Optical Properties of III-nitride Semiconductors
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This dissertation, "Optical Properties of III-nitride Semiconductors" by Qing, Li, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author.Abstract of thesis entitled OPTICAL PROPERTIES OF III-NITRIDE SEMICONDUCTORS submitted by Li Qing for the Degree of Doctor of Philosophy at The University of Hong Kong in December 2002 III-Nitrides represent a family of wide band-gap semiconductors which cover a color range of UV-blue-red. Being an important member of this materials family, indium gallium nitride (InGaN) has been successfully employed to act as an active layer in blue light-emitting diodes and blue laser-diodes. However, the luminescent mechanism in InGaN is still an unsolved problem, due to sample-dependent multiple factors governing the luminescent processes in InGaN. Among these factors, the carrier localization due to the so-called indium phase separation, the existence of a huge piezoelectric eld, and their combination play crucial roles in the recombination processes. As a common characteristic of InGaN alloys and quantum wells (QWs), car- rier localization is suggested to benet the luminescence eciency and is found to cause anomalous behavior, e.g., an \S-shaped" shift of the emission peak and shrinking of the peak linewidth, in the temperature-dependent photolu-minescence (PL) spectra. A novel carrier distribution function describing the thermodynamics of carriers within the localized states was derived from a rate equation. Based on this carrier distribution function, the observed anomalies in the PL temperature dependence can be quantitatively modeled over the whole studied temperature range for the rst time. In principle, the theoretical model can be employed to explain the temperature-dependent luminescence behavior of other material systems with ensemble localized states, such as InGaAs/GaAs quantum dots. Combinationofthequantum-connedStarke(R)ect, causedbythehugepiezo- electric eld, and the e(R)ect of carrier distribution within the localized states in InGaN QWs strongly indicated the existence of a \negative" barrier which the localizedcarriershavetoovercometothermallyescape. Thevalueofthis\nega- tive"barrierheightwasextractedfromtheexperimentaldataforthetwoInGaN samples. The relationship between the strength of the piezoelectric eld and the \negative" barrier height was qualitatively analysed. The e(R)ective screening e(R)ect of photo-generated carriers on the piezoelectric eldinInGaNQWswasdemonstratedbothexperimentallyandtheoretically. A blueshiftaslarge as120 meVofthedominantPLpeak wasobservedwhenthe excitation power was increased by two orders of magnitude. A self-consistent calculation by simultaneously solving the SchrAodinger equation and the Poisson equation was performed for interpretation of the experimental results. The hydrostatic-pressure dependennce of the PL spectra of the InGaN QWs at di(R)erent experimental conditions were studied. The pressure coecients of the PL peaks were found to be excitation-power and temperature dependent. The results show that the quantum-conned Stark e(R)ect induced by the huge piezoelectric eld and strong screening e(R)ect of the carriers on the piezoelectric eld resulted in the observed excitation-power dependence of the pressure co-ecients of the PL peaks. It was also found that the PL spectrum consists of multiple peaks which exhibit di(R)erent dependences on the excitation power and temperature. The assignments of the various emissions are discussed in details and suggested. 10.5353/th_b3016248Semiconductors - Optical propertiesNitrides - Optica