Gallium arsenide single crystal and preparation method thereof

Abstract

The present application discloses a gallium arsenide single crystal and preparation method thereof. The gallium arsenide single crystal has a carrier concentration of 1×10.sup.18-4×10.sup.18/cm.sup.3, and a migration rate of 1700-2600 cm.sup.2/v.Math.s; at a same carrier concentration, B atom density in the gallium arsenide single crystal obtained using Si.sub.xAs.sub.y compound as a dopant is at least 20% lower than that obtained using Si substance as a dopant; B content in the gallium arsenide single crystal is 5×10.sup.18/cm.sup.3 or lower. The preparation method for the gallium arsenide single crystal is that, before growth of the gallium arsenide single crystal, the Si.sub.xAs.sub.y compound is distributed into a gallium arsenide polycrystal.

Claims

1. A preparation method for a gallium arsenide single crystal, comprising the following steps: before growth of the gallium arsenide single crystal, distributing a Si.sub.xAs.sub.y compound into a gallium arsenide polycrystal by: synthesizing the Si.sub.xAs.sub.y compound, adding the Si.sub.xAs.sub.y compound and a raw material gallium arsenide polycrystal into a single crystal growing vessel, and then growing a single crystal, which comprises: Step 1: synthesizing the Si.sub.xAs.sub.y compound, comprising: (1) charging arsenic and silicon by a weight ratio of (0.5-5):1 into a first quartz boat and a second quartz boat, respectively; (2) baking the first quartz boat and the second quartz boat for 2-4 h in a vacuum environment with a vacuum degree of 1×10.sup.−4-9×10.sup.−2 Pa; and (3) heating the first quartz boat to 650-700° C., heating the second quartz boat to 1050-1450° C.; and holding for 2-4 h to obtain the Si.sub.xAs.sub.y compound, wherein a temperature of the second quartz boat is decreased by a gradient of 5-8° C./cm; and Step 2: growing the single crystal, comprising: placing the Si.sub.xAs.sub.y compound, the gallium arsenide polycrystal and boron oxide into the single crystal growing vessel to grow the single crystal.

2. The preparation method for the gallium arsenide single crystal according to claim 1, wherein, the gallium arsenide single crystal has a carrier concentration of 1×10.sup.18-4×10.sup.18/cm.sup.3, and a migration rate of 1700-2600 cm.sup.2/v.Math.s; and a B content of the gallium arsenide single crystal is 5×10.sup.18/cm.sup.3 or lower.

3. The preparation method for the gallium arsenide single crystal according to claim 1, wherein, during synthesizing the Si.sub.xAs.sub.y compound in Step 1, the second quartz boat is heated to 1120-1150° C.

4. The preparation method for the gallium arsenide single crystal according to claim 1, wherein, in Step 2, the Si.sub.xAs.sub.y compound, the gallium arsenide polycrystal and the boron oxide are mixed by a weight ratio of (0.2-2):10000:(15-100).

Description

DETAILED DESCRIPTION

(1) In existing preparing process of the gallium arsenide for n-type opto-semiconductors, Si substance is used as a main dopant. However, Si substance used as dopant will inevitably introduce a large amount of B melt, such that the prepared gallium arsenide single crystal chip is polluted by B, and the electrical performance of gallium arsenide single crystal chip is degraded.

(2) Over the years, the researchers have conducted a lot of researches on the preparing process of gallium arsenide single crystal. They found that a Si atomic radius is 113 pm (covalent radius), a Ga atomic radius is 126 pm, and the Si atomic radius is close to that of As and Ga. Therefore, Si may replace Ga atom in a gallium arsenide material to be a donor impurity, or replace As atom to be an acceptor impurity. Si has a variety of positions in crystals: a. Si replaces Ga to be Si.sub.Ga; b. Si replaces as to be Si.sub.As; c. Si is located at grain boundaries or near large grain dislocation and does not occupy a crystal lattice position.

(3) For the above reasons, in the present application, the Si.sub.xAs.sub.y compound replaces Si substance as dopant and is added into a gallium arsenide polycrystal before growing the gallium arsenide single crystal, so that a Si valence state can be improved, the probability of silicon occupying gallium sites can be increased, reaction Si(melt)+B.sub.2O.sub.3⇔SiO (B.sub.2O.sub.3)+B (melt) can be inhibited, the probability of B element entering the melt can be decreased, and B impurity content in prepared gallium arsenide single crystal can be decreased to below 5×10.sup.18/cm.sup.3. This technical solution especially applies to a case with large carrier concentrations, and particularly to a case where Si-doped carrier concentrations is greater than 1×10.sup.18/cm.sup.3. Comparing with the gallium arsenide single crystal prepared with Si substance as dopant, a migration rate of the gallium arsenide single crystal prepared in the present application is at least increased by 20% at a same carrier concentration.

EXAMPLES

Example 1

(4) A 4-inch gallium arsenide single crystal was prepared by the following steps:

(5) (1) charging

(6) 5.35 kg arsenic was charged into a first PBN boat and 5 kg gallium was charged into a second PBN boat according to a weight ratio of 1.07:1;

(7) 0.1 g silicon was charged at an tail end of the second PBN boat, a weight ratio of the silicon to the gallium was 0.2:10000;

(8) the first PBN boat and the second PBN boat were horizontally placed into a quartz tube, and a distance between the first PBN boat and the second PBN boat was 300 mm, which ensured that there was a sufficient temperature difference between them.

(9) (2) baking: the charged quartz tube was fixedly mounted on a stove and baked for 2 h in a vacuum environment with a vacuum degree of 1×10.sup.−4 Pa;

(10) (3) synthesizing a gallium arsenide polycrystal containing Si.sub.xAs.sub.y compound: after the baked quartz tube was welded and installed in the stove, the first PBN boat was heated to 660° C., the second PBN boat was heated to 1200° C. After holding for 2 h, the gallium arsenide polycrystal and the Si.sub.xAs.sub.y compound were obtained;

(11) a temperature of the second PBN boat from a head end to the tail end was decreased by a gradient of 4° C./cm by controlling temperature in the quartz tube via a program, and a horizontal condensation rate was 6 cm/h.

(12) (4) taking the gallium arsenide polycrystal out of the stove: when the temperature in the quartz tube was decreased to 200° C. or lower, the gallium arsenide polycrystal containing Si.sub.xAs.sub.y compound was taken out of the stove;

(13) (5) growing single crystal: the synthesized gallium arsenide polycrystal containing Si.sub.xAs.sub.y compound and boron oxide were added into a 4-inch crucible. A charged single crystal quartz tube was placed into a single crystal stove according to traditional VGF process, after which the single crystal was grown according to traditional VGF process.

(14) According to the test method specified in SJ/T 11488-2015, the carrier concentration and migration rate of the above-mentioned prepared crystals were tested, and the test results were as follows:

(15) TABLE-US-00001 Test items Carrier Migration Si B Concentration Rate Content Content Test Sites (/cm.sup.3) (cm.sup.2/v .Math. s) (ppm) (ppm) Head Piece 1.2 × 10.sup.18 2480 10 8 Tail Piece 2.2 × 10.sup.18 1850 19 14

Example 2

(16) A 6-inch gallium arsenide single crystal was prepared by the following steps:

(17) (1) charging

(18) 6.4 kg arsenic was charged into a first PBN boat and 5 kg gallium was charged into a second PBN boat according to a weight ratio of 1.28:1;

(19) 2.5 g silicon was charged at a tail end of the second PBN boat, a weight ratio of silicon to gallium was 5:10000;

(20) the first PBN boat and the second PBN boat were horizontally placed into a quartz tube, and a distance between the first PBN boat and the second PBN boat was 300 mm, which ensured that there was a sufficient temperature difference between them.

(21) (2) baking: a charged quartz tube was fixedly mounted on a stove and baked for 4 h in a vacuum environment with a vacuum degree of 9×10.sup.−2 Pa;

(22) (3) synthesizing polycrystal: after the baked quartz tube was welded and installed in the stove, the first PBN boat was heated to 620° C., the second PBN boat was heated to 1400° C. After holding for 4 h, the gallium arsenide polycrystal was obtained;

(23) a temperature of the second PBN boat from head to tail end was decreased in a gradient of 2° C./cm by controlling temperature gradient in the quartz tube via a program, and a horizontal condensation rate was 4 cm/h.

(24) (4) taking polycrystal out of the stove: when the temperature in the quartz tube was decreased to 200° C. or lower, the gallium arsenide polycrystal containing Si.sub.xAs.sub.y compound was taken out of the stove;

(25) (5) growing single crystal: the synthesized gallium arsenide polycrystal containing Si.sub.xAs.sub.y compound and boron oxide were added into a 6-inch crucible;

(26) a charged single crystal quartz tube was placed into a single crystal stove according to traditional VGF process, after which the single crystal was grown according to the traditional VGF process.

(27) According to the test method specified in SJ/T 11488-2015, the carrier concentration and migration rate of the above-mentioned prepared crystals were tested, and the test results were as follows:

(28) TABLE-US-00002 Test Items Carrier Migration Si B Concentration Rate Content Content Test Sites (/cm.sup.3) (cm.sup.2/v .Math. s) (ppm) (ppm) Head Piece 1.2 × 10.sup.18 2500 12 9 Tail Piece 2.6 × 10.sup.18 1880 22 17

Example 3

(29) This example provided a 6-inch gallium arsenide single crystal, and the difference between this example and Example 2 lied in: in the charging step, a weight ratio of Si for doping to Ga was different, and the weight ratio of Si for doping to Ga in this example was 1:10000.

(30) According to the test method specified in SJ/T 11488-2015, the carrier concentration and migration rate of the above-mentioned prepared crystals were tested, and the test results were as follows:

(31) TABLE-US-00003 Test Items Carrier Migration Si B Concentration Rate Content Content Test Sites (/cm.sup.3) (cm.sup.2/v .Math. s) (ppm) (ppm) Head Piece 1.2 × 10.sup.18 2530 11 6 Tail Piece 2.4 × 10.sup.18 1840 21 14

Example 4

(32) This example provided a 6-inch gallium arsenide single crystal, and the difference between this example and Example 1 lied in: in the charging step, a weight ratio of Si for doping to Ga was different, and the weight ratio of Si for doping to Ga in this example was 1.2:10000.

(33) According to the test method specified in SJ/T 11488-2015, the carrier concentration and migration rate of the above-mentioned prepared crystals were tested, and the test results were as follows:

(34) TABLE-US-00004 Test Items Carrier Migration Si B Concentration Rate Content Content Test Sites (/cm.sup.3) (cm.sup.2/v .Math. s) (ppm) (ppm) Head Piece 1.2 × 10.sup.18 2550 12 6 Tail Piece 2.4 × 10.sup.18 1860 22 15

Example 5

(35) A 4-inch gallium arsenide single crystal was prepared by the following steps:

(36) Step 1. synthesizing Si.sub.xAs.sub.y compound

(37) (1) charging: 5 g arsenic and 10 g silicon were charged in a first quartz boat and a second quartz boat respectively, then the first quartz boat and the second quartz boat were horizontally placed into a quartz tube;

(38) (2) baking: the charged quartz tube was fixedly mounted and baked for 2 h in a vacuum environment with a vacuum degree of 1×10.sup.−4 Pa;

(39) (3) synthesizing Si.sub.xAs.sub.y compound: after the baked quartz tube was welded and installed in the stove, the first quartz boat was heated to 650° C., and the second quartz boat was heated to 1050° C. After holding for 4 h, the Si.sub.xAs.sub.y compound was obtained;

(40) a temperature of the second quartz boat from a head end to the tail end was decreased by a gradient of 5° C./cm by controlling temperature in the quartz tube. When the temperature in the quartz tube was 200° C. or lower, the Si.sub.xAs.sub.y compound was taken out.

(41) Step 2. growing single crystal

(42) 0.2 g prepared Si.sub.xAs.sub.y compound, 10 kg gallium arsenide polycrystal and 15 g boron oxide were added into a crucible, then the crucible was placed into a single crystal quartz tube. The charged single crystal quartz tube was placed into a single crystal stove according to traditional VGF process, after which the single crystal was grown according to traditional VGF process.

(43) According to the test method specified in SJ/T 11488-2015, the carrier concentration and migration rate of the above-mentioned prepared crystals were tested, and the test results were as follows:

(44) TABLE-US-00005 Test Items Carrier Migration Si B Concentration Rate Content Content Test Sites (/cm.sup.3) (cm.sup.2/v .Math. s) (ppm) (ppm) Head Piece 1.4 × 10.sup.18 2220 12 8 Tail Piece 2.8 × 10.sup.18 1850 27 16

Example 6

(45) A 6-inch gallium arsenide single crystal was prepared by the following steps:

(46) Step 1. synthesizing Si.sub.xAs.sub.y compound

(47) (1) charging: 50 g arsenic and 10 g silicon were charged into a first quartz boat and a second quartz boat respectively, then the first quartz boat and the second quartz boat were horizontally placed into a quartz tube;

(48) (2) baking: the charged quartz tube was fixedly mounted and baked for 4 h in a vacuum environment with a vacuum degree of 1×10.sup.−4 Pa;

(49) (3) synthesizing Si.sub.xAs.sub.y compound: after the baked quartz tube was welded and installed in the stove, the first quartz boat was heated to 700° C., and the second quartz boat was heated to 1450° C. After holding for 2 h, the Si.sub.xAs.sub.y compound was obtained;

(50) a temperature of the second quartz boat from head to tail end was decreased in a gradient of 8° C./cm by controlling temperature gradient in the quartz tube. When the temperature in the quartz tube was 200° C. or lower, the Si.sub.xAs.sub.y compound was taken out.

(51) Step 2. growing single crystal

(52) 20 g prepared Si.sub.xAs.sub.y compound, 10 kg gallium arsenide polycrystal and 100 g boron oxide were added into a 6-inch crucible, then the crucible was placed into a single crystal quartz tube. The charged single crystal quartz tube was placed into a single crystal stove according to traditional VGF process, after which the single crystal was grown according to the traditional VGF process.

(53) According to the test method specified in SJ/T 11488-2015, the carrier concentration and migration rate of the above-mentioned prepared crystals were tested, and the test results were as follows:

(54) TABLE-US-00006 Test Items Carrier Migration Si B Concentration Rate Content Content Test Sites (/cm.sup.3) (cm.sup.2/v .Math. s) (ppm) (ppm) Head Piece 1.4 × 10.sup.18 2310 14 10 Tail Piece 2.8 × 10.sup.18 1820 30 18

Example 7

(55) This example provided a 6-inch gallium arsenide single crystal, and the difference between this example and Example 6 lied in: in the charging of Step 1, a weight ratio of Si to Ga was different, and the weight ratio of Si to Ga in this example was 1:10000.

(56) According to the test method specified in SJ/T 11488-2015, the carrier concentration and migration rate of the above-mentioned prepared crystals were tested, and the test results were as follows:

(57) TABLE-US-00007 Test Items Carrier Migration Si B Concentration Rate Content Content Test Sites (/cm.sup.3) (cm.sup.2/v .Math. s) (ppm) (ppm) Head Piece 1.4 × 10.sup.18 2400 12 7 Tail Piece 3.0 × 10.sup.18 1760 28 16

Example 8

(58) This example provided a 6-inch gallium arsenide single crystal, and the difference between this example and Example 6 lied in: in the charging of Step 1, a weight ratio of Si to Ga was different, and the weight ratio of Si to Ga in this example was 1.2:10000.

(59) According to the test method specified in SJ/T 11488-2015, the carrier concentration and migration rate of the above-mentioned prepared crystals were tested, and the test results were as follows:

(60) TABLE-US-00008 Test Items Carrier Migration Si B Concentration Rate Content Content Test Sites (/cm.sup.3) (cm.sup.2/v .Math. s) (ppm) (ppm) Head Piece 1.4 × 10.sup.18 2440 14 9 Tail Piece 3.2 × 10.sup.18 1730 30 16

Example 9

(61) This example provided a 6-inch gallium arsenide single crystal, and the difference between this example and Example 8 lied in: in synthesizing Si.sub.xAs.sub.y compound of Step 1, the second quartz boat was heated in different temperature, and the second quartz boat was heated at 1120° C. in this example.

(62) According to the test method specified in SJ/T 11488-2015, the carrier concentration and migration rate of the above-mentioned prepared crystals were tested, and the test results were as follows:

(63) TABLE-US-00009 Test Items Carrier Migration Si B Concentration Rate Content Content Test Sites (/cm.sup.3) (cm.sup.2/v .Math. s) (ppm) (ppm) Head Piece 1.4 × 10.sup.18 2480 14 8 Tail Piece 3.2 × 10.sup.18 1700 28 15

COMPARATIVE EXAMPLE

(64) A 4-inch gallium arsenide single crystal was prepared by the following steps:

(65) growing single crystal: the gallium arsenide polycrystal, boron oxide and appropriate amount of silicon were added into a crucible, then the crucible was placed into a single crystal quartz tube.

(66) The charged single crystal quartz tube was placed into a single crystal stove according to traditional VGF process, after which the single crystal was grown according to traditional VGF process.

(67) According to the test method specified in SJ/T 11488-2015, the carrier concentration and migration rate of the above-mentioned prepared crystals were tested, and the test results were as follows:

(68) TABLE-US-00010 Test Items Carrier Migration Si B Concentration Rate Content Content Test Sites (/cm.sup.3) (cm.sup.2/v .Math. s) (ppm) (ppm) Head Piece 1.2 × 10.sup.18 2020 12 14 Tail Piece 2.6 × 10.sup.18 1550 24 26

(69) Analysis of Test Results

(70) Comparative Example was traditional preparation method for gallium arsenide, in which Si substance was taken as a dopant. Comparing with Example 1, at a same carrier concentration (1.2×10.sup.8/cm.sup.3), the migration rate of the gallium arsenide single crystal was only 2020 cm.sup.2/v s, which was much lower than 2480 cm.sup.2/v s in Example 1. Meanwhile, after testing element content, it can be seen that, B content in Example 1 was only 8 ppm, which was much lower than that of the gallium arsenide single crystal prepared in Comparative Example, and the effective proportion of Si in Examples 1 and 3 were higher.

(71) The difference between Example 1 and Example 5 only lied in: an timing of adding Si.sub.xAs.sub.y compound was different. As can be seen from the test results of Example 1 and 3, a method for preparing single crystal that synthesizing Si.sub.xAs.sub.y compound first and then blending with the gallium arsenide polycrystal was able to improve the carrier concentration and migration rate of the gallium arsenide single crystal more effectively.

(72) The above are preferred embodiments of the present application, which are not intended to limit the protection scope of the present application. Therefore, all equivalent changes made according to the structure, shape and principle of the present application should be within the protection scope of the present application.