GaAsN/GaAs量子井蕭基二極體在照光下之光電容模擬

Abstract

在本論文中，首先介紹研究動機，主要是探討樣品在照光之後，量測電容值會有抬升的現象，因此先探討GaAsN/GaAs量子井在照光後，實驗量測得到之C-V曲線抬升的機制，由前人的研究可以得知，在照光之後，量子井會產生「光伏」的現象，照光所產生之過量載子，因電場影響，而在樣品中形成光電流，而量子井扮演的角色為一電容性負載，可以儲存電荷並且佔一跨壓，進而影響蕭基接面之跨壓；接續前人的研究，在本論文中使用2種不同的方式計算量子井在外加小偏壓(蕭基接面空乏區還未抵達量子井)時之光電容值，第一種方式使用電容電壓量測配合電流電壓量測；分別計算量子井之跨壓和因照光多儲存進量子井的載子，並且將兩者相除，得到實驗光電容值；第二種方式使用平行電容板公式，並且代入量子井之能態密度和費米迪拉克函數，計算出量子井之光電容值。

In this study, we introduce photovoltaic effect first, we found that measured capacitance would increase and form a plat form after we illuminate GaAsN/GaAs quantum well schottky diode sample. Photovoltaic effect had been researched by the other study. The electric field would deplete the excess carriers which generated by illumination to form a photo current. The photo current would charge quantum well, and form a voltage drop across quantum well. Quantum well could store charges and hold a voltage drop that serves as a capacitive loading. In this study, we use two methods to obtain quantum well photo capacitance when we apply little bias (Schottky junction depletion region has not arrived quantum well). First, we apply C-V plot and I-V plot to calculate quantum well photo voltage drop and carriers which charged into quantum well respectively. Divide the carriers and voltage drop, we can obtain experiment photo capacitance. Second, we express quantum well photo capacitance as a parallel plate capacitor substitute charge Q by quantum well density of state and Fermi-Dirac distribution. Sovle the equation, we can obtain the simulated photo capacitance.