GaN buffer layers (thickness ～60nm) grown on GaAs(001) by low-temperature MOCVD are investigated by X-ray diffraction pole figure measurements using synchrotron radiation in order to understand the heteroepitaxial growth features of GaN on GaAs(001) substrates.In addition to the epitaxially aligned crystallites,their corresponding twins of the first and the second order are found in the X-ray diffraction pole figures.Moreover,{111} φ scans with χ at 55° reveal the abnormal distribution of Bragg diffractions.The extra intensity maxima in the pole figures shows that the process of twinning plays a dominating role during the growth process.It is suggested that the polarity of {111} facets emerged on (001) surface will affect the growth-twin nucleation at the initial stages of GaN growth on GaAs(001) substrates.It is proposed that twinning is prone to occurring on {111}B,N-terminated facets.
根据电子镇流器控制器对基准电源的设计要求,利用不同电流密度下两晶体管基极-发射极电压差的正温度特性,通过镜像电流源方式产生PTAT(proportional to absolute temperature)电流,再结合基极-发射极电压本身的负温度特性产生的电流,形成带隙基准电流源。仿真结果表明,该基准源的性能指标能满足系统设计的要求。
