InAsSb量子點表面活化及相分離現象以及熱退火影響InAsSb量子點光性電性

Abstract

本論文主要研究Sb摻入InAs QDs所引起的表面活化效應以及相分離情形。藉由Varshni材料參數解析出InAs+Sb QDs在成長當中會形成一群長波長的InSb QDs以及一群尺寸大小不一的InAs-rich QDs。並由表面活化效應延遲量子點生長速率解釋InAs+Sb QDs因遭受Sb不同程度表面活化效應影響使得InAs-rich QDs形成尺寸大小不一的量子點。 另將InAs+Sb QDs熱退火處理，發現高溫熱退火(700oC, 750oC)會引起InAs-rich QDs發生相分離情形，趕出原本少數摻入InAs-rich QDs的Sb，而顯現InAs QDs的發光行為，使均勻性變佳。但熱退火同時也提供InAs+Sb QDs相分離出的長波長InSb QDs熱能，使長波長InSb QDs發生晶格鬆弛現象，減弱長波長InSb QDs發光強度。 而InSb QDs因熱退火引發晶格鬆弛產生的缺陷，其中缺陷活化能和缺陷捕捉截面積和Deep Level Transient Spectroscopy (DLTS)量測的填充偏壓時間有干係。填充偏壓時間愈大(80 ms)缺陷活化能(0.29 eV)和捕捉截面積愈小；反之(1 ms)缺陷活化能(0.95 eV)和捕捉截面積愈大。由此，推測存在一個缺陷捕捉位能障進而影響缺陷捕捉截面積。 不只DLTS顯現缺陷訊號，室溫Capacitance Voltage (C-V)頻譜經由轉縱深發現在樣品表面0.2µm附近有缺陷訊號，此缺陷訊號為DLTS所測量到的熱退火缺陷，熱退火缺陷在低溫下不影響量子點行為，200 K之後牽制量子點行為，並將量子點位置從原本的0.4µm拉近0.3µm左右。此為熱退火缺陷將整個能帶彎曲造成的影響，故可在較小偏壓就偵測到缺陷訊號以及提前的量子點訊號。另外也可以從C-V縱深頻譜看到載子傳輸行為，其轉換溫度跟PL互相呼應。 Atomic Force Microscope (AFM)所提供的2.2 ML和2.8 ML量子點尺寸不均現象和2.2 ML RTA650 Tunneling Electron Microscope (TEM)可瞧見缺陷存在，皆與上述光性、電性量測結果符合。

We show that InAs-rich quantum dots (QDs) and InSb QDs would be formed in the growth of InAs+Sb QDs since Varshni fitting shows that the long wavelength emission has InSb QDs emission properties.

This phenomenon can be attributed to antimony (Sb) which causes phase separation and surfactant effects on InAs+Sb QDs. Surfactant effect delays QDs growth rate and thus, with strong surfactant effect, InAs QDs size decreases and vice versa. Hence, the Photoluminescence (PL) result displays large Full Width Half Maximum (FWHM) of InAs-rich QDs and the Atomic Force Microscope (AFM) picture shows worse size uniformity in InAs+Sb QDs.

After thermal annealing, a few Sb are swept out in InAs-rich QDs; therefore, InAs QDs emission behavior shows up. Furthermore, annealing destroys InSb QDs emission intensity and a defect signal can be detected by Deep Level Transient Spectroscopy (DLTS). This defect is induced by relaxation of InSb QDs after high temperature thermal annealing. The defect activation energy which is related to its capture cross section varies from 0.29 eV to 0.95 eV as filling pulse changes from 80 ms to 1 ms. That can be explained by a capture barrier which influences the capture cross section.

Capacitance-Voltage (C-V) measurement can also detect a defect peak at 0.2 µm and the carriers transfer between InAs-rich QDs and InSb QDs can also be observed by temperature dependent C-V depth profile.

Tunneling Electron Microscope (TEM) and AFM presenting misfit-like defect and worse size uniformity match our discussions in electricity and optics.