量子點的載子動力學與氮化銦磊晶層經快速熱退火效應的特性

Carrier dynamics in quantum dots and effects of rapid thermal annealing on the properties of InN epilayers

許嘉緯(Chia-Wei Hus)

指導教授 ： 沈志霖

中原大學/理學院/應用物理研究所/博士(2007年)

https://doi.org/10.6840/cycu200700151

摘要

摘要
本論文利用光激螢光、光激螢光激發光、時間解析光激螢光研究氮化銦磊晶層與半導體量子點之光學特性研究。本論文內容包含以下部分：
（1）氮化銦磊晶層經熱退火的光學與電學特性:
研究氮化銦磊晶層經過熱退火處理的光學與電學特性。氮化銦磊晶層經過熱退火處理溫度增加，發現光激螢光強度和載子遷移率隨著處理溫度增加而增加。我們合理推測在熱退火處理之後由於受體增加導致補償效應使得改善氮化銦的品質。此外，從光激螢光光譜的螢光峰值能量位置可以提供一種可能的方法估計簡併氮化銦的載子濃度。
（2）氮化銦磊晶層在不同載子濃度下侷域化現象：
我們利用時間鑑別光激螢光探討氮化銦磊晶層中在不同載子濃度下瞭解載子在磊晶層中的侷域現象。從偵測不同的輻射能量的光激螢光衰減與載子受熱游離產生抑制光激螢光強度，尋找隨著載子濃度的增加產生侷域化深度有所不同。藉由在自由電子在導電帶與在侷域電洞在價帶深的能量尾端之模型說明在氮化銦磊晶層中隨著載子濃度變化的載子侷域化深度，因而我們說明載子被侷域在雜質所產生的波動的無序位能中。
（3）覆蓋砷化銦鎵的自聚式砷化銦量子點之螢光衰減時間：
我們研究覆蓋砷化銦鎵磊晶層之自聚式砷化銦量子點隨溫度變化的時間鑑別光激螢光。隨著溫度從50至170 K光激螢光衰減時間呈現增加，而溫度高於170 K後螢光衰減時間則減少。由量子點基態與連續態之間藉由聲子相關躍遷的模型可以說明上述受溫度影響的光激螢光衰減時間變化。此項結果說明連續能態在量子點內載子被捕捉的過程中扮演著重要的角色。
（4）膠溶態硒化鎘量子點在氧氣壓力下之螢光特性：
我們利用光激螢光及時間解析光激螢光研究膠溶態硒化鎘/硫化鋅量子點在氧氣下與真空環境下的效應。將樣品放置在真空中相較於一大氣壓氧氣下，我們發現光激螢光強度增強近十倍，這是由於氧氣吸附在樣品的表面使得樣品表面缺陷被鈍化。光激螢光衰減強度可以用雙指數函數擬合模擬得兩個載子生命期，時間較短的生命期大約快近似1 ns與時間較長的生命期大約快近似10 ns。由不同放射能量的載子生命期與兩個載子生命期相對強度振幅比率，我們提出膠溶態硒化鎘量子點中較短的螢光衰減是來自於量子點內未侷域的載子，而較長的螢光衰減是由於表面侷域的載子所造成。

關鍵字

快速熱退火 ； 量子點 ； 氮化銦 ； 時間解析光激螢光 ； 光激螢光 ； 硒化鎘 ； 光激螢光激發光 ； 砷化銦

並列摘要

Abstract
This dissertation studies the optical properties of InN epilayers, self-assembled InAs quantum dots (QDs) and colloidal CdSe QDs. Different optical techniques such as photoluminescence (PL) and time- resolved photoluminescence (TRPL) measurements are carried out to investigate the physical properties of InN epilayers and semiconductor QDs. These results are presented in the following :

(1) Effects of rapid thermal annealing on the optical electrical properties of InN epilayers
We studied the optical and electrical properties of InN epilayers with rapid thermal annealing (RTA). The intensity of the PL and the carrier mobility were found to increase as the temperature of RTA was increased. We suggest that the formation of compensating acceptors (indium vacancies) after RTA is responsible for the improvement of the quality in InN. The dependence of the PL emission peak on carrier concentration provides a possible method for estimating the carrier concentration in degenerate InN.
(2) Concentration dependence of carrier localization in InN epilayers
The concentration dependence of carrier localization in InN epilayers was studied using time-resolved PL. Based on the emission-energy dependence of the PL decays and the PL quenching in thermalization, the localization energy of carriers in InN is found to increase with carrier concentration. The dependence of carrier concentration on the localization energy of carriers in InN can be explained by a model based on the transition between free electrons in the conduction band and localized holes in the deeper tail states. We suggest that carrier localization originates from the potential fluctuations of randomly located impurities.
(3) The PL decay time of self-assembled InAs quantum dots covered by InGaAS layers
The temperature dependence of the time-resloved PL in self-assembled InAs QDs with InGaAs covering layers was investigated. The PL decay time increases with temperature from 50 to 170 K, and then decreases as the temperature increases further above 170 K. A model based on the phonon-assisted transition between the QD ground state and the continuum state is used to explain the temperature dependence of the PL decay time. This result reveals that the continuum states are important in carrier capture in self-assembled InAs QDs.
(4) PL in colloidal CdSe QDs under oxygen atmosphere
The effects of oxygen versus vacuum ambients on colloidal CdSe/ZnS QDs were studied using both continuous and time-resolved PL measurements. The PL intensities were found to be an order of magnitude higher in an oxygen atmosphere, which is explained by the passivation of surface defects by oxygen absorption. The decay of PL intensities can be best fitted by a biexponential function with lifetimes of approximately 1 ns for the fast decay and approximately 10 ns for the slow decay. Based on the emission-energy dependence of carrier lifetimes and of the amplitude ratio of the fast-decay component to the slow-decay component, we suggest that the fast and slow PL decay of colloidal CdSe/ZnS QDs is caused by the recombination of delocalized carriers in the internal core states and the localized carriers in the surface states, respectively.

並列關鍵字

TRPL ； PL ； RTA ； InN ； InAs ； CdSe ； quantum dots ； PLE

參考文獻

[3] S. Strite and H. Morkoc, J. Vac. Sci. Technol. B 10, 1237 (1992).

[4] S. N. Mohammad and H. Morkoc, Prog., Quantum Electron. 20, 361(1992)

[7] S. Nakamura, M. Senoh, and T. Mukai, Jpn., J. Appl. Phys., Part 2 32, L8(1993)

[10] V. Y. Davydov et al., Phys. Status Solidi B 229, R1 (2002)

[11] V. Y. Davydov et al., Phys. Status Solidi B 230, R4 (2002)