.4 cm.sup.2/(Vs), I.sub.on/I.sub.off of 10.sup.410.sup.5, and V.sub.TH of 4.21.3 V.

[0041] FIG. 13. (a) Negative-bias stress (NBS) test of Te.sub.0.8Se.sub.0.2O.sub.0.8 TFT. Extracted (b) threshold voltages and (c) on currents of Te.sub.0.8Se.sub.0.2O.sub.0.8 TFT in NBS study. After being gated at 20 V for 2 hours, the corresponding V.sub.TH shifted negatively from 5 to 8.8 V without noticeable subthreshold swing variation under NBS.

[0042] FIG. 14. (a) Transfer curve and (b) output curve of Te.sub.0.8Se.sub.0.2O.sub.0.8 TFT measured after fabrication. (c) Transfer curve and (d) output curve of Te.sub.0.8Se.sub.0.2O.sub.0.8 TFT measured after 300-day storage in ambient. After 300 days of ambient storage, the FET performances are not significantly degraded even without device encapsulation, benefiting from the partial oxidation in TeSeO thin films.

[0043] FIG. 15. (a) SEM images of the nanosphere lithography process that consists of (a) nanosphere assembling, (b) size reduction, (c) TeSeO deposition, and nanosphere lift-off.

[0044] FIG. 16. (a) FEA simulation of the TeSeO layer/PI substrate model at a bending radius of 1.5 mm. (b) Top view of strain distribution on the bent TeSeO flat film. (c) Top view of strain distribution on the bent TeSeO honeycomb layer.

[0045] FIG. 17. The Te.sub.0.7Se.sub.0.3O.sub.0.59 thin film (without nanopatterned) device photocurrent under on/off switching light illumination (0.2 Hz) measured before bending tests, after 2000, 4000, and 6000 bending cycles, respectively.

[0046] FIG. 18. Time-resolved photoresponse of Te.sub.0.7Se.sub.0.3O.sub.0.59 honeycomb layer measured at 1550 nm illumination with a chopped frequency of 10 KHz.

[0047] FIG. 19. Summary of composition ratios of TeSeO films and mole ratios between Te.sup.0 and Te.sup.4+.

[0048] FIG. 20. Summary of the Hall mobilities and hole concentrations of TeSeO thin films.

[0049] FIG. 21. Performance summary of TFTs based on p-type semiconducting thin films, including metal oxides, metal halides, perovskites, organic materials, CNT thin films, and TeSeO.

[0050] FIG. 22. Performance summary of PDs based on Te, perovskite halides, metal oxides, Group III-Vs, layered materials, and TeSeO.

DETAILED DESCRIPTION

Definitions

[0051] The following terms shall be used to describe the present invention. In the absence of a specific definition set forth herein, the terms used to describe the present invention shall be given their common meaning as understood by those of ordinary skill in the art.

[0052] Throughout the present disclosure, unless the context requires otherwise, the word comprise or variations such as comprises or comprising, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. It is also noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as comprises, comprised, comprising and the like can have the meaning attributed to it in U.S. Patent law; e.g., they can mean includes, included, including, and the like; and that terms such as consisting essentially of and consists essentially of have the meaning ascribed to them in U.S. Patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the present invention.

[0053] Furthermore, throughout the present disclosure and claims, unless the context requires otherwise, the word include or variations such as includes or including, will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0054] The use of the singular herein includes the plural (and vice versa) unless specifically stated otherwise. In addition, where the use of the term about is before a quantitative value, the present teachings also include the specific quantitative value itself, unless specifically stated otherwise. As used herein, the term about refers to a 10%, 7%, 5%, 3%, 1%, or 0% variation from the nominal value unless otherwise indicated or inferred.

[0055] As used herein, the term substantially free means the indicated compound, material, component, etc., is minimally present or not present at all, e.g., at a level of about 5% by weight or less, 1% by weight or less, 4% by weight or less, 3% by weight or less, 2% by weight or less, 1% by weight or less, 0.75% by weight or less, 0.50% by weight or less, 0.25% by weight or less, 0.2% by weight or less, 0.15% by weight or less, 0.10% by weight or less, or 0.05% by weight or less, or 0.01% by weight or less, or 0.001% by weight or less, or not present, unless otherwise specified.

[0056] As used herein, the term crystalline indicates that the material has a regular ordered internal structure at the molecular level when in the solid phase, and the crystalline material gives a distinctive X-ray diffraction partem with defined peaks.

[0057] As used herein, the term polycrystalline refers to a compound, material, component, etc. comprising a plurality of crystallites (grains) that are bonded directly together by interparticle bonds. The size of the grains may be on the nanoscale, microscale, millimeter scale or vary from nanometers to millimeters, nanometers to micrometers, or micrometers to millimeters. The crystal structures of the individual grains may be randomly oriented in space within the polycrystalline material.

[0058] As used herein, the term substantially polycrystalline refers to a material in which greater than 70%; or greater than 75%; or greater than 80%; or greater than 85%; or greater than 90%; or greater than 95%, or greater than 99% of the material is polycrystalline. Substantially crystalline can also refer to material that has no more than about 10% amorphous, or no more than about 10% amorphous, or no more than about 5% amorphous, or no more than about 2% amorphous.

[0059] As used herein, the term substantially amorphous refers to a material in which greater than 70%; or greater than 75%; or greater than 80%; or greater than 85%; or greater than 90%; or greater than 95%, or greater than 99% of the material is amorphous. Substantially amorphous can also refer to a material that has no more than about 20% crystallinity, or no more than about 10% crystallinity, or no more than about 5% crystallinity, or no more than about 2% crystallinity.

[0060] Provided herein is a semiconductor composition comprising tellurium, selenium, and oxygen. The semiconductor composition can comprise Te.sup.0, Se.sup.0, and Te.sup.4+, e.g., in the form of TeO.sub.2.

[0061] In certain embodiments, the semiconductor composition is substantially free of Se.sup.4+ (e.g., in the form of SeO.sub.2). In certain embodiments, the semiconductor composition comprises less than 1% by weight Se.sup.4+, less than 0.75% by weight Se.sup.4+, less than 0.5% by weight Se.sup.4+, less than 0.25% by weight Se.sup.4+, less than 0.2% by weight Se.sup.4+, less than 0.1% by weight Se.sup.4+, less than 0.05% by weight Se.sup.4+, less than 0.01% by weight Se.sup.4+, or no Se.sup.4+. In certain embodiments, Se.sup.4+ cannot be detected by XPS.

[0062] Regions of the semiconductor composition comprising Te.sup.0 and/or Se.sup.0 may have a predominately crystalline structure. However, it is not a requirement that the entire semiconductor composition region comprising Te.sup.0 and/or Se.sup.0 be uniformly crystalline or polycrystalline. In certain embodiments, regions of the semiconductor composition comprising Te.sup.0 and/or Se.sup.0 may be polycrystalline where crystalline regions are interrupted by grain boundaries. The grain boundaries may have a random and/or textured orientation. The crystalline regions comprising Te.sup.0 and/or Se.sup.0 may account for greater than 90% by volume of the semiconductor composition regions comprising Te.sup.0 and/or Se.sup.0, in certain embodiments. In other embodiments, the crystalline regions comprising Te.sup.0 and/or Se.sup.0 may account for greater than 92%, 95%, 97%, 98%, 99%, or 99.9% of the volume of the regions of the semiconductor composition comprising Te.sup.0 and/or Se.sup.0. In certain embodiments, the crystalline regions comprising Te.sup.0 and/or Se.sup.0 may account for a volume of the regions of the semiconductor composition comprising Te.sup.0 and/or Se.sup.0 in the range of 70% to 100%, 80% to 100%, 90% to 100%, 95% to 100%, 96% to 100%, 97% to 100%, 98% to 100%, 99% to 100%, 99.9 to 100%, or any value or range of values within those ranges.

[0063] Regions of the semiconductor composition comprising Te.sup.4+ may have a predominately amorphous structure. The amorphous regions comprising Te.sup.4+ may account for greater than 90% by volume of the semiconductor composition regions comprising Te.sup.4+, in certain embodiments. In other embodiments, the amorphous regions comprising Te.sup.4+ may account for greater than 92%, 95%, 97%, 98%, 99%, or 99.9% of the volume of the regions of the semiconductor composition comprising Te.sup.4+. In certain embodiments, the amorphous regions comprising Te.sup.4+ may account for a volume of the regions of the semiconductor composition comprising Te.sup.4+ in the range of 70% to 100%, 80% to 100%, 90% to 100%, 95% to 100%, 96% to 100%, 97% to 100%, 98% to 100%, 99% to 100%, 99.9 to 100%, or any value or range of values within those ranges.

[0064] The semiconductor composition can comprise Se and Te in a molar ratio of 3:7 or less, 1:3 or less, 1:4 or less, 3:17 or less, 1:9 or less, 9:91 or less, 8:92 or less, 7:93 or less, 6:94 or less, 5:95 or less, 4:96 or less, 3:97 or less, 2:98 or less, 1:99 or less, respectively. In certain embodiments, the semiconductor composition comprises Se and Te in a molar ratio of 5:95 to 3:7, 1:9 to 3:7, 5:95 to 3:7, 3:17 to 3:7, 1:4 to 3:7, or 1:3 to 3:7, respectively.

[0065] In certain embodiments, the semiconductor composition can be represented by the chemical formula: Te.sub.(1-x)Se.sub.xO.sub.y, wherein x is 0.1x0.9 and y is 0.04y0.98. In certain embodiments, x is 0.1x0.8 and y is 0.09y0.98, 0.1x0.7 and y is 0.15y0.98, 0.1x0.6 and y is 0.23y0.98, 0.1x0.5 and y is 0.32y0.98, 0.1x0.3 and y is 0.44y0.98, 0.1x0.3 and y is 0.59y0.98, or 0.1x0.2 and y is 0.80y0.98. In certain embodiments, the semiconductor composition is represented by the chemical formula: Te.sub.(1-x)Se.sub.xO.sub.y, wherein x is 0.1x0.3 and y0.01, 0.05, or 0 is 1.18-1.95x. In certain embodiments, the semiconductor composition is represented by the chemical formula: Te.sub.0.7Se.sub.0.3O.sub.0.59, Te.sub.0.8Se.sub.0.2O.sub.0.80, or Te.sub.0.9Se.sub.0.1O.sub.0.98.

[0066] Advantageously, the hole mobility and band gap of the semiconductor composition can be modified by adjusting the chemical composition of the semiconductor composition described herein.

[0067] In certain embodiments, the semiconductor composition has a bandgap of 0.7 eV to 2.2 eV, 0.9 eV to 2.2 eV, 1.0 eV to 2.2 eV, 1.1 eV to 2.2 eV, 1.3 eV to 2.2 eV, 1.4 eV to 2.2 eV, 1.5 eV to 2.2 eV, 1.6 eV to 2.2 eV, 1.7 eV to 2.2 eV, 1.8 eV to 2.2 eV, 1.9 eV to 2.2 eV, 2.0 eV to 2.2 eV, 2.1 eV to 2.2 eV, 0.7 eV to 2.1 eV, 0.7 eV to 2.0 eV, 0.7 eV to 1.9 eV, 0.7 eV to 1.8 eV, 0.7 eV to 1.7 eV, 0.7 eV to 1.6 eV, 0.7 eV to 1.5 eV, 0.7 eV to 1.4 eV, 0.7 eV to 1.3 eV, 0.7 eV to 1.2 eV, 0.7 eV to 1.1 eV, 0.7 eV to 1.0 eV, 0.7 eV to 0.9 eV, or 0.7 eV to 0.8 eV.

[0068] In certain embodiments, the semiconductor composition has a hole mobility at room temperature between 23.1-65.6 cm.sup.2/(Vs), 48.5-65.6 cm.sup.2/(Vs), 23.1-48.5 cm.sup.2/(Vs), 25-60 cm.sup.2/(Vs), 30-55 cm.sup.2/(Vs), 35-50 cm.sup.2/(Vs), 40-45 cm.sup.2/(Vs), 25-55 cm.sup.2/(Vs), 25-50 cm.sup.2/(Vs), 25-45 cm.sup.2/(Vs), 25-40 cm.sup.2/(Vs), 25-35 cm.sup.2/(Vs), 25-30 cm.sup.2/(Vs), 30-60 cm.sup.2/(Vs), 35-60 cm.sup.2/(Vs), 40-60 cm.sup.2/(Vs), 45-60 cm.sup.2/(Vs), 50-60 cm.sup.2/(Vs), or 55-60 cm.sup.2/(Vs).

[0069] The semiconductor composition described herein can be readily prepared from readily available by persons of ordinary skill in the art using starting materials. In certain embodiments, the semiconductor composition described herein is prepared according a method comprising: combining tellurium (Te) powder and selenium (Se) powder thereby forming a TeSe mixture; depositing the TeSe mixture on a surface of a substrate by physical vapor deposition thereby forming a TeSe film; and contacting the TeSe film with oxygen plasma thereby forming the semiconductor composition.

[0070] The particle size of the Te powder and Se powder is not particularly limited. In certain embodiments, each of the Te powder and Se powder is Mesh 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, or 300. The Te powder and Se powder can be purchased directly or can optionally be prepared from Te powder and Se powder having a larger size. There are various known methods for controlling the particle size of substances, including reduction by comminution or de-agglomeration by milling and/or sieving. Exemplary methods for particle reduction include, but are not limited to jet milling, hammer milling, compression milling and tumble milling processes (e.g., ball milling).

[0071] The Se powder and Te powder can be combined in a molar ratio of 3:7 or less, 1:3 or less, 1:4 or less, 3:17 or less, 1:9 or less, 9:91 or less, 8:92 or less, 7:93 or less, 6:94 or less, 5:95 or less, 4:96 or less, 3:97 or less, 2:98 or less, 1:99 or less, respectively. In certain embodiments, Se powder and Te powder are combined in a molar ratio between 5:95 to 3:7, 1:9 to 3:7, 5:95 to 3:7, 3:17 to 3:7, 1:4 to 3:7, or 1:3 to 3:7, respectively.

[0072] The substrate is not particularly limited, and all substrates are contemplated by the present disclosure. In certain embodiments, the substrate is a metal or metal alloy, such as gold, copper, platinum; a polymer, such as polyimide or a photoresist; a ceramic, such as alumina or zirconia; silicon, geranium, or SiO.sub.2.

[0073] Physical vapor deposition of the TeSe mixture on the substrate can be conducted using thermal evaporation at a chamber pressure below 410.sup.6 Torr at room temperature.

[0074] The approporate oxygen plasma treatment conditions can be readily selected by a person of ordinary skill in the art based on the chemical composition of the starting material and the desired amount of oxygen implanation in the desired semicondutor composition. In certain embodiments, oxygen plasma is generated at a power of 10-100 W, 20-100 W, 30-100 W, 40-100 W, 50-100 W, 60-100 W, 70-100 W, 80-100 W, 90-100 W, 10-90 W, 10-80 W, 10-70 W, 10-60 W, 10-50 W, 10-40 W, 20-40 W, or 25-35 W under a pressure of 0.1-10 Torr, 0.1-9 Torr, 0.1-8 Torr, 0.1-7 Torr, 0.1-6 Torr, 0.1-5 Torr, 0.1-4 Torr, 0.1-3 Torr, 0.1-2 Torr, 0.1-1 Torr, 0.1-0.9 Torr, 0.1-0.8 Torr, 0.1-0.7 Torr, 0.1-0.6 Torr, 0.1-0.5 Torr, or 0.2-0.4 Torr. In certain embodiments, oxygen plasma is generated at a power of about 30 W and a pressure of about 0.26 Torr. Oxygen plasma treatment can be conducted until the desired amount of oxygen implamanetion is acehived. In certain embodiments, oxygen plasma treatment is conducted for about 60 seconds.

[0075] The present disclosure also provides a semiconductor device comprising the semiconductor material described herein. Exemplary semiconductor devices include, but are not limited, to a thin-film transistor, a photodetector, a solar cell, and other optoelectronic devices. In certain embodiments, the semiconductor device is a thin-film transistor having a hole mobility between 23.1-65.6 cm.sup.2/(Vs) or a photodetector having a response speed of about 5 s.

TeSeO Synthesis and Microstructure Characterization

[0076] To satisfy the scalable processing, in this work, TeSeO thin films were produced by room-temperature physical vapor deposition (PVD) combined with post-oxygen implantation. The crystal structures of TeSeO thin films were characterized by a GIXRD. As shown in FIG. 1b, the TeSeO samples with relatively high Te content (Te:Se7:3) show a polycrystalline nature, while the Se-rich samples (Te:Se6:4) are found to be amorphous. The diffraction peaks located at 23.1, 27.6, 40.5, and 49.7 agree well with those of (100), (101), (110), and (201)

[0077] planes, respectively, of hexagonal system with P3.sub.121 space group that is composed of chalcogen chains along the c axis. All the diffraction peak positions slightly shift to higher angles with increasing Se content (FIG. 6), indicating the decrease of the lattice constant. At the same time, the increased full width at half-maximum of the diffraction peaks also reveals the suppressed material crystallinity. As strong glass former, the further addition of Se contents (Te:Se6:4) completely disturbs the crystallization process of TeSeO, leading to the polycrystalline-to-amorphous phase transition. Remarkably, with the vigorous compositional changing of TeSeO thin films, the samples undergo significant color changes from metallic luster for TeO.sub.1.16 to dark red for Se-rich samples, as the photographs depicted in the insets of FIG. 1b.

[0078] The Raman spectroscopy presented in FIG. 7 identified three first-order Raman active Te/Se helical chain modes, including E.sub.1 transverse (TO) phonon mode, A.sub.1 mode, and E.sub.2 mode. Also, Se substituted for Te gives rise to an increase in the stretching frequency and the broadening of Raman bands. The undiscovered O-related Raman vibrations suggest the disordered nature of corresponding oxides that cannot efficiently enable the inelastic scattering of photons. To directly check the elemental distribution, a combination of EDS mapping and XPS were conducted on TeSeO thin films (FIGS. 8 and 9), where the uniform elemental distributions of Te, Se, and O are observed across the probed region. Moreover, the surface morphologies of TeSeO thin films with different composition ratios were examined by atomic force microscopy (AFM) with a scanning area of 1010 m (FIG. 1c). All the TeSeO thin films are smooth, uniform, and crack-free, which is crucial for practical devices. The extracted arithmetic mean deviation of roughness decreases from 1.8 nm to 0.3 nm with increasing Se content (inset of FIG. 1c), mainly due to the decreasing grain sizes.

[0079] The microscopic structures of the TeSeO thin films were further analyzed by cross-sectional high-resolution transmission electron microscopy (HRTEM), as depicted in FIG. 1d. The HRTEM image shows clear lattice fringes with lattice spacings of 3.2 and 2.2 for Te.sub.0.7Se.sub.0.3O.sub.0.59, which corresponds to the (1011) and (1120) crystalline planes of hexagonal Te/Se, respectively. The corresponding selected-area electron diffraction (SAED) pattern of Te.sub.0.7Se.sub.0.3O.sub.0.59 shows a few diffraction spots (FIG. 1e), further indicating its polycrystalline structure. The observed characteristic diffuse halo, particularly evident in Te.sub.0.5Se.sub.0.5O.sub.0.32, indicates that the addition of Se induces a polycrystalline-to-amorphous phase transition in TeSeO. Overall, no O-related phase diffraction pattern was detected in the SAED study, suggesting an amorphous state of oxides in TeSeO. The above microstructure analysis agrees well with that from XRD and Raman studies.

Chemical Bonding and Band Structure of TeSeO

[0080] To obtain the details of chemical bonding and atomic coordination in TeSeO thin films, core energy level spectra of Te 3d, O 1s, and Se 3d were studied using XPS (FIGS. 2a to 2c). All three XPS core energy levels of TeSeO exhibit redshifts of up to 800 meV with increasing Se content, resulting from the electron injection process. In detail, the Te.sup.4+ and Te.sup.0 peaks coexist in the Te 3d spectra of TeSeO thin films (FIG. 2a), which means the partial oxidation of Te. The corresponding Te.sup.4+/(Te.sup.0++Te.sup.4+) ratios decrease from 58% (TeO.sub.1.16) to 25% (Te.sub.0.3Se.sub.0.7O.sub.0.15) with increasing Se content (FIG. 10 and FIG. 18), revealing that the Se content could suppress the binding process between Te and O. At the same time, no Se.sup.4+. (typically around 60 eV) peak is found from Se 3d spectra in FIG. 2c, mainly owing to its larger electronegativity (2.55) than that of Te (2.1), which make it difficult to react with oxygen molecules to form SeO.sub.2. The distinct peaks observed around 530.2 eV in the O 1s spectra imply the O only acts as lattice oxygen species of OTeO (FIG. 2b and FIG. 11). Generally, the adsorbed oxygen or hydroxyl group has higher binding energy around 532 eV, which is not witnessed in our TeSeO films. The gathered information on chemical bonding in inorganic-blended TeSeO, including TeTe, TeSe, and OTeO, is summarized in Table 1. Overall, the Se-regulating Te oxidation provides a window to change the material compositions among TeO.sub.2 (p-type wide-bandgap semiconductor), Te.sub.xSe.sub.y (p-type semiconductor), and Te (p-type semimetal), and thus modify their corresponding physical/chemical properties in a wide range.

TABLE-US-00001 TABLE 1 The chemical bonding information of inorganic-blended TeSeO Bond Type Bandgap Character Function TeTe Covalent 0.31 eV p-type High hole semimetal mobility TeSe Covalent 0.31~1.87 eV p-type Bandgap semiconductor modulation OTeO Polar 3.7 eV p-type wide- Stability covalent bandgap enhancement semiconductor

[0081] In general, continuously tuning bandgaps and band-edge energies in conventional p-type semiconductors is difficult. Apart from the low formation energy of the electron donor, incorporating foreign atoms could inevitably perturb the host lattice thermodynamic equilibrium, possibly counteracting the p-doping effect. These factors restrict the tuning feasibility on hole density and mobility of conventional p-type thin films. This work applies an inorganic blending strategy on the p-type TeSeO system, which combines intrinsic p-type semimetal, semiconductor, and wide-bandgap semiconductor in a single compound. As a result, the p-type TeSeO could be manufactured into scalable thin-film form with reliable and tunable material properties. As presented in FIG. 2d, the optical bandgaps of TeSeO thin films were extracted from the absorption spectra by using the Tauc plot method. With increasing Se content, the energy bandgaps of TeSeO were broadening, with corresponding bandgap values monotonically shifting from 0.7 eV to 2.2 eV. The continuously tunable bandgaps achieved from TeSeO thin films cover ultraviolet (UV), visible, and short-wave infrared (SWIR) regions, revealing potentials in high-mobility p-channel transistors, solar cells, wideband photodetectors, etc.

[0082] The quantitatively predictable and available band structures of the TeSeO system are the prerequisite for device-level engineering. To this aim, the electronic structure variations of TeSeO thin films were identified by UPS. The positions of Fermi energy levels and VBM levels could be extracted from the secondary electron cut-off region (FIG. 2e) and valence-band region (FIG. 2f), respectively. Besides, the conduction band minimum (CBM) was calculated by subtracting the bandgap of each sample from its VBM. The corresponding energy band diagrams of TeSeO samples are presented in FIG. 2g. Obviously, for all TeSeO samples, their Fermi energy levels are always underlying the mid-point of bandgaps and relatively close to the valance band, which means that the inorganic-blended TeSeO system keeps p-type electrical properties. It is also found that the energy level of the VBM shifts faster with compositions than that of CBM. Fitting these results to the modified Vegard's law, the energy changes of VBM energies are nearly linear with the composition, while the CBM energies change with a strong bowing of 1 eV. This result could be explained by the synergistic effect of Se substitution and partly oxidation in Te.

Transport Properties and Electrical Robustness of TeSeO

[0083] To investigate the hole transport properties of TeSeO thin films, a series of bottom-gate top-contact (BGTC) thin-film transistors (TFTs) are constructed on SiO.sub.2/p.sup.+-Si wafers with Ni as source/drain electrodes. To guarantee low gate leakage currents and reliable parameter extraction, both channel layers and electrodes are patterned (inset in FIG. 3a). The channel thickness of 10 nm, which is verified by cross-sectional STEM, is used to balance the conductivity and the on/off current ratio. As the corresponding electrical characteristics of Te.sub.0.7Se.sub.0.3O.sub.0.59, Te.sub.0.8Se.sub.0.2O.sub.0.8, and Te.sub.0.9Se.sub.0.1O.sub.0.98 are shown in FIG. 3, typical p-channel transistor behaviors were observed for those devices, agreeing well with their energy band structures. The Se-poor Te.sub.0.9Se.sub.0.1O.sub.0.98 TFT exhibited high conductance and always-on transistor operation, which reflected high hole concentration in the channel layer that could not be completely depleted. The Se alloying reduced the current level and mobility in slope and shifted threshold voltage (ITH) in the negative direction (FIGS. 3d to 3f). Meanwhile, the Hall effect measurements of TeSeO films show a similar trend to the electrical properties observed in the TFTs study (FIG. 17).

[0084] Notably, among all the samples, the Te.sub.0.8Se.sub.0.2O.sub.0.8 TFT showed well-optimized electrical performance (FIG. 3e), including a high hole field-effect mobility (.sub.FE) of 48.5 cm.sup.2/(Vs) while maintaining a high I.sub.on/I.sub.off ratio of 10.sup.5. As summarized in FIG. 20, such .sub.FE and I.sub.on/I.sub.off surpass most previously reported conventional scalable p-channel TFTs, including metal oxides, metal halides, perovskite halides, and organic materials. Besides, the negligible counterclockwise hysteresis indicates the small amounts of electrical traps within TeSeO or at the interface between channel and dielectric layers. To study the scalability and uniformity of TeSeO TFTs, wafer-scale TFT arrays (1010 array) are fabricated, and their statistical distribution of device performance is displayed in FIG. 12. The TFT array shows 100% device yield with a hole mobility of 48.28.4 cm.sup.2/(Vs), I.sub.on/I.sub.off of 10.sup.410.sup.5, and V.sub.TH of 4.21.3 V. Such highly uniform electrical performance on the wafer scale is of high significance in the scalable applications of p-type thin-film semiconductors.

[0085] After successfully investigating the intrinsic transport properties of TeSeO thin films, the operational stability in ambient was also checked. As shown in FIG. 3g, with 10,000 times on/off switching, the Te.sub.0.8Se.sub.0.2O.sub.0.8 device maintains its output current and good current modulation ability. Meanwhile, a control experiment was also carried out on Te.sub.0.8Se.sub.0.2 samples without oxygen implantation. After 1500 times on/off switching, the Te.sub.0.8Se.sub.0.2 device loses its transistor performance, possibly because of the electrical/thermal induced phase segregation. Negative-bias stress (NBS) testing was also investigated on TeSeO thin films (FIG. 13). After being gated at 20 V for 2 hours, the corresponding V.sub.TH shifted negatively from 5 to 8.8 V without noticeable subthreshold swing variation under NBS. Using the equation of .sub.N=C.sub.iV.sub.GS/2e, the charge-trapping states density (.sub.N) was calculated to be 8.210.sup.11 cm.sup.2, indicating the defect-state creation is negligible within the NBS test. In addition, benefiting from the partial oxidation in TeSeO thin films that could block the environmental influences, the devices exhibited stable operational stability under the long-term storage test (FIG. 14). After 300 days of ambient storing, the TeSeO TFT performances show no discernible degradation in output current, .sub.FE, or hysteresis, even without device encapsulation. To the best of our knowledge, the superior operating/environmental durability of TeSeO is unachievable by other p-type thin-film counterparts.

Broadband Photodetection and Mechanical Robustness of Nanopatterned TeSeO

[0086] Semiconducting nanostructures are promising for optoelectronics because of their high absorption coefficient and superior flexibility. A maskless nanosphere lithography was employed as a low-cost submicron-scale structure fabrication method to produce honeycomb TeSeO nanostructures on flexible polyimide (PI) substrates (FIG. 4a and FIG. 15, fabrication details shown in Method section). To achieve a good trade-off between flexibility and conductivity, an inter-aperture wire width of 100 nm was employed in both experimental study and theoretical modeling. After that, room-temperature photodetecting measurements were carried out using different UV (261 nm), visible (532 nm), and SWIR (1550 nm) light sources. The Te.sub.0.7Se.sub.0.3O.sub.0.59, Te.sub.0.5Se.sub.0.5O.sub.0.32, and Te.sub.0.3Se.sub.0.7O.sub.0.15 samples show good photoresponse to these tested wavelengths and yield significant photocurrent under periodic illumination (FIGS. 4c to 4e). Determined by their optical bandgap and absorption efficiency, weak SWIR response was observed at the Se-rich device (FIG. 4f), while the TeO.sub.1.16 device is highly photosensitive to the SWIR (FIG. 4b). All the performance parameters of flexible TeSeO photodetectors (PDs) are calculated and summarized in FIG. 4g. Specifically, the responsivities of TeO.sub.1.16 and Te.sub.0.7Se.sub.0.3O.sub.0.59 under SWIR irradiation are 603 and 225 A/W, respectively, better than the reported intrinsic Te PDs and comparable to those state-of-the-art wideband PDs (FIG. 21)

[0087] Honeycomb structures with nano/micro-scale geometric dimensions can accommodate mechanical deformations and thereby contribute to the superior flexibility of soft (opto-) electronics. Here, the mechanical response of honeycomb TeSeO nanostructure subject to bending was evaluated by finite element analysis (FEA, see Method section). Impressively, benefiting from the porous structure, the strain on the TeSeO honeycomb channel located on the substrate center is efficiently dispersed with a bending radius of 1.5 mm (FIGS. 5a to 5c and FIG. 16). After that, the simulation conditions were fully reproduced in a real bending experiment to check the mechanical durability of nanopatterned TeSeO PDs directly. The whole bending test with bending times up to 6000 shows no detectable photocurrent deterioration (FIG. 5d). In contrast, the TeSeO flat film without the nanopattern process displayed a significant resistance increase with the bending times (FIG. 17), and eventually, the device broke down because of the appearance of micro-cracks after bending. Thus, it is indicated that the strain-induced structural damage (e.g., plastic deformation and crack initiation) and electrical deterioration in nanopatterned flexible TeSeO could be avoided effectively.

[0088] In addition to the high sensitivity and good mechanical flexibility demonstrated above, we benchmark our flexible PD performance with the transient response speed, which highly depends on the efficient collection/transport of photo-generated carriers. The transient output signals of nanopatterned Te.sub.0.7Se.sub.0.3O.sub.0.59 PDs were measured under modulated 1550 nm illumination. Even with a chopping frequency high to 10 kHz, the devices exhibit high response reliability without signal distortion (FIG. 18). More importantly, the Te.sub.0.7Se.sub.0.3O.sub.0.59 devices exhibit ultra-fast optical response with the rise and decay times being 5 s and 7 s (FIG. 5e). The s-level response time is better than most p-channel PDs reported in the literature (FIG. 5f), mainly due to the intrinsic high hole mobility of inorganic-blended TeSeO and the high surface-to-volume ratio of honeycomb structure (FIG. 5g). These observations promise future air-stable and high-speed optoelectronic applications based on p-type band-tunable semiconductors.

[0089] To summarize, TeSeO, a versatile p-type inorganic semiconductor system, was designed and deposited as thin films and honeycomb nanostructures at room temperature. By utilizing an inorganic blending strategy, the band structure of TeSeO was engineered to meet the specific technical requirements. For instance, by optimizing the TeSeO formulation, Te.sub.0.8Se.sub.0.2O.sub.0.8 TFTs show high/FE of 48.5 cm.sup.2/(Vs) and I.sub.on/I.sub.off of 10.sup.5, while the flexible honeycomb Te.sub.0.7Se.sub.0.3O.sub.0.59 broadband PDs show fast optical response down to 5 s. Importantly, benefiting from the partial oxidation in TeSeO, the devices exhibited good operational robustness under long-term storage and persistent bias. These performance parameters surpass those of conventional p-type thin films (e.g., metal oxides, metal halides, perovskite halides, and organic materials) and are on par with the state-of-art n-type scalable metal oxides (e.g., a-InGaZnO). In this regard, the inorganic-blended TeSeO system could be applied to diverse functional utilization beyond the immediate interests in (opto-) electronics.

EXAMPLES

[0090] Material synthesis. The whole fabrication process of TeSeO films was conducted at room temperature in a scalable manner. First, the SiO.sub.2 and polyimide (PI) substrates used in this work were ultrasonically cleaned in acetone, ethanol, and deionized water and dried by nitrogen gas. Before using, Te (Sigma-Aldrich, 99.997%, powder) and Se (Sigma-Aldrich, 99.99%, powder) were mixed and then ground for 30 minutes. Due to the higher vapor pressure of Se than Te, less Se powder compared with the desired Te/Se ratio was added to the mixed source powder. For instance, to achieve the Te/Se ratios of 7/3, 5/5, and 3/7, the Se powder with percentages of 17%, 38%, and 55% was added to the mixed source, respectively. After that, a thermal evaporation process with a deposition rate of 2 /second was utilized to deposit TeSe thin films with a chamber pressure below 410.sup.6 Torr at room temperature. The film thickness is proportional to the deposition time, monitored by an INFICON SQC-310 deposition controller combined with a quartz crystal oscillator. To achieve oxygen implantation in TeSeO thin films, a standard oxygen implantation technique (PC-150, JunSun Tech Co., Ltd.) was employed with a plasma power of 30 W and an O.sub.2 gas flow of 50 sccm. The chamber pressure was set to 0.26 Torr during the oxygen implantation process with a duration of 60 seconds.

[0091] Material characterization. Surface morphologies of TeSeO films were examined with scanning electron microscopy (SEM, FEI Quanta 450 FEG SEM) and atomic force microscopy (AFM, Bruker Dimension Icon AFM). A Rigaku SmartLab X-ray Diffractometer (XRD) with Cu K radiation was used to evaluate the crystallinity and crystal structure of the TeSeO films. To get a stronger signal from the TeSeO film and avoid signal from the substrate, grazing-incidence XRD measurement was performed with a fixed grazing incidence angle of 1. Crystal structures were also determined by high-resolution transmission electron microscopy (HRTEM, JEOL 2100F). Elemental mappings were performed using an energy-dispersive X-ray spectroscopy (EDS) detector attached to a spherical-aberration-corrected scanning transmission electron microscopy (STEM, JEOL JEM-ARM300F2). To realize the elemental and chemical analysis of samples, a Thermo Scientific ESCALAB 250Xi system was employed to perform UPS and XPS. Before UPS and XPS measurement, the samples were cleaned by Ar.sup.+ ion etching to remove surface contamination. All the XPS peaks were calibrated by carbon (C 1s) peaked at 284.8 eV.

[0092] Nanosphere lithography. The monodispersed suspension of polystyrene (PS) nanospheres (10 wt %, in water, diameter of 600 nm) was used in this work. First, PS nanospheres were self-assembled into close-packed hexagonal arrays at the water-air interface. Then, the close-packed monolayers of PS nanospheres were transferred onto a flexible PI substrate, serving as lithographic masks. After that, a time-dependent dry oxygen etching process was used to tailor the diameter of PS nanospheres to 500 nm, which was performed under O.sub.2 (50 sccm) at a pressure of 0.26 Torr and a radio frequency power of 30 W for 45 seconds. After TeSeO film deposition, the nanospheres were lifted off by ultrasonicating the samples in toluene for 60 seconds, and the TeSeO honeycomb layer with an inter-aperture wire width of 100 nm was formed on the PI substrates.

[0093] Finite element analysis (FEA). The mechanical performance of honeycomb TeSeO nanostructures on flexible PI substrates under bending behavior was simulated and analyzed using FEA with the commercial software ABAQUS. The model used in this simulation was developed based on real bending experiments and incorporated the actual geometries and loading history. The PI substrate bent into a semi-circle with a radius of 1.5 mm, causing the attached honeycomb TeSeO nanostructures to deform accordingly. The slip between the substrate and the TeSeO film in the model is neglected. The linear elastic constitutive model was considered in the FEA simulation, where TeSeO has a Young's modulus of 31.1 GPa, and PI has a Young's modulus of 2.5 GPa, while their Poisson's ratios are 0.33 and 0.39, respectively. The maximum principle strain distribution of the TeSeO film was obtained in this model.

[0094] Device fabrication and characterization. Bottom-gate top-contact thin-film transistors were constructed on p.sup.+-Si/SiO.sub.2 substrates, in which the thermally grown oxide thickness is 50 nm. Both channel layers and source/drain electrodes are patterned through shadow masking to guarantee low gate leakage currents and reliable parameter extraction. The TeSeO channel thickness is 10 nm in this work. The 70-nm thick Ni source/drain electrodes were deposited by electron beam evaporation, with a channel width/length of 100 m/40 m. Ni electrodes have a high work function of 5.1 eV, suitable for contact with p-type semiconductors. Agilent 4155C semiconductor analyzer was employed to realize electrical characterizations with help from a standard electrical probe station. Field-effect mobility (.sub.FE) in the linear regime can be calculated using .sub.FE=Lg.sub.m/(WC.sub.iV.sub.DS), where L, W, C.sub.i, and V.sub.DS are the channel length, channel width, gate capacitance per unit area, drain-source voltage, respectively. The g.sub.m was transconductance defined as I.sub.DS/V.sub.GS, where I.sub.DS is drain-source current and V.sub.GS is gate-source voltage. The C.sub.i was calculated from the parallel plate capacitor model, using C.sub.i=(A)/d, where the dielectric constant () and film thickness (d) of the SiO.sub.2 dielectric layer are 3.9 and 50 nm, respectively. The Ecopia HMS 5300 Hall effect measurement system, equipped with a 0.54 T permanent magnet, was employed to measure the carrier concentration and Hall mobility using the van der Pauw method. For the photodetector measurements, lasers with different wavelengths of ultraviolet (261 nm), visible (532 nm), and short-wave infrared (1550 nm) were used as the light sources, in which their incident light powers (P) were determined by a power meter (PM400, Thorlabs). To quantify the photodetecting performance, responsivity (R) was estimated using R=I.sub.p/(PA), where I.sub.p is photocurrent (defined as light current minus dark current) and A is the effective irradiated area. The rise and decay times of photodetectors are determined as the time to vary from 10% to 90% of the peak photocurrent and vice versa.