非極性氮化鎵量子井結構與發光二極體元件特性研究

Abstract

本論文中，我們利用有機金屬氣相沉積磊晶技術成長不同厚度之非極性"a"平面氮化銦鎵/氮化鎵多重量子井作為研究對象。我們利用光激發螢光(PL)光譜技術進行樣品的光學特性分析。 在室溫PL實驗中，顯示了非極性氮化銦鎵/氮化鎵多重量子井的內建電場並不影響其位能，且其發光強度隨著量子井厚度由3奈米增加到12奈米而減弱。除此之外，變溫PL實驗顯示了一個較明顯的載子侷限效應(localization effect)存在於量子井較厚的樣品中。成長非極性結構的另一優勢在於極化發光(polarized light emission)的價值，我們所測得的發光極化率大約在60%左右。 另外，我們也成功成長了非極性氮化銦鎵/氮化鎵綠光發光二極體，並且探討相關的元件特性。我們所測得的發光極化率大約在67.4%左右。此外，電激發光頻譜顯示，當注入電流增加至20 mA時，光譜有藍位移的現象產生。此現象可能由於能帶填充效應所致，其後隨著注入電流的增加，發光波長則維持不變。此非極性綠光發光二極體之順向電壓大約為3.43 V，微分串聯電阻在20 mA時大約為24歐姆，注入電流在100 mA時，光輸出功率約為240 □W。

In this thesis, a-plane InGaN/GaN multiple quantum wells with different widths from 3 to 12 nm were grown on r-plane sapphire by metal organic chemical vapor deposition for investigation. We utilized photoluminescence (PL) technique to investigate the optical characteristics of our samples. The PL experiments revealed that the PL emission intensity would decrease with increasing the well width of the samples from 3 to 12 nm. Meanwhile, the power dependent PL measurement indicated no apparent emission peak shift for all samples due to no built-in electric field in a-plane MQWs. Moreover, the temperature dependent PL reveals that a more apparent localization effect exist in the sample with a thicker well width which is most likely due to more serious indium fluctuations or worse crystalline quality in the MQWs. In-plane polarization effect of a-plane InGaN/GaN MQWs emission was also investigated, which pointed out an average polarization degree ρ from our samples is about 60%. Furthermore, we have successfully grown a-plane green light-emitting diodes on r-plane sapphire and investigated the device characteristics of a-plane green LEDs. The apparent emission polarization anisotropy was observed and the polarization degree was as high as 67.4%. In addition, the electroluminescence (EL) spectra first revealed a wavelength blue-shift with increasing drive current to 20 mA, which could be attributed to the band-filling effect, and then the EL peak become constant. The current–voltage curve showed the forward voltage of a-plane LED grown on r-plane sapphire substrate was 3.43 V and the differential series resistance was measured to be about 24 □ as 20-mA injected current. Furthermore, the output power was 240 □W at 100-mA drive current. These results should provide a useful guidance for fabrication of light emitting devices using a-plane InGaN/GaN MQW structures.