CN100419976C - A kind of method for preparing P-type Zn0 ohmic electrode - Google Patents

Abstract

The invention belongs to the technical field of semiconductor materials, and relates to a method for preparing a P-type ZnO ohmic electrode. Use vacuum evaporation equipment to first vapor-deposit metal Ni on p-type ZnO to form the first layer of Ni electrode material, then vapor-deposit metal Au to form the second layer of Au electrode material as the electrode, and then place the prepared electrode under low temperature in nitrogen Perform rapid thermal annealing. Due to the large work functions of Ni and Au, Ni can form alloys with metals such as Au. During rapid thermal annealing, the atoms in the metal Ni and Au and in the thin layer on the surface of the metal and p-type ZnO semiconductor material diffuse each other. The barrier height of the metal-semiconductor interface is reduced to achieve the purpose of ohmic contact. Since the adhesion between Ni and the semiconductor is better than that of Au, and Ni can reduce the "shrinking ball" effect when the metal and the semiconductor are in contact, especially after annealing, the ohmic characteristics of the electrode can be greatly improved; in addition, the chemical stability of Au is better, Evaporating the Au film on Ni can effectively avoid the degradation of the electrode characteristics caused by the direct contact between the electrode material and the external environment, and improve the stability and life of the electrode.

Description

A kind of method for preparing P-type ZnO ohmic electrode

technical field

The invention belongs to the technical field of semiconductor materials and relates to a method for preparing a P-type ZnO ohmic electrode by utilizing Ni and Au materials and vacuum evaporation and thermal annealing techniques.

Background technique

Since the first discovery of room temperature ultraviolet stimulated emission of ZnO in 1997, ZnO-based semiconductor materials and devices have become a hot spot in the current international frontier topics. Making optoelectronic devices such as ultraviolet semiconductor lasers and light-emitting diodes is one of the most important practical applications of ZnO. However, since ZnO is usually n-type when undoped, it is difficult to prepare p-type samples, which has become a major obstacle to the preparation of ZnO optoelectronic devices. At the same time, these semiconductor optoelectronic devices need to transmit current through electrodes. Good electrode contact can reduce the working voltage and power dissipation, while poor electrode contact can lead to deterioration of device performance and eventually lead to device failure. Therefore, the quality of the electrode preparation is directly related to the electrical and optical characteristics of the device. Relatively speaking, the preparation of n-type ZnO ohmic contact electrodes is relatively easy, but due to the large work function of p-type ZnO, it is difficult to find a suitable single electrode material. Therefore, preparing a good p-type ohmic contact electrode has become another difficulty in device preparation. At present, there are not many research results on the preparation of p-type ZnO ohmic electrodes reported internationally, and most of them use noble metals such as Au as materials for p-type ZnO ohmic contact electrodes. It has disadvantages such as poor adhesion to materials, which seriously affects the performance and stability of the device. Secondly, the current-voltage relationship curve given in the report shows that the voltage applied to the ohmic contact is low. If the potential barrier of metal and semiconductor is high, it is difficult to explain the ohmic characteristics of the electrode from the current-voltage curve.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a p-type ZnO ohmic electrode with good repeatability and superior performance. Vacuum evaporation of Ni and Au, and low-temperature rapid thermal annealing technology are used to effectively utilize the interaction between metals and metals and semiconductors to prepare ohmic electrodes with stable performance and good contact characteristics.

To achieve the above goals, the present invention uses vacuum evaporation technology and rapid thermal annealing technology. Metal Ni is vapor-deposited on the p-type ZnO by vacuum evaporation equipment to form the first layer of Ni electrode material. Then metal Au is vapor-deposited to form a second layer of Au electrode material as an electrode. Next, the prepared electrode is subjected to rapid thermal annealing at a low temperature in nitrogen, such as below 500°C. Since both Ni and Au have large work functions, Ni can form alloys with metals such as Au. In rapid thermal annealing, the interdiffusion of atoms between the metal Ni and Au and in the thin layer of the metal and p-type ZnO semiconductor material surface reduces the barrier height of the metal-semiconductor interface and achieves the purpose of ohmic contact.

In order to clearly understand the present invention, the preparation process of the p-type ZnO ohmic electrode is described in detail.

Firstly, the p-type ZnO sheet should be cleaned. Ultrasonic cleaning was performed with acetone and absolute ethanol respectively for 5 to 10 minutes. After rinsing with deionized water, dry with dry _N2 to remove surface impurities and improve electrode adhesion.

The electrode pattern with the required shape and spacing is fabricated on the metal or other material mask by mechanical processing technology or other physical and chemical methods, and the area of the mask is at least several times larger than the area of the ZnO sheet. The mask has a front surface and a back surface. Place the p-type ZnO sheet facing the pattern on the back surface of the mask, stick the back of the ZnO sheet to the non-pattern area on the back of the mask with tape, and put them together into the vacuum evaporation chamber of the vacuum evaporation coating machine. On the sample holder, place the front surface of the mask plate downwards toward the evaporation source, and the distance between the mask plate and the evaporation source is between 10 and 15 cm. Ni and Au with a purity of 99.99% were placed in respective tungsten boats of evaporation sources as evaporation materials. The vacuum of the vacuum chamber is evacuated to below 6.6×10 ^-3 Pa by a mechanical pump and a diffusion pump. Ni is evaporated first, and then Au is evaporated after Ni is evaporated. The film thickness of Ni and Au is generally on the order of several microns.

After the vacuum evaporation, remove the evaporated electrode sheet from the mask plate, remove the tape on the back of the ZnO sheet, and put it into an annealing furnace for rapid thermal annealing in a nitrogen (N ₂ ) atmosphere below 500°C. The rapid thermal annealing time is generally 150 seconds.

The invention utilizes Ni and Au double-layer films, which can greatly reduce the disadvantage of poor adhesion when a single-layer Au film is used, and avoid the phenomenon of "ball shrinkage". The interdiffusion has a great effect on reducing the barrier between metal and semiconductor interface. The above Au film can also serve the purpose of protecting the electrodes, avoiding the influence of the external environment on the characteristics of the electrodes. The rapid thermal annealing temperature adopted is relatively low, which avoids changes in the structure and physical and chemical properties of semiconductor materials at high temperatures, and the current-voltage characteristics are significantly improved, and the resistance is significantly reduced. These are of great significance for the preparation of good p-type ZnO ohmic electrodes. It lays the foundation for the preparation and application of ZnO-based ultraviolet semiconductor lasers and light-emitting diodes and other optoelectronic devices, and also provides a reference for the preparation of other wide-bandgap semiconductor materials and device ohmic electrodes.

The combination of vacuum evaporation technology and rapid thermal annealing process to prepare ohmic electrodes has the advantages of simple equipment, simple and easy operation, and low operating cost. Low-temperature rapid thermal annealing after vacuum evaporation electrodes can promote the mutual diffusion between metal and semiconductor materials, improve the adhesion ability between electrode materials and semiconductors, thereby effectively reducing the resistance between them, and further improving the ohmic contact characteristics.

Ni and Au double-layer metal film is used as the electrode material. On the one hand, because Ni has many advantages when it is in contact with the semiconductor, its adhesion to the semiconductor is better than that of Au. At the same time, Ni can reduce the "shrinkage" when the metal is in contact with the semiconductor. effect, can also promote the interface reaction, especially after annealing can greatly improve the ohmic characteristics of the electrode; on the other hand, due to the good chemical stability of Au, evaporation of Au film on Ni can effectively prevent the electrode material from being directly contacted with the external environment. The degradation of electrode characteristics caused by contact can achieve the purpose of improving the stability and life of the electrode.

Description of drawings

代表实例1中在N₂中300℃下快速热退火150秒的样品的实验值。Fig. 1 is the current-voltage (IV) relationship curve of the ohmic electrode prepared according to the experimental conditions of Example 1 of the present invention, wherein "■" represents the experimental value of the sample in N in ₂₀₀ °C for 150 seconds under rapid thermal annealing in Example 1 ,

Represents the experimental values of the sample in Example 1 that was rapidly thermally annealed at 300 °C in _N for 150 s.

Fig. 2 is the current-voltage (IV) relationship curve of the ohmic electrode prepared according to the experimental conditions of Example 2 of the present invention, wherein "▲" represents the experimental value of the sample in _N in 300°C for 150 seconds under rapid thermal annealing in Example 2 , "●" represents the experimental value of the sample in Example 2 that was rapidly thermally annealed at 400 °C for 150 s in _N2 .

Detailed ways

Example 1, on high-resistance p-type ZnO, after evaporating Ni and Au, rapid thermal annealing is carried out at 200° C. or 300° C. in nitrogen for 150 seconds.

Selection of experimental conditions:

The p-type ZnO flakes are nitrogen-doped high-resistance p-type ZnO grown on sapphire (Al ₂ O ₃ ) by molecular beam epitaxy (MBE), with an area of about 1 cm ² and a resistivity of about 60Ω·cm.

First, the p-type ZnO sheet was cleaned by ultrasonic cleaning with acetone and absolute ethanol for 5 minutes respectively; rinsed with deionized water and blown dry with dry N ₂ . A tantalum sheet with a thickness of 0.2mm and an area of 6×6cm2 is used as a metal mask, and two small circular holes with ^an area of ^1mm2 are formed on the tantalum sheet by machining as the electrode shape. The distance between the two electrodes is 2mm. The distance between the membrane plate and the evaporation source is 12 cm, and the purity of Ni and Au is 99.99%. The vacuum in the vacuum chamber was evacuated to 5.85×10 ^-3 Pa by a mechanical pump and a diffusion pump. Ni is first evaporated to a thickness of about 1 μm, and then Au is evaporated to a thickness of about 1 μm. After the evaporation, take out the sheet and put it into an annealing furnace for rapid thermal annealing at 200°C and 300°C in _N2 for 150 seconds, and the measurement of the current-voltage (IV) relationship is carried out in a dark room.

Utilize the present invention, on the high-resistance p-type ZnO, by evaporating Ni and Au, through 200 ℃, 300 ℃, thermal annealing, find from current-voltage (I-V) characteristic curve, in larger test voltage range (greater than ±10V), the linearity of the curve is very good, compared with the sample without annealing, the ohmic contact characteristics are greatly improved.

Example 2, on the low-resistance p-type ZnO, after evaporating Ni and Au, rapid thermal annealing is carried out at 300° C. or 400° C. in nitrogen for 150 seconds.

P-type ZnO flakes are nitrogen-doped low-resistance p-type ZnO grown on sapphire (Al ₂ O ₃ ) by molecular beam epitaxy (MBE), with an area of about 1 cm ² and a resistivity of about 4Ω·cm.

First, the p-type ZnO sheet was cleaned by ultrasonic cleaning with acetone and absolute ethanol for 5 minutes respectively; rinsed with deionized water and blown dry with dry N ₂ . A tantalum sheet with a thickness of 0.2mm and an area of 6×6cm2 is used as a metal mask, and two small circular holes ^with an area of ^1mm2 are formed on the tantalum sheet by machining as the electrode shape, and the distance between the two electrodes is 2mm. The distance between the mask plate and the evaporation source is 12 cm. Ni and Au are 99.99% pure. During vacuum evaporation, the vacuum degree is 5.85×10 ^-3 Pa, Ni is evaporated first, and the thickness is 1 μm, and then Au is evaporated, and the thickness is also 1 μm. After the evaporation, take out the sheet, put it into the annealing furnace for rapid thermal annealing at 300°C, 400°C, and _N2 for 150 seconds. Measurements of the current-voltage (IV) relationship were performed in a dark room.

Utilizing the present invention, on the low-resistance p-type ZnO, by evaporating Ni and Au, after thermal annealing at 300°C and 400°C, the current-voltage characteristic curve also proves that a good ohmic contact electrode is obtained.

Claims (5)

1. A method for preparing p-type ZnO ohmic electrodes, comprising utilizing vacuum evaporation equipment to vapor-deposit metal Ni on p-type ZnO earlier to form a first layer of Ni electrode material, and then vapor-deposit metal Au to form a second layer of Au electrode material, Form a Ni and Au double-layer film; next, the prepared electrode is subjected to rapid thermal annealing at a low temperature in nitrogen, which is characterized by: (a) ultrasonically clean the p-type ZnO sheet with acetone and absolute ethanol respectively for 5 to 10 minutes, rinse with deionized water and blow dry with dry _N2 ; (b) making an electrode mask, and fixing the p-type ZnO sheet on the mask; (c) using vacuum evaporation equipment to evaporate Ni under the condition of less than 6.6×10 ^-3 Pa, and the purity of Ni is at least 99.99%; (d) evaporating Au on Ni, the purity of Au is at least 99.99%; (e) Perform rapid thermal annealing at a temperature lower than 500° C. in a nitrogen atmosphere, and the thermal annealing time is 150 seconds. 2. the method for preparing P-type ZnO ohmic electrode according to claim 1 is characterized in that the electrode pattern of desired shape and spacing is made on metal or other materials as mask plate by machining process or other physicochemical methods , the area of the mask is at least several times larger than the area of the ZnO sheet, the mask has a front surface and a rear surface; the p-type ZnO sheet is placed facing the pattern on the rear surface of the mask, and the ZnO sheet The back side is adhered to the non-graphic area on the back of the mask plate with adhesive tape, and then placed together on the sample holder of the vacuum evaporation chamber of the vacuum evaporation coating machine, so that the front surface of the mask plate is placed downwards towards the evaporation source, and the mask plate and The distance between the evaporation sources is between 10 and 15 cm: Ni and Au are placed as evaporation materials in the tungsten boats of the respective evaporation sources; the vacuum of the vacuum chamber is pumped to 6.6×10 ^-3 Pa by a mechanical pump and a diffusion pump Next, first evaporate Ni, and then evaporate Au after Ni evaporates. The film thickness of Ni and Au is on the order of several microns; The tape is placed in an annealing furnace for rapid thermal annealing. 3. the method for preparing p-type ZnO ohmic electrode according to claim 2, is characterized in that p-type ZnO sheet is low-resistance or high-resistance material. 4. the method for preparing p-type ZnO ohmic electrode according to claim 3, it is characterized in that p-type ZnO sheet is to adopt the molecular beam epitaxy (MBE) method to grow on the high resistance p-type ZnO of nitrogen doping on sapphire, area is 1cm ² , with a resistivity of 60Ω·cm; the p-type ZnO sheet was ultrasonically cleaned with acetone and absolute ethanol for 5 minutes; a tantalum sheet with a thickness of 0.2mm and an area of 6×6cm ² was used as a metal mask, and mechanically Process the tantalum sheet to form two circular holes with an area of ^1mm2 as the electrode shape, the distance between the two electrodes is 2mm, and the distance between the mask plate and the evaporation source is 12cm; the vacuum chamber is pumped by a mechanical pump and a diffusion pump Vacuum to 5.85×10 ^-3 Pa; the thickness of evaporated Ni is 1 μm, and the thickness of re-evaporated Au is also 1 μm; after evaporation, take out the sheet and put it into an annealing furnace for rapid thermal annealing at 200°C and 300°C respectively. 5. the method for preparing p-type ZnO ohmic electrode according to claim 3, it is characterized in that p-type ZnO sheet is to adopt molecular beam epitaxy (MBE) method to grow the low resistance p-type ZnO of nitrogen doping on sapphire, area is 1cm ² , with a resistivity of 4Ω·cm; the p-type ZnO sheet was ultrasonically cleaned with acetone and absolute ethanol for 5 minutes; a tantalum sheet with a thickness of 0.2mm and an area of 6×6cm ² was used as a metal mask, and passed Machining forms two small circular holes with an area of ^1mm2 on the tantalum sheet as the electrode shape, the distance between the two electrodes is 2mm, and the distance between the mask plate and the evaporation source is 12cm; the vacuum degree during vacuum evaporation is 5.85× 10 ^-3 Pa, the thickness of evaporating Ni is 1 μm, and the thickness of re-evaporating Au is also 1 μm; after evaporation, take out the sheet and put it into an annealing furnace for rapid thermal annealing at 300°C and 400°C respectively.

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