在InAs量子點上成長不同厚度InAlAs層對於光電容特性的影響

Abstract

本論文主要探討在InAs量子點上成長不同厚度的In0.14AlAs層，在照光後電容抬升的機制與差異。首先我們先以照光暫態電容的實驗來分析探討照光後光電容的產生機制，搭配深層能階暫態分析DLTS，與照光下暫態電流的實驗，來了解光生載子在樣品中遷移的機制。而在照光後儲存載子所形成的光電容，在關光後有暫存的特性，我們利用在關光後改變外加偏壓一段時間後，切換回起始偏壓由光電容的改變量以觀察儲存載子的改變量。加大逆向偏壓下，會因為成長了In0.14AlAs層載子依然會儲存在前方的量子井或二維電子氣，隨著In0.14AlAs層厚度減小，載子侷限的能力也會隨之降低；為了移除二維電子氣中的載子，則需要加入順向偏壓來使In0.14AlAs層前方的能帶變平緩，將二維電子氣中的電子掃回空乏區中。所以當In0.14AlAs層厚度增加，則是加強了量子井或二維電子氣的侷限能力，進而產生較大的光電容。

In this study, we discuss the mechanism of the apparently photocapacitance in InAs/GaAs quantum dots (QDs) sample covered by In0.14AlAs layer, and study the difference of photocapacitance in the sample with different In0.14AlAs thickness. At first, we use the transient photocapacitance, deep level transient spectroscopy and transient current to analyze the mechanism of light-induced carrier transmission in sample. The large capacitance increase induced by light can sustain even light is removed. We change the bias after light off for a while, then sweep back to initial bias to check the change of storage carrier. Under applying larger reverse bias, the carriers stored in front of the In0.14AlAs layer can’t tunnel through the barrier. So the capacitance do not change after sweeping back to initial bias. To erase the carriers in QW or 2DEG, we apply a forward-direction voltage to flatten the band-bending and sweep the electrons back into the depletion region of the Schottky diode. As increasing the In0.14AlAs layer thickness, the confinement of QW or 2DEG become better and cause the larger photocapacitance.