III-V or II-VI compound semiconductor films on graphitic substrates

Abstract

A composition of matter comprising a film on a graphitic substrate, said film having been grown epitaxially on said substrate, wherein said film comprises at least one group III-V compound or at least one group II-VI compound.

Claims

1. A composition comprising a continuous film on a graphitic substrate, wherein said composition comprises, in the following order, (a) a graphitic substrate having a thickness of 20 nm or less, (b) a base layer comprising a group III-V compound other than AlN; and (c) a film comprising a group III-V compound selected from a binary group III-V compound, a ternary group III-V compound, a quaternary group III-V compound, or a plurality of such compounds in different layers; wherein the binary group III-V compound is selected from InAs, GaAs, AlAs, InP, GaP, AlP, InSb, GaSb, and AlSb; wherein the ternary group III-V compound is defined by formula XYZ, wherein X is a group III element, Y is a group III or group V element, and Z is a group V element, with the proviso that Y is different than X and Z; and wherein the quaternary group III-V compound consists of elements of Group III and one or more elements of Group V, wherein the elements of Group III in the quaternary group III-V compound are selected from Al, Ga, and In; with the proviso that the group III-V compound of film (c) is different than the base layer; and wherein film (c) is grown directly on the base layer.

2. The composition of claim 1, wherein the base layer comprises GaSb, InAs, AsSb, SbBi, Sb, AlAsAb, AllnSb, or InAsSb.

3. The composition of claim 1, wherein film (c) or part of film (c) is doped.

4. The composition of claim 1, wherein the graphitic substrate is on a support.

5. The composition of claim 1, wherein the graphitic substrate is free of grain boundaries.

6. The composition of claim 1, wherein film (c) does not comprise AlN.

7. The composition of claim 1, wherein the base layer does not comprise GaN.

8. The composition of claim 1, wherein film (c) is grown using molecular beam epitaxy (MBE), migration-enhanced epitaxy (MEE), metal organic CVD (MOCVD), atomic layer molecular beam epitaxy (ALMBE), or a combination thereof.

9. The composition of claim 1, wherein the thickness of the base layer and film (c) is at least 250 nm.

10. The composition of claim 1, wherein film (c) comprises a plurality of group III-V compounds in different layers.

11. The composition of claim 1, wherein a lattice mismatch of the base layer is 2.5% or less to that of graphene.

12. A process for preparing the composition of claim 1, the process comprising the steps of: (I) providing the base layer on said graphitic substrate, said base layer having a lattice mismatch of 2.5% or less to that of graphene; and (II) contacting said base layer with group III-V elements so as to grow the film comprising the group III-V compound.

13. The process as claimed in claim 12, wherein deposition of the base layer or formation of the film grown epitaxially on the graphitic substrate involves migration-enhanced epitaxy (MEE) followed by atomic layer molecular beam epitaxy (ALMBE), in that order.

14. The process as claimed in claim 12, wherein the base layer, the film, or a combination thereof is grown using molecular beam epitaxy (MBE), migration-enhanced epitaxy (MEE), metal organic CVD (MOCVD), atomic layer molecular beam epitaxy (ALMBE), or a combination thereof.

15. The process as claimed in claim 12, wherein the film is grown using molecular beam epitaxy (MBE), metal organic CVD (MOCVD), or a combination thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1a-d shows the atomic arrangements when semiconductor atoms are placed above 1) H- and B-sites (FIGS. 1a, b, and d), and 2) H- or B-sites (FIG. 1c) on graphene. In FIG. 1e the bandgap energies of the III-V semiconductors (as well as Si and ZnO) are plotted against their lattice constants. Vertical solid (dashed) coloured lines depict the lattice constant of an ideal crystal that would give perfect lattice match with graphene for a cubic (hexagonal) crystal with the four different atomic arrangements (FIG. 1a-d) with respect to graphene. In the case of some binary semiconductors, the lattice mismatch with graphene is very small (e.g. InAs, GaSb, and ZnO) for one suggested atomic configuration. For other binary semiconductors like GaAs, the lattice mismatch is quite large and in-between two different atomic configurations (as in FIG. 1b or FIG. 1c). It can be realized from the figure that many ternary, quaternary and quintinary semiconductors can be perfectly lattice-matched to graphene.

(2) FIG. 1e shows artificial lattice-matched lattice constants for the atomic arrangements in (a), (b), (c) and (d). Dashed and solid lines correspond to the hexagonal (a.sub.1) and cubic (a=a.sub.1×√2) crystal phases of these lattices, respectively. The square (.square-solid.) and the hexagon represent the cubic and the hexagonal phases, respectively, for Si, ZnO, and binary III-V semiconductors.

(3) FIG. 2 shows an MBE experimental set up.

(4) FIG. 3 is a theoretical side view of a support, graphene layer, base layer and top semiconductive layer.

(5) FIG. 4 shows a thin film of GaSb grown directly on a Kish graphite surface.

(6) FIG. 5 shows that for SbGp13, triangle-like shaped GaSb platelets confirm the epitaxial relation with graphite substrate.

EXPERIMENTAL PROCEDURE

(7) Thin film is grown in a Varian Gen II Modular molecular beam epitaxy (MBE) system equipped with a regular Al filament cell, a Ga dual filament cell, an In SUMO dual filament cell, an As valved cracker cell, and an Sb valved cracker cell allowing to fix the proportion of dimers and tetramers. In the present study, the major species of arsenic are As.sub.2, and antimony are Sb.sub.2.

(8) Growth of thin film is performed either on a Kish graphite flake or on a graphene film (1 to 7 monolayers thick, preferably only one monolayer thick) grown either by a chemical vapor deposition (CVD) technique directly on a metal film such as Cu, Ni, and Pt, or grown on SiC substrates by using a high-temperature sublimation technique. The graphene film samples are purchased from external suppliers. The CVD graphene films are purchased from “Graphene Supermarket”, USA.

(9) The CVD graphene film samples are cleaned by isopropanol followed by a blow dry with nitrogen, and then indium-bonded to a silicon wafer. The graphene/SiC substrates are blow dried with nitrogen, and then indium-bonded to a silicon wafer.

(10) The samples are then loaded into the MBE system for the thin film growth. The samples are annealed at a substrate temperature of 550° C. (or higher) for a duration of 10 minutes to get rid of any oxide residues on the substrate. The deposition of III-V film is typically done by a three-step (if a base layer is used) or a two-step growth method. In case a base layer is used, the first step involves the deposition of a group V element (or of an alloy of group V elements) on the graphitic layers at lower substrate temperatures as described below. The second step involves the growth of III-V film at a lower substrate temperature similar as was used for the deposition of group V element (or group V alloy). The third step involves the deposition of III-V film(s) at higher temperature typical for normal epitaxial growth of the III-V compound in question. The second step above is preferred to avoid desorption of group V element (or group V alloy) during the third step.

Example 1

(11) After annealing the graphene substrate at 550° C., the substrate temperature is then decreased to typically between 200° C. and 300° C. for Sb deposition. Sb flux is first supplied to the surface during a time interval typically in the range 5 s to 1 minute, dependent on Sb flux and substrate temperature. A few nm, preferably less than a few tens of nm, of Sb are then grown, preferably by MEE or ALMBE. Then, the substrate temperature is increased to a temperature suitable for GaSb thin film growth: i.e. around 450° C. The temperature of the Ga effusion cell is preset to yield a nominal planar growth rate of 0.3 μm per hour. The Sb.sub.2 flux is set to 1×10.sup.−6 Torr to grow the GaSb thin film at this temperature. The GaSb thin film is doped to a level appropriate for which device structure will be grown on top of this thin film template structure.

Example 2

(12) After annealing the graphene substrate at 550° C., the substrate temperature is decreased to between 15° C. and 80° C. for As deposition, the temperature being dependent on which deposition rate is wanted. As flux is first supplied to the surface during a time interval typically in the range 5 s to 1 minute. A few nm, preferably less than a few tens of nm, InAs are then grown, preferably by MEE or ALMBE. Then, the substrate temperature is increased to a temperature suitable for InAs thin film growth: i.e. around 450° C. The temperature of the In effusion cell is preset to yield a nominal planar growth rate of up to 0.7 μm per hour. The As.sub.2 flux is set to 6×10.sup.−6 Torr to form the InAs thin film at this temperature. The InAs thin film is doped to a level appropriate for which device structure will be grown on top of this thin film template structure.

(13) The substrates prepared in examples 1 and 2 hereby called as III-V/GP thin film substrate can be used as a template for the fabrication of various optoelectronic or electronic devices, and solar cells.

(14) In Examples 3-4 below, we describe the deposition of 1) p-i-n doped homojunction GaSb thin film on III-V/GP thin film substrate, and 2) p-n doped heterostructure GaSb/InGaAsSb thin film on III-V/GP thin film substrate. These thin film structures are intended to use for applications such as light emitting diodes and photo detectors.

Example 3

(15) p-i-n doped homojunction GaSb thin film is further grown on III-V/GP thin film substrate of example 1 to use it as a photodetector. The thickness of each of the p-doped, n-doped, and intrinsic III-V epilayer is typically kept between 0.5 and 3 μm. For p-type doping, Be is used. Te is used as an n-dopant. The Be cell temperature is set to 990° C. which gives a nominal p-type doping concentration of 3×10.sup.18 cm.sup.−3. The Te cell temperature is set to 440° C. which gives a nominal n-type doping concentration of 1×10.sup.18 cm.sup.−3. The deposition temperature for all the layers is set to 450° C. The temperature of the Ga effusion cell is preset to yield a nominal planar growth rate of 0.7 μm per hour, and the Sb.sub.2 flux is set to 1×10.sup.−6 Torr to grow the GaSb thin film.

Example 4

(16) p-type_GaSb/intrinsic_GaInAsSb/n-type_GaSb thin film is further grown on III-V/GP thin film substrate. The composition of the intrinsic GalnAsSb is tailored such that it is lattice-matched to GaSb. The thickness of each these three epilayers is typically kept between 0.5 and 3 μm. For p-type doping, Be is used. Te is used as an n-dopant for the GaInAsSb epilayer. The Be cell temperature is set to 990° C. which gives a nominal p-type doping concentration of 3×10.sup.18 cm.sup.−3. The Te cell temperature is set to 440° C. which gives a nominal n-type doping concentration of 1×10.sup.18 cm.sup.−3.

Example 5

(17) n-type GaSb/n+GaInAsSb/p-GaInAsSb/p+GaInAsSb thin film is further grown on III-V/GP thin film substrate to use it as a photodetector. The composition of the GaInAsSb is tailored such that it is lattice-matched to GaSb. The thickness of each of these epilayers is typically kept between 0.5 and 3 μm. For p-type doping, Be is used. Te is used as an n-dopant for the GaInAsSb epilayer. The Be cell temperature is set to 990° C. which gives a nominal p+ type doping concentration of 1×10.sup.18 cm.sup.−3, and the Be cell temperature is set to 940° C. which gives a nominal p-type doping concentration of 9×10.sup.16 cm.sup.−3 The Te cell temperature is set to 440° C. which gives a nominal n-type doping concentration of 1×10.sup.18 cm.sup.−3.

Example 6

(18) A series of thin films were grown directly on a Kish graphite. The conditions of growth are summarised in table 1. After annealing the sample at 550° C., the substrate temperature is reduced to the temperature shown in column 2 which the thin film is grown. The SEM images in FIG. 4 show that we have grown GaSb crystal material on Kish graphite.

(19) Nucleation: Samples SbGp13, SbGp 22 and SbGp 17 show that GaSb nucleates on Kish graphite and forms triangle-like shaped GaSb platelets due to epitaxial relation with the graphitic surface. Nucleation can be achieved with regular MBE at 300° C. and with MEE (Migration-Enhanced Epitaxy method in MBE) at 200° C. and at 300° C. The material deposited on the Kish graphite is the equivalent of 3 monolayers (ML) of GaSb in each case.

(20) Thin film: Samples SbCp24/26/27/31 show that an almost continuous film of GaSb with nominal thickness 100 nm can be grown on Kish graphite using a two-step growth method (MEE nucleation step at 300° C.+MBE growth at 300-520° C.).

(21) The samples SbGp26/27/31 are grown according to such two-step method (MEE step at low temp+MBE step at higher temp), i.e. Sb base layer was not used for these samples.

(22) TABLE-US-00001 Sample Number Growth details Short description of the sample SbGp 13 GaSb thin film: 5 sec (3 ML), Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.7 MLs−1, Tc = 300° C. 3 ML GaSb dep at Tc = 300 C. SbGp 14 Sb flux predep = 1 × 10{circumflex over ( )}−6, 5 min at Tc = 400° C. GaSb thin film: 5 sec (3 ML), Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.7 MLs−1, Tc = 300° C. SbGp 15 GaSb thin film: MEE 5 sec (3 ML), Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.7 MLs−1, Tc = 3 ML MEE GaSb dep at Tc = 300 C. 300° C. [Open Sb 1.4 sec + Open Ga 1.4 sec + wait 2] × 3 times SbGp 16 GaSb thin film: 5 sec (3 ML), Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.7 MLs−1, Tc = 350° C. 3 ML GaSb dep at Tc = 350 C. SbGp 17 GaSb thin film: MEE 5 sec (3 ML), Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.3 MLs−1, 3 ML MEE GaSb dep at Tc = 300 C., Ga = 0.3 Tc = 300° C. [Open Sb 3.4 sec + Open Ga 3.4 sec + wait 2] × 3 times MLs−1 SbGp 18 GaSb thin film: MEE 5 sec (3 ML), Sb flux = 6 × 10{circumflex over ( )}−7, Ga = 0.3 MLs−1, 3 ML MEE GaSb dep at Tc = 300 C., Ga = 0.3 Tc = 300° C. [Open Sb 3.4 sec + Open Ga 3.4 sec + wait 2] × 3 times MLs−1, LOW Sb flux SbGp 19 GaSb thin film: MEE 5 sec (3 ML), Sb flux = 1.5 × 10{circumflex over ( )}−6, Ga = 0.3 MLs−1, 3 ML MEE GaSb dep at Tc = 300 C., Ga = 0.3 Tc = 300° C. [Open Sb 3.4 sec + Open Ga 3.4 sec + wait 2] × 3 times MLs−1, High Sb flux SbGp 20 GaSb thin film: Two temp MEE, Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.3 MLs−1, Tc = 300° C. Two temp MEE: 1 ML at 300 C. and 2 MLs [Open Sb 1.7 sec + Open Ga 1.7 sec + wait 2] × 2 times + Tc = 400° C. [Open at 400 C. Sb 3.4 sec + Open Ga 3.4 sec + wait 2] × 2 times SbGp 21 GaSb thin film: Two temp MEE, Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.3 MLs−1, Tc = 300° C. Two temp MEE: 1 ML at 300 C. and 2 MLs [Open Sb 1.7 sec + Open Ga 1.7 sec + wait 2] × 2 times + Tc = 375° C. [Open at 375 C. Sb 3.4 sec + Open Ga 3.4 sec + wait 2] × 2 times SbGp 22 GaSb thin film: MEE 5 sec (3 ML), Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.3 MLs−1, 3 ML MEE GaSb dep at Tc = 200 C., Ga = 0.3 Tc = 200° C. [Open Sb 3.4 sec + Open Ga 3.4 sec + wait 2] × 3 times MLs−1 SbGp 23 GaSb thin film: MEE 5 sec (3 ML), Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.3 MLs−1, 3 ML MEE GaSb dep at Tc = 325 C., Ga = 0.3 Tc = 325° C. [Open Sb 3.4 sec + Open Ga 3.4 sec + wait 2] × 3 times MLs−1 SbGp 24 GaSb thin film: 100 nm thick, Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.3 MLs−1, Tc = 300° C. 100 nm GaSb dep at Tc = 300 C., Ga = 0.3 [Open Sb 3.4 sec + Open Ga 3.4 sec + wait 2] × 20 times + GaSb 980 sec. MLs−1 SbGp 25 GaSb thin film: MEE 5 sec (3 ML), Sb flux = 8 × 10{circumflex over ( )}−7, Ga = 0.1 MLs−1, 3 ML MEE GaSb dep at Tc = 300 C., Ga = 0.1 Tc = 300° C. [Open Sb 3.4 sec + Open Ga 3.4 sec + wait 2] × 9 times MLs−1 SbGp 26 GaSb thin film: 100 nm thick, Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.3 MLs−1, Tc = 300° C. 100 nm GaSb dep: 3 nm at Tc = 300 C., 98 [Open Sb 3.4 sec + Open Ga 3.4 sec + wait 2] × 30 times + GaSb 980 sec at nm at Tc = 450 C. Tc = 450 C. SbGp 27 GaSb thin film: 100 nm thick, Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.3 MLs−1, Tc = 300° C. 100 nm GaSb dep: 3 nm MEE + 10 nm at [Open Sb 3.4 sec + Open Ga 3.4 sec + wait 2] × 30 times + 100 sec at Tc = 300 C., 80 nm at Tc = 450 C. Tc = 300 C. + GaSb 800 sec at Tc = 450° C. SbGp 28 GaSb_Te thin film: MEE 5 sec (3 ML), Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.3 MLs−1, GaTe = 600 C., Tc = 300° C. [Open Sb 3.4 sec + Open Ga and GaTe 3.4 sec + wait 2] × 3 times SbGp 29 GaSb_Te thin film: MEE 5 sec (3 ML), Sb flux = 1 × 10{circumflex over ( )}−6, Ga = 0.3 MLs−1, GaTe = 550 C., Tc = 300° C. [Open Sb 3.4 sec + Open Ga and GaTe 3.4 sec + wait 2] × 3 times