氮化鎵族量子侷限結構之光學特性研究

Abstract

本論文主要為兩種不同氮化鎵族量子侷限結構之研究，第一種為利用δ-TMIn流量成長之氮化銦鎵/氮化鎵多重量子井結構之光學與材料特性研究，第二種材料為利用氮化鋁奈米洞成長氮化鎵量子點結構之光學特性研究。 第一、利用X光繞射光譜分析、穿透式電子顯微影像、光激發螢光光譜與螢光激發光光譜分析有無利用δ-TMIn流量成長氮化銦鎵/氮化鎵多重量子井結構。由穿透式電子顯微鏡影像與X光繞射光譜得知，無論是有無使用δ-TMIn流量之試片，其介面結構與量子井週期性仍非常平整；且銦聚集區域均在氮化銦鎵量子井中出現。且由光激發螢光光譜與螢光激發光光譜分析得知，利用δ-TMIn流量成長之試片其活化能 (Ea)、載子侷限程度 (σ)與史托克位移 (Stoks' shift)均呈現較大的趨勢。其結果指出利用δ-TMIn流量成長，會導致其空間上成分變動較明顯，因而造成較大的量子侷限效應。且由光激發螢光光譜之半高寬結果得知，δ-TMIn流量成長之試片具有較窄之半高寬，其顯示出具有大小較均勻的銦聚集區域。最後、利用δ-TMIn流量成長之試片其光輸出功率提高了24%。 第二、利用氮化鋁奈米洞成長之氮化鎵量子點。我們利用穿透式電子顯微鏡影像，發現其呈現倒置角錐狀，其長度與深度分別40/40 奈米。利用微光激發螢光光譜進行變溫實驗，發現氮化鎵量子點80K之訊號較氮化鎵塊材藍移了63 meV。且在溫度變化從80到300K，其能帶間隙變化為較35 meV，較塊材變化之60 meV為小。最後我們發現其半高寬隨溫度有變化的趨勢，再100K時為最小，我們將此現象歸因於載子在量子點中重新分部的結果。

In this dissertation, two kinds of GaN-based quantum confined structure were studied. The first one was the effect of δ-TMIn-flow process on optical and materials properties in InGaN/GaN MQWs. The second one was the structural and optical studies on inverted pyramid-shaped GaN QDs grown on AlN nanoholes. First, the effects of δ-TMIn-flow process on optical and material properties in InGaN/GaN MQWs were investigated with XRD, TEM, PL and PLE measurement. According to TEM and XRD measurement, good layer periodicity and structural quality of the InGaN/GaN MQW were observed. And the In-rich clusters in the InGaN/GaN MQW were resided in both sample whether δ-TMIn-flow process or not. And from PL results, the PL peak energies were different at 10 K even though the same composition extracted from XRD measurement. From the FWHM results of PL measurement, In-rich clusters were more uniform in size of sample B as compared to sample A. And according to the PL and PLE measurement result, the larger values of σ, Ea and Stokes’ shift in sample B indicated that the δ-TMIn flow resulted in the increase the composition fluctuation in InGaN MQW regions and showed the stronger carrier localization effect. And the light output of the GaN LEDs with the δ-TMIn-flow process was increased up to 24% without obvious deterioration of interfacial abruptness. Second, we performed the structural and optical studies on inverted pyramid-shaped GaN QDs with dimensions of 40/40 nm (length/depth). The μ-PL measurements of these GaN QDs were performed over a temperature range from 80 to 300 K. Comparing with GaN bulk structure, the ground state of GaN QDs was blueshifted by 63 meV. PL emission peak energy did not change much in temperature range from 80 to 300 K, the energy gap shrinkage was just about 35 meV in the QD structures compared with 60 meV in GaN bulk materials. Finally we observed the narrowing of full-width at half maximum (FWHM) with increasing temperature to 100 K, this phenomenon can be attributed to carrier redistribution of different GaN QD sizes