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Epitaxial growth on nonplanar substrates is an attractive method for producing high quality quantum wire structures for applications in low-threshold lasers. However, a crucial factor in this application is the transfer of carriers between extended (3D) three-dimensional and confined (1D) one-dimensional states. In this paper we present a joint theoretical and experimental investigation of 3D-to-1D scattering in GaAs V-groove quantum wires confined either, within GaAs AlAs short-period superlattice or bulk GaAlAs barriers. The scattering rates were computed using accurate wavefunctions for both the one-dimensional and the extended three-dimensional states. The rates are in good agreement with time-resolved luminescence measurements.

Raman spectroscopy has been used to measure phonons in GaAs v-groove quantum wire structures containing (001) and (111) GaAs/AlAs superlattice barrier regions. Resonance enhancement permits the identification of modes in different regions of the structure, and the measured phonon frequencies provide structural information which shows clear evidence of GaAs migration during growth from (001) surfaces into the grooves. Confined and interface phonons with large in-(111) plane wavevectors are observed. (C) 1996 American Institute of Physics.

The mechanisms of carrier transfer from barrier regions (superlattices, side-wall and vertical quantum wells) into arrays of quantum wires are investigated by time-resolved photoluminescence. The wires are grown by different techniques on V-groove substrates. The transfer times range from 25 to 900 ps, depending on the details of the whole structure. The fast carrier transfer is modeled by a diffusion equation which allows one to estimate the quantum mechanical capture time from a two-dimensional vertical QW into a one-dimensional QWR to be

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.

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.

We have investigated the electro-optic properties of strained InGaAs/GaAs quantum wires of lateral width below 20 nm by means of electroluminescence and luminescence under electric bias. A novel room temperature electroluminescence is observed in MBE grown samples. The optical spectra reveal a strong red-shift and the suppression of the luminescence with increasing polarization either under reverse or direct bias. This anomalous Stark shift is due to the combination of the internal piezoelectric field and the external field.

We present a comprehensive discussion of the excitonic properties of V-shaped GaAs and InGaAs quantum wires grown on patterned substrates. Systematic linear and non-linear spectroscopic studies have been performed in order to clarify the impact of lateral confinement on the exciton wave function, namely: enhanced exciton binding energy, localization in magnetic field, recombination from excited states and multiphoton absorption. The careful evaluation of the electron confinement energies, based on the actual quantum wire profile obtained by TEM micrographs, including the internal piezoelectric field induced by off-diagnoal terms of strain tensor, reproduces quite well the measured one-dimensional states. Finally, application of quantum wires in a p-i-n wave guide for bistable operation is demonstrated.

We have measured hot carrier relaxation in GaAs V-groove quantum wires using time-resolved photoluminescence. Relaxation between confined one-dimensional subbands is clearly observed on the time scale of several hundred picoseconds. A simulation of the experiment using a hybrid multisubband Monte Carlo method which includes hot phonon and degeneracy effects gives good agreement with the measurements.© 1995 American Institute of Physics.

We report on the imaging of a molecular beam epitaxially grown GaAs/(AlAs)n(GaAs)m quantum well‐wire array by means of cross‐sectional scanning tunneling microscopy (XSTM) and scanning tunneling‐induced luminescence (STL). XSTM provides atomically resolved cross‐sectional images of sets of quantum well wires with chemical sensitivity within the group III species and electrical sensitivity to single dopant atoms. This permits the precise observation of growth mechanisms and the identification of defects responsible for inhomogeneities in the growth morphology, as well as the determination of dopant incorporation throughout the structure. STL permits the relative quantum efficiency of individual quantum wires to be quantified.

We investigated the relaxation of excitons and free-carriers in V-shaped GaAs and InGaAs quantum wires with distinct one-dimensional properties. Trapping of carrier in the wires and simultaneous recombination of higher index transitions are studied by spectrally and time resolved luminescence measurements performed at the relevant energies of the quantized states observed in photoluminescence excitation spectra. The effect of disorder in low-crystalline quality quantum wires (inferred by TEM studies) is also discussed.

The exciton-to-free-carrier transition in GaAs and In_xGa_{1-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 Schrodinger 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 In_xGa_{1-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.

Hot carrier dynamics in semiconductor quantum wires is the subject of much current interest, since unique characteristics of inter- and intra-subband carrier-carrier (CC) and carrier-phonon (CP) interactions in quasi-one-dimensional (ID) systems have been predicted [1]. Previous studies of carrier dynamics in etched rectangular GaAs/AlGaAs wires using time-resolved photoluminescence (PL) have reported that relaxation is slower than that measured in similar 2D systems [2,3]. Hot phonon reabsorption was suggested as a possible cause. In these experiments, however, both the confining barriers and the wires were strongly excited, and so the measured relaxation times are influenced by carrier capture into the wires. V-groove structures present an alternative method of realizing quantum wires, and high optical quality has been obtained, as demonstrated by their application in efficient, low-threshold lasers [4]. Here we present picosecond time-resolved PL measurements of carrier relaxation in GaAs v-groove quantum wires which were directly photoexcited at relatively low density with respect to previous experiments. We compare our measurements with the results of a hybrid Monte Carlo simulation which allows us to evaluate the important energy relaxation processes.

We present a joint theoretical and experimental investigation of GaAs v-groove quantum wires confined in GaAs/AlAs superlattice barriers. We have computed the electronic states for both the quantum wire and the barriers. The intrinsic bending of the superlattice layers, together with systematic spatial variations of their thickness, create localized states in the barriers that are separated from the wire. This effect has a strong impact on the overall luminescence efficiency of the wires. The results are in excellent agreement with photoluminescence and photoluminescence excitation spectra.© 1995 American Institute of Physics.

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.

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 quantized energy levels based on the respective model potential.

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.

Fabrication of InGaAs/InP quantum well wires obtained by growing InGaAs/InP superlattices on V-grooved surface (001) InP substrates is evidenced. The density of planar defects propagated through the epilayers of these heterostructures depends on the type (A or B) of atoms which constitute the surface of the V-grooved (111) planes. The (111)B V-grooved surfaces are shown to generate more defects propagating through the heterostructure.

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.

The incorporation of In in the growth of crescent-shaped In0.12Ga0.88As quantum wires embedded in (AlAs)(4)(GaAs)(8) superlattice barriers is studied in atomic detail using cross-sectional scanning tunneling microscopy. It is found that the In distribution in both the surface and the first subsurface layer can be atomically resolved in the empty- and filled-state images, respectively. Strong In segregation is seen at the InGaAs/GaAs interfaces, but neither an expected enhancement of the In concentration at the center of the quantum wire compared to the planar quantum well nor In clustering beyond the statistical expectation is observed. (C) 1995 American Institute of Physics.