以砷化鎵穿隧能障調控披覆銻砷化鎵之砷化銦量子點載子生命期及光學特性研究

Abstract

本論文第一部分利用光激螢光光譜及時間解析光譜探討嵌入不同砷化鎵材料厚度之砷化銦/銻砷化鎵量子點的光學特性。隨著嵌入層厚度的增加，量子點有發光藍移及激子復合生命期增加的現象。透過k‧p八能帶理論分析發光藍移及激子復合生命期延長原因，發現兩者是來自於量子點受到壓縮應力及電子與電洞的波函數在空間上的分離所造成，且電洞的波函數分布對於嵌入層厚度的變化是非常敏感的。而論文第二部份是利用變功率及變溫度螢光光譜探討第二型能帶排列之特徵。對於只披覆銻砷化鎵樣品，電洞透過熱能的吸收而有機會由銻砷化鎵披覆層躍遷至量子點中進行第一型能帶排列之躍遷。而對於在砷化銦/銻砷化鎵嵌入 5 nm和7 nm的GaAs樣品，透過比較低溫及高溫之螢光譜線可推論，在低溫時電洞落至砷化銦量子點中透過穿隧效應至銻砷化鎵披覆層復合，而在高溫時電洞透過熱能吸收躍遷至高能階後再藉由穿隧效應至量子點中進行復合。

Optical properties of type-II InAs/GaAsSb quantum dots (QDs) with different inserted GaAs thickness are investigated by photoluminescence (PL) and time-resolved PL measurements. With increasing GaAs thicknesses, the QD emission shows a blueshift in energy and a lengthening in lifetime. These two phenomena are caused by enhanced compressive strain and spatial separation of electron-hole wave function. Theoretical calculations based on eight-band k‧p model indicates that quantum confinement of hole states and their wave function distribution are sensitive to the thickness of inserted GaAs. We demonstrate that controlling the thickness of the inserted GaAs thickness is a feasible way to manipulate the carrier lifetime for QD-based intermediate-band solar cell applications. Furthermore, type-I transitions can be observed at high temperature. Comparing the PL spectra, we found two conditions. First, only the type-II transition can be observed at low temperature. Second, both transitions can be observed at high temperature due to the thermal excitation and tunneling effect. In InAs/GaAsSb system, the hole is thermal excited from GaAsSb layer into InAs QD, and carriers recombine in the InAs QDs. In InAs/GaAs/GaAsSb system, hole has to tunnel from GaAsSb layer into the InAs QDs in addition to these thermal excitation.