Mg掺杂的Al_xGa_(1-x)N/GaN超晶格紫外峰的性质

Ultraviolet Luminescence from Mg-doped Al_xGa_(1-x)N/GaN Superlattice

观测了不同Mg含量的AlxGa1-xN/GaN超晶格(SLs)样品在不同退火温度和激发强度下的光致发光(PL)光谱。结合霍尔测量,分析了其紫外发射(UVL)峰的起源及相关影响因素。实验发现:同一样品在N2气氛中高温退火,UVL峰强随退火温度的升高,先增至饱和继而急剧下降,峰位红移;而在相同退火条件下,随着掺杂Mg的流量增加,样品空穴浓度下降,峰强减弱,峰位红移。结果表明:UVL峰是来自于易热分解的浅施主(VNH)与浅受主(MgGa)之间的跃迁,并受到深施主(MgGaVN)与浅受主(MgGa)自补偿效应的影响。实验上随着PL光谱激发强度的增强,UVL峰位约有260meV的蓝移,结合超晶格极化场下的能带模型分析,认为这是极化效应导致的锯齿状能带中,VNH与MgGa之间跃迁方式的改变引起的现象。

Investigation on the origin and relative factors of ultraviolet luminescence （UVL） by photoluminescence and Hall measurements for the Mg-doped AlxGa1-xN/GaN superlattice with varying annealing temperature and excitation intensity is presented. The intensity of UVL increases to the maximum and then decreases sharply and the peak exhibites a redshift when the annealing temperature increased in the N2 atmosphere; at the same activating condition, the hole concentration of the sample and the intensity of UVL decreases and the peak shifts to the lower energy as the Mg content increases. The results indicated that the transition between the shallow donors （VNH） that is easily disassembled by heat and shallow acceptors （MgGa） caused UVL, which also competes with the transition between deep donors （MgGaVN ） and shallow acceptors （Mgga） due to the effect of self-compensation by redshift. The blueshift of UVL is about 260 meV with increasing the excita- tion density. Studying by the model of band structure of superlattice on the effect of polarization, it was suggested that UVL arises from the change of the transition between VNH and MgGa in a sawtooth-like band structure due to polarization effect. According to the early reports, the origin of UVL in Mg-doped GaN is still unclear. In this report, UVL is found in Mg-doped AlxGa1-xN/GaN superlattice and the difference from Mgdoped GaN is observed through the photoluminescence due to the strong polarization effect in superlattice. This study will help us to disclose the process of the radiative transition especially caused by defects in superlattice clearly and understand the origin of ultraviolet luminescence in these Mg-doped GaN-based materials further.