CN101603208A - Quartz tube for growing semi-insulating gallium arsenide and method for doping carbon in gallium arsenide - Google Patents

Abstract

A method for doping gallium arsenide with carbon by using a quartz tube growing semi-insulating gallium arsenide, comprising the following steps: step 1: polycrystalline synthesis of 7N Ga and 7N As to form GaAs polycrystal; step 2: synthesizing Good GaAs polycrystal, seed crystal and _B2O3 put into PBN crucible; Step 3: Put PBN crucible into the quartz body of the quartz tube; Step ₄ : Fix the pure graphite in the quartz groove on the quartz cap of the quartz tube Inside; step 5: cover the quartz body and the quartz cap, vacuumize, weld the quartz body and the quartz cap of the quartz tube with an oxyhydrogen flame; step 6: put the welded quartz tube into a VGF single crystal furnace, and carry out atmosphere doping Miscellaneous, single crystal growth; step 7: soak the PBN crucible after crystal growth in methanol to obtain GaAs single crystal, and complete the preparation of GaAs single crystal.

Description

Quartz tube for growing semi-insulating gallium arsenide and method for doping carbon in gallium arsenide

technical field

The invention relates to the VGF (vertical gradient solidification) technology of high-performance compound semiconductor SI-GaAs single crystal. The material is widely used mainly in the field of high-speed microelectronics, such as power amplifiers in radio frequency circuits, microwave monolithic integrated circuits (MMICs), etc.

Background technique

GaAs has excellent electrical properties such as high electron mobility, direct band gap, and wide band gap, and has been widely used in the fields of optoelectronics and microelectronics. For microelectronic ultra-high-speed circuits, semi-insulating SI-GaAs single crystals are required, that is, they have high resistance (greater than 10 ⁷ Ω·cm). Generally speaking, high-purity GaAs itself is semi-insulating, but due to the complicated preparation process and high cost, industrial production uses compensation principles to achieve high resistance.

With the continuous development of GaAs single crystal growth process, the compensation mechanism in the material is constantly changing. After the PBN crucible replaces the quartz crucible, the silicon contamination is greatly reduced. Therefore, it is possible to obtain stable semi-insulating properties without intentional doping. It is generally believed that the semi-insulating properties of non-doped SI-GaAs crystals are due to the compensation balance between the deep-level trap EL ₂ energy level and the shallow acceptor impurity C in the crystal.

According to Martin's three-level model,

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}<span\; class="notranslate">\; \&Proportional;</span>\frac{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; EL</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ]</span>}{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; SD</span>}<span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

ρ is resistivity, [EL2] is EL2 defect concentration, [C] is C concentration, and [SD] is shallow donor concentration. It can be seen from formula (1) that the single crystal resistivity depends on the compensation degree of the material: [EL2]/([C]-[SD]). EL2 is a kind of energy level trap in GaAs, which is related to the point defect AsGa (arsenic occupies the gallium site). Its concentration is mainly controlled by controlling the GaAs polycrystalline composition and growth conditions. In the process, its uniformity is relatively easy Control, generally its concentration is 10 ¹⁶ cm ^-3 . Secondly, the purity of conventional polycrystalline materials is at least 6N, so the concentration control of shallow donors is relatively easy, and the concentration can be lower than 10 ¹⁵ cm ^-3 . Therefore, controlling the C concentration becomes an important factor for obtaining a semi-insulating GaAs single crystal, and it is also a technical difficulty. To obtain high resistance, the C concentration generally needs to be around 1-3×10 ¹⁵ cm ^-3 .

A commonly used method is to pre-dope GaAs polycrystalline with C. According to 2 inches of GaAs per furnace, the required polycrystalline material is about 2Kg, and the theoretical C demand is 0.05mg. The current method used in production is to achieve quantification through high-precision balance weighing, which is extremely difficult to operate. Secondly, the segregation coefficient of C in GaAs is greater than 1, and it tends to exist in solid crystals. Therefore, in the crystal, C is distributed exponentially along the axial direction, the concentration of C in the tail is low, the compensation degree is insufficient, and the carrier concentration is sharp. increase, prone to low resistance.

Atmosphere doping is a way to control the C concentration. However, under the vertical gradient solidification process of the quartz tube-PBN system currently used, it is difficult to achieve atmosphere doping. First, there is no contact with ℃ in the entire growth system, and secondly, the currently used quartz tube is mainly designed to provide a high vacuum environment for crystal growth, and the structure of the quartz tube cannot meet the requirements of atmosphere doping.

Contents of the invention

The purpose of the present invention is to solve the difficult problem of weighing and controlling trace amounts of C, and at the same time, make the distribution of C concentration in the crystal uniform and improve the overall electrical performance. The basic principle of the invention is to control the amount of C doped by controlling the concentration in the atmosphere, so as to realize the semi-insulation of GaAs.

A quartz tube for growing semi-insulating gallium arsenide of the present invention comprises: a quartz body and a quartz cap covered therewith, wherein a quartz groove is fixed on the inner top of the quartz cap, and the height of the covered quartz groove is Less than the depth of the quartz cap.

Wherein said quartz tank is cylindrical or square or clip-shaped.

A method for doping carbon in gallium arsenide by using the quartz tube for growing semi-insulating gallium arsenide as claimed in claim 1, is characterized in that it comprises the following steps:

Step 1: Polycrystalline synthesis of 7N Ga and 7N As to form GaAs polycrystal;

Step 2: Put the synthesized GaAs polycrystal, seed crystal and B ₂ O ₃ into the PBN crucible;

Step 3: Put the PBN crucible into the quartz body of the quartz tube;

Step 4: Fix pure graphite in the quartz groove on the quartz cap of the quartz tube;

Step 5: Cover the quartz body and the quartz cap, vacuumize, and weld the quartz body and the quartz cap of the quartz tube with an oxygen-hydrogen flame;

Step 6: Put the welded quartz tube into the VGF single crystal furnace for atmosphere doping and single crystal growth;

Step 7: Soak the PBN crucible after crystal growth in methanol to obtain GaAs single crystal, and complete the preparation of GaAs single crystal.

The growth temperature of the single crystal mentioned therein is 1220°C-1245°C.

The single crystal growth described therein takes 110 hours to 130 hours.

The methanol immersion mentioned therein is carried out in an ultrasonic atmosphere.

Wherein the methanol soaking time is 8 hours-12 hours, and the soaking temperature is normal temperature.

Wherein said B ₂ O ₃ dosage is 15 grams.

Description of drawings:

In order to further disclose the specific technical content of the present invention, the following detailed description is as follows in conjunction with the embodiments and accompanying drawings, wherein:

Figure 1 is a schematic diagram of the structure of a quartz tube suitable for atmosphere doping.

Wherein: 1 is a quartz body, 2 is a quartz cap, and 3 is a quartz groove.

Detailed ways

The purpose of the present invention is to provide an atmosphere C-doped method for growing semi-insulating gallium arsenide by the vertical gradient solidification technology of the quartz tube-PBN system, which has the advantages of easier control of C concentration and better electrical uniformity of the material.

In order to achieve the above object, the present invention provides a new quartz tube structure, as shown in Fig. 1, comprising: a quartz body 1 and a quartz cap 2 covered therewith, wherein the inner top of the quartz cap 2 is fixed There is a quartz groove 3; It is characterized in that:

The height of the cover quartz groove 3 is less than the depth of the quartz cap 2; this can avoid the oxidation of graphite in the welded quartz tube stone; the position of graphite in the quartz tube can be quantified by the depth of the quartz groove 3, and it can be realized by adding a verified temperature field heating temperature.

The quartz groove 3 described therein is cylindrical or square or clip-shaped; the effect of the quartz groove 3 is to fix the graphite, to ensure that there is sufficient friction between the quartz groove 3 and the graphite, and prevent the graphite from falling into the gallium arsenide Polycrystalline; the structure of this quartz cap 2 can be realized by setting a mould.

A method of doping carbon in gallium arsenide using a quartz tube as shown in Figure 1 of the present invention comprises the following steps:

Step 1: Polycrystalline synthesis of 7N Ga and 7N As to form GaAs polycrystalline; compound semiconductors are not as pure as elemental semiconductors such as silicon and germanium, and the use of higher purity gallium and arsenic can avoid the impact of impurity elements on electrical properties , while eliminating C in raw materials;

Step 2: Put the synthesized GaAs polycrystal, seed crystal and B ₂ O ₃ into the PBN crucible; the role of the seed crystal is to guide the crystal growth, so that the grown crystal has a definite crystal orientation; B ₂ O ₃ is very, very An important liquid sealant, which can prevent the direct contact between the melt and the crucible and increase the crystallization rate; at the same time, it can getter and prevent arsenic volatilization. The water content of B ₂ O ₃ should not only ensure that B ₂ O ₃ and PBN crucible have a certain degree of wettability, but also not be too high, so as not to generate air bubbles and cause pits on the crystal surface;

Step 3: Put the PBN crucible into the quartz body 2 of the quartz tube; the main function of the quartz tube is to provide a high vacuum growth environment, and its basic structure is the quartz body 1 and the quartz cap 2;

Step 4: Fix pure graphite in the quartz groove 3 on the quartz cap 2 of the quartz tube; to achieve atmosphere doping, there must be a C source, and adding a quartz groove on the quartz cap can add a C source to achieve atmosphere doping , the advantage of atmosphere doping is that there is a better degree of freedom to control the distribution of C concentration in the crystal, so that the overall performance of the material is more uniform;

Step 5: Cover the quartz body 1 and the quartz cap 2, evacuate, and weld the quartz body 1 and the quartz cap 2 of the quartz tube with a hydrogen-oxygen flame; the crystal growth must be grown in the absence of oxygen and other impurities. The first is that oxygen will oxidize arsenic to form arsenic trioxide, and the second is that it will bring impurities into the material and change the properties of the material;

Step 6: Put the welded quartz tube into the VGF single crystal furnace for atmosphere doping and single crystal growth, the growth temperature is 1220°C-1245°C, and the growth time is 110 hours-130 hours; solidify in the vertical gradient In technology, crystal growth is driven by temperature gradient, which is generally achieved by designing a suitable temperature field;

The atmosphere is doped in the following way:

The route of C incorporation into GaAs is:

Free Ga in GaAs undergoes the above chemical reaction with CO and _CO2 in the atmosphere, C is introduced into GaAs, and the pressure of CO and _CO2 is maintained to be equal, so that the doped C is uniform along the axial direction, maintaining CO and _CO2, etc. The path of pressure is the balance of its formation and precipitation.

The formation pathways of CO and _CO2 are:

O ₂ and H ₂ O are derived from graphite, and their generation rate can be controlled by adjusting the appropriate content.

The precipitation route of C:

The C in the crystal will react with B ₂ O ₃ and the H ₂ O in it to precipitate C and reduce the C content; at the same time, it will increase the CO concentration in the atmosphere.

Step 7: Soak the PBN crucible after crystal growth in methanol, the methanol immersion is carried out in an ultrasonic atmosphere, the time of methanol immersion is 8 hours to 12 hours, and the temperature of immersion is normal temperature to obtain a GaAs single crystal, The preparation of GaAs single crystal is completed.

PBN crucibles are very expensive, brittle, and easy to crack. Generally, they need to be recycled and reused to reduce production costs. Generally, at room temperature, the grown crystal is closely combined with the crucible wall, and the crucible is easily damaged when the crystal is taken out. Using chemical methods, the B ₂ O ₃ can be dissolved through the chemical reaction of methanol and B ₂ O ₃ to take out the crystals.

What is disclosed in the present invention is one of the preferred embodiments. All partial changes or modifications derived from the technical idea of the present invention and easily deduced by those familiar with the technology are all within the scope of the claims of the present invention. category.

Claims (8)

1. A quartz tube for growing semi-insulating gallium arsenide, comprising: a quartz body and a quartz cap covered therewith, wherein a quartz groove is fixed on the inner top of the quartz cap, and the height of the covered quartz groove is Less than the depth of the quartz cap. 2. The quartz tube for growing semi-insulating gallium arsenide according to claim 1, wherein the quartz tank is in the shape of a cylinder, a square cylinder or a clip. 3. A method for doping gallium arsenide with carbon by using the quartz tube for growing semi-insulating gallium arsenide as claimed in claim 1, comprising the following steps: Step 1: Polycrystalline synthesis of 7N Ga and 7N As to form GaAs polycrystal; Step 2: Put the synthesized GaAs polycrystal, seed crystal and B ₂ O ₃ into the PBN crucible; Step 3: Put the PBN crucible into the quartz body of the quartz tube; Step 4: Fix pure graphite in the quartz groove on the quartz cap of the quartz tube; Step 5: Cover the quartz body and the quartz cap, vacuumize, and weld the quartz body and the quartz cap of the quartz tube with an oxygen-hydrogen flame; Step 6: Put the welded quartz tube into the VGF single crystal furnace for atmosphere doping and single crystal growth; Step 7: Soak the PBN crucible after crystal growth in methanol to obtain GaAs single crystal, and complete the preparation of GaAs single crystal. 4. The method for doping gallium arsenide with carbon according to claim 3, wherein the growth temperature of said single crystal growth is 1220°C-1245°C. 5. The method for doping gallium arsenide with carbon according to claim 3, wherein said single crystal growth takes 110 hours to 130 hours. 6. The method for doping gallium arsenide with carbon according to claim 3, wherein said soaking in methanol is carried out in an ultrasonic atmosphere. 7. The method for doping gallium arsenide with carbon according to claim 3, wherein the soaking time in methanol is 8 hours to 12 hours, and the soaking temperature is normal temperature. 8. The method for doping gallium arsenide with carbon according to claim 3, wherein the amount of B ₂ O ₃ used is 15 grams.

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