Method for producing a UV photodetector

Abstract

This invention relates to a method for producing a photodetector based on the deposition of precursor system having a liquid phase. The photodetectors are characterized by a certain group of semiconductor materials which can be used as the absorber in solar-blind UV detectors. A facile route for the formation of thin layers of such absorber materials is disclosed.

Claims

1. A method for producing a solar-blind UV photodetector, comprising depositing a liquid composition comprising a liquid carrier and gallium metal ions onto a substrate, where one or more of the gallium metal ions is bound to an oximate or hydroxamate ligand, processing the deposited composition by evaporating the liquid carrier and heating residual material at a temperature of from 240 to 600 C., resulting in a UV photodetector material which consists of Ga.sub.2O.sub.3, and providing electrodes to the UV photodetector material to result in a solar-blind UV photodetector.

2. The method for producing a solar-blind UV photodetector according to claim 1, wherein the processing of the deposited composition comprises heating in the presence of oxygen.

3. The method for producing a solar-blind UV photodetector according to claim 1, wherein the liquid composition comprises an oximate ligand.

4. The method for producing a solar-blind UV photodetector according to claim 1, wherein the liquid composition comprises a hydroxamate ligand.

5. A printed solar-blind UV photodetector produced by the process of claim 1, comprising a substrate, a printed layer of UV photodetector material consisting of Ga.sub.2O.sub.3, and a pair of electrodes connected to the layer of UV photodetector material, wherein the electrodes are configured in a manner such that incident UV light can be absorbed by the layer of UV photodetector material connected to the electrodes.

6. The method for producing a solar-blind UV photodetector according to claim 1, wherein one or more of the gallium metal ions is bound to an oximate ligand and the oximate ligand has formula A: ##STR00003## wherein R.sub.1 is H, CH.sub.3 or CH.sub.2CH.sub.3 , and R.sub.2 is H, C.sub.1 to C.sub.6 alkyl, phenyl or benzyl.

7. The method for producing a solar-blind UV photodetector according to claim 1, wherein one or more of the gallium metal ions is bound to a hydroxamate ligand and the hydroxamate ligand has formula B: ##STR00004## wherein R.sup.1 is C.sub.1 to C.sub.15 alkyl, phenyl or benzyl, and R.sup.2 is H, or C.sub.1 to C.sub.6 alkyl.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a photodetector device comprising a substrate (1) from e.g. quartz, a layer of photoconductor (2) placed on the substrate (1), and two electrodes (3) connected to the photoconductor (2).

(2) FIG. 2 depicts the absorbance spectrum of IZO films of Example 1 after annealing at 250 C. The continuous line indicates the absorbance of a layer consisting of 7 layers, and the baseline (dotted) is adjusted to the quartz substrate before coating.

(3) FIG. 3 depicts the current-voltage curve (IV curve) for the IZO film of Example 1 upon irradiation with light at 254 nm, 302 nm, and 365 nm and in darkness. The curve for dark condition overlaps with the baseline at 0 nA.

(4) FIG. 4 depicts the absorbance spectrum of Ga.sub.2O.sub.3 films of Example 2 after annealing at 250 C. The dotted line indicates the absorbance of 6 layers, and the dashed line is the baseline adjusted to the quartz substrate before coating.

(5) FIG. 5 depicts the current-voltage curve (IV curve) for the Ga.sub.2O.sub.3 film of Example 2 upon irradiation with light at 254 nm (ascending curve) and in darkness (overlaps with baseline at 0 nA).

(6) The examples below shall illustrate the invention without limiting it. The skilled person will be able to recognize practical details of the invention not explicitly mentioned in the description, to generalize those details by general knowledge of the art and to apply them as solution to any special problem or task in connection with the technical matter of this invention.

EXAMPLES

Example 1

Formation of a UV Photodetector with Indium Zinc Oxide (IZO) Active Layer Formed by Spin-coating an Ink Containing Indium and Zinc Oximates

(7) In a glass vial, 48.0 mg of zinc bis(2-methoxyiminopropanoate) was dissolved in 3 ml of methoxypropanol. In a separate vial, 125.5 mg of indium tris(2-methoxyiminopropanoate) was dissolved in 3 ml of methoxypropanol. The solutions were sonicated briefly until clear. 0.5 ml of each solution was combined in a new glass vial to achieve a 3 wt % solution of oximates with In:Zn in a 5:2 ratio.

(8) The ink was spin coated onto clean quartz slides (25 mm25 mm) using 50 L of ink per layer and a rotational speed of 2000 rpm. After each layer, the film was annealed at 250 C. for 4 minutes to yield the semiconductor material containing indium zinc oxide (IZO). The coating procedure is repeated until seven layers are formed. The UV absorbance was seen to increase with film thickness.

(9) To test the photoresponse of the material, two gold pads were sputtered on the substrate to a final thickness of approximately 20 nm. A 3.3 mm linear mask was used to form the active area. Accordingly, the active area between the electrodes was 3.3 mm broad and 25 mm in length. Following deposition, the device was tested for an IV response using four different light conditions: dark, a 6 W 365 nm light source, a 6 W 302 nm light source, and a 6 W 254 nm light source (hand-held fluorescent tube, VWR). The distance to the lamp was about 13 cm.

(10) FIG. 3 shows the IV response of the IZO film upon irradiation with light at 254 nm/302 nm/365 nm compared to the IV curve in the dark state. The detector shows a good responsiveness in the deeper UV (254 nm), but no response at lower energies or in darkness. The sensitivity of the UV detector hat a clear cut-off between 254 nm and 301 nm in favour of shorter wavelengths.

Example 2

Formation of a UV Photodetector with Gallium Oxide (Ga2O3) Active Layer Formed by Spin-coating a Ga-Oximate Ink

(11) In a glass vial, 282 mg of gallium tris(2-methoxyiminopropanoate) was dissolved in 3.6 ml of methoxyethanol to achieve a 4 wt % solution of the oximate. The mixture was sonicated briefly until clear.

(12) The ink was spin coated onto clean quartz slides using 50 l of ink per layer and a speed of 2000 rpm. After each layer, the film was annealed at 250 C. for 4 minutes to yield the semiconductor material containing gallium(III) oxide. The UV absorbance was observed to increase with film thickness, i.e. the number of coating steps.

(13) FIG. 1 depicts the absorbance spectrum of Ga.sub.2O.sub.3 films after annealing at 250 C. as a function of film thickness. The quartz substrate was used as a baseline.

(14) To test the photoresponse of the material, two gold pads were sputtered on the substrate to a final thickness of approximately 20 nm. A 3.3 mm linear mask was used to form the active area (3.3 mm25 mm). Following deposition, the devices were tested for an IV response in the dark and under the illumination of a 6 W 254 nm light source.

(15) In FIG. 4 is depicted the IV response of the Ga.sub.2O.sub.3 film upon irradiation at 254 nm compared to the IV curve in the dark state.

Example 3

Formation of a UV Photodetector with Gallium Oxide (Ga2O3) Active Layer Formed by Spin-coating a Ga-Hydroxamate Ink

(16) In a glass vial, 144 mg of gallium tris(N-methyl-acetohydroxamate) was dissolved in 3.6 ml of methoxyethanol to achieve a 4 wt % solution of the hydroxamate. The solutions was sonicated briefly until clear. The ink was spin coated onto clean quartz slides using 50 l of ink per layer and a speed of 2000 rpm. After each layer, the film was annealed at 350 C. for 4 minutes to yield the semiconductor material containing gallium(III) oxide.

(17) To test the photoresponse of the material, two gold pads were sputtered on the substrate to a final thickness of approximately 20 nm. A 3.3 mm linear mask was used to form the active area (3.3 mm25 mm). Following deposition, the devices were tested for an IV response in the dark and under the illumination of a 6 W 254 nm light source.

(18) Further combinations of the embodiments of the invention and variants of the invention are disclosed by the following claims.