CN100437908C - Process for preparing nitrigen-aluminium co-blended hole zinc oxide thin film material - Google Patents

Abstract

The invention relates to a nitrogen-aluminum co-doped hole-type zinc oxide film and a preparation process thereof. The ultrasonic spray pyrolysis method is used to obtain an organic or inorganic salt solution of Zn, an organic or inorganic salt solution of N and an inorganic salt solution of Al. The mixed solution is the precursor, by adjusting Zn ²⁺ : NH ₄ ⁺ : Al ³⁺ = 1: (1-3): (0.01-0.2) and controlling the substrate temperature at 600-900 ° C to achieve p-type ZnO Control of thin film electrical properties. The resistivity of the p-type ZnO thin film prepared by the present invention is in the range of 10 ^-1 -10 ^-2 Ωcm, the mobility can reach up to 103 cm ² V ^-1 s ^-1 , and the grain size of the thin film is uniform and densely arranged, and the thin film has strong The (101) orientation crystallization characteristics and room temperature ultraviolet luminescence characteristics.

Description

Preparation process of a nitrogen-aluminum co-doped hole-type zinc oxide thin film material

technical field

The invention relates to a preparation process of a nitrogen-aluminum co-doped hole-type zinc oxide film material used for zinc oxide-based light-emitting diodes (LEDs), laser diodes (LDs) and ultraviolet detectors and other optoelectronic devices, belonging to the field of semiconductor materials.

Background technique

The huge market potential of ZnO-based optoelectronic devices has stimulated a research boom of ZnO materials. The core of ZnO-based optoelectronic devices is the junction ZnO material, and the key issues in realizing pn junction growth and developing ZnO homogeneous and ZnO-based heterojunction optoelectronic devices are to solve the self-compensation of ZnO and realize p-type doping efficiently and controllably. . The high-quality p-type ZnO thin film with low resistance and high mobility is of great significance for improving the luminous efficiency of light-emitting devices and the photoelectric conversion efficiency of detection devices. However, there are many intrinsic donor defects in ZnO, such as interstitial zinc Zn _i and oxygen vacancies V _o , whose energy levels are located at the bottom of the conduction band at 0.05eV and 0.3eV, respectively, which have a high degree of self-compensation for acceptors. Therefore, it is difficult to realize the p-type transition of ZnO. Moreover, the acceptor energy level of ZnO is generally very deep (except for N), holes are not easily excited into the valence band by thermal excitation, and the solid solubility of acceptor doping is also very low. Therefore, p-type doping with low resistance and high mobility is difficult to achieve. At present, the performance of the p-type ZnO thin film developed by Daban Chuanhe Laboratory in Japan has reached a relatively high level, its resistivity is 2-5Ωcm, and the carrier mobility is 0.1-0.4cm ² V ^-1 s ^-1 (Xin-Li Guo et al., Optical Materials 19, 229 (2002)).

There are five main channels for doping p-type ZnO thin films: 1. N doping 2. Ga, N co-doping 3. In, N co-doping 4. As doping 5. P doping. In the first type, the active N source generally comes from N ₂ , N ₂ O or NH ₃ , but when N replaces O atoms, the Madelung Energy is increased, which causes the localization of the N energy level, and the N energy level Deeper, the doping effect is not very ideal. The second and third types need to use Ga and In sources with higher prices, and the production cost is high. The latter two acceptor energy levels are relatively deep, the doping effect is not ideal, and both As and P are poisonous. Theory predicts that co-doping of N and Al will be superior to other doping combinations for more efficient p-type transition of ZnO (Wang, LG et al., Phys. Rev. Lett. 90, 256401 (2003) and Yamamoto, T. et al., Physica B, 302-303, 155 (2001)).

At present, magnetron sputtering and pulsed laser deposition (PLD) techniques are mostly used in the preparation of p-type ZnO thin films. However, it is quite difficult to obtain p-type ZnO thin films with low resistance and high mobility. For example, Ohshima et al. from Kumamoto University in Japan used N ⁺ or N ₂ ⁺ ions emitted by ion guns to sputter Al mesh electrodes to perform N-Al co-doping on undoped ZnO films deposited by KrF excimer pulse laser (People such as T.Ohshima, Thin Solid Films, 435,49 (2003)), but the result does not obtain p-type ZnO thin film; Carry out N-Al co-doping to ZnO by DC reactive magnetron sputtering (Ye Zhizhen et al., Journal of Crystal Growth 265, 127 (2004)) obtained p-type ZnO film, its resistivity is 10 ² -10 ⁴ Ωcm, mobility is 0.3-19cm ² V ^-1 s ^-1 ; The relatively high level p-type ZnO film developed by the PLD method in the laboratory has a high resistivity and a low carrier mobility, which cannot meet the practical requirements. The reason is that these two methods require high vacuum conditions, so the resulting ZnO film has a high concentration of oxygen vacancies, which makes the self-compensation effect in the film significantly enhanced, and the concentration of N acceptors is very low, so it is necessary to make N provide It is very difficult to obtain enough hole carriers to realize the p-type conduction of ZnO. In addition, magnetron sputtering and PLD equipment are expensive, and the cost of film formation is high, making it difficult to achieve large-area deposition. The ultrasonic spray pyrolysis method is carried out under normal pressure, which can greatly reduce the oxygen defects. Moreover, the thermochemical reaction of the mixed solution occurring in the process of ultrasonic spray pyrolysis is very beneficial to the doping of ZnO thin films. Therefore, co-doping ZnO thin films with N and Al by ultrasonic spray pyrolysis should be one of the effective methods to prepare p-type ZnO thin films with low resistance and high mobility. The method has simple equipment, convenient operation, abundant raw materials and low production cost.

Contents of the invention

The object of the present invention is to provide a preparation process of nitrogen-aluminum co-doped hole-type (p-type) zinc oxide film.

The present invention is a p-type ZnO thin film with low resistance and high mobility prepared by thermochemical reaction of a mixed solution composed of Zn-containing organic or inorganic salt solution, N-containing organic or inorganic salt solution and Al-containing inorganic salt solution. Its resistivity is 10 ^-1 -10 ^-2 cm, and its mobility can reach up to 103cm ² V ^-1 s ^-1 , which is at a relatively high level in the world (resistivity 2-5Ωcm, carrier mobility 0.1-0.4 cm ² V ^-1 s ^-1 ), the resistivity is reduced by 2 orders of magnitude, the Hall mobility is increased by 2-3 orders of magnitude, and the grain size of the film is uniform and densely arranged, and the film has a strong (101 ) Oriented crystallization characteristics and room temperature ultraviolet luminescence characteristics.

The preparation process of the nitrogen-aluminum co-doped hole-type ZnO thin film of the present invention adopts the ultrasonic spray pyrolysis method, first cleans the substrate surface and puts it into the film-forming chamber and heats the substrate, and then uses an ultrasonic atomizer to Atomize the precursor solution, then use air or high-purity N ₂ , O ₂ , NH ₃ or Ar as the gas to input the atomized product into the film forming chamber, and finally deposit low-resistance materials on the surface of different material substrates heated to 600-900°C , High-mobility p-type ZnO film, the growth time is determined by the required thickness.

The Zn-containing organic or inorganic salt in the above-mentioned precursor solution can be zinc acetate or zinc nitrate or zinc chloride, the N-containing organic salt or inorganic salt can be ammonium acetate or ammonium nitrate, and the inorganic salt containing Al can be aluminum nitrate or chlorine Aluminum. The electrical properties of ZnO-based films, especially the resistivity and mobility, can be controlled by adjusting the doping ratio of Zn, N, Al atoms and the substrate temperature.

The realization process of the present invention can be divided into following two parts:

1. Preparation of precursor solution:

The precursor solution is an aqueous solution, and the main solute is selected as:

The Zn source is zinc acetate (Zn(CH ₃ COO) ₂ ) or zinc nitrate (Zn(NO ₃ ) ₂ ) or zinc chloride (ZnCl ₂ ).

The concentration of the Zn ²⁺ solution is 0.1-1 mol/L.

Doping element selection N, Al, where:

The N source is ammonium acetate (CH ₃ COONH ₄ ) or ammonium nitrate (NH ₄ NO ₃ ).

The concentration of NH ₄ ⁺ is 1~5mol/L;

The Al source is aluminum nitrate (Al(NO ₃ ) ₃ ) or aluminum chloride (AlCl ₃ ).

The concentration of Al ³⁺ is 0.1～1mol/L;

The molar ratio of the precursor solution is Zn ²⁺ :NH ₄ ⁺ :Al ³⁺ =1:(1-3):(0.01-0.2).

2. Deposition of p-type ZnO thin film:

The precursor solution is atomized by an ultrasonic atomizer, and the atomized gas enters the film forming chamber through the gas-liquid separation tube, and deposits a p-type ZnO thin film on the surface of the heated substrate. The deposition rate of ZnO film depends on the substrate type, substrate temperature, gas flow rate, distance between nozzle and substrate, etc., where:

The substrate is single crystal silicon wafer, quartz glass wafer or sapphire wafer.

The substrate temperature is controlled at 600-900°C.

The gas is air or high-purity N ₂ , O ₂ , NH ₃ or Ar.

The consumption rate of the atomized solution is 0.06-0.6ml per square centimeter per minute.

The distance between the nozzle and the substrate is 3-10 cm.

Advantage of the present invention has:

1) The present invention has simple equipment, convenient operation, rich Al raw material, and low production cost.

2) The electrical properties of the film are controllable and stable, and the resistivity and mobility of the film can be controlled by adjusting the doping ratio of Zn, N, and Al atoms and the substrate temperature.

3) The resistivity of the N-Al co-doped p-type ZnO thin film obtained in the present invention is in the range of 10 ^-1 -10 ^-2 Ωcm, and the mobility can reach up to 103cm ² V ^-1 s ^-1 , which is higher than the current international level (resistivity 2-5Ωcm, carrier mobility 0.1-0.4cm ² V ^-1 s ^-1 ), the resistivity is reduced by 2 orders of magnitude, the Hall mobility is increased by 2-3 orders of magnitude, and has The grain size of the thin film is uniform, densely arranged, and has such excellent characteristics as strong (101) oriented crystallization characteristics and room temperature ultraviolet luminescence characteristics, so it can better meet the application of ZnO-based optoelectronic devices.

Description of drawings

Fig. 1 is a schematic diagram of an improved ultrasonic spray pyrolysis device adopted according to the method of the present invention.

The device includes an ultrasonic nebulizer 1 , an atomizing cup 2 , a gas-liquid separation tube 3 , a film forming chamber 4 , a substrate 5 , and a substrate heater 6 .

Fig. 2 is a scanning electron microscope (SEM) photo of a nitrogen-aluminum co-doped p-type ZnO thin film. This figure shows that the crystal grains of the p-type ZnO thin film obtained in the present invention are uniform in size and densely arranged.

Fig. 3 is an X-ray diffraction (XRD) spectrum of a nitrogen-aluminum co-doped p-type ZnO thin film. This figure shows that the p-type ZnO thin film obtained in the present invention has a strong (101) oriented crystal structure, and the crystal quality of the thin film is relatively high.

Fig. 4 is a room temperature photoluminescence (PL) spectrum of a nitrogen-aluminum co-doped p-type ZnO thin film. This figure shows that the p-type ZnO film obtained by the present invention has a very strong near-band-edge ultraviolet emission peak (378nm), but the emission peak (510nm) related to structural defects is hardly detected, which proves that the film has high optical quality. And the defect concentration in the film is very low.

Detailed ways

Below with reference to Fig. 1, through the embodiment to further illustrate the concrete implementation process of the present invention and substantive characteristic and remarkable progress, but the present invention is by no means limited to embodiment.

Example 1

The substrate is a (100) plane single crystal silicon wafer. The ratio of the precursor solution is: 1mol/L Zn(CH ₃ COO) ₂ 5mL, 5mol/L CH ₃ COONH ₄ 3mL, 0.5mol/L Al(NO ₃ ) ₃ 0.5mL. The solvent used was deionized water. Pour the prepared precursor solution into the ultrasonic atomization cup. After the single crystal (100) silicon wafer was etched with hydrofluoric acid for 3 minutes, it was immediately fixed on the furnace plate, and the furnace plate was heated to 700 ° C. After the substrate reached the set temperature, the ultrasonic atomizer was started to Pure N ₂ (99.999%) is used as the gas, and the film-forming chamber maintains an atmospheric atmosphere. The atomized gas enters the film-forming chamber through the gas-liquid separation tube, and the distance between the nozzle and the substrate is kept at about 5 cm, and the spraying is stopped for about 10 minutes. The consumption rate of the precursor solution was 0.2 ml per square centimeter per minute. After incubation at 700°C for 5 minutes, it was cooled to room temperature.

The Hall effect test of the ZnO film grown under the above conditions shows that the conductivity type is p-type, that is, hole conduction. The resistivity is 1.7×10 ^-2 Ωcm. The carrier mobility is 73.6cm ² V ^-1 s ^-1 . The carrier concentration is 5.09×10 ¹⁸ cm ^-3 . Seebeck effect test results confirm that the conductivity type of the grown ZnO film is p-type.

Example 2

The ratio of the precursor solution is: 1mol/L Zn(CH ₃ COO) ₂ 5mL, 5mol/L CH ₃ COONH ₄ 2mL, 0.5mol/L AlCl ₃ 0.5mL. The substrate temperature was 650°C. The spray time is 6 minutes. After the deposition of the thin film, it was kept at 650° C. for 5 minutes and then lowered to room temperature. Other conditions are the same as Example 1. The Hall effect test of the grown ZnO thin film shows that the conductivity type is p-type, that is, hole conduction. The resistivity is 1.6×10 ^-2 Ωcm, the carrier mobility is 103cm ² V ^-1 s ^-1 , and the carrier concentration is 3.81×10 ¹⁸ cm ^-3 .

Claims (7)

1. A process for preparing a nitrogen-aluminum co-doped hole-type zinc oxide thin film material, comprising the following steps: (1) Prepare the precursor solution of zinc source, nitrogen source and aluminum source, the molar ratio in the solution is Zn ²⁺ : NH ₄ ⁺ : Al ³⁺ =1: (1-3): (0.01-0.2); (2) The precursor solution is atomized by an ultrasonic atomizer, and then air or high-purity N ₂ , O ₂ , NH ₃ or Ar is used as the gas to transport the atomized precursor solution into the film-forming chamber through the gas-liquid separation tube, and then The nozzle sprays out and deposits a hole-type ZnO film on the surface of a heated single crystal silicon wafer, quartz glass wafer or sapphire wafer substrate, and the substrate temperature is controlled at 600-900°C. 2. The preparation process of a nitrogen-aluminum co-doped hole-type zinc oxide film material according to claim 1, characterized in that the zinc source is an organic or inorganic salt solution of Zn, and the nitrogen source is an organic solution of N. Or inorganic salt solution, the aluminum source is the inorganic salt solution of Al. 3. The preparation process of a nitrogen-aluminum co-doped hole-type zinc oxide film material according to claim 1, characterized in that the zinc source is zinc acetate (Zn(CH ₃ COO) ₂ ) or zinc nitrate (Zn(NO ₃ ) ₂ ) or zinc chloride (ZnCl ₂ ), the concentration of Zn ²⁺ solution is 0.1-1mol/L. 4. The preparation process of a nitrogen-aluminum co-doped hole-type zinc oxide film material according to claim 1, characterized in that the nitrogen source is ammonium acetate (CH ₃ COONH ₄ ) or ammonium nitrate (NH ₄ NO ₃ ), the concentration of NH ₄ ⁺ is 1-5 mol/L. 5. The preparation process of a nitrogen-aluminum co-doped hole-type zinc oxide film material according to claim 1, characterized in that the aluminum source is aluminum nitrate (Al(NO ₃ ) ₃ ) or aluminum chloride (AlCl ₃ ), the concentration of Al ³⁺ is 0.1-1 mol/L. 6. The preparation process of a nitrogen-aluminum co-doped hole-type zinc oxide thin film material according to claim 1 or 2 or 3 or 4, characterized in that the consumption rate of the atomized precursor solution is per minute per square centimeter The upper consumption is 0.06-0.6ml. 7. The preparation process of a nitrogen-aluminum co-doped hole-type zinc oxide thin film material according to claim 1 or 2 or 3 or 4, characterized in that the distance between the nozzle and the substrate is 3-10 cm.

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