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SEMI-INSULATING GALLIUM ARSENIDE SINGLE CRYSTAL, PREPARATION METHOD AND GROWTH DEVICE THEREFOR

20240093402 ยท 2024-03-21

    Inventors

    Cpc classification

    International classification

    Abstract

    A semi-insulating gallium arsenide single crystal preparation method includes: adding crystal material to a PBN crucible; adding graphite in a quartz cap; loading the hermetically connected quartz cap and quartz crucible into a VGF single crystal furnace in different temperature zones; controlling the temperature zone in which the quartz crucible is located at a temperature of material melting, while controlling the temperature zone is which the quartz cap is located at 1000?50? C.; preserving the temperature of material melting when the temperature zone in which the quartz crucible is located reaches the temperature of material melting, and controlling the temperature zone in which the quartz cap is located at 1200?50? C. and preserving the temperature for 4 to 50 h; lowering a temperature in the temperature zone to 1000?50? C.; and cooling and discharging.

    Claims

    1. A preparation method of a semi-insulating gallium arsenide single crystal, comprising the follow steps: Step 1: adding GaAs polycrystals, a crystal seed and boron oxide to a pyrolytic boron nitride (PBN) crucible, and transferring the PBN crucible to a quartz crucible; and adding graphite to a quartz cap, and connecting the quartz cap to the quartz crucible hermetically; Step 2: loading the hermetically connected quartz cap and quartz crucible in Step 1 into a vertical gradient freeze (VGF) single crystal furnace, wherein the quartz cap and the quartz crucible are located in different temperature zones within the VGF single crystal furnace; Step 3: controlling the temperature zone in which the quartz crucible is located at a temperature of material melting, while controlling the temperature zone is which the quartz cap is located at 1000?50? C.; Step 4: after the temperature zone in which the quartz crucible is located reaches the temperature of material melting, preserving the temperature for material melting, controlling the temperature zone in which the quartz cap is located at 1200?50? C. and preserving the temperature at 1200?50? C. for 4 to 50 h; Step 5: after the material melting is completed, lowering a temperature in the temperature zone in which the quartz cap is located to 1000?50? C. and preserving the temperature to allow atmosphere doping and crystal growth; and Step 6: cooling and discharging.

    2. The preparation method of the semi-insulating gallium arsenide single crystal according to claim 1, wherein the graphite is pre-treated before placing in the quartz cap, and the pre-treating comprises removal of moisture.

    3. The preparation method of the semi-insulating gallium arsenide single crystal according to claim 2, wherein the PBN crucible, the quartz crucible, the quartz cap and the VGF single crystal furnace are subjected to the pre-treating before using.

    4. The preparation method of the semi-insulating gallium arsenide single crystal according to claim 2, wherein the pre-treating comprises vacuuming, and the vacuuming is performed at an absolute vacuum degree of (1 to 9?10.sup.?4) to (1 to 9?10.sup.?2) Pa.

    5. The preparation method of the semi-insulating gallium arsenide single crystal according to claim 1, wherein the crystal growth is performed at a cooling rate of 0.1 to 10? C./h and a temperature gradient of 0.1 to 10? C./cm in Step 5.

    6. The preparation method of the semi-insulating gallium arsenide single crystal according to claim 1, wherein the semi-insulating gallium arsenide single crystal has a resistivity of 0.1?10.sup.8 to 5?10.sup.8 ?.Math.cm, a radial resistivity variation within the semi-insulating gallium arsenide single crystal of less than 8%, a Si concentration within the semi-insulating gallium arsenide single crystal is 1.14?10.sup.13 to 4.5?10.sup.15 Atoms.Math.cm 3, and a C concentration within the semi-insulating gallium arsenide single crystal is 6?10.sup.15-2.0?10.sup.16 Atoms.Math.cm.sup.?3.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0041] FIG. 1 is a schematic structural diagram of a growth device in Example 1 of the present application.

    [0042] FIG. 2 is a schematic structural diagram of a growth device in Example 2 of the present application.

    [0043] FIG. 3 is an element content test results graph of semi-insulating gallium arsenide crystal of Example 1 of the present application.

    [0044] FIG. 4 is an element content test results graph of semi-insulating gallium arsenide crystal of Example 2 of the present application.

    DETAILED DESCRIPTION

    Preparation Examples

    [0045] In Preparation example 1, a graphite column was obtained by pre-treatment, which particularly included placing the graphite column into a quartz tube, placing the quartz tube into an oven, connecting to a vacuum device hermetically, then evacuating the quartz tube to a vacuum degree of 9?10.sup.?4 Pa, placing the quartz tube in the oven, and baking at 200? C. for 4 h to obtain the graphite column.

    [0046] In Preparation example 2, a graphite column was obtained by pre-treatment, which particularly included placing the graphite column into a quartz tube, placing the quartz tube in an oven, connecting to a vacuum device hermetically, then evacuating the quartz tube to a vacuum degree of 1?10.sup.?2 Pa, placing the quartz tube in the oven, and baking at 220? C. for 2 h to obtain the graphite column.

    [0047] In Preparation example 3, a graphite column differs from that obtained in Preparation example 1 in that the graphite column was not pre-treated.

    EXAMPLES

    Example 1

    [0048] The present application provided a preparation method of semi-insulating gallium arsenide single crystal, in which the preparation process adopted a growth device of semi-insulating gallium arsenide single crystal for VGF method to grow crystal. Referring to FIG. 1, the growth device includes a VGF single crystal furnace 1, the VGF single crystal furnace 1 is loaded with a quartz crucible 2, the quartz crucible 2 is loaded with a PBN crucible 4, and an opening of the quartz crucible 2 is capped with a quartz cap 3. A main body of the quartz cap 3 includes a receiving groove 31, and a bottom of the quartz cap 3 is provided with a transition tube 32 which communicates with the receiving groove 31, and a diameter of the transition tube 32 is smaller than a width of the receiving groove 31.

    [0049] The VGF single crystal furnace 1 includes a first temperature zone 5 and a second temperature zone 6, the first temperature zone 5 corresponds to the quartz crucible 2, and the second temperature zone 6 corresponds to the quartz cap 3. Further, the first temperature zone 5 includes Tz1 to Tz6, and the second temperature zone 6 includes Tz7 to Tz9 arranged along an axial direction of the VGF single crystal furnace 1 from bottom to top, and a temperature of each of the temperature zones is controlled independently.

    [0050] The preparation method included the following steps:

    [0051] Step 1: adding 10 kg of 7N GaAs polycrystals, 30 g of crystal seeds and boron oxide into a 4-inch PBN crucible 4, and transferring the PBN crucible 4 to a quartz crucible 2 to finish loading; then adding the graphite column (prepared in Preparation example 1) with 50 mm diameter and 20 mm thickness (length) to a receiving groove 31 inside the quartz cap 3 in such a way that a round bottom surface of the graphite column contacts the receiving groove 31, and then connecting (welding) the quartz cap 3 to the quartz crucible 2 hermetically.

    [0052] Step 2: loading the quartz cap 3 and the quartz crucible 2 connected hermetically in Step 1 into the VGF single crystal furnace 1, so that the quartz cap 3 was located in the Tz7 to the Tz9 of the VGF single crystal furnace 1, and the quartz crucible 2 was located in the Tz1 to the Tz6 of the VGF single crystal furnace 1.

    [0053] Step 3: raising a temperature in the Tz1 to the Tz6 to 1238? C. (a temperature of material melting), while raising a temperature in the Tz7 to the Tz9 to 1000?50? C.

    [0054] Step 4: after the Tz1 to the Tz6 reached 1238? C. (the temperature of material melting), preserving the temperature for 6 to 12 h for melting; while raising a temperature in the Tz7 to the Tz9 to 1200?50? C. within 30 min and preserving the temperature for 10 h.

    [0055] Step 5: after the GaAs polycrystals were melted, performing crystal growth by using VGF method, in which a cooling rate of the Tz1 to the Tz6 was 2 to 6? C./h and a temperature gradient was 0.1 to 5? C./cm; meanwhile, cooling the Tz7 to the Tz9 down to 1000?50? C. within 1 h and preserving the temperature to ensure a reaction occurring between the graphite and the quartz and formation of a CO atmosphere with stable content.

    [0056] Step 6: cooling and discharging, during which, when the temperature in the Tz1 to the Tz6 was in the range of 1200 to 1238? C., the cooling rate was 2?1? C./h; when the temperature in the Tz1 to the Tz6 was in the range of 1000 to 1200? C., the cooling rate was 5 to 15? C./h; when the temperature in the Tz1 to the Tz6 was in the range of 50 to 1000? C., the cooling rate was 30?10? C./h; and cooling down the Tz7 to the Tz9 gradually to the temperature of discharging to obtain the final semi-insulating gallium arsenide crystal with a length of 200 m.

    [0057] The resistivity and mobility of the above-prepared crystals were tested according to the test methods specified in SJ/T 11488-2015, and the test results were as follow:

    TABLE-US-00001 Test project Deviation from Sampling Resistivity/ resistance mean Mobility Test position position ? .Math. cm value (cm.sup.2/v .Math. s ) Head piece A 1.37E+08 2.49% 5656 B 1.38E+08 3.24% 5602 C 1.26E+08 ?5.74% 5637 Tail piece A 1.38E+08 0.73% 5265 B 1.34E+08 ?2.19% 5282 C 1.39E+08 1.46% 5232


    A radial resistivity variation rate within the crystal (Deviation from resistance mean value)=(a resistance value of a test point/a mean value of test piece)?100%

    A ratio of head-to-tail resistance within the crystal: a mean value of the head piece/a mean value of the tail piece=0.97.

    [0058] The test results of the elemental content were shown in FIG. 3.

    [0059] Referring to FIG. 3, it can be seen that the content of Si lies between 1.14*10.sup.13 and 4.5*10.sup.15 Atoms.Math.cm.sup.?3, and the content of C lies between 6*10.sup.15 and 2.0*10.sup.16 Atoms.Math.cm.sup.?3.

    Example 2

    [0060] The present application provided a preparation method of semi-insulating gallium arsenide single crystal, in which the preparation process adopted a growth device of semi-insulating gallium arsenide single crystal for VGF method to grow crystal. Referring to FIG. 2, the growth device includes a VGF single crystal furnace 1, the VGF single crystal furnace 1 is loaded with a quartz crucible 2, the quartz crucible 2 is loaded with a PBN crucible 4, and an opening of the quartz crucible 2 is capped with a quartz cap 3. A main body of the quartz cap 3 includes a receiving groove 31, and a bottom of the quartz cap 3 is provided with a transition tube 32 which communicates with the receiving groove 31, and a diameter of the transition tube 32 is smaller than a width of the receiving groove 31.

    [0061] The VGF single crystal furnace 1 includes a first temperature zone 5 and a second temperature zone 6, the first temperature zone 5 corresponds to the quartz crucible 2, and the second temperature zone 6 corresponds to the quartz cap 3. Further, the first temperature zone 5 includes Tz1 to Tz6, and the second temperature zone 6 includes Tz7 to Tz9, arranged along an axial direction of the VGF single crystal furnace 1 from bottom to top, and a temperature of each of the temperature zones is controlled independently.

    [0062] The preparation method included the following steps:

    [0063] Step 1: adding 24 kg of 7N GaAs polycrystals, 65 g of crystal seeds and boron oxide into a 6-inch PBN crucible 4, and transferring the PBN crucible 4 to the quartz crucible 2 to finish loading; then adding the graphite column (prepared in Preparation example 2) with 60 mm diameter and 20 mm thickness into a receiving groove 31 inside the quartz cap 3 in such a way that a round bottom surface of the graphite column contacts the receiving groove 31, and then connecting the quartz cap 3 to the quartz crucible 2 hermetically.

    [0064] Step 2: loading the quartz cap 3 and the quartz crucible 2 connected hermetically in Step 1 into the VGF single crystal furnace 1, so that the quartz cap 3 was located in the Tz7 to the Tz9 of the VGF single crystal furnace 1, and the quartz crucible 2 was located in the Tz1 to the Tz6 of the VGF single crystal furnace 1.

    [0065] Step 3: raising a temperature in the Tz1 to the Tz6 to 1238? C. (a temperature of material melting), while raising a temperature in the Tz7 to the Tz9 to 1000?50? C.

    [0066] Step 4: after the Tz1 to the Tz6 reached 1238? C. (the temperature of material melting), preserving the temperature for 6 to 10 h for melting; while raising a temperature in the Tz7 to the Tz9 to 1200?50? C. within 30 min and preserving the temperature for 50 h.

    [0067] Step 5: after the GaAs polycrystals were melted, performing crystal growth by using VGF method, in which a cooling rate of the Tz1 to the Tz6 was 5 to 10? C./h and a temperature gradient was 3 to 8? C./cm; meanwhile, cooling the Tz7 to the Tz9 down to 1000?50? C. within 1 h and preserving the temperature to ensure a reaction occurring between the graphite and the quartz and formation of a CO atmosphere with stable content.

    [0068] Step 6, cooling and discharging, during which, when the temperature in the Tz1 to the Tz6 was in the range of 1200 to 1238? C., the cooling rate was 2?1? C./h; when the temperature in the Tz1 to the Tz6 was in the range of 1000 to 1200? C., the cooling rate was 5 to 15? C./h; when the temperature in the Tz1 to the Tz6 was in the range of 50 to 1000? C., the cooling rate was 30?10? C./h; and cooling down the Tz7 to the Tz9 gradually to the temperature of discharging to obtain a final semi-insulating gallium arsenide crystal with a length of 200 m.

    [0069] The resistivity and mobility of the above-prepared crystals were tested according to the test methods specified in SJ/T 11488-2015, and the test results were as follows:

    TABLE-US-00002 Test project Deviation from Sampling Resistivity/ resistance mean Mobility Test position position ? .Math. cm value (cm.sup.2/v .Math. s ) Head piece A 3.00E+08 ?0.66% 5176 B 2.94E+08 ?2.65% 5256 C 3.03E+08 0.33% 5164 D 2.94E+08 ?2.65% 5183 E 3.19E+08 5.63% 5085 Tail piece A 3.48E+08 ?1.75% 5021 B 3.75E+08 5.87% 4914 C 3.40E+08 ?4.01% 4935 D 3.51E+08 ?0.90% 5048 E 3.57E+08 0.79% 5075


    A radial resistivity variation rate within the crystal=(a resistance value of a test point/a mean value of test piece)?100%

    A ratio of head-to-tail resistance within the crystal: a mean value of the head piece/a mean value of the tail piece=0.72.

    [0070] The test results of the elemental content were shown in FIG. 4.

    [0071] Referring to FIG. 4, it can be seen that the content of Si lies between 1.14*10.sup.13 and 4.5*10.sup.15 Atoms.Math.cm.sup.?3, and the content of C lies between 6*10.sup.15 and 2.0*10.sup.16 Atoms.Math.cm.sup.3.

    Example 3

    [0072] The present application provided a preparation method of semi-insulating gallium arsenide single crystal, which differs from Example 1 in that the preparation steps included:

    [0073] Step 1: adding 10 kg of 7N GaAs polycrystals, 30 g of crystal seeds and boron oxide into a 4-inch PBN crucible 4, and transferring the PBN crucible 4 to a quartz crucible 2 to finish loading; then adding the graphite column (prepared in Preparation example 1) with 50 mm diameter and 20 mm thickness into a receiving groove 31 inside the quartz cap 3 in such a way that a round bottom surface of the graphite column contacts the receiving groove 31, and then connecting the quartz cap 3 to the quartz crucible 2 hermetically.

    [0074] Step 2: loading the quartz cap 3 and the quartz crucible 2 connected hermetically in Step 1 into the VGF single crystal furnace 1, so that the quartz cap 3 was located in the Tz7 to the Tz9 of the VGF single crystal furnace 1, and the quartz crucible 2 was located in the Tz1 to the Tz6 of the VGF single crystal furnace 1.

    [0075] Step 3: raising a temperature in the Tz1 to the Tz6 to 1238? C. (the temperature of material melting), while raising a temperature in the Tz7 to the Tz9 to 1000?50? C.

    [0076] Step 4: after the Tz1 to the Tz6 reached 1238? C. (the temperature of material melting), preserving the temperature for 6 to 12 h for melting; while raising a temperature in the Tz7 to the Tz9 to 1200?50? C. within 30 min and preserving the temperature for 4 h.

    [0077] Step 5: after the GaAs polycrystals were melted, performing crystal growth by using to VGF method, in which a cooling rate of the Tz1 to the Tz6 was 0.1 to 5? C./h and a temperature gradient was 2 to 7? C./cm; meanwhile, cooling the Tz7 to the Tz9 down to 1000?50? C. within 1 h and preserving the temperature to ensure a reaction occurring between the graphite and the quartz and formation of the CO atmosphere with stable content.

    [0078] Step 6: cooling and discharging, during which, when the Tz1 to the Tz6 in the range of 1200 to 1238? C., the cooling rate was 2?1? C./h; when the Tz1 to the Tz6 was in the range of 1000 to 1200? C., the cooling rate was 5 to 15? C./h; when the Tz1 to the Tz6 was in the range of 50 to 1000? C., the cooling rate was 30?10? C./h; and cooling the Tz7 to the Tz9 down gradually to the temperature of discharging to obtain a final semi-insulating gallium arsenide crystal with a length of 200 m.

    [0079] The resistivity and mobility of the above-prepared crystals were tested according to the test methods specified in SJ/T 11488-2015, and the test results were as follows:

    TABLE-US-00003 Test project Deviation from Sampling Resistivity/ resistance mean Mobility Test position position ? .Math. cm value (cm.sup.2/v .Math. s ) Head piece A 2.05E+08 ?0.65% 5528 B 2.09E+08 1.29% 5739 C 2.05E+08 ?0.65% 5779 Tail piece A 3.26E+08 1.98% 5043 B 3.19E+08 ?0.21% 5192 C 3.14E+08 ?1.77% 5156
    A ratio of head-to-tail resistance within the crystal: a mean value of the head piece/a mean value of the tail piece=0.65.

    Example 4

    [0080] The present application provided a preparation method of semi-insulating gallium arsenide single crystal, which differs from Example 1 in that in Step 1; the graphite column was the one prepared in Preparation example 3.

    [0081] The resistivity and mobility of the above-prepared crystals were tested according to the test methods specified in SJ/T 11488-2015, and the test results showed that, absence of moisture removing of the graphite led to poor consistency of parameters in a same batch of crystals, and the resistivity of the crystals obtained under the same process environment might be 1?10.sup.8 ?.Math.cm or 5?10 8 ?.Math.cm, or even could not be measured due to inappropriate parameters in the crystals; and from the perspective view of a single crystal, there are some normal crystals with relatively consistent parameters.

    Example 5

    [0082] The present application provided a preparation method of semi-insulating gallium arsenide single crystal, which differs from Example 1 in that the preparation steps included:

    [0083] Step 1: adding 10 kg of 7N GaAs polycrystals, 30 g of crystal seeds and boron oxide into the 4-inch PBN crucible 4, transferring the PBN crucible 4 to the quartz crucible 2 to finish loading; then adding the graphite column (prepared in Preparation example 1) with 30 mm diameter and 20 mm thickness into the receiving groove 31 inside the quartz cap 3 in such a way that a round bottom surface of the graphite column contacts the receiving groove 31, then connecting the quartz cap 3 to the quartz crucible 2 hermetically.

    [0084] Step 2: loading the quartz cap 3 and the quartz crucible 2 connected hermetically in Step 1 into the VGF single crystal furnace 1, and the quartz cap 3 was located in the Tz7 to the Tz9 of the VGF single crystal furnace 1, and the quartz crucible 2 was located in the Tz1 to the Tz6 of the VGF single crystal furnace 1.

    [0085] Step 3: raising a temperature in the Tz1 to the Tz6 to 1238? C. (the temperature of material melting), while raising a temperature in the Tz7 to the Tz9 to 1000?50? C.

    [0086] Step 4: after the Tz1 to the Tz6 reached 1238? C. (the temperature of material melting), preserving the temperature for 6 to 12 h for melting; while raising a temperature in the Tz7 to the Tz9 to 1200?50? C. within 30 min and preserving the temperature for 6 h.

    [0087] Step 5: after the GaAs polycrystals were melted, performing crystal growth by using VGF method, in which a cooling rate of the Tz1 to the Tz6 was 2 to 6? C./h and a temperature gradient was 0.1 to 5? C./cm; meanwhile, cooling the Tz7 to the Tz9 down to 1000?50? C. within 1 h and preserving the temperature to ensure a reaction occurring between the graphite and the quartz and the formation of a CO atmosphere with stable content.

    [0088] Step 6: cooling and discharging, during which, when the Tz1 to the Tz6 was in the range of 1200 to 1238? C., the cooling rate was 1 to 3? C./h; when the Tz1 to the Tz6 was in the range of 1000 to 1200? C., the cooling rate was 5 to 15? C./h; when the Tz1 to the Tz6 was in the range of 50 to 1000? C., the cooling rate was 20 to 40? C./h; and cooling the Tz7 to the Tz9 down gradually to the temperature of discharging to obtain a final semi-insulating gallium arsenide crystal with the length of 200 m.

    [0089] The resistivity and mobility of the above-prepared crystals were tested according to the test methods specified in SJ/T 11488-2015, and the test results were as follows:

    TABLE-US-00004 Test project Deviation from Sampling Resistivity/ resistance mean Mobility Test position position ? .Math. cm value (cm.sup.2/v .Math. s ) Head piece A 4.43E+07 ?3.06% 6101 B 4.55E+07 ?0.44% 6120 C 4.73E+07 3.50% 6139 Tail piece A 5.77E+07 3.84% 6167 B 6.44E+07 ?2.10% 6122 C 5.46E+07 ?1.74% 6024
    A ratio of head-to-tail resistance within the crystal: a mean value of the head piece/a mean value of the tail piece=0.78.

    Comparative Example

    Comparative Example 1

    [0090] The present application provided a preparation method of semi-insulating gallium arsenide single crystal, in which the preparation process adopted a growth device of semi-insulating gallium arsenide single crystal for VGF method to grow crystal. The growth device includes a VGF single crystal furnace 1, the VGF single crystal furnace 1 is loaded with a quartz crucible 2 and a quartz cap 3 which is capped with the quartz crucible 2, wherein a receiving groove 31 is set inside the quartz cap 3, and the height of the receiving groove 31 is smaller than the depth of the quartz cap 3, and the quartz crucible 2 is loaded with a PBN crucible 4.

    [0091] The VGF single crystal furnace 1 is provided with Tz1 to Tz6 along the axial direction of the VGF single crystal furnace 1, in which each of the temperature zones is equipped with an independent heating source, and the quartz crucible 2 and the quartz cap 3 are located in the range of the Tz1 to the Tz6.

    [0092] The preparation method included the following steps:

    [0093] Step 1: adding 10 kg of 7N GaAs polycrystals, 30 g of crystal seeds and boron oxide into the 4-inch PBN crucible 4, and transferring the PBN crucible 4 to the quartz crucible 2 to finish loading; then adding the graphite column with 50 mm diameter and 20 mm thickness into a receiving groove 31 inside the quartz cap 3, then connecting the quartz cap 3 to the quartz crucible 2 hermetically.

    [0094] Step 2: loading the quartz cap 3 and the quartz crucible 2 connected hermetically in Step 1 into the VGF single crystal furnace 1.

    [0095] Step 3: raising a temperature in the Tz1 to the Tz6 to 1238? C. (the temperature of material melting).

    [0096] Step 4: after the Tz1 to the Tz6 reached 1238? C. (the temperature of material melting), preserving the temperature for 6 to 10 h for melting.

    [0097] Step 5: after the GaAs polycrystals were melted, performing crystal growth by using to VGF method, in which a cooling rate of the Tz1 to the Tz6 was 1 to 5? C./h and a temperature gradient was 2 to 6? C./cm

    [0098] Step 6: cooling and discharging, during which, when the Tz1 to the Tz6 was in the range of 1200 to 1238? C., the cooling rate was 2?1? C./h; when the Tz1 to the Tz6 was in the range of 1000 to 1200? C., the cooling rate was 5 to 15? C./h; when the Tz1 to the Tz6 was in the range of 50 to 1000? C., the cooling rate was 30?10? C./h to obtain a final semi-insulating gallium arsenide crystal with a length of 200 m.

    [0099] The resistivity and mobility of the above-prepared crystals were tested according to the test methods specified in SJ/T 11488-2015, and the test results were as follow:

    TABLE-US-00005 Test project Deviation from Sampling Resistivity/ resistance mean Mobility Test position position ? .Math. cm value (cm.sup.2/v .Math. s ) Head piece A 7.73E+07 11.01% 5700 B 6.83E+07 ?1.91% 5823 C 6.33E+07 ?9.10% 5738 At 60 mm A 4.74E+08 ?6.94% 4306 B 5.08E+08 ?0.26% 4102 C 5.46E+08 7.20% 4234 Tail piece A 105 no 105 B 105 no 105 C 105 no 105

    [0100] From the above table, it can be seen that the data at the tail piece of the crystal was of a reverse type, that is, a P-type semiconductor crystal, so that a high Hall resistance could not be measured, showing as 105.

    Comparative Example 2

    [0101] The present application provided a preparation method of semi-insulating gallium arsenide single crystal, which differs from Comparative example 1 by using the growth device of semi-insulating gallium arsenide single crystal in Example 1 to grow crystal, and controlling the temperature of the Tz7 to Tz9 in the range of 1200?50? C. at all times.

    [0102] The preparation method includes the following steps:

    [0103] Step 1: adding 10 kg of 7N GaAs polycrystals, 30 g of crystal seeds and boron oxide into the 4-inch PBN crucible 4, and transferring the PBN crucible 4 to the quartz crucible 2 to finish loading; then adding the graphite column (prepared in Preparation example 1) with 50 mm diameter and 20 mm thickness into the receiving groove 31 inside the quartz cap 3, then connecting the quartz cap 3 to the quartz crucible 2 hermetically.

    [0104] Step 2: loading the quartz cap 3 and the quartz crucible 2 connected hermetically in Step 1 into the VGF single crystal furnace 1, so that the quartz cap 3 was located in the Tz7 to the Tz9 of the VGF single crystal furnace 1, and the quartz crucible 2 was located in the Tz1 to the Tz6 of the VGF single crystal furnace 1.

    [0105] Step 3: raising the temperature in the Tz1 to the Tz6 to 1238? C. (the temperature of material melting), while raising the temperature in the Tz7 to the Tz9 to 1200?50? C. and then preserving the temperature.

    [0106] Step 4: after the Tz1 to the Tz6 reached 1238? C. (the temperature of material melting), preserving the temperature for 8 h for melting, while controlling the temperature in the Tz7 to the Tz9 at 1200?50? C.

    [0107] Step 5: after the GaAs polycrystals were melted, performing crystal growth by using VGF method, in which a cooling rate of the Tz1 to the Tz6 was 2 to 6? C./h and a temperature gradient was 0.1 to 5? C./cm; meanwhile, controlling a temperature in the Tz7 to the Tz9 at 1200?50? C. to ensure a reaction occurring between the graphite and the quartz and formation of the CO atmosphere with stable content.

    [0108] Step 6: cooling and discharging, during which, when the Tz1 to the Tz6 in the range of 1200 to 1238? C., the cooling rate was 2?1? C./h; when the Tz1 to the Tz6 in the range of 1000 to 1200? C., the cooling rate was 5 to 15? C./h; when the Tz1 to the Tz6 in the range of 50 to 1000? C., the cooling rate was 30?10? C./h; and cooling the Tz7 to the Tz9 down gradually to the temperature of discharging to obtain a final semi-insulating gallium arsenide crystal with a length was 200 m.

    [0109] The resistivity and mobility of the above-prepared crystals were tested according to the test methods specified in SJ/T 11488-2015, and the test results were as follows:

    TABLE-US-00006 Test project Deviation from Sampling Resistivity/ resistance mean Mobility Test position position ? .Math. cm value (cm.sup.2/v .Math. s ) Head piece A 1.27E+08 7.63% 5935 B 1.05E+08 ?11.02% 5812 C 1.22E+08 3.39% 5650 At 40 mm A 6.91E+08 9.39% 2013 B 5.50E+08 ?12.93% 2013 C 6.54E+08 3.54% 1929 Tail piece A 105 no 105 B 105 no 105 C 105 no 105

    [0110] From the above table, it can be seen that the data at the tail piece of the crystal was of an inverse type, that is, P-type semiconductor crystal, and high Hall resistance could not be measured, showing as 105.

    [0111] Analysis of the test results:

    [0112] From Examples 1 to 5 in comparison with Comparative example 1 to 2, it can be seen that in Examples 1 to 5, the graphite and the quartz crucible for gallium arsenide crystal growth are located in different temperature zones, and the temperature in the temperature zone in which the graphite is located is controlled to reach a suitable reaction temperature, so as to achieve the carbon doping of semi-insulating gallium arsenide; In contrast, in Comparative example 1, the conventional VGF method is used for the growth of semi-insulating gallium arsenide. The experimental results show that the resistivity distribution of the crystals obtained from Example 1 to 5 is significantly more homogeneous and the ratio of head-to-tail resistance within the crystal is smaller compared with Comparative example 1.

    [0113] The reason may be that in the present application, the CO content in the atmosphere is controlled by the reaction: SiO.sub.2+C.Math.CO+SiO, in which the higher the reaction temperature is, the more the reaction moves right; the longer the reaction time is, the higher the CO content in the atmosphere is; and the larger the contact area between the graphite (C) and the quartz tube (SiO.sub.2) is, the higher the CO content is. This reaction process is easy to control and can produce the CO gas in the growth device relatively quickly, providing relatively homogeneous CO content at all positions in the growth device, and thus guaranteeing the homogeneity of the carbon doping in gallium arsenide crystals. In contrast, in Comparative example 1, the CO content in the atmosphere is mainly controlled by the reaction between the graphite and oxygen released in the quartz cap (produced by the quartz cap and the boron oxide) or the graphite and water (produced by the graphite or the quartz cap). Due to a slow release rate of oxygen in high temperature environment, the increase and diffusion of the CO content in the atmosphere is extremely slow, so that the grown gallium arsenide crystals as produced have poor homogeneity in the internal carbon content and inferior electrical properties.

    [0114] In Comparative example 2, since the Tz7 to the Tz9 are always at the high temperature of 1200?50? C., and the graphite is kept in contact with the quartz, the reaction: SiO.sub.2+C.Math.CO+SiO keeps going and the CO is continuously generated, resulting in sharp changes in carbon content and crystal parameters of the crystals, which fluctuate more than 8%, making it difficult to control the final resistivity and mobility of the product.

    [0115] The specific examples are only used to illustrate the present application and not used to limit the protection scope of the present application. After reading the specification, those skilled in the art can make modifications to present application without creative contribution as needed, However, it is protected by the patent law as long as it is within the scope of the claims in the present application.

    LISTING OF REFERENCE SIGNS

    [0116] 1. VGF single crystal furnace [0117] 2. Quartz crucible [0118] 3. Quartz cap [0119] 31. Receiving groove [0120] 32. Transition tube [0121] 4. PBN crucible [0122] 5. First temperature zone [0123] 6. Second temperature zone