Optical and Material Studies of InGaN/GaN Quantum Well Light Emitting Diode Wafers
Date Issued
2005
Date
2005
Author(s)
Chen, Jeng-Hung
DOI
en-US
Abstract
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.
Subjects
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
InGaN
QW
LED
PL
XRD
TEM
Type
thesis
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