砷化鎵／砷化銦 量子點的電-光性質

Electro-Optical Properties of InAs/GaAs Quantum Dots

李佳任(Jia-Ren Lee)

指導教授 ： 陸健榮

國立臺灣師範大學/理學院/物理學系/碩士(2000年)

摘要

摘要
我們分別以光調制反射實驗(PR)和光激螢光實驗(PL)來研究由有機金屬化學氣相沈積法(MOCVD)所長成的 砷化銦／砷化鎵 量子點系統結構在不同溫度下其電-光性質的變化。由於兩種實驗的機制不同，譜線強調的部分也就不一樣，將兩者實驗結果互相比較對照，對譜線的解釋有莫大的助益，並得到完整可靠的光譜訊息。
經由我們對PR的實驗結果以羅倫茲譜形的擬合與分析，發現在砷化鎵能隙以下的一組譜形結構是來自於厚度為2ML的砷化銦wetting layer(WL)的貢獻，並且觀測到砷化銦WL的光譜強度相對於砷化鎵能隙的光譜強度有越往低溫越大的現象。
經由我們對PL實驗結果以高斯曲線的擬合與分析，發現量子點相鄰能階有幾乎相同的能量差，並根據理論模型計算結果推測量子點系統受到來自於樣品內部電場的史塔克效應(Stark effect)影響使得實驗能階譜峰能量位置因為位能井的傾斜而有更大的紅移幅度。我們發現PL能階譜形的寬化參數從低溫開始隨著升溫而增加，但在200K時卻有明顯的窄化現象，接著又隨著升溫而寬化，並不像一般在量子井或塊材中所觀察到的展寬隨著溫度持續增加。我們發現隨著溫度上升，各能階的螢光積分強度皆隨著升溫而減小，基態與其他能階的螢光強度比值在200K時較其他溫度時為大。
根據PR與PL實驗分別只觀察到來自於WL與量子點能階躍遷訊號的比較對照下，我們認為來自於樣品結構中的高摻雜及樣品之表面態捕獲電子使得費米能階介於量子點的最高能階與WL的最低能階之間，以致於兩種實驗機制所對應的訊號來源有所區別。

關鍵字

砷化銦/砷化鎵 ； 量子點 ； 光調制反射 ； 光激螢光

並列摘要

ABSTRACT
The electro-optical properties of InAs/GaAs Quantum Dots have been studied by comparing the photoreflectance and photoluminescence spectra at various temperatures. The samples used in our experiments were grown by Metal-Organic Chemical Vapor Deposition on the n+ dopped GaAs substrates.
The photoreflectance spectral features below the energy gap of GaAs originate from the InAs wetting layer , and the relative spectral intensity between the InAs wetting layer and the GaAs energy gap increases with the decreasing of temperature .
The photoluminescence spectral profiles consist of contributions from the equal spacing energy levels of the InAs quantum dots, and agree with the prediction of the disc-shaped quantum dots theoretical calculations. The red shifts of the quantum dots energy levels with the increasing temperature may be influenced by the internal electric fields induced Stark effect.
Since the quantum dots transitions were observed in the photoluminescence spectra and the wetting layer transitions were observed in the photoreflectance spectra, we propose that the Fermi level of the system is located between the highest energy level of the wetting layer and the lowest energy level of the quantum dots.

並列關鍵字

InAs/GaAs ； quantum dots (QD) ； photoreflectance (PR) ； photoluminescence (PL)

參考文獻

2. M. Grundmann, D. Bimberg, Jpn. J. Appl. Phys. 36, 4181 (1997).

relaxation processes in self-organized InAs/GaAs quantum dots," Appl. Phys. Lett, vol.68, pp. 361-363, 1996.

4. N. Kirstaedter, O. G. Schmidt, N. N. Ledentsov, D. Bimberg, V. M. Ustinov, A. Yu. Egorov, A. E. Zhukov, M. V. Maximov, P. S. Kop'ev and Zh. I. Alferov," Gain and differential gain of single layer InAs/GaAs quantum dot injection lasers," Appl. Phys. Lett, vol. 69, pp. 1226-1228, 1996.

5. N. N. Ledentsov, I. L. Krestnikov, M. V. Maximov, S. V. Ivanov, C. M. Sotomayor Torres, "Response to ``Comment on `Ground state exciton lasing in CdSe submonolayers inserted in a ZnSe matrix' '' [Appl. Phys. Lett. 70, 2765 (1997)],"Appl. Phys. Lett. 70, pp. 2766-2767, 1997.

6. Y. Arakawa and K. Sakaki, Appl. Phys. Lett. 40, pp. 939-941, 1982.