InAs/GaAs量子點電容-電壓和深層能階暫態頻譜之電性研究

Abstract

摘要 我們用電性量測來研究不同厚度的single QD與 superlattice QDs。從I-V的量測中我們發現superlattice QDs樣品的漏電流比single QDs樣品的漏電流還大。C-V量測中可觀察到InAs厚度3.4ML的single QD樣品有載子空乏的現象，可知3.4ML的single QD樣品已經晶格鬆弛了。我們在InAs量子點厚度7.56Å的 Superlattice QDs樣品中觀察到兩個載子堆積的地方，其峰值位置相差500Å，與其InAs量子點層與層間的距離相同，但是溫度下降時，觀察到自由載子濃度下降，推論是晶格鬆弛所造成的。另外，Superlattice QDs RTA(rapid thermal annealing)過後樣品在變溫C-V量測中，觀察到峰值的位移量隨RTA溫度升高而減小。 對single QD 3.4ML的樣品做DLTS量測，觀察到3種缺陷，其中活化能為0.63eV缺陷在彈性應變的GaAs塊材當中也有量測到，而活化能為0.51 eV和0.37eV的缺陷則在1000ÅIn0.2Ga0.8As /GaAs單層量子井結構中也有量到類似的缺陷，是由於晶格鬆弛所產生的缺陷。對superlattice QDs樣品做DLTS的量測發現了兩個缺陷能階，其中活化能為0.54eV的缺陷就是我們在S2樣品中量測到的0.51eV的缺陷。而活化能為0.39eV的缺陷只分布於樣品 的表面，RTA的樣品觀察到0.51eV和0.39eV的缺陷濃度下降。

Abstract The samples of single InAs/GaAs QD and superlattice InAs/GaAs QDs with RTA (rapid thermal annealing) at different temperature are investigated by capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS) measurement. The C-V measurement shows carrier confinement for 2.3ML single QD and 7.56Å superlattice QDs samples. And the carrier depletion by lattice relaxation is observed in 3.4ML QD sample. For the 2.3ML single QD sample, the quantum-confinement peak concentration of at low temperature is higher than at room temperature. However, in superlattice QDs, the quantum peak concentration is found lower at low temperature than at room temperature. These effects are found to reduce for samples after annealing at high temperature. In contrast with the 2.3ML single QD sample which no traps is found, three traps at 0.63, 0.51 and 0.37eV are detected in the 3.4ML single QD sample. The trap at 0.63eV has been found in plastic deformation GaAs bulk material. The traps at 0.51 and 0.37eV are found similar to the traps observed in relaxed 1000Å In0.2Ga0.8As/GaAs single quantum well structure and are suspected to be related to lattice relaxation. In superlattice QDs samples, two traps at 0.39 and 0.54eV are detected. The trap at 0.54eV is similar to the 0.51eV trap found in 3.4ML single QD indicating that the superlattice QD sample is relaxed. Moreover the concentration of both traps can be decreased with increasing RTA temperature.