氮化銦鎵/氮化鎵量子井結構發光二極體之光學與材料特性研究

在本研究中，我們針對氮化銦鎵/氮化鎵量子井結構的樣品，有系統地探討其光學特性與發光機制。首先，針對一個氮化銦鎵/氮化鎵多重量子井的樣品，透過光激螢光光譜、光激螢光激發光譜、X光繞射以及穿透式電子顯微鏡實驗來研究其光學與材料特性。由X光繞射及穿透式電子顯微鏡實驗，我們可以測定樣品的量子井厚度以及量子井中的銦含量；在螢光光譜的實驗中，我們觀察到一些隨溫度變化的反常現象，這些現象可以用載子侷限效應來解釋，隨著溫度升高，載子可以在不同的發光中心間傳輸；透過光激螢光激發實驗，我們觀察到很大的史托克位移，這主要是由於銦濃度變化與量子侷限史塔克效應的影響。在第二部分的研究中，我們研究藍光及綠光之氮化銦鎵/氮化鎵多重量子井樣品的光學及材料特性，在其間我們觀察到不同的隨溫度以及隨激發功率變化的螢光光譜行為，由此推論此二藍光與綠光樣品具有不同的發光機制。藉由比較兩個結構參數類似但生長條件不同的樣品，我們可以得知量子井中的銦濃度變化程度以及載子侷限程度與樣品的生長條件有密切關聯。接著，我們發現綠光樣品隨溫度淬熄的現象並不符合傳統的亞罕尼斯行為，反而類似於非晶型半導體的行為，這可以用合金位能變動的觀點來解釋，觀察改變激發功率之螢光光譜行為，我們可以推論能帶充填效應及量子侷限史塔克效應在發光的過程會扮演一個重要的角色。在第三部份的研究中，我們研究三個具有不同量子井結構的藍光發光二極體，穿透式電子顯微鏡可以清楚地辨認這些樣品在結構上的區別，在其間我們亦觀察到不同的隨溫度以及隨激發功率變化的螢光光譜行為，由於不同程度的銦含量變化程度以及載子侷限程度，使得這些藍光樣品間具有不同的發光機制，而這又與樣品的結構及生長條件有關，實驗證明使用似階梯形量子井結構能產生較強的侷限能階及較大的量子效率。

關鍵字

氮化銦鎵；量子井；發光二極體；光激螢光光譜； X光繞射；穿透式電子顯微鏡

並列摘要

In this research, the optical characteristics and　recombination mechanisms of the InGaN/GaN quantum well structures are systematically studied. First, we focused on an InGaN/GaN multiple quantum well (MQW) sample. Photoluminescence (PL), photoluminescence excitation (PLE), X-ray diffraction (XRD), and transmission electron microscopy (TEM) experiments were carried out to study the optical and material properties. From the XRD and TEM experimental results, we can determine the period thickness and indium composition of the sample. The temperature-dependent PL spectra revealed many unusual temperature dependent behaviors. These phenomena can be well explained by the carrier localization effect. With increasing temperature, carriers transfer between different luminescent centers. From the results of PLE experiment, a large Stokes shift (SS) was observed. The large Stokes shift can be attributed to the variation in indium composition or the quantum confined Stark effect (QCSE). Second, we studied the optical and material properties of the blue and green MQW LED samples. Different temperature-dependent and excitation-power dependent PL behaviors were observed between them. We believe that different emission mechanisms occur between our blue and green LED. By comparing two blue LED samples with similar structural parameters but different growth conditions, we suggest that the indium fluctuation and carrier localization strongly depends on the growth conditions of the InGaN active layers. For the green LED sample, the temperature quenching behavior does not fit in with Arrhenius formula but is similar to the behavior of amorphous semiconductors. The results can be explained by alloy potential fluctuations in a consistent way. From excitation power dependent PL results, we can expect that band-filling and QCSE both play an important role in the recombination process. Third, we investigated the optical properties of three blue LED wafers with different quantum well structures. From the TEM images, we can clearly distinguish their differences of the structure. Different temperature-dependent PL and excitation-power dependence of PL behaviors were also observed among the three blue LED samples. We believe that different emission mechanisms occur among these blue LED samples due to different degrees of indium fluctuation and localization effect. The degree of indium fluctuation and the localization energy depth correspond to the growth conditions and the structure of the sample. Using the stair-shaped SQW structure, stronger localization energy and higher internal quantum efficiency at room temperature can be obtained.

並列關鍵字

InGaN ； QW ； LED ； PL ； XRD ； TEM

參考文獻

Chapter 1

1.4 S. Nakamura, S. Pearton, and G. Fasol, The Blue Laser Diode, 2nd ed. (Springer, Berlin, 2000).

1.9 M. Kneissl, D. P. Bour, C. G. Van de Walle, L. T. Romano, J. E. Northrup, R. M. Wood, M. Teepe, and N. M. Johnson, Appl. Phys. Lett. 75, 581 (1999).

1.10 J.I. Pankove, M. Leksono, S.S. Chang, C. Walker, B. Van Zeghbroeck, MRS Internet Journal of Nitride Semiconducting Research 1, 39 (1996).

1.16 Koga K and Yamaguchi T, Prog. Crystal Growth Character 23, 127 (1991).

國際替代計量

氮化銦鎵/氮化鎵量子井結構發光二極體之光學與材料特性研究

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