Physics.Crystal Structure of Heavily Doped GaAs and In GaAs

采用金属有机分子束外延法（MOMBE）生长重碳掺杂GaAs (C-GaAs)，主要通过透射电子显微镜（TEM）、光致发光（PL）、电致发光（EL）、x射线衍射和霍尔测量等方法研究生长和退火后的C-GaAs的材料性能。在生长样品中，碳作为受体具有电活性，空穴浓度高达10^<21>cm^<-3>。由于碳原子的尺寸小，重碳掺杂降低了晶格常数，导致与砷化镓衬底的晶格常数不匹配。发现即使有错配位错的形成，平面内的拉伸应变也是不完全松弛的。C-GaAs高温退火可以降低空穴浓度，提高晶格常数。详细的TEM分析显示碳沉淀和错配位错数量增加。我们提出了一种模型来解释随着温度的升高空穴浓度的降低。在退火初期，残余应变因失配位错的形成而进一步松弛。在后期，砷处的碳原子缓慢移动到间隙处并形成沉淀。由于碳在砷化镓中的扩散系数非常小，所以这个过程很慢。碳原子从砷位点的移动导致空穴浓度的降低。它也增加了晶格常数。然而，形成的错配位错已经松弛了C-GaAs与GaAs衬底之间晶格错配引起的拉伸应变。因此，必须消除已经形成的错配位错。为此，形成了与已形成的错配位错的Burgers向量相反的更多错配位错。上述模型很好地解释了TEM和XRD的结果。退火前后均观察到C-GaAs的电致发光，电致发光的原因是错配位错。这项研究有助于我们了解重c掺杂GaAs的热不稳定性。少

Heavily carbon-doped GaAs (C-GaAs) was grown by metalorganic molecular beam epitaxy (MOMBE), and the material properties of the as-grown and annealed C-GaAs were mainly studied by transmission electron microscopy (TEM), photoluminescence (PL), electroluminescence (EL), X-ray diffraction, and Hall measurements. In the as-grown sample, carbon is electrically active as an acceptor, and the hole concentration as high as 10^<21>cm^<-3> was obtained. Because of a small size of a carbon atom, heavy carbon doping decreases the lattice constant and results in a misfit with that of a GaAs substrate. The tensile strain in a plane is found to be incompletely relaxd even with formation of misfit dislocations.Annealing of C-GaAs at high temperature was found to reduce the hole concentration and increases the lattice constant. The detailed TEM analysis revealed carbon precipitates and an increased number of misfit dislocations. We proposed a model to explain a decrease of the hole concentration as fo … More llows. In the early stage of annealing, the residual strain is further relaxd by formation of misfit dislocations. In the later stage, the carbon atoms at arsenic slowly move to the interstitial sites and form precipitates. Since the diffusivity of carbon in GaAs is extremely small, this process is slow. The movement of carbon atoms from the arsenic sites results in a decrease of the hole concentration. It also increases the lattice constant. However, the formed misfit dislocations have already relaxd the tensile strain which resulted from the lattice mismatch between C-GaAs and GaAs substrate. Therefore, the already-formed misfit dislocations must be canceled. For this purpose, more misfit dislocations with the Burgers vector opposite to those of the already-formed misfit dislocations are formed.The above model well explains the TEM and XRD results. Electrominescence was observed from C-GaAs before and after the anneal, and the origin of EL was attributed to the misfit dislocations. This study helps us understand thermal instability of heavily C-doped GaAs. Less