分子束磊晶成長碲化鋅/硒化鎘鋅量子點經快速熱退火後之熟成機制研究

Abstract

本實驗利用分子束磊晶系統於砷化鎵(001)基板上成長碲化鋅／硒化鎘鋅量子點，並利用低溫光激螢光光譜、變溫光激螢光光譜與時間解析光譜分析量子點經快速熱退火後的光性變化。 對於鎘含量為12 %之樣品，使用光激螢光光譜觀察到3.2原子層厚度之碲化鋅／硒化鎘鋅量子點經快速熱退火後有明顯的紅移現象，其紅移現象源自於量子點熟成機制。而為了研究經熱退火後熟成量子點載子生命期的變化，利用時間解析光譜觀察到載子生命期因量子點平均尺寸增加而下降。然而鎘含量為22 %的碲化鋅／硒化鎘鋅量子點光譜峰值無明顯偏移，推測是晶格不匹配較小不易形成量子點或量子點密度較低熟成效應被抑制所致。 本研究證實量子點密度較高的碲化鋅／硒化鎘鋅量子點，可經由快速熱退火調控量子點大小並使量子點尺寸分佈較集中。

In this work, ZnTe/ZnCdSe quantum dots sample were grown on GaAs (001) substrate with ZnSe buffer layer by molecular beam epitaxy (MBE). Photoluminescence (PL), temperature-dependent PL (TDPL), and time-resolved PL (TRPL) were used to investigate the optical properties of rapid thermal annealed samples. For annealed 3.2 MLs ZnTe/Zn0.88Cd0.12Se quantum dots, the PL peak position exhibited a redshift resulted from the ripening effect. On the other hand, TRPL spectrum showed that the carrier lifetime of the ripened sample decreased as the average dot size became larger. However, there was no obvious PL energy shift in annealed ZnTe/Zn0.78Cd0.22Se quantum dots. It could be more difficult to form quantum dots because the lattice mismatch between ZnTe and Zn1-xCdxSe decreased as the Cd composition (x) increasing from 0.12 to 0.22. As a result , the reduced dot density suppressed the ripening effect. We demonstrated that the rapid thermal annealing can be used to control the dot size and uniformity of high density ZnTe/ZnCdSe quantum dots.