Physics.Crystal Structure of Heavily Doped GaAs and In GaAs

采用金属有机分子束外延（MOMBE）方法生长了重掺碳GaAs（C-GaAs），并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了生长态和退火态C-GaAs的材料特性。在所生长的样品中，碳作为受体是电活性的，并且获得了高达10 μ cm-3的空穴浓度<21><-3>。由于碳原子的小尺寸，重碳掺杂降低晶格常数并导致与GaAs衬底的晶格常数失配。发现即使有失配位错的形成，平面内的拉伸应变也不完全松弛，高温退火可降低C-GaAs的空穴浓度，提高晶格常数。详细的TEM分析显示碳沉淀和错配位错的数量增加。我们提出了一个模型来解释空穴浓度随着温度的升高而降低的现象。 ...更多信息 lllows。在退火的早期阶段，残余应变通过形成失配位错而进一步弛豫。在后期，砷上的碳原子缓慢地移动到间隙位置并形成沉淀。由于碳在GaAs中的扩散率非常小，这个过程很慢。碳原子从砷位置的移动导致空穴浓度的降低。它还增加了晶格常数。然而，形成的失配位错已经松弛了由C-GaAs和GaAs衬底之间的晶格失配引起的张应变。因此，已经形成的失配位错必须被消除。这一模型很好地解释了TEM和XRD结果。在退火前后观察到C-GaAs的电致发光，电致发光的起源归因于失配位错。这项研究有助于我们理解重掺C 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