U. Marti

Hot carrier relaxation in GaAs V‐groove quantum wires

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.

Electronic states in GaAs v‐groove quantum wire structures with superlattice barriers

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.

Photoluminescence and electroluminescence of high-density GaAs quantum wires arrays

SummaryPhotoluminescence (PL) and electroluminescence (EL) measurement of GaAs/AlGaAs quantum wires (QWR) located in the active region of a p-i-n junction are reported. The samples are fabricated by molecular-beam epitaxial growth on V-grooved substrates. Good control of the interface, defect density and doping profile have been achieved. Homogeneous current injection into the quantum wires is achieved with efficiencies comparable to current injection into a quantum well control sample. PL with and without an applied voltage across the junction was measured at 86 K and 300 K for different excitation densities. Peaks appearing with an applied voltage correspond to the active-region QWR transitions and are also observed on the EL spectra measured at 120 K and at 300 K. Clear evidence of 1D confinement is observed in both PL and EL spectra. They show a one-dimensional splitting of about 24 meV and a saturation of the ground state at high excitation density. The polarisation of the PL and EL is in good agreement with the expected anisotropy of the 1D matrix elements.

Modulated reflectance and resonant Raman scattering of GaAs quantum wires grown on nonplanar substrates

Modulated reflectance spectroscopy and resonant Raman scattering have been used to study the quantized states of crescent‐shaped GaAs quantum wires. Distinct one‐dimensional excitonic transitions originating from the quantum wires together with the expected resonances from the bent quantum wells are observed. The quantum wire transition energies compare very well with those calculated using a V‐shaped potential derived from transmission electron microscopy measurements of the lateral variation of the GaAs well width. The spectroscopic techniques employed here provide alternative methods of probing the confined states in quantum wires of low luminescence efficiency.

3D-to-1D carrier scattering in GaAs V-groove quantum wires

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 GaAsAlAs 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.

Relaxation Processes in GaAs And InGaAs V-Shaped Quantum Wires

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.

Carrier Trapping Into Quantum Wires

Trapping into the active region is one of the most important design considerations in quantum well lasers. This process becomes crucial for the operation of quantum wire devices since the very small active volume demands strong coupling to the external region, otherwise trapping is greatly inhibited. We report the first measurements of electron trapping from extended three-dimensional (3D) states into one-dimensional (ID) states of a semiconductor quantum wire structure. Our joint theoretical and experimental investigation shows that the trapping time is extremely fast, ~10 ps.

Reduced Carrier Cooling in GaAs V-Groove Quantum Wires due to Non-Equilibrium Phonon Population

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.

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

SummaryQuantum wire heterostructures, such as V- and T-shaped wires, are very promising candidates for low-threshold lasing. A crucial issue is the excitonicvs. 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.