Bridgment Growth And Characterization Of Bi-dopend GaAs Crystals

GaAs is the typical second semiconductor material, and it is belong to direct band gap semiconductor. Its intrinsic features include high electron mobility(8500cm2 v-1 s-1)、good thermo-stability and anti-radiation and so on, which make it widely used in optoelectronic and microelectronic application. As the doping of Bi can improve the temperature sensibility and adjust the band gap, searching for Bi-doped GaAs alloy has become the hotspot of this field. It was reported that the GaAs:Bi film has been grown by the molecular beam epitaxy and metal organic vapor phase epitaxy. The study shows that doping of Bi can adjust the band gap and has almostno effect to electronic mobility. GaAs:Bi crystals are hopeful to achieve the better result of properties control. However, It is difficult to growth GaAs:Bi crystal of high quality due to Bi segregation.Several growth methods are suitable for GaAs crystals, such as the liquid encapsulated Czochralski(LEC)method, horizontal Bridgman(HB)method and vertical gradient freeze(VGF) method.The Bridgman method is an effective way to growth of GaAs crystals, and realize the remarkable achievement on productive of GaAs crystals. In our work, the industrialization of Si-GaAs crystal was realized by this method.In this paper, based on the growth of GaAs crystals, using <511> oriented GaAs seed and pBN crucible, B2O3 as the encapsulated liquid, 2-inch GaAs1-xBix crystal with a nominal composition of x=0.025 was obtained. Few of pits exist at the surface of crystal, and the top of crystal have a little of precipitates. Bi-rich inclusions were observed by Scanning Electron Microscope (SEM).The wafers were polished and etched by KOH solution, high dislocation density and many dislocation lines were observed. Transmittance spectra and Bi-related peaks were observed in Energy Dispersive Spectroscopy (EDS) spectra, means that Bi has entered into GaAs lattices. The double-crystal X-ray rocking curve has been measured and the FWHM value is about 42 arcsec, crystal quality should be improved further. Compared with undoped GaAs crystal, the band gap of as-grown crystal shifted to red wave from 1.43ev to 1.39ev.The results show that GaAs0.975Bi0.025 crystal is a potential substrate material for semiconductor lasers application in infrared wavelength range.