Magnetotransport Properties of Gallium Indium Phosphide/gallium Arsenide Quantum Semiconductor Heterostructures

My dissertation focuses on the study of persistent photoconductivity and interface roughness scattering in the unintentionally doped InGaP/GaAs quantum semiconductor heterostructures. We use both the Shubnikov-de Haas and the low field Hall effect to measure the transport coefficients and to calculate the sample parameters. To study the persistent photoconductivity, we illuminated the sample, using a red light emitting diode, at low temperatures and then measured the transport coefficients. We found that, unlike the undoped AlGaAs/GaAs structure, a persistent photocurrent is present in this undoped material after illumination. We believe that the presence of the DX-center a deep defect center associated with doping and which is responsible for the persistent photoconductivity in AlGaAs/GaAs heterostructures and, is not necessary to explain the persistent photocurrent observed in InGaP/GaAs. To investigate interface roughness scattering, we studied several narrow quantum wells. We found that, unlike in thin AlAs/GaAs quantum wells, interface roughness does not dominate the scattering mechanism in thin undoped InGaP/GaAs quantum wells. We believe that the height of the potential confining electrons in the quantum well plays an important role in reducing the effect interface roughness scattering. Finally, we investigate the influence the sample current has on the amplitudes of the Shubnikov-de Haas oscillations. We found that as the sample current increases, the amplitudes of these oscillations decrease to vanishing values. Data analysis reveals that the quantum scattering time decreases with as the sample current increases, whereas the classical scattering time is hardly sensitive to the sample current. We believe that the increase in the sample current values induce a broadening of the Landau levels, leading to a smearing out of the Shubnikov-de Haas oscillations.