Study of competition mechanism between ripening and interdiffusion in ZnTe/ZnMgSe quantum dots by rapid thermal annealing
|Keywords:||分子束磊晶系統;碲化鋅量子點;熱退火;MBE;ZnTe quantum dots;thermally anneal|
|Abstract:||利用分子束磊晶系統以 Stranski-Krastanov 成長模式在不同鎂濃度的硒化鎂鋅上沉積碲化鋅量子點，量子點的厚度分別為4.0、5.0、6.0與7.0原子層，另外在硒化鋅上成長4.0原子層厚度的碲化鋅量子點做為參考樣品。並利用快速熱退火、光激螢光光譜、變溫光激螢光光譜與時間解析光譜等實驗技術來探討碲化鋅/硒化鎂鋅量子點熱退火後熟成與內擴散競爭之機制研究。
ZnTe quantum dots were grown by Stranski-Krastnov mode on ZnMgSe of different Mg composition by Molecular Beam Epitaxy. The coverage thickness of quantum dots were 4.0, 5.0, 6.0, and 7.0 MLs. ZnTe quantum dots grown on ZnSe was investigated for reference. The physical characteristics were studied by rapid thermal annealing (RTA), photoluminescence (PL) spectroscopy, temperature dependent PL, and time resolved PL (TRPL). Different coverage of ZnTe quantum dots were annealed at temperature from 350°C to 550°C for 30 seconds by RTA. Two mechanisms, ripening and inter-diffusion, were observed in PL spectra of annealed samples. For the samples of annealing temperature larger than 470°C, a red shift of PL peak position was observed in quantum dots of smaller coverage. It is the signature of ripening of quantum dots. However, for the quantum dots with larger coverage, there was a blue shift of PL peak position with increasing annealing temperature. It results from the inter-diffusion of Mg from the barrier layers to the quantum dots. For the quantum dots with moderate coverages, two mechanisms balance and it results in no shift of PL peak position for different annealing temperatures. Three different activation energies were found from the Arrhenius fitting of the temperature-dependent PL. The activation energies also vary with ripening and inter-diffusion mechanisms, and the effect of ripening and inter-diffusion on the band structure could be understood. By using two recombination lifetimes to fit the TRPL spectra, the effect of annealing mechanisms on the carrier lifetime was studied. Current study showed that the dot density and size can be controlled by different coverage thickness of quantum dots and the ripening and inter-diffusion mechanisms of rapid thermal annealing.
|Appears in Collections:||Thesis|