GaN基异质外延生长的ZnO单晶电输运特性研究

Electronic Transport Properties of Monocrystalline ZnO-Plate Synthesized by Chemical Vapor Transport Deposition

报道了一种新方法生长的ZnO单晶的电输运特性,利用该方法在GaN外延膜表面生长了尺寸为25 mm×25 mm,平均厚度7 mm的ZnO单晶块。通过研究ZnO单晶不同深度处的电输运特性,判断了ZnO单晶内部不同位置的结晶质量。以GaN表面为起始面,沿[0002]方向,随着距GaN表面距离的增加,常温下的ZnO单晶载流子浓度从1.28×10^19降到4.00×10^17 cm^-3,载流子迁移率从64.9升至144 cm^2/(V·s),电阻率从7.53×10^-3升至1.09×10^-1Ω·cm。位错密度计算结果表明,随着远离GaN衬底,晶体内位错密度逐渐减少,二次离子质谱测试结果中,Ga+等杂质含量随着远离GaN衬底逐渐减少,在距离GaN表面约4 mm以后,主要杂质含量明显降低。由此表明,采用价格相对较低的GaN衬底可以获得较大尺寸,品质较好的ZnO单晶。

The large-sized monocrystalline ZnO-plate(25 mm×25 mm×7 mm),an advanced laser material,was synthesized by chemical vapor transport deposition on the fairly cheap substrate of sapphire pre-coated with epitaxial GaN(0002)transition-layer.The non-homogeneous depth distributions of the microstructures,phase-structures and electric transport behavior was studied with X-ray diffraction,energy dispersive spectroscopy,scanning electron microscopy and time-of-flight secondary ion mass spectroscopy.The results show that the top-layer of quasi intrinsic ZnO-semiconductor coexisted with the bottom-layer of quasi degenerated ZnO-semiconductor,because of the great variations in the crystallinity and purity.Specifically,as the top-down depth increased,when measured at 300 K the dislocation density and Ga/Li/Na/K/Si-impurity densities increased,resulting in the significant decreases of resistivity and carrier-mobility,and bringing about a considerable increase of carrier concentration.We suggest that the synthesized bulk ZnO-material be of some technological interest in fabrication of photoelectric devices.