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  4. Influences of Silicon-doping and Interfacial Layers on the Optical Characteristics and Nanostructures of InGaN/GaN Quantum Wells
 
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Influences of Silicon-doping and Interfacial Layers on the Optical Characteristics and Nanostructures of InGaN/GaN Quantum Wells

Date Issued
2004
Date
2004
Author(s)
Cheng, Yung-Chen
DOI
en-US
URI
http://ntur.lib.ntu.edu.tw//handle/246246/50726
Abstract
In this dissertation, we systematically study the optical characteristics and associated nanostructure of InGaN/GaN multipl-quantum-well samples of different average indium contents and different silicon doping layers. A nanostructure model is built for describing the potential fluctuation differences between the samples. From the results of strain state analysis, we find that indium-rich clustering is the strongest in the barrier-doped sample, followed by the well-doped sample and then un-doped sample among the samples of the same average indium content. Among the samples of the same doping condition, the higher indium content leads to stronger clustering behavior. Based on the model, the dominance of either carrier localization or quantum-confined Stark effect (QCSE) determines the optical behaviors. Generally speaking, QCSE results in the S-shape of photoluminescence (PL) peak position, strong photoluminescence excitation (PLE) intensity, large Stokes shift, and long PL decay time. On the other hand, carrier localization leads to the blue shift of PL peak position, high radiative efficiency (also due to weaker QCSE), PL decay time enhancement, and the behavior of 3-D-like confinement in radiative decay time. Meanwhile, the amplified spontaneous emission (ASE) behaviors showed that stronger carrier localization in the cases of stronger clustering behaviors leads to higher ASE intensities or gains. In temperature-dependent variations, the weaker carrier localization results in the evolution of a two-peak spectral ASE feature at low temperatures into a broad spectrum with Fabry-Perot resonance. In a strongly clustering sample, particularly in the sample of high-indium-content and barrier doping, the ASE spectrum evolves from a broad spectrum with Fabry-Perot resonance at low temperatures into a single major peak feature at room temperature. Such evolution is attributed to carrier liquidation when carriers gain thermal energy. We also compare four InGaN/GaN multiple quantum-well (QW) samples of different interfacial layers in optical property and nano-structure. In two of the samples, InN interfacial layers are placed between wells and barriers for improving the QW interface quality. Compared with a standard barrier-doped QW sample, the addition of the InN interfacial layers does improve the QW interface quality and hence the photon emission efficiency. The insertion of intrinsic InN layers in a sample leads to a reasonably good QW structure and the highest PL and electro-luminescence (EL) efficiencies. However, clustering structures are observed, resulting in carrier localization for a strong S-shape variation in PL spectral peak, a relatively strong PLE intensity, and a sharp PL decay time variation beyond its peak in temperature dependence. With silicon-doped InN interfacial layers, another sample shows the highest QW quality and relatively higher PL and EL emission efficiencies. It is speculated that both carrier localization and QCSE are relatively weaker in this sample. Then, the broadening of InGaN well layer in another sample by inserting silicon-doped InGaN interfacial layers leads to quantum dot-like structures and the strongest carrier localization. Therefore, in this sample we observe quite high PL and EL efficiencies, increasing EL spectral peak position with temperature, strong PLE intensity, and sharp PL decay time variation beyond its peak in temperature dependence. Compared with the aforementioned samples, the normally used QW sample (a reference sample) shows the lowest PL and EL emission efficiencies, the lowest PL and EL emission photon energies, the weakest PLE intensity, and generally longest PL decay times. It is speculated that the quantum-confined Stark effect is strongest in this sample.
Subjects
量子井
介面層
奈米結構
光電特性
氮化銦鎵/氮化鎵
矽摻雜
Nanostructures
Quantum Wells
Optical Characteristics
InGaN/GaN
Interfacial Layers
Silicon-doping
Type
thesis
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