Research On The Growth,Microstructure And Properties Of GaSb Crystal

Long-wavelength light is usually used in the field of optical fiber communications for information transmission because it can reduce the transmission loss.There will be less loss for some non-silicon optic fibers using the light whose wavelength is 2⁴?m.The spectral range of some III-V ternary and quaternary solid solution alloys?0.8⁴.0?m?matches the spectral range of light.Because the lattice constants of these solid solution alloys are similar with those of Gallium Antimonide?GaSb?crystals,GaSb crystals are often used as substrates to prepare these materials.In addition,GaSb crystals with its excellent photoelectric properties are also widely used in the field of laser equipment,infrared detectors and solar cells.In this paper,GaSb ingots with the size of?37?25×120mm were grown by the vertical Bridgman crystal growth technique in quartz crucibles with the carbon film.From characterization of the scanning electron microscope?SEM?,the morphology of carbon film was influenced by gas pressure.The binding force between the carbon film and the inner wall of the crucible were tested and studied.The crystal phases were identified and analyzed and tested by X-ray diffractometer?XRD?,metallographic microscope,Vickers hardness tester and Hall Effect Measurement System.The effects of carbon film,temperature gradient and accelerated crucible rotation technique?ACRT?on the microstructure and performance of crystals were investigated.The results were as follows:The smooth carbon film was coated on the inner wall of the quartz crucible by the chemical vapor deposition?CVD?with the optimized coating parameters,including the gas pressure of 4 Pa,the coating temperature of 1100°C and the coating time of 4 h.No large particles were observed on the surface of carbon film and the binding force between the carbon film and the inner wall was large,indicating the carbon film with the best quality was suitable for the crystal growth experiment.With the increasing of gas pressure,some large particles and pits appeared on the surface of carbon film.The surface became rough and the binding force between the carbon film and the inner wall of the crucible decreased greatly.The effects of carbon film on the microstructure and performance of GaSb crystals were investigated.With absence of carbon film on the inner wall of the crucible,there were a few of large-sized pits appeared on the surface of the prepared ingot,causing difficulty to take the ingot out from the crucible.The etch pit density?EPD?of the crystal was8.286×10⁴ cm^-2.The hardness and the resistivity of the wafer were relatively large,however,the resistivity was low.When the inner wall of the crucible was coated by carbon film,no large-sized pits were found on the surface of the ingots and it was easy for the ingots to be taken out from the crucible.When the gas pressure was 4 Pa,there were no pits on the surface of carbon film,resulting in absence of obvious defects on the surface of the ingot with the high flatness.The EPD inside the ingot decreased to 1785 cm^-2.The hardness and the resistivity of the wafer became low,but the carrier mobility was large.When increasing the gas pressure,some particles were found on the surface of carbon film.And thus,a small number of pits with small area appeared on the surface of the ingot.It was found that the EPD inside the ingot increased,the carrier mobility decreased but the hardness and the resistivity increased.The electrical performance of the wafer became unsatisfied.When the gas pressure was 12 Pa,some big particles appeared on the surface of carbon film and the number of pits on the surface of the fabricated ingot increased significantly.The EPD inside the ingot,the hardness and the resistivity of the wafer were further raised,but the carrier mobility reached a low level.The effects of temperature gradient on the microstructure and properties of GaSb crystals were investigated.When the temperature gradient was 5°C/cm,the crystallinity of the GaSb crystal was high.And the EPD inside this ingot was 3928 cm^-2.The hardness,carrier mobility and resistivity of the wafer were in a medium level.When the temperature gradient increased to 7°C/cm,the crystallinity of the GaSb crystal increased,and the EPD inside the ingot decreased to 1785 cm^-2.The values of hardness and resistivity were low but the carrier mobility was large.The electrical properties of the wafer were optimal.With the increased temperature gradient,the crystallinity of the GaSb crystal decreased and the crystallization conditions were poor.Under this condition,the EPD inside the fabricated ingot increased to 9609 cm^-2.There were many grain boundaries inside the ingot,resulting in high values of hardness and the resistivity of the wafer and low value of carrier mobility.The effects of ACRT on the crystallization of GaSb were investigated.The forced convection was generated in the melt with presence of ACRT.The heat distribution inside the melt was improved and the heat transfer in the melt was enhanced.When the ACRT was not applied during crystal growth,the heat inside the melt was too much,resulting in more holes inside the ingot.The dislocation density was large with many etch pits.When the ACRT was used during the crystallization process,the volume of single crystal increased and the number of holes inside the crystal decreased.Meanwhile,the number of etch pits inside the crystal decreased slightly.The arrangement of etch pit became neat,and thus,the crystal quality was improved.