InAs量子點蕭基二極體之導納模擬及照光下的光電壓效應

Abstract

本論文主要分為兩個部分，第一部分探討砷化鎵蕭基二極體內含量子點成長於量子井(Dot-in-well)結構的導納量測，分為空乏區跨過及未跨過量子層之兩種情形作探討。在確立樣品中電荷分佈情形後，解出空乏區之電場、電位及電位能，並利用小訊號分析的方式，分析量子點(量子井)內載子隨外加偏壓改變的運動情形，得到樣品的導納。論文的第二部分討論樣品在外加光源照射情形下的電容量測，引入光電壓(Photovoltaic)效應的機制解釋在空乏區尚未跨過量子層前，量子結構在照光下具有電容器的特性，因此光電流在流經量子結構時會產生一壓降順向偏壓於空乏區，導致光電容及C-V量測上充電平台的產生。樣品受限於電流值的大小，光電壓效應的時間常數被限制在秒的等級，因此與時間相關的量測，如改變掃動速率之C-V及I-V量測上皆能觀察到光電壓效應所造成量測曲線的變化。本論文將模擬的結果與實驗數據相互對照，以此佐證理論建立的正確性。

In this study, we demonstrate an analytical expression for admittance of InAs/InGaAs dot-in-well layer embedded in a GaAs Schottky diode. There are two cases we need to consider: QD layer is located inside the depletion region and QD layer is located outside the depletion region. By solving the electrical field and potential energy of the depletion region and analyzing the carrier distribution in quantum confine states, we obtain capacitance and conductance as a function of both bias and frequency. We also discuss the capacitance measurement under illumination. Since QD layer serves as a capacitor under illumination, the photocurrent will charge QDs and cause photovoltaic effect. We find that the photocapacitance and an additional plateau in C-V measurement are all caused by photovoltaic effect. Furthermore, the time constant of photovoltaic effect is limited by the value of current. Thus we can observe the photovoltaic effect on C-V and I-V measurement by changing sweeping rate. Analytical expression for C-V measurement under illumination have been deduced and used to fit experimental data.