CN104634767B - Manufacturing method of gallium nitride (GaN) based resonant cavity gas sensor - Google Patents

Abstract

The invention discloses a preparation method of a gallium nitride-based resonant cavity gas sensor, relating to the gas sensor. Fabricate a patterned distributed Bragg reflector on a sapphire substrate GaN-based epitaxial wafer, then evaporate or sputter the first metal-containing layer on the surface; evaporate or sputter the second metal-containing layer on the substrate surface; combine the first metal-containing layer and The second metal-containing layer is bonded, bonded in a vacuum or nitrogen atmosphere, and then the sapphire substrate is removed by laser lift-off technology; the GaN-based epitaxial wafer after removing the sapphire substrate is separated to form a two-dimensional array structure, and then evaporated Or sputter metal electrodes, distributed Bragg reflectors, and finally deposit polymer coatings to complete device fabrication. The detection sensitivity is high, and it is easy to be made into a two-dimensional array structure to achieve the purpose of detecting multiple gases at the same time, with low cost and high efficiency. Based on the gallium nitride-based resonant cavity structure, the content of the gas to be detected is determined by using the shift of the resonant luminescent wavelength of the device. The principle is simple, the fabrication is easy and the detection sensitivity is high.

Description

A preparation method of GaN-based resonant cavity gas sensor

technical field

The invention relates to a gas sensor, in particular to a preparation method of a gallium nitride-based resonant cavity gas sensor.

Background technique

Gallium nitride-based materials are direct bandgap semiconductor materials with continuously adjustable bandgap. The emission wavelengths at room temperature cover the near-infrared, visible light and deep ultraviolet bands. They are the third-generation semiconductor materials. Due to its stable mechanical and chemical properties, optoelectronic devices based on GaN-based materials have broad application prospects in lighting, full-color display, optical storage, signal detection, laser printing, and communication.

Gas sensor is a research hotspot in recent years. One of its uses is to detect the content of harmful volatile organic compounds (such as formaldehyde and acetone) in the environment, which is very important to the health of people working in a specific environment. The currently reported signal transduction mechanisms for detecting the gas content of these volatile organic compounds mainly include polymer coated cantilevers, thin-film resistors, and optical fibers (H. Jensenius, J. Thaysen, et al., A microcantilever-based alcohol vapor sensor-application and response model, Appl. Phys. Lett., 76:2615 (2000); J. Li, Y. Lu, et al., Carbon nanotube sensors for gas and organic vapor detection, NanoLett., 3:929 (2003); DKCWu, BT Kuhlmey, et al., Ultrasensitive photonic crystal reactive index sensor, Opt.Lett., 34:322(2009)), these detection methods all have high response sensitivity. Among them, the method of depositing polymers has unique advantages. Its advantage is that there is a one-to-one correspondence between the responses of polymers and volatile organic gases. Different polymer coatings can be deposited to simultaneously detect the content of various organic gases. The purpose is to improve the detection efficiency and reduce the cost.

Contents of the invention

The object of the present invention is to provide a method for preparing a gallium nitride-based resonant cavity gas sensor.

The present invention comprises the following steps:

1) Fabricate a patterned distributed Bragg reflector on a GaN-based epitaxial wafer on a sapphire substrate, and then evaporate or sputter the first metal-containing layer on the surface;

2) evaporating or sputtering a second metal-containing layer on the surface of the substrate;

3) bonding the first metal-containing layer and the second metal-containing layer together, bonding them under a vacuum or nitrogen atmosphere, and then removing the sapphire substrate by laser lift-off technology;

4) Separate the GaN-based epitaxial wafer after removing the sapphire substrate to form a two-dimensional array structure, then evaporate or sputter metal electrodes, distribute Bragg reflectors, and finally deposit a polymer coating to complete the device fabrication.

In step 1), methods such as photolithography, stripping, corrosion or etching can be used for making the patterned distributed Bragg reflector; the distributed Bragg reflector is formed by interleaved superposition of two dielectric films with different refractive indices, The thickness of each layer of dielectric film can be 1/4 of the central wavelength, and the combination of dielectric films can be TiO ₂ /SiO ₂ or Ta ₂ O ₅ /SiO ₂ , etc.;

The composition of the first metal-containing layer may be at least one or an alloy of at least two common bonding metals such as Au, In, Sn, Cu, and Pb.

In step 2), the substrate can be a silicon wafer or the like; the composition of the second metal-containing layer can be at least one or at least two of common bonding metals such as Au, In, Sn, Cu, Pb, etc. alloy.

In step 4), the separation of the device can use corrosion or inductively coupled plasma etching method; the metal electrode can use Ni/Au, Cr/Au or Ti/Au, etc.; the metal electrode, distributed Bragg reflector 1. The polymer coating can adopt methods such as photolithography, stripping, corrosion or etching; the selection of the polymer coating depends on the gas to be detected, and the polymer coating must be able to cause thickness and refraction after absorbing the gas to be detected. Rate changes, such as detection of acetone can choose polystyrene and so on.

The invention provides a preparation scheme of a novel gallium nitride-based resonant cavity gas sensor, which uses changes in the thickness and refractive index of the polymer after absorbing organic gas to change the reflectivity of the reflector on the resonant cavity, thereby causing the shift of the resonant luminescent wavelength. Determine the content of the gas to be detected according to the amount of change in the luminescent wavelength. The advantage of the invention is that the GaN-based material has stable mechanical and chemical properties and can work normally in various harsh environments. At the same time, the sensor has high detection sensitivity and is easy to be fabricated into a two-dimensional array structure, thereby achieving the purpose of simultaneously detecting multiple gases, reducing costs and improving efficiency.

The invention is based on a gallium nitride-based resonant cavity structure, uses the movement of the resonant luminescent wavelength of the device to determine the content of the gas to be detected, has a simple principle, is easy to manufacture and has high detection sensitivity, and is a new type of gas sensor with broad application prospects.

The invention can easily realize the two-dimensional array arrangement of sensors, and realize simultaneous detection of multiple volatile organic compound gases. The detection principle is simply stated as follows: when the polymer coating absorbs a specific organic gas, its thickness and refractive index will change. Since these polymers are directly deposited on the upper mirror of the resonator, the two can be regarded as a unified whole, and changes in the thickness and refractive index of the polymer will cause changes in the reflectivity of the upper mirror of the resonator, resulting in resonance The resonant emission wavelength of the cavity is shifted. The greater the refractive index change, the more pronounced the wavelength shift. According to this principle, if the quantitative relationship between the change of resonance luminescence wavelength and the concentration of absorbed organic gas is found, the concentration of a certain organic gas in the environment can be determined by the change of resonance luminescence wavelength Δλ of the sensor.

Description of drawings

FIG. 1 is a schematic diagram of the structure of the gallium nitride-based epitaxial wafer used;

Figure 2 is a schematic diagram of fabricating a patterned distributed Bragg reflector on p-type gallium nitride;

Figure 3 is a schematic diagram of metal bonding;

Fig. 4 is a schematic diagram of removing the sapphire substrate by laser lift-off and separating the device by inductively coupled plasma etching;

5 is a schematic diagram of a two-dimensional array of GaN-based resonant cavity light-emitting devices;

Fig. 6 is a schematic diagram of a two-dimensional array of gas sensors after depositing a polymer coating.

detailed description

The process flow of the present invention will be described in detail below in conjunction with the accompanying drawings.

1) As shown in Figure 1, a GaN low-temperature buffer layer (30nm), an undoped GaN layer (2.5 μm), and a Si-doped n-type GaN layer (2.5 μm) are sequentially grown on a sapphire substrate 11 by MOCVD method , InGaN/GaN multi-quantum well active layer (2nm/5nm×5), Mg-doped AlGaN layer (200nm) and Mg-doped p-type GaN layer (800nm) and other GaN-based epitaxial layers 12, and grown on the epitaxial wafer After high temperature annealing, in order to increase the hole concentration.

2) As shown in Figure 2, the epitaxial wafer is subjected to photolithography, and then electron beam evaporation or magnetron sputtering methods are used to grow a distributed Bragg reflector, and then a patterned distributed Bragg reflector 21 is obtained by stripping; the distributed Bragg reflector The mirror is stacked by 25 layers of Ta ₂ O ₅ /SiO ₂ , the thickness of each layer of dielectric film is 1/4 of the central wavelength, and the reflectivity is above 99%.

3) Evaporate a 4 μm first metal-containing layer (Au) 31 on one side of the distributed Bragg reflector, and evaporate a second metal-containing layer (Au) 32 on a clean silicon wafer 33; in a vacuum environment, 350 ° C, 4 MPa pressure The first and second gold-containing layers are bonded together, as shown in FIG. 3 .

4) The sapphire substrate is removed by laser lift-off technology, the GaN-based epitaxial structure is transferred to the silicon wafer substrate, and the GaN-based epitaxial structure is separated by inductively coupled plasma etching, as shown in FIG. 4 .

5) Fabricate the n-type metal electrode 51 and the patterned distributed Bragg reflector 52 by the same method as in step 2) to form a complete resonant cavity structure, as shown in FIG. 5 . Here, the reflectivity of the DBR 52 is slightly lower than the reflectivity of the DBR 21 .

6) Finally, a polymer coating 61 is deposited on the surface of the upper mirror of the resonant cavity to complete the preparation of the gas sensor, as shown in FIG. 6 .

The polymer coating deposited on the mirror on the GaN-based resonator can be the same polymer or an array of several different polymers.

GaN-based epitaxial wafers can be prepared by methods such as molecular beam epitaxy, metal-organic chemical vapor phase epitaxy, hydride vapor phase epitaxy, or magnetron sputtering.

The invention is realized by depositing a layer of special polymer coating on the surface of the upper reflector of the gallium nitride-based resonant cavity light-emitting device. This gas sensor is mainly used to detect the concentration of harmful volatile organic compounds in the environment, such as formaldehyde and acetone. Due to the stable mechanical and chemical properties of gallium nitride-based materials, this sensor can adapt to various harsh environments. When the sensor is powered on, it has a fixed resonant luminous wavelength λ when it does not absorb the detected gas. When the polymer coating absorbs the detected organic gas, the thickness and refractive index of the polymer layer will change, so that the sensor's The resonant luminescence wavelength becomes λ'. According to the change of resonance wavelength Δλ=λ′-λ before and after absorbing the gas, the concentration of the detected organic gas in the environment can be determined. The advantage of this gas sensor is that it is easy to realize a two-dimensional array structure, that is, to detect multiple gases simultaneously by depositing different polymer coatings, which greatly improves the detection efficiency and reduces the production cost.

Claims (12)

1. a kind of preparation method of gallium nitride based resonant cavity gas sensor is it is characterised in that comprise the following steps：

1) make graphical distribution Bragg reflector on Sapphire Substrate GaN base epitaxial wafer, then in surface evaporation or splash Penetrate the first metal-containing layer；

2) in sapphire substrate surface evaporation or sputtering the second metal-containing layer；

3) the first metal-containing layer and the second metal-containing layer are fitted, be bonded under vacuum or nitrogen atmosphere, then pass through laser lift-off Technology removes Sapphire Substrate；

4) device isolation carried out to the GaN base epitaxial wafer removing after Sapphire Substrate, forms two-dimensional array structure, then evaporation or Splash-proofing sputtering metal electrode, distribution Bragg reflector, last deposited polymeric coatings, complete element manufacturing.

2. as claimed in claim 1 a kind of preparation method of gallium nitride based resonant cavity gas sensor it is characterised in that in step 1), in, the graphical distribution Bragg reflector of described making adopts photoetching, stripping, corrosion or lithographic method.

3. as claimed in claim 1 a kind of preparation method of gallium nitride based resonant cavity gas sensor it is characterised in that in step 1), in, described distribution Bragg reflector is formed by the staggered superposition of deielectric-coating of two kinds of different refractivities, the thickness of every layer dielectric Spend for 1/4 centre wavelength, deielectric-coating combination adopts TiO₂/SiO₂Or Ta₂O₅/SiO₂.

4. as claimed in claim 1 a kind of preparation method of gallium nitride based resonant cavity gas sensor it is characterised in that in step 1) in, at least one consisting of in Au, In, Sn, Cu, Pb bond wire of described first metal-containing layer.

5. as claimed in claim 1 a kind of preparation method of gallium nitride based resonant cavity gas sensor it is characterised in that in step 1) in, described first metal-containing layer consist of in Au, In, Sn, Cu, Pb bond wire at least two alloy.

6. as claimed in claim 1 a kind of preparation method of gallium nitride based resonant cavity gas sensor it is characterised in that in step 2) in, at least one consisting of in Au, In, Sn, Cu, Pb bond wire of described second metal-containing layer.

7. as claimed in claim 1 a kind of preparation method of gallium nitride based resonant cavity gas sensor it is characterised in that in step 2) in, described second metal-containing layer consist of in Au, In, Sn, Cu, Pb bond wire at least two alloy.

8. as claimed in claim 1 a kind of preparation method of gallium nitride based resonant cavity gas sensor it is characterised in that in step 4), in, described device isolation is using corrosion or sense coupling method.

9. as claimed in claim 1 a kind of preparation method of gallium nitride based resonant cavity gas sensor it is characterised in that in step 4), in, described metal electrode adopts Ni/Au, Cr/Au or Ti/Au.

10. as claimed in claim 1 a kind of preparation method of gallium nitride based resonant cavity gas sensor it is characterised in that in step 4), in, described metal electrode, distribution Bragg reflector, polymer coating adopt photoetching, stripping, corrosion or lithographic method.

11. as claimed in claim 1 a kind of preparation method of gallium nitride based resonant cavity gas sensor it is characterised in that in step 4), in, the selection of described polymer coating depends on detected gas, and this polymer coating is necessary after absorbing detected gas The change of thickness and refractive index can be caused.

12. as claimed in claim 11 a kind of preparation method of gallium nitride based resonant cavity gas sensor it is characterised in that described Detected gas is acetone, and polymer coating selects polystyrene.