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研究了在分子束外延制备的AlN/蓝宝石模板上采用金属有机物化学气相外延生长的非故意掺杂GaN的材料性质.采用X射线衍射(XRD)、透射电镜(TEM)和原子力显微镜研究了AlN模板的晶体质量和表面相貌对GaN的影响.结果表明,当AlN的表面粗糙度较小时,尽管AlN模板的位错密度较高((102)面XRDω扫描半高全宽900—1500arcsec),但生长得到的GaN依然具有和在蓝宝石衬底上采用“二步法”生长的GaN可比拟的晶体质量((002)面XRDω扫描半高全宽200—300arcsec,(102)面400—500arcsec)和表面粗糙度(0.1—0.2nm).TEM照片表明GaN中位错密度降低的原因是AlN中的一部分位错在AlN和GaN的界面处被终止而未能延伸至GaN中.这可能是因为Ga原子尺寸较大,具有修复晶格缺陷的作用.而当AlN的表面粗糙度较大时,Ga原子在MOVPE生长过程中的迁移受到影响,得到的GaN晶体质量非常差.此外,采用范德堡法测量的GaN电阻率为105—106Ω·cm,比蓝宝石衬底上生长的GaN高大约6个数量级,这被认为是采用AlN代替GaN低温缓冲层所致.
The properties of unintentionally doped GaN grown by chemical vapor-phase epitaxy of metal-organic-organic on AlN / sapphire template prepared by molecular beam epitaxy have been investigated. The effects of AlN template The results show that when the surface roughness of AlN is small, although the dislocation density of AlN template is high (the FWHM of XRDω scan of (102) plane is 900-1500arcsec), the growth of GaN still has comparable crystal quality ((002) plane XRD [omega] scan full width at half maximum 200-300 arcsec, (102) plane 400-500 arcsec) to GaN grown on a “sapphire substrate” on sapphire substrate and surface roughness (0.1-0.2 nm) .TEM pictures indicate that the reason for the decrease in dislocation density in GaN is that a portion of the dislocations in AlN are terminated at the AlN-GaN interface and failed to extend into GaN.This may be because the Ga atom size is smaller Large, with the role of repairing lattice defects.When the surface roughness of AlN is larger, the migration of Ga atoms in MOVPE growth process is affected, the quality of GaN crystals obtained is very poor.In addition, the measured by the Vanderbilt method The GaN resistivity is 105 -106 Ω · cm, about six orders of magnitude higher than GaN grown on a sapphire substrate, which is believed to be caused by the use of AlN instead of the GaN low temperature buffer layer.