The thesis investigates hot carrier relaxation and carrier recombination mechanism of a InN thin film grown on LAO(LiAlO2) substrate with a ultrafast time-resolved photoluminescence apparatus. Carriers were excited with laser pulses of energy 1.5 eV and of pulsewidth 150 fs from a Ti:sapphire laser. The photoexcited carriers relax excessive energy mostly within 10 ps thorough carrier-LO-phonon interaction. The effective carrier-LO-phonon emission times were estimated 197 to 58 fs in the temperature range from 250 to 35 K. The Shockley-Read-Hall coefficient was found around 0.8 ns-1. The Auger recombination was trivial at 35 K and become significant at 250 K. The fitted radiative recombination was much smaller than the theoretical estimate. Both effective carrier-LO-phonon scattering times and the radiative and nonradiative decay rates of the studied m-plane InN were found to be smaller than those of c-plane InN in other reports.

All-optical time-resolved measurement techniques provide a powerful tool for investigating critical parameters that determine the performance of infrared photodetector and emitter semiconductor materials. Narrow-bandgap InAs/GaSb type-II superlattices (T2SLs) have shown great promise as next generation materials, due to superior intrinsic properties and versatility. Unfortunately, InAs/GaSb T2SLs are plagued by parasitic Shockley-Read-Hall recombination centers that shorten the carrier lifetime and limit device performance. Ultrafast pump-probe techniques and time-resolved differential-transmission measurements are used here to demonstrate that "Ga-free" InAs/InAs₁₋xSbx T2SLs and InAsSb alloys do not have this same limitation and thus have significantly longer carrier lifetimes. Measurements of unintentionally doped MWIR and LWIR InAs/InAs₁₋xSbx T2SLs demonstrate minority carrier (MC) lifetimes of 18.4 µs and 4.5 µs at 77 K, respectively. This represents a more than two order of magnitude increase compared to the 90 ns MC lifetime measured in a comparable MWIR and LWIR InAs/GaSb T2SL. Through temperature-dependent differential-transmission measurements, the various carrier recombination processes are differentiated and the dominant recombination mechanisms identified for InAs/InAs₁₋xSbx T2SLs. These results demonstrate that these Ga-free materials are viable options over InAs/GaSb T2SLs and potentially bulk Hg₁₋xCdxTe photodetectors. In addition to carrier lifetimes, the drift and diusion of excited charge carriers through the superlattice layers (i.e. in-plane transport) directly aects the performance of photo-detectors and emitters. All-optical ultrafast techniques were successfully used for a direct measure of in-plane diffusion coeffcients in MWIR InAs/InAsSb T2SLs using a photo-generated transient grating technique at various temperatures. Ambipolar diffusion coefficients of approximately 60 cm²/s were reported for MWIR InAs/InAs₁₋xSbxT2SLs at 293 K.

Esta tese apresenta um estudo experimental em sistemas eletrônicos multicamadas formados em diversas heteroestruturas semicondutoras de alta qualidade crescidas por epitaxia de feixes moleculares. Especificamente, poços quânticos isolados baseados em InGaAs/InP e super-redes baseadas em GaAs/AlGaAs foram caraterizados por meio de medidas de fotoluminescência (PL) em função da temperatura, potência de excitação e do campo magnético. O estudo de efeitos na dinâmica de processos de recombinação destes sistemas eletrônicos é a base principal deste trabalho. Além disso, exploramos os efeitos da desordem sobre os processos de recombinação e demonstramos que o espalhamento por rugosidade interfacial é responsável pela resposta óptica destes sistemas. Nas amostras de InGaAs/InP com maior largura do espaçador observamos um novo efeito, o tempo de recombinação Auger aumenta notavelmente com a potência de excitação. Atribuímos este novo efeito à distribuição de elétrons fotoexcitados em diferentes vales da banda de condução. E em amostras de menor largura do espaçador, o relaxamento da regra de seleção do momento induzido pela desordem faz que o tempo de recombinação Auger diminua com o aumento da potência. Por outro lado, nas amostras de GaAs/AlGaAs, evidenciamos que a desordem gerada pela rugosidade interfacial afeta consideravelmente o transporte dos elétrons da banda de condução, e em poços quânticos de largura apropriada resulta em uma transição metal-isolante. A borda de mobilidade Ec, energia crítica que separa os estados estendidos dos estados localizados, foi determinada a partir das medidas do tempo de recombinação em função da energia de emissão de PL. Para uma desordem crítica, a Ec mostra uma interseção com a energia do nível de Fermi, a qual corresponde à transição metal-isolante. Além disso, realizamos medidas de PL resolvida no tempo em função do campo magnético. Observamos que a redistribuição espacial de elétrons causada pelo campo magnético afeta os tempos de recombinação. Nas amostras metálicas, os resultados mostraram deslocamento da Ec para altas energias, devido à quantização da energia dos elétrons provocada pelo campo magnético. No entanto, nas amostras isolantes, o campo magnético foi responsável pelo relaxamento significativo da regra de seleção do momento, que aumenta a probabilidade de recombinação dos elétrons localizados com os buracos fotoexcitados da banda de valência e, por consequência, diminui o tempo de recombinação. / This thesis presents an experimental study in multilayer electronic systems formed in several high quality semiconductor heterostructures grown by molecular beam epitaxy. Specifically, GaAs/AlGaAs based superlattices and isolated quantum wells based on InGaAs/InP were characterized by photoluminescence (PL) measurements as a function of temperature, pump power and magnetic field. The study of effects on the dynamics of the recombination processes of these electronic systems is the principal goal of this work. In addition, we explore the effects of the disorder on the recombination processes and show that the interfacial roughness scattering is responsible for the optical response in these systems. In the small spacer InGaAs/InP samples, we observed a new effect, the Auger recombination time becomes larger with the increasing the pump power. We propose that the distribution of photoexcited electrons over different conduction band valleys might account for this effect. In large spacer quantum wells, the non-radiative recombination time is reduced with the increasing pump power, as a consequence the disorder-induced relaxation of the momentum rule. On the other hand, in GaAs/AlGaAs samples, we showed that the disorder generated by interfacial roughness considerably affects transport of the conduction band electrons and at appropriate quantum wells width results in a metal-to-insulator transition. The mobility edge energy Ec was determined from the measurements of the recombination time as a function of energy allowed. At a critical disorder, the mobility edge energy demonstrates intersection with the Fermi level energy which correspond to the metal-insulator transition. In addition, we perform time-resolved PL measurements as a function of the magnetic field. We observed that the spatial distribution of electrons caused by the magnetic field influence on the recombination time. In the metallic samples was observed a shift of the mobility edge to higher energy due to the magnetic field quantization of conduction band electron energy. However, in the insulating samples, the magnetic field was responsible to cause a significant relaxation of the momentum selection rule which enhances the probability of recombination of the localized electrons with the photoexcited holes of the valence band, and consequently the recombination time is reduced.