CN103898600B - A kind of preparation method who reduces GaAs film impurities content - Google Patents

Abstract

The invention discloses a preparation method for reducing the impurity content of a GaAs thin film. The method includes two steps of mother liquor purification and epitaxial growth. The steps are: put raw materials Ga and GaAs into a graphite boat, vacuumize, pass hydrogen, and regulate the upper furnace Form a stable temperature difference with the lower furnace and start to purify the mother liquor; after purification, open the valve so that the mother liquor in the upper left chamber of the graphite boat flows into the right chamber, and adjust the temperature of the furnace to be the same as that of the upper furnace. After the mother liquor is homogenized, remove the baffle , insert the substrate control rod until the substrate is immersed in the mother liquid, cool down at a constant speed, and start epitaxial growth. After the end, pull the control rod until the substrate leaves the liquid surface, turn the control rod, shake off the residual mother liquid, and cool to room temperature. The invention has the advantages that the purification step reduces the impurity content of the film, expands the application range, has simple process and can be mass-produced on a large scale.

Description

A preparation method for reducing impurity content of GaAs thin film

technical field

The present invention relates to a preparation method of GaAs film, in particular to a method for purifying saturated mother liquor by utilizing the Soret effect of the solution (that is, if a constant temperature difference is formed at both ends of the solution, the solute will generally diffuse from the high temperature area to the low temperature area), thereby reducing the thickness of the film. The film preparation method of the impurity content, and provides a graphite boat with a new structure to realize the method, especially suitable for the preparation of high-purity III-V, II-VI group compound semiconductor films, such as: GaAs, InAsSb, HgCdTe and other high-purity film.

Background technique

The type and concentration of impurities are important parameters of semiconductor materials. For example, when Be ions are doped, GaAs exhibits p-type semiconductor characteristics; when Te ions are doped, GaAs exhibits n-type semiconductor characteristics. At the same time, by changing the impurities of Be and Te ions Concentration can adjust the mobility and conductivity of GaAs. However, impurities can also form defects or traps in the GaAs thin film, generate non-radiative recombination centers, and reduce the mobility and photoelectric conversion efficiency of the device. Therefore, it is very important to control the impurity type and content of the GaAs thin film according to the structural design requirements of the device.

The infrared focal plane detector with blocking impurity band has the characteristic of long response wavelength, and is especially suitable for the observation and research of infrared astronomy. It is a kind of infrared detection device that has received wide attention. As) covers 10-25 μm, silicon-doped antimony (Si:Sb) covers 20-40 μm, germanium-doped gallium (Ge:Ga) covers 40-70 μm, strained germanium-doped gallium (Ge:Ga) covers 70-200 μm, especially GaAs Tellurium-doped (GaAs:Te) has a response wavelength range of 30-300 μm, and is the optimal detector for detecting cold objects in deep space. A common feature of this type of device is that it requires the growth of a high-purity barrier layer, for example, GaAs barrier The carrier concentration of the layer is required to be <10 ^-13 cm ^-3 , which is difficult to achieve by conventional film growth techniques (see literature: Proc.SPIE Vol.4486:200).

Contents of the invention

The object of the present invention is to provide a kind of preparation method that utilizes the Soret effect of solution to reduce the impurity content of GaAs film, and provide a kind of novel graphite boat that realizes this method, it is characterized in that comprising the following steps:

①Using high-purity Ga and GaAs as raw materials, use a common method to clean the surface of high-purity GaAs, dry it with nitrogen, and put GaAs and Ga into the left chamber of a special graphite boat;

② After evacuating the system until the pressure of the system is <10 ^-4 Pa, introduce high-purity hydrogen, and then adjust the temperature of the three-stage vertical furnace so that a stable temperature difference is formed between the upper furnace and the lower furnace. The temperature of the upper furnace is 700-850°C. 50-150°C higher than the lower furnace, start to purify the mother liquor;

③Insulate for 5-10 hours, after the mother liquor is purified, open the valve in the middle of the graphite boat, so that the purified GaAs saturated mother liquor on the left side of the graphite boat flows into the right side of the graphite boat;

④ Adjust the temperature of the intermediate furnace and the lower furnace to keep them consistent with the temperature of the upper furnace, and then keep warm for 2 to 4 hours. After the mother liquor is re-homogenized, remove the substrate baffle and slowly insert the substrate control rod so that The substrate is just immersed in the GaAs saturated mother liquor in the right chamber of the graphite boat, and then the vertical furnace cools down at a constant rate of 2-10°C/h to start the epitaxial growth of the GaAs film;

⑤ After the epitaxy is completed, pull up the substrate control rod, so that the substrate just leaves the liquid level of the GaAs saturated mother solution, and then rotate the substrate control rod at a speed of 350-850rpm to shake off the residual mother solution on the substrate surface;

⑥ Cool down to room temperature and end the growth.

The structure of the special graphite boat is different from the graphite boat used in the current vertical centrifugal liquid phase epitaxy method, and is characterized in that:

①The graphite boat is divided into left and right chambers. The height of the left chamber is about twice that of the right chamber. The left chamber is used to purify the mother liquor, and the right chamber is used to epitaxially grow GaAs thin films;

②There is a hole in the middle of the left chamber and the right chamber, which is separated by graphite blocks, and is used to transfer the purified mother liquor from the upper part to the right growth chamber.

The advantages of the present invention are:

1. The GaAs film is purified in the left chamber of the graphite boat before the epitaxial growth, which greatly reduces the content of various types of impurities in the film. This is because the left chamber of the graphite boat is very long. By controlling the temperature difference between the upper and lower furnaces of the three-stage vertical furnace, according to the Soret effect, it can be seen that the impurities in the saturated mother liquor gradually diffuse to the low-temperature area located in the lower section of the furnace, so that the upper part of the mother liquor is purified. , and then transfer this part of the purified mother liquor to the growth chamber on the right side of the graphite boat for epitaxial growth, thereby reducing the impurity content of the film.

2. The present invention can set the structure and temperature difference distribution of the three-stage vertical furnace for a certain specific impurity, so as to achieve the best purification effect for this impurity.

3. The present invention has simple structure, low preparation cost and easy popularization and application.

Description of drawings

Fig. 1 is a graphite boat according to an embodiment of the present invention, wherein: (a) is a front view, (b) is a left view, and (c) is a top view.

Fig. 2 is a schematic diagram of the corresponding system state when the mother liquor is purified in the embodiment of the present invention.

FIG. 3 is a schematic diagram of a corresponding system state during epitaxial growth in an embodiment of the present invention.

detailed description

The process technology for preparing GaAs thin films with low impurity content by using a preparation method for reducing the impurity content of GaAs thin films according to the present invention will be described in detail below in conjunction with the accompanying drawings and specific examples:

According to the solubility of GaAs in Ga at different temperatures, combined with the substrate floating technology to determine the quality of Ga and GaAs, then use the general method to clean the surface of high-purity GaAs, dry it with nitrogen, and put GaAs and Ga into a special graphite boat 2 Inside chamber 21 on the left side. Three views of the graphite boat 2 are shown in FIG. 1 .

After evacuating the system until the pressure of the system is <10 ^-4 Pa, high-purity hydrogen gas is introduced, and then the temperature of the three-stage vertical furnace 1 is adjusted so that the temperature of the upper furnace 11 is 700-850°C, which is 50-80°C higher than that of the lower furnace 13. At 150°C, the mother liquor was purified. The state diagram of the system at this time is shown in Fig. 2 .

After 5-10 hours of heat preservation, the valve 23 in the middle of the graphite boat 2 is opened, so that the partially purified GaAs saturated mother liquor 6 on the left side chamber 21 of the graphite boat flows into the right side chamber 22 of the graphite boat.

Adjust the temperature of the intermediate furnace 12 and the lower furnace 13 so that they are kept the same temperature as the upper furnace 11, and then keep warm for 2 to 4 hours, remove the substrate baffle plate 4, and slowly insert the substrate control rod 3 to make the substrate The bottom 5 is just immersed in the GaAs saturated mother liquor in the right chamber 22 of the graphite boat, and then the vertical furnace 1 cools down at a constant rate of 2-10°C/h to start the epitaxial growth of the GaAs film. The state diagram of the system at this time is shown in Fig. 3 .

After the epitaxy is completed, the substrate control rod 3 is pulled upward so that the substrate 5 just leaves the liquid level of the GaAs saturated mother liquid, and then the substrate control rod 3 is rotated at a speed of 350-850 rpm to shake off the residual liquid on the surface of the substrate 5 . Finally, the system was cooled to room temperature and the growth was terminated.

By adjusting the temperature and temperature difference between the upper and lower furnaces in the mother liquor purification step, and the temperature of the vertical furnace in the epitaxial growth step, the impurity content can be effectively controlled, and GaAs films with different impurity concentrations can be obtained.

Claims (1)

1. A preparation method that reduces the impurity content of GaAs thin film, is characterized in that comprising the following steps: ①Using high-purity Ga and GaAs as raw materials, adopt a common method to clean the surface of high-purity GaAs, dry GaAs and Ga with nitrogen after drying, and put GaAs and Ga in the left chamber (21) of the special graphite boat (2); Special graphite boat (2) is divided into left and right two chambers, and the height of left chamber (21) is twice that of right chamber (22), and left chamber (21) is used for purifying mother liquor (6), right The side chamber (22) is used for the epitaxial growth of GaAs thin films; there is a hole in the middle of the left chamber (21) and the right chamber (22), which is isolated with a graphite block (23), and is used to transfer the purified mother liquor from the upper part into Right growth chamber (22); ②Vacuumize the system until the pressure of the system is <10 ^-4 Pa, then introduce high-purity hydrogen, then adjust the temperature of the three-stage vertical furnace (1), so that the upper furnace (11) and the lower furnace (13) form a stable temperature difference, the upper furnace The temperature of the furnace (11) is 700 to 850°C, which is 50 to 150°C higher than the temperature of the lower furnace (13), and the purification of the mother liquor (6) begins; 3. keep warm for 5～10 hours, after the mother liquor is purified, open the graphite block (23) in the middle of the graphite boat (2), so that the GaAs saturated mother liquor after the part purification on the left side chamber of the graphite boat (21) flows into the right side chamber of the graphite boat ( twenty two); ④ Adjust the temperature of the intermediate furnace (12) and the lower furnace (13) so that they are consistent with the temperature of the upper furnace (11), and then keep warm for 2 to 4 hours. After the mother liquor is re-homogenized, remove the substrate baffle ( 4), slowly insert the substrate control rod (3), so that the substrate (5) is just immersed in the GaAs saturated mother liquor in the right chamber (22) of the graphite boat, and then the vertical furnace (1) is heated at a constant temperature of 2 to 10°C/h. The temperature is lowered at a low rate, and the epitaxial growth of GaAs film is started; ⑤ Pull up the substrate control rod (3) after the epitaxy is completed, so that the substrate (5) just leaves the liquid level of the GaAs saturated mother liquid, and then rotate the substrate control rod (3) at a speed of 350-850rpm to shake off the substrate ( 5) residual mother liquor on the surface; ⑥ Cool down to room temperature and end the growth.