以光激發光研究鍺半導體之光學躍遷機制

Abstract

本論文中，我們藉由光激發光的激發方式，觀察到鍺的直接能隙和非直接能隙的放光現象，同時我們探討兩者之間競爭性的發光復合機制。 高濃度磣雜N型的鍺可使電子的費米能階往高能量移動並使得直接能隙的放光有所增加，高濃度磣雜P型的鍺可減少直接能隙與非直接能隙的能帶差，累積更多的電子在直接能隙並產生增強放光的現象。無論是直接能隙或非直接能隙都可藉由物理模型去加以模擬並解釋。 外加雙軸張應力可減少直接能隙與非直接能隙的能帶差，或者降低直接能隙與費米能接的差，而累積更多的電子在直接能隙並產生增強放光的現象。藉由物理模型得到的能帶值和藉由理論計算出的能帶值兩者相當吻合。 在降低溫度的光激發光實驗，利用SRH模型及Thermal quenching 模型，提出電子電洞可經由缺陷非輻射復合，而使得放光的總強度減少。

In this thesis, both direct and indirect transitions of photoluminescence are observed in Ge and the competitive radiative recombination between direct and indirect transition are discussed. High doping concentration in n type Ge moves the electron Fermi level upwards and the increase in electron population in direct valley enhance the luminescence. In p type Ge, the reduction in bang gap difference between the L and Γ valleys results in the enhancement of direct band gap emission. Each spectrum can be fitted by the sum of direct and indirect transition models. The reduction in band gap difference between the L and Γ valleys by biaxial tensile strain increases the electron population in the direct valley and leads to strong enhancement on (100) and (110) Ge. On the other hand, the reduction in the energy difference between the EcΓ and Efn, which is responsible to the enhanced PL on (111) Ge. The direct and indirect band gaps can be extracted from the photoluminescence spectra and is consistent with the calculations using K．P and deformation potential methods for valence band and conduction band, respectively. We demonstrate SRH model and thermal quenching model to explain the temperature dependent photoluminescence experiments. At high temperature, minority carriers would be captured by traps, which results in non-radiative recombination. Hence the integrated photoluminescence decreases with high temperature.