分子束磊晶成長碲化鎘／碲化鋅量子點經熱退火之光學特性

Abstract

在砷化鎵基板上利用分子束磊晶以成長碲化鋅在硒化鋅上做為緩衝層，並且於碲化鋅上成長碲化鎘二維量子井及零維量子點，其中碲化鎘厚度被控制在1.2，1.8，2.4，3.6和4.8原子層。在低溫光致螢光光譜下，厚度小於2.4原子層時，光譜峰值隨著碲化鎘覆蓋厚度快速紅移。然而，當厚度大於3.6原子層時，碲化鎘峰值隨著碲化鎘覆蓋厚度緩慢紅移。此時，碲化鎘正從二維層狀成長轉換為零維量子點。在變溫光致螢光光譜下，樣品從1.2原子層至2.4原子層之變化曲線與Varshni方程式吻合。3.6原子層和4.8原子層的樣品則無法被單一個Varshni方程式所描述。其曲線在低溫時被量子點主導，高溫時則是被樣品的界面缺陷所主導。而快速熱退火（RTA）後成功地抑制3.6原子層之CdTe量子點樣品的界面缺陷發光，使得高溫下的光致螢光光譜被量子點所主導。

CdTe two-dimensional (2D) quantum wells (QWs) and zero-dimensional (0D) quantum dots (QDs) were grown on ZnTe with a ZnSe buffer layer and GaAs substrate by molecular beam epitaxy (MBE). The CdTe coverage was varied from 1.2, 1.8, 2.4, 3.6 to 4.8 monolayers (MLs). The peak energy of low temperature photoluminescence (PL) has an initial fast red shift with the increasing CdTe coverage and then a gentle red shift. The temperature dependent PL of samples from 1.2 MLs to 2.4 MLs follows the Varshni’s equation. However, the PL study of the other two samples, 3.6 MLs and 4.8 MLs, reveals two energy states which are related to QDs and interface defects at low temperature and high temperature, respectively. The rapid thermal annealing (RTA) was performed to suppress the emission from the defects successfully for CdTe QDs of the 3.6 MLs coverage.