H. Arakaki

Crystal structure and optical characterization of heterostructured GaAs/AlGaAs/GaAs nanowires

Structural and optical properties of heterostructured GaAs/AlGaAs/GaAs core/inner shell/outer shell nanowires are studied. Transmission electron microscopy and Raman scattering measurements unambiguously identify the presence of segments crystallized in zincblende and wurtzite phases, which spread to the shells. Four observed photoluminescence lines are assigned to the radiative recombination of photoexcited electrons confined in the center of the GaAs core and at the heterointerface between the outer GaAs shell and the inner AlGaAs shell with the holes localized at the heterointerface between the core and the inner AlGaAs shell; both recombinations take place in zincblende and wurtzite phases. One additional photoluminescence line is attributed to the spatially indirect recombination between the electrons in zincblende and the holes in wurtzite phases. The bandgap of the wurtzite phase and the band offsets between the zincblende and wurtzite phases are determined.

Photoluminescence of radial heterostructured GaAs/AlGaAs/GaAs nanowires

Photoluminescence (PL) of high-density GaAs nanowires (NWs) encapsulated by a double AlGaAs/GaAs shell is studied. Two lines are found and assigned to the radiative recombinations of photoexcited electrons confined in the center of the GaAs core and at the heteroboundary between the outer GaAs shell and the inner AlGaAs one with the holes in the core and the holes confined at the heteroboundary between the core and the inner AlGaAs shell. The simple model, based on representation of the valence band structure using two levels, well accounts for the observed temperature dependence of the integrated photoluminescence intensities. The proposed double shell structure with tunneling transparent inner shell sets conditions for easy control of the emission energy of the heterostructured nanowires.

Dynamics of photoexcited carriers in the presence of disorder in radial heterostructured GaAs/AlGaAs/GaAs nanowires

Time-resolved photoluminescence was employed to study electron-hole dynamics in radial heterostructured GaAs/AlGaAs/GaAs core/inner shell/outer shell nanowires. It was found that impurity random potential results in a red shift of the recombination time maximum with respect to the photoluminescence peak energy.

Manipulation of emission energy in GaAs/AlGaAs core-shell nanowires with radial heterostructure

Photoluminescence was studied in GaAs/AlGaAs nanowires (NWs) with different radial heterostructures. We demonstrated that manipulation of the emission energy may be achieved by appropriate choice of the shell structure. The emission at highest energy is generated in the NWs with tunneling thin AlGaAs inner shell and thin GaAs outer shell due to recombination of the photoexcited electrons confined in the outer shell with the holes in the core. Lower energy emission was shown to occur in the NWs with thick outer shell grown in the form of a short-period GaAs/AlGaAs multiple quantum well structure. In this case, the tunneling probability through the multiple quantum wells controls the energy emitted by the NWs. The doping of core results in dominated low energy emission from the GaAs core.

INHOMOGENEITY OF ELECTRON LIQUID AND EFFECTS OF INTERLAYER COUPLING IN GaAs/AlGaAs SUPERLATTICES IN THE REGIME OF THE QUANTUM HALL EFFECT

Formation of the electron state with the integer filling factor was studied by magneto-capacitance and magneto-photoluminescence measurements in weakly coupled GaAs/AlGaAs multilayers where quasi-two dimensional electrons revealed the integer Quantum Hall Effect. The disorder modulated compressibility of the quantized Hall phase with the filling factor ν=2 was determined. The incompressible fraction of this phase was shown to rapidly disappear with the increasing temperature. The quantized Hall phase of the weakly coupled multilayers was shown to emit the asymmetrical photoluminescence lines. We demonstrated that the observed asymmetry is caused by a partial population of the extended electron states formed in the quantized Hall conductor phase due to the disorder induced interlayer tunneling.

Optical properties of GaAs/AlAs superlattices grown on (311)A GaAs surfaces

Abstract We present a temperature-dependence photoluminescence of (GaAs) 5 /(AlAs) 5 superlattice grown on (311)A-oriented semi-insulating substrate by molecular beam epitaxy. The temperature dependence reveals an anomalous decrease of the PL width, which is explained in terms of phonon-assisted thermal activation of localized excitons.

DISORDER INDUCED COHERENCE-INCOHERENCE CROSSOVER IN RANDOM GaAs/AlGaAs SUPERLATTICES

The coherence of electrons was studied in intentionally disordered GaAs/AlGaAs superlattices as a function of the vertical interlayer coupling. Depending on the relation of the disorder energy and the Fermi energy the coherent and incoherent diffusive transport regimes were distinguished. New features of weakly coupled layered electron systems such as the vertical coupling energy and the in-plane phase-breaking time were observed by magnetoresistance measurements in the coherent and incoherent regimes respectively. Both of them were found to decrease with increasing disorder strength. This demonstrates the disorder induced break-down of the interlayer coherence of quasi-particles which drastically affected their intralayer coherence.