利用有機金屬氣相沈積法成長氮化鎵量子侷限發光元件之研究

Abstract

氮化鎵材料由於擁有極寬的直接能隙結構及優異的材料特性，因此成功的開發出高亮度之藍光、綠光和紫外光之短波長發光二極體，以及藍光雷射二極體等發光元件，成為極具潛力之開發材料。為了發展下一世代的氮化鎵系發光元件以及提升元件之內部及外部的量子效率，本論文在研究以有機金屬氣相化學沉積法(Metalorganic chemical vapor deposition, MOCVD)製作氮化鎵系量子侷限發光之結構。其中包括氮化鎵系半導體微共振腔以及氮化銦鎵量子點等結構之開發。

在本研究中，為了製作高品質的氮化鎵系微共振腔結構，我們先發展氮化鎵系高反射率布拉格反射鏡的結構。藉由設計和模擬布拉格反射鏡的結果，選擇了氮化鋁和氮化鎵材料作為氮化鎵系的布拉格反射鏡的基材來減少布拉格反射鏡的層數和增加高反射區域的寬度。本研究利用MOCVD技術成長高反射率的氮化鎵系布拉格反射鏡，以優化過的磊晶參數以及不對稱的布拉格反射鏡結構，成功製作出不會崩裂的高反射率的氮化鎵系布拉格反射鏡。

接著，利用發展出的高反射率氮化鎵系布拉格反射鏡為下反射鏡以及介電質氧化物布拉格反射鏡為上反射鏡，我們成功製作出一個3波長長度的高品質氮化鎵系微共振腔結構。利用光激發的方式測試製作出來的氮化鎵系面射型雷射結構，已可成功在室溫下觀測到激發輻射的雷射現象，其等效的臨界電流密度為53mJ/cm2，證明微共振腔結構的品質已達到要求。在元件開發上，我們也成功製做了電激發式的氮化鎵系微共振腔發光元件，觀察到微共振腔對自發輻射的侷限效應並使其發光波長對注入電流有極高的穩定性及較高的光輸出量子效率。

最後，我們成功的利用MOCVD成長了氮化銦鎵量子點結構並研究中斷成長對氮化銦鎵量子點的效應。以優化過的磊晶參數成長氮化銦鎵量子點結構其量子點密度已可達到4.5 □ 1010 cm-2且其量子點的平均側向大小為11.5奈米，平均高度為1.6奈米。研究結果顯示中斷成長能調製量子點的大小尺寸及其發光波長。優化的中斷成長參數可以增加量子點的密度和發光效率。對未來製作氮化銦鎵量子點的電激發式發光元件提供了良好的基礎。

GaN materials are very interested for their direct wide bandgap structures and many advantages of material properties. Therefore they are likely to be the basis of a strong development of novel family semiconductor devices, for optronics as well as for electronics. Recently, III-V nitride semiconductors have been the commercial productions with a extremely wide applications; high brightness light emitting diodes (LEDs) emitting from green to near UV can be used as any kind of lighting, room-temperature violet laser light emission has paved the way to wider possibilities in optical storage, and high-power, high-temperature electronic devices have been used in harsh environments like automotive engines, space, and avionics.

In this study, in order to develop new generation device and to resolve some material issues on nitride-based light emitting devices, we have developed the optical and electric quantum confined structure grown by metal organic chemical vapor deposition (MOCVD). They are included the developments of GaN-based microcavity structures and InGaN Quantum dots (QDs) structure.

For the fabrication of high quality nitride-based microcavity structures, we started this study from design and simulation to obtain a high reflectance nitride-based distributed Bragg reflector (DBR) with a reasonable numbers of pair and stopband width in DBR structure. The monolithically grown AlN/GaN DBR structure has been demonstrated and the fabrication issues of AlN/GaN DBR structure have been resolved. By optimizing the growth condition and developing an non-quarterwave stacks DBR structure to control the accumulative strain energy, A high reflectance AlN/GaN DBR structure with crack-free surface have been successful growth.

Using the high reflectance AlN/GaN DBR as the bottom mirror, and a dielectric oxide DBR structure as the top mirror, we have fabricated a 3□ nitride-based microcavity with the hybrid DBR mirrors resonant structure. The feasibility of this nitride-based microcavity structure is examined by the performance of optical pumped, and the laser action has been achieved under the optical pumping at room temperature with a threshold pumping energy density of about 53 mJ/cm2. The nitride-based microcavity emits 448 nm with a linewidth of 0.25 nm. Following, the electrically driven device with nitride-based microcavity structure has been fabricated and the characteristics of the 3□ GaN-based microcavity light emitting device structures have been discussed. A much less red-shift with injection current and a higher output power caused by the resonance effect in this MCLED has been observed. Finally, the electric quantum confined structure with a quantum dots (QDs) structure has also been grown and the characteristic were also been studied. We have grown a self-assembled InGaN QDs structure with the growth interruption by MOCVD. The density of InGaN QDs was about 4.5 x 10^10 cm^-2 with an average lateral size of 11.5 nm and an average height of 1.6 nm. The effects of the interruption time on the morphological and optical properties were studied. The results suggested that the interruption growth could modify the size of InGaN QDs and extend the emission wavelength to the short wavelength region, and at the same time improve optical quality of the QDs.