| InGaN based light emitting devices demonstrate excellent luminescence properties and have great potential in lighting applications. Though these devices are already being produced on an industrial scale, the nature of their radiative transition is still not well understood. In particular, the role of the huge (>1MV/cm), built-in electric field in these transitions is still under debate. The luminescence characteristics of InGaN quantum well structures were investigated as a function of excitation power, temperature, and biaxial strain, with an intent of discerning the effects of the electric field and inhomogenous indium distribution in the QW on the radiative transition.; It was found that the luminescence energy did not scale only with the indium concentration but that the QW thickness must also be taken into account. The thickness affects the transition energy due to quantum confinement and carrier separation across a potential drop in the QW. The luminescence peak width was shown to increase with increased indium fraction, due to increased indium inhomogeneity. The carrier lifetime increased exponentially with QW thickness and luminescence wavelength, due to increased carrier separation.; Measuring the luminescence energy and carrier lifetime as a function of excitation density showed that the electric field can be screened by strong excitation and, as a consequence, the carrier separation reduced. The temperature dependence of the luminescence showed evidence for bandtails in the density of states, a phenomenon that has been previously related to transition in indium-rich nano-clusters, yet could be accounted for by fluctuations in other parameters that affect the transition energy. Room temperature luminescence efficiency was shown to weakly decrease with increased QW thickness.; The application of biaxial strain resulted in either a redshift or blueshift of the luminescence, depending on the sample. The direction and magnitude of the shift in luminescence energy is interpreted in terms of a newly introduced parameter Lr, which can be regarded as the effective separation of electrons and holes participating in the luminescence transition. Strong carrier separation due to the built-in electric field usually results in a blueshift and Lr close to the QW width, Lw, whereas weak carrier separation usually can be a redshift. The carrier lifetime decreases with applied strain, indicating a reduction of the effective electron-hole (e-h) separation achieved by the strain-induced field-reduction in the well. (Abstract shortened by UMI.)... |
