中文摘要：

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.

英文摘要：

Properties of unintentionally-doped GaN re-grown on molecular beam epitaxy grown AlN/Sapphire templates by metal organic vapor phase epitaxy （MOVPE ） are studied in this article.X-ray diffraction （XRD ）,transmission electron microscope （TEM）,and atomic force microscope are used to investigate the influence of the crystal quality and surface morphology of AlN on the GaN.It is found that when surface roughness of AlN is small,the GaN has a full width at half maximum （FWHM） values of XRD rocking curves （200—300 and 400—500 arcsec for （002） and （102） plane ω-scan,respectively） and surface roughness （0.1—0.2 nm）,which are comparable to those grown on sapphire substrates by using＂two-step＂method,although the FWHMs of （102） plane XRD ω-scan curves of AlN are 900—1500 arcsec.The reason for dislocation reduction in GaN shown by TEM image is that a part of dislocations in AlN are eliminated in the interface between AlN and GaN.This is probably due to the lattice restoration from Ga atoms for their large size.On the other hand,when surface roughness of AlN is large,the surface migration of Ga atoms is nestricted during the MOVPE growth,which results in a poor GaN quality.Moreover,the resistivity of GaN confirmed with Van der Pauw method is between 105 and 106 Ω·cm,which is about six orders of magnitude higher than that in GaN grown on sapphire substrates.This is attributed to the replacement of low temperature GaN buffer layer by the AlN.