CN104393093A - High-detectivity gallium-nitride-based Schottky ultraviolet detector using graphene - Google Patents

Abstract

The high detection rate gallium nitride-based Schottky type ultraviolet detector using graphene, its basic structure from bottom to top is heavily doped n-type gallium nitride, lightly doped n-type gallium nitride, silicon dioxide insulating layers, metal electrodes, and graphene films. Metal electrodes are transparent, conductive, and semi-metallic. In the case of direct contact with lightly doped n-type GaN, a potential barrier of about 0.5 eV can be formed. The formed potential barrier shows that the internal energy band of GaN close to the metal electrode bends, and the space charge region can be formed to separate electrons and holes, thereby generating photoelectromotive force and photocurrent. The responsivity of the detector can be greatly improved by introducing surface defects. This structure has a simple process and high efficiency; thereby increasing the separation ability of electron-hole pairs, increasing the quantum efficiency in the detector, and increasing the detection rate and responsivity.

Description

High detection rate GaN-based Schottky ultraviolet detector using graphene

technical field

The invention relates to a novel GaN-based Schottky type ultraviolet detector structure and preparation method, belonging to the technical field of semiconductor optoelectronic devices.

Background technique

There are many applications of ultraviolet detection technology, which can be used for resin curing of polymeric materials, water purification treatment, flame detection, biological effects, and environmental pollution monitoring and ultraviolet light storage. In terms of ultraviolet photodetection devices, GaN materials have excellent performance: (1) GaN does not absorb visible light, and the ultraviolet detectors made can be blinded to visible light and do not require a filter system. (2) No need to make shallow junctions, This can greatly improve the quantum efficiency. (3) GaN has strong anti-radiation ability and can play a role in exploring the mysteries of the universe. GaN ultraviolet detectors are currently mainly divided into the following types: such as photoconductive type, pn junction type, pin type, Schottky junction type, MSM type, and heterojunction type. Among them, the GaN-based Schottky structure ultraviolet detector has received great attention because of its high responsivity, fast response speed, simple process, and large photosensitive surface.

Schottky UV detectors work by using a Schottky junction formed of semi-transparent metal and GaN semiconductor. After the Schottky junction is formed between the translucent metal and GaN, the energy band of the semiconductor bends near the metal. Taking the Ni/Au-nGaN Schottky junction as an example, due to the higher work function of the metal and the lower work function of the semiconductor, the energy band of the semiconductor is bent upward near the part of the metal, and this part is close to the surface of the semiconductor. When ultraviolet light is irradiated on the semiconductor surface, light absorption will occur on the semiconductor surface, and electron-hole pairs will be generated. The electron-hole pairs will be separated in this region, that is, the space charge region, due to the bending of the energy band, resulting in photogenerated current or photoelectromotive force. .

Traditional Schottky-type devices mainly use semi-transparent metals, but the translucent metal Ni/Au (2nm/2nm) usually used as a Schottky contact has a light transmittance of only about 60% at 300nm, which affects the detection rate. very serious. Studies have shown that for every 1nm increase in metal, the light transmittance decreases by 10%. Moreover, the work function of metal is fixed and difficult to change. At present, only changing the metal material is the most effective way. But even the most ideal metal materials are still not ideal. We found in the fabrication of this device that surface defects of the device can greatly increase the responsivity (A/W) of the device, while the detection rate remains unchanged or slightly increased.

Contents of the invention

The object of the present invention is to provide an improved structure of the Schottky type ultraviolet detector and a preparation method thereof. Graphene, a new material, is rationally applied to this detector structure to increase the light transmittance of the window and increase the Schottky barrier to enhance its ability to separate electrons and holes. Therefore, the detection performance of the Schottky detector is improved.

The structure of a Schottky type ultraviolet detector provided by the present invention, its basic structure is as follows from bottom to top: heavily doped n-type gallium nitride 101, lightly doped n-type gallium nitride 102, silicon dioxide insulating Layer 103, metal electrode 104, graphene film 105.

In the present invention, the metal electrode 104 is transparent, conductive, and semi-metallic, and its intrinsic work function is 4.5 eV. In the case of direct contact with lightly doped n-type GaN, a potential barrier of about 0.5 eV can be formed. The formed potential barrier shows that the internal energy band of GaN close to the metal electrode 104 bends to form a space charge region, which can separate electrons and holes, thereby generating photoelectromotive force and photocurrent. The light transmittance of single-layer graphene is 97.7%, which is much higher than that of semi-metal layer (60%). The typical value of the square resistance of single-layer graphene is 300-1000 ohms/square, although this value is greater than that of the translucent metal layer (10-30 ohms/square), but for this kind of ultraviolet detector, it is generally used in the reverse situation The square resistance of the conductive layer has little effect on its detection performance. The responsivity of the detector can be greatly improved by introducing surface defects.

The invention provides a Schottky-type graphene-GaN-based ultraviolet detector and a preparation method thereof,

Step 1. Use metal-organic chemical vapor deposition (or molecular beam epitaxy system, liquid phase epitaxy technology, etc.) to sequentially fabricate heavily doped n-type gallium nitride 101 on sapphire (or silicon wafer, silicon carbide, etc. substrate), with a thickness of 1-2 microns; lightly doped n-type gallium nitride 102, with a thickness of 300-800 nanometers.

Step 2, using inductively coupled plasma etching to etch the surface of the epitaxial wafer, the etching depth is 10-50 nm, and increasing the defect density on the surface of the epitaxial wafer. Or increase the surface defect density of the epitaxial wafer by means of surface etching and ion implantation.

Step 3: Clean the epitaxial wafer, perform photolithography, and etch to form a mesa structure, that is, heavily doped n-type GaN 101 and lightly doped n-type GaN 102 .

Step 4, growing a layer of silicon dioxide on top of 102, and performing photolithography and etching to form a silicon dioxide insulating layer 103 with a thickness of 100-500 nanometers.

Step 5, photolithographic electrode patterns, sputtering or evaporation to make metal electrodes 104 (Ti/Au, Cr/Au), with a thickness of 15-50/30-3000 nanometers, on the silicon dioxide insulating layer 103, that is, the silicon dioxide The silicon insulating layer 103 is between the lightly doped n-type gallium nitride 102 and the metal electrode 104 .

Step 6. Transfer graphene to the surface of the device, the number of layers is 1-10, photolithographically etch the graphene pattern, and plasma etch the graphene to form a graphene film 105 . The plasma etching gas is oxygen, the flow rate is 10-70L/min, the power is 50-100W, and the etching time is 30s-600s.

Step 7. Thinning the epitaxial wafer substrate, laser cutting, and splitting.

Wherein step 5 and step 6 can be interchanged.

Compared with the prior art, the present invention has the following beneficial effects.

1. The graphene-gallium nitride ultraviolet detector mainly consists of two parts, one part is gallium nitride material, and the other part is graphene film. Using the semi-metallic nature of graphene, it combines with gallium nitride to form a Schottky junction, thereby forming a built-in electric potential field. After gallium nitride absorbs photons, electron-hole pairs are generated near the surface of gallium nitride, and the built-in electric potential field The electron-hole pair is separated, thereby forming a photocurrent and a built-in potential difference. This structure has simple process and high efficiency;

2. As mentioned in the technical background, it is difficult for metals to change the co-function, and the co-function is an important factor affecting such devices. Graphene is a single atomic layer material, and its co-function can be easily changed by chemical modification and other methods. The change of co-function can enhance the built-in potential field, thereby increasing the separation ability of electron-hole pairs, increasing the quantum efficiency in the detector, and increasing the detection rate and responsivity.

3. The experiment found that by increasing the surface damage of the device, the device responsivity can be increased, but the leakage current also increases. Through calculation, the detection rate of the device did not decrease, but increased.

Description of drawings

Figure 1 is a schematic diagram of a graphene-gallium nitride Schottky ultraviolet detector.

Figure 2 is the light-dark I-V curve of the graphene-gallium nitride Schottky ultraviolet detector.

Figure 3 is the light-dark I-V curve of the graphene-surface eroded gallium nitride Schottky ultraviolet detector.

In the figure: 101, heavily doped n-type gallium nitride; 102, lightly doped n-type gallium nitride; 103, silicon dioxide insulating layer; 104, metal electrode; 105, graphene film.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, the structure of a Schottky type ultraviolet detector, its basic structure from bottom to top is heavily doped n-type gallium nitride 101, lightly doped n-type gallium nitride 102, silicon dioxide An insulating layer 103, a metal electrode 104, and a graphene film 105.

Its manufacturing process is shown in the example below.

Example 1

Step 1. Use metal-organic chemical vapor deposition (or molecular beam epitaxy system, liquid phase epitaxy technology, etc.) to sequentially fabricate heavily doped n-type gallium nitride 101, lightly doped hetero n-type gallium nitride 102 .

Step 2, cleaning the epitaxial wafer, photolithography, and etching to form a mesa structure, such as heavily doped n-type GaN 101 and lightly doped n-type GaN 102 .

Step 3, growing a layer of silicon dioxide, and performing photolithography and etching to form a silicon dioxide insulating layer 103 .

Step 4, photoetching the electrode pattern, sputtering or evaporating to make the metal electrode 104 .

Step 5, transfer the graphene to the surface of the device, photolithographically etch the graphene pattern, and plasma etch the graphene to form a graphene film 105 . The plasma etching gas is oxygen, the flow rate is 10-70L/min, the power is 50-100W, and the etching time is 30s-600s. The contact area between graphene and gallium nitride, that is, the photosensitive area has a size of 1×1mm ² .

Step 6. Thinning the epitaxial wafer substrate, laser cutting, and splitting.

After the test of the ultraviolet detection and testing system of the Institute of Semiconductors, Chinese Academy of Sciences, the 365nm wavelength responsivity is 0.18A/W. The corresponding spectra are shown in Figure 2.

After testing, the specific detectivity is 1.05e12cm Hz ^1/2 W ^-1 at -6V under the irradiation of parallel ultraviolet light of 5.6w/cm ² and main wavelength of 254nm.

Example 2

Step 1. Use metal-organic chemical vapor deposition (or molecular beam epitaxy system, liquid phase epitaxy technology, etc.) to sequentially fabricate heavily doped n-type GaN 101 on sapphire (or silicon wafer, silicon carbide, etc. substrates), lightly doped hetero n-type gallium nitride 102 .

Step 2, using inductively coupled plasma etching to etch the surface of the epitaxial wafer, the etching depth is 10-50 nm, and increasing the defect density on the surface of the epitaxial wafer.

Step 3: Clean the epitaxial wafer, perform photolithography, and etch to form a mesa structure, such as heavily doped n-type GaN 101 and lightly doped n-type GaN 102 .

Step 4, growing a layer of silicon dioxide, and performing photolithography and etching to form a silicon dioxide insulating layer 103 .

Step 5, photoetching the electrode pattern, sputtering or evaporating to make the metal electrode 104 .

Step 6, transfer the graphene to the surface of the device, photolithographically etch the graphene pattern, and plasma etch the graphene to form a graphene film 105 . The plasma etching gas is oxygen, the flow rate is 10-70L/min, the power is 50-100W, and the etching time is 30s-600s. The contact area between graphene and gallium nitride, that is, the photosensitive area has a size of 1×1mm ² .

Step 7. Thinning the epitaxial wafer substrate, laser cutting, and splitting.

After testing, the responsivity is 357A/W at -6V under the irradiation of 5.6w/cm ² parallel ultraviolet light with a dominant wavelength of 254nm. The specific detectivity is 1.07e12cm Hz ^1/2 W ^-1 . The corresponding spectra are shown in Figure 3.

Claims (2)

1. A high detection rate gallium nitride-based Schottky type ultraviolet detector using graphene, characterized in that: the basic structure of the laser is successively heavily doped n-type gallium nitride (101), lightly doped n-type gallium nitride (102), a silicon dioxide insulating layer (103), a metal electrode (104), and a graphene film (105). 2. A preparation method of a high detection rate GaN-based Schottky type ultraviolet detector using graphene, characterized in that: the implementation process of the method is as follows, Step 1. Use metal-organic chemical vapor deposition or molecular beam epitaxy system or liquid phase epitaxy to sequentially fabricate heavily doped n-type gallium nitride (101) on sapphire or silicon wafer or silicon carbide, with a thickness of 1-2 microns; lightly doped hetero n-type gallium nitride (102), with a thickness of 300-800 nanometers; Step 2. Use inductively coupled plasma etching to etch the surface of the epitaxial wafer with an etching depth of 10-50 nm to increase the surface defect density of the epitaxial wafer; or increase the surface defect density of the epitaxial wafer by surface etching and ion implantation; Step 3, cleaning the epitaxial wafer, photolithography, and etching to form a mesa structure, that is, heavily doped n-type gallium nitride (101) and lightly doped n-type gallium nitride (102); Step 4, growing a layer of silicon dioxide on the lightly doped n-type gallium nitride (102), and performing photolithography and etching to form a silicon dioxide insulating layer (103) with a thickness of 100-500 nanometers; Step 5, photoetching electrode patterns, sputtering or evaporation to make metal electrodes (104), with a thickness of 15-50/30-3000 nanometers, on the silicon dioxide insulating layer (103), that is, the silicon dioxide insulating layer (103 ) between the lightly doped n-type gallium nitride (102) and the metal electrode (104); Step 6, transfer graphene to the surface of the device, the number of layers is 1-10 layers, photolithographic graphene graphics, plasma etching graphene, forming a graphene film (105); plasma etching gas is oxygen, and the flow rate is 10 -70L/min, power 50-100W, etching time 30s-600s; Step 7, the thinned epitaxial wafer substrate, laser cutting, splitting; Wherein step 5 and step 6 can be interchanged.