InAsSb/GaAs自聚式量子點之電性研究

Abstract

本論文主要是探討InAsSb/GaAs自聚式量子點之光電特性。我們成長三片不同厚度的InAsSb量子點，厚度分別為2、2.2及2.8ML。隨著InAsSb厚度增加，波長往長波長移動，從1235nm移動至1285nm。2.8ML樣品的峰值強度比另外兩片樣品低落許多，這表示其臨界厚度介於2.2~2.8ML。由C-V量測顯示出三片樣品都具有載子被侷限的現象，表現出位能井的特性。但是對於2.8ML樣品出現載子被空乏現象，這代表2.8ML的樣品已發生晶格鬆弛，發生在top GaAs與InAsSb的界面。再由DLTS的量測，我們發現2ML與2.2ML樣品沒有缺陷存在，而在2.8ML樣品有觀察到兩個缺陷，一個在GaAs頂端約0.64eV，另一個在量子點附近約0.35eV。這些缺陷在其他發生晶格鬆弛的樣品(3.4ML InAs QDs、3.33ML InAsSb/GaAs DWELL及1000Å InGaAs QW)也有觀察到。再透過TEM及transient量測，我們得知0.35eV的缺陷為misfit dislocation defect且隨著填充偏壓時間增加DLTS訊號有飽和的趨勢，這個缺陷為exponential function；另外0.64eV的缺陷為threading dislocation defect且DLTS訊號與填充偏壓時間成線性關係，此缺陷為logarithm function。

The electrical and optical properties of InAsSb/GaAs self-assembled quantum dots are investigated by photoluminescence(PL), current-voltage (I-V), capacitance-voltage (C-V), admittance spectroscopy(C-F), deep-level transient spectroscopy(DLTS), and cross-sectional transmission electron microscopy(TEM).Three samples with different InAsSb deposition of 2,2.2 and 2.8 ML, are grown by molecular beam epitaxy (MBE).When the InAsSb thickness is increased, PL spctra show a redshift of QD emission from 1235 nm to 1285 nm.The PL intensity of 2.8 ML sample is much weaker than the other samples, indicating that there is a critical thickness on the InAsSb quantum dots.The capacitance-voltage(C-V) measurement shows a carrier confinement for three samples.With increasing the InAsSb thickness to 2.8 ML, significant carrier depletion caused by the relaxation is observed in the top GaAs,leading us to deduce that relaxation occurs in the top GaAs/InAsSb interface.From DLTS data,while no traps are detected in the 2 and 2.2 ML samples, two traps at 0.64 eV and 0.35 eV are observed in the 2.8 ML sample. The trap at 0.64 eV lies in the top GaAs and the trap at about 0.35 eV lies close to the QD region.These traps are found to be similar to the traps observed in relaxed InAs QDs, and relaxed quantum well(QW) structures.By comparing with TEM and transient data, the trap at 0.35 eV is related to the misfit dislocation defects, and the trap at 0.64 eV is related to threading dislocation defects in GaAs.