雙模態砷化銦量子點間載子傳輸機制與應力鬆弛發生雙模態之探討

Abstract

使用MBE 系統成長出超越臨界厚度的氮砷化銦量子點樣品，藉由摻雜氮原子造成應力鬆弛的方式誘發形成雙模態量子點，並透過光性與電性量測分析來探討雙模態量子點形成的機制與特性。為了聯結量子點的光特性與電特性，我們利用分光儀產生各波長的光激發下，當光激發了量子點能階產生電子電洞對時，電子電洞會經由兩種機制產生訊號，分別為再複放射合以及載子放射，並貢獻在三種訊號：分別為螢光、光電流和光電容。因此，比較了不同熱退火樣品之光電流和光電容變化，以及藉由改變溫度及波長觀察光電流與光電容變化趨勢；當電子與電洞放射速率相差較大時，光電容的訊號變強而光電流的訊號變弱。藉由光電流與光電容的量測分析出在氮砷化銦量子點樣品中的電子放射機制為熱放射，而經熱退火後的樣品中，量子點的電子放射機制則是藉由熱放射至砷化銦鎵覆蓋層後再穿遂至砷化鎵層。而配合光電容的量測結果以及我們提出的理論計算模型，確立電子與電洞的放射速率並確認了在氮砷化銦/砷化鎵材料中導帶與價帶能量比例為6比4。

In this work we study a method for controlling of the structure of the InAs quantum dots (QDs) with InGaAs capping layer fabricated by molecular beam epitaxy (MBE) deposition. When the InAs with a large nitrogen incorporating, strain in the InAsN QDs is relaxed. At the same time, the bimodal QDs start to form. The characteristics of the bimodal QDs are studied by optical and electrical measurements. The excitation of the electron-hole pairs in the QDs by illumination on the QDs is also studied. The electron-hole pairs can lead to the photoluminescence, photocurrent and photocapacitance by mechanisms of carrier recombination and emission. Furthermore, we analyze temperature and energy dependences of photocurrent and photocapacitance on samples of before and after annealing. Comparing with the electron and hole emission rates from the InAs quantum state, photocapacitance is obviously found as the difference of electron and hole emission rate enhance. On the photocurrent analysis, electron escape process is thermal emission from the quantum state to the GaAs band edge on the sample before annealing, and the electron escape process is the phonon-assisted tunneling from quantum state via the InGaAs capping layer state to the GaAs conduction band edge on the sample after annealing. A theory model by a simple rate equation can explain the mechanisms of illumination on QDs, estimate the hole emission rate, and the conduction-band offset ratio is roughly 60% (6：4) for the InAsN/GaAs material system.