矽鍺合金和其量子井結構中電洞的傳輸及光電特性之研究

Abstract

本論文中三個重要的主題：矽鍺合金中在高電場和低電場下電洞的傳輸特 性，矽鍺量子井中二維電洞的傳輸現象，以及矽鍺量子井中的光電特性。 為了計算晶格變形的效應和高能電洞的傳輸，因此我們提出了以束縛軌域 模型法計算變形矽鍺合金及其量子井中之能帶結構。以蒙地卡羅法模擬矽 鍺合金中電洞之移動率並變化不同的溫度、參雜濃度及鍺含量，且模擬的 移動率和實驗值相當吻合。並以同樣的方法模擬高電場下電洞的傳輸，其 中包含了漂移速度及衝擊游離率，且電場加到500kV/cm。在二維電洞的傳 輸物理中，我們也對矽鍺量子井中的量子侷限效應有所研究。其中考慮了 能帶混合效應的波函數及二維電洞的能帶結構對散射率的影響。我們發現 二維電洞的移動率隨量子井寬度增加而增加並趨近到矽鍺合金的移動率。 最後，我們亦研究ｐ－型矽鍺量子井中紅外線的吸收特性。在計算過程中 包含了以帕松和薛丁格兩方程式來處理能帶彎曲效應。計算的量子效率之 結果和實驗值相當吻合。在變化量子井寬度，參雜濃度及鍺含量的情況下 可改變量子井中紅外線的吸收特性。我們的研究指出最佳的吸收係數發生 在受激態接近量子井的頂端。 In this thesis, three important research topics have been accomplished which include low-field and high-field hole trans- port characteristics in SiGe alloys, two-dimensional hole trans- port behaviors in SiGe/Si quantum wells,and optical transitional properties in SiGe/Si quantum structures.In order to high energy hole transport, a bond-orbital model is developed for the first time to calculate the band-structures in SiGe alloys. The depen- dence of low-field hole mobility in strained SiGe/Si(001) layers is calculated using a Monte Carlo technique.In addition,we study the high-field hole transport characteristics in strained SiGe alloys. With respect to the low-dimensional hole transport, the quantum confinement effects in the strained SiGe/Si quantum structures are investigated.The simulation results show that the 2D hole mobility increases with a well width in a SiGe/Si quantum well and converges to a saturated value of intrinsic SiGe alloy mobility.A study of infrared absorption due to intersubband tran- sitions in p-type SiGe/Si quantum wells has been also performed. By varying a well width, our study reveals that a maximum absorp- tion coefficient is achievable when the energy level of the excited- state subband is near the top of a quantum well.