AuthorMohs, Georg Heinrich, 1968-
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PublisherThe University of Arizona.
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AbstractThis dissertation presents an investigation of the charge-carrier dynamics in highly excited III-V semiconductor compounds. More precisely, after femtosecond excitation the photoluminescence of the GaN and related materials based Nichia NLPB 500 blue-light emitting diode (LED) is temporally and spectrally resolved using streak-camera techniques. Emission spectra are gathered both at 20K and room temperature. In addition, the emission of a pure GaN film grown by metal organic chemical vapor deposition is studied and compared to the more complicated structure of the diode. In either case, two spectrally distinct emission bands are found. Both samples show a large emission close to the band edge of the material. For the LED, amplified spontaneous emission is found in this band under very high excitation. The time resolved data shows simple, almost exponential, decays independent of pumping power or lattice temperature except for the amplified spontaneous emission in LED. The second emission band is impurity related and very different for the two samples. In the LED, impurities are deliberately doped into the active region of the device to provide luminescence centers whereas the pure GaN film is not intentionally doped. The LED emission shows a two component decay that changes its time constant with pump power which is well explained with in a three-level rate-equation model with saturable intermediate state. In the case of the GaN film an exponential decay independent of excitation density is observed up to a certain pump power where a fast initial component appears. Furthermore, spectral-hole burning experiments are performed on GaAs/AlGaAs multiple quantum wells. A new measurement technique for precise investigations of temporal gain evolution is given and subpicosecond gain in type II multiple quantum wells is demonstrated. Additionally, the experimental evidence for phonon sidebands of spectral holes in cool electron-hole plasmas is presented and theoretically investigated based on the Boltzmann equation coupled to the semiconductor Bloch equations. The carrier-dephasing time is studied as a function of plasma temperature, and indication for a strong dependence of carrier-carrier scattering rates on the temperature of the plasma is given. The findings are explained in a simple picture of blocked scattering channels for cold plasmas.
Degree ProgramGraduate College