V-shaped Quantum Wires Research Articles

Dynamics of Exciton Relaxation in GaAs V-Shaped Quantum Wires

Dynamics of Exciton Relaxation in GaAs V-Shaped Quantum Wires

High spatial resolution spectroscopy of a single V-shaped quantum wire

We report on microscopic photoluminescence of a single V-shaped AlGaAs/GaAs quantum wire. The experiments are performed at low temperature by selectively exciting 1 μm2 of the sample. The main photoluminescence line is split into sharp peaks of width less than 0.5 meV and separated by a few meV. The energy position and the intensity of the peaks are characteristic of the scanned quantum wire. First microphotoluminescence results suggest that localization phenomena are predominant in the quantum wire. They are due to the formation of extended monolayer-step islands, larger than the exciton radius, as in the case of high-quality quantum wells.

Conduction-band mixing in T- and V-shaped quantum wires

By means of a tight-binding approach, we have studied the influence of barrier states on the conduction band of the T- and V-shaped quantum wires. For AlAs/GaAs superlattices or pure AlAs barriers, $X$-related states induce strong modifications in the wire conduction band that cannot be accounted for by a simple effective-mass approximation. With respect to quantum wells, we show that the quasi-one-dimensional confinement of quantum wires enhances valley mixing and leads to a reduction in the energy of lower lying states.

Band structure and optical anisotropy in V-shaped and T-shaped semiconductor quantum wires

We present a theoretical investigation of the electronic and optical properties of V- and T-shaped quantum wires. Valence band mixing as well as realistic sample geometries are fully included through an accurate and efficient approach that is described here in detail. We investigate the resulting valence band structure, which shows some significant peculiarities, such as an anomalously large spin splitting in the lowest heavy hole subband of T-shaped wires. For both classes of wires we obtain good agreement between calculated optical absorption and recent experimental spectra, and we demonstrate that the analysis of optical anisotropy can be used as an effective tool to extract information on valence states, usually very difficult to obtain otherwise.

Valence band spectroscopy in V-grooved quantum wires

We present a combined theoretical and experimental study of the anisotropy in the optical absorption of V-shaped quantum wires. By means of realistic band structure calculations for these structures, we show that detailed information on the heavy- and light-hole states can be singled out from the anisotropy spectra independently of the electron confinement, thus allowing accurate valence band spectroscopy.

Thermal ionization of excitons in V-shaped quantum wires.

The exciton-to-free-carrier transition in GaAs and ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As V-shaped quantum wires is revealed by means of temperature-dependent magnetoluminescence experiments. The experimental results are in excellent agreement with the diamagnetic shift obtained from a solution of the full two-dimensional Schr\"odinger equation for electrons and holes including magnetic-field and excitonic effects. In the GaAs wires, the exciton-to-free-carrier transition is found to occur at temperature consistent with the exciton binding energies. In the ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As wires the diamagnetic shift of the luminescence is found to be free-carrier-like, independent of temperature, due to the weakening of the exciton binding energy induced by the internal piezoelectric field. \textcopyright{} 1996 The American Physical Society.

Optical spectroscopy of InGaAs/GaAs V-shaped quantum wires

We have investigated the multisubband recombination of V-shaped InGaAs/GaAs quantum wires as a function of the excitation density under stationary and transient conditions. The experimental results compare well with theoretical calculations of the quantized states, taking into account the effect of the nontetragonal strain and of the internal piezoelectric field. The changes of the optical properties of the quantum wires induced by external magnetic and electric fields are measured to elucidate the basic mechanisms of recombination.

Current bistability in InGaAs quantum wire p- i- n heterostructures

We report a clear evidence of bistability in the current-voltage (I-V) characteristics of p- i- n heterostructures containing InGaAs V-shaped quantum wires. The observed phenomenon is explained in the framework of a single carrier transport model in which the quantum wires act like traps for the vertical current. The charge trapping phenomenon is indeed demonstrated by capacitance-voltage (C-V) and photocurrent experiments.

Excitons in quantum well wires: V-shaped wire, T-shaped wire and strain-induced lateral confinement

We calculated the energy and the wave function of the exciton for i) a V-shaped quantum wire, ii) a T-shaped quantum wire and iii) a quantum wire resulting from strain-induced lateral confinement. The full Luttinger and Bir-Pikus Hamiltonian are taken into account in the three calculations. We used different parameters inside the well and at the barrier. The basis states |3/2m> are defined with respect to [110], the direction of the wire in the three kinds of structures, instead of the usual [001] direction. The hole dispersion curve allows one to define an effective mass which is to be introduced in the variational calculation of the exciton binding energy. We show that the hole is confined in a wire only in case i).

Magnetic-field effects in the luminescence of V-shaped quantum wires

Quantum wire heterostructures, such as V- and T-shaped wires, are very promising candidates for low-threshold lasing. A crucial issue is the excitonic vs. free-carrier nature of the radiative recombination. Here, we report on magnetophotoluminescence studies of GaAs and InGaAs V-shaped wires that allow to discriminate different regimes of radiative recombination.

Exciton binding energy in GaAs V-shaped quantum wires.

We have determined the main parameters of the quasi-one-dimensional excitons confined in GaAs V-shaped quantum wires, namely exciton Bohr radius and binding energy, by two-photon absorption and magnetoluminescence experiments. The experimental results are in excellent agreement with our calculations, based on realistic wave functions for the actual wire geometry.

Evidence of one-dimensional excitons in GaAs V-shaped quantum wires

We have investigated the optical properties of excitons in GaAs quantum wires grown on nonplanar patterned substrates (V-shaped quantum wires) by photoluminescence and magnetophotoluminescence. The experimentally observed transitions are in agreement with the theoretical evaluation of the quantized energy levels based on TEM measurements. The clear evidence of the ${\mathit{n}}_{\mathit{y}}$=1 and 2 excitonic recombination in the photoluminescence spectra is exploited to directly measure the anisotropy of the optical matrix elements.

One-dimensional excitons in V-shaped quantum wires

We report a detailed study of one-dimensional excitons in a planar array of single V-shaped GaAs quantum wires. Two-photon absorption, magnetoluminescence and linear photoluminescence spectroscopy have been used to measure the exciton binding energy, the excited 2p states of the excitons, the higher index transitions and the extension of the confined wavefunctions in the V-shaped region of the quantum wires.

Optical properties of excitons in GaAs quantum wires

We report the result of a detailed spectroscopic investigation of the optical properties of excitons in rectangular (etched) and V-shaped (grown on non-planar substrates) GaAs quantum wires. High index excitonic transitions and strong polarization anisotropy of the optical spectra have been observed. The experimentally observed trasitions are in agreement with the theoretical evaluation of quantified energy levels based on the respective model potential