Angular dependent characteristics of a 1.3-mu m GaInNAs/GaAs quantum-well resonant cavity enhanced photodetect

Characteristics of a 1.3-mum GaInNAs RCE PD with respect to the incident light angle were analyzed both in theoretical simulation and experiments. The results show the influence can be neglected when the light incidence angle is less than 3degrees. This is a requirement for the PD to be applied in WDM networks. (C) 2002 Wiley Periodicals, Inc.

In-plane propagation of cavity polaritons in a quantum semiconductor microcavity

Considering that the coupling among the heavy-hole exciton, light-hole exciton and the cavity photon can form bipolaritons in a quantum semiconductor microcavity, we calculate the group velocities of the cavity polaritons at different incident angles using the coupling model of three harmonic oscillators. The result indicates that the group velocities of the low and middle branches of the cavity polaritons have extrema, but the group velocities of the high branch increase with the increasing incident angle.

Electronic structure of diluted magnetic semiconductor superlattices: In-plane magnetic field effect

The electronic structure of diluted magnetic semiconductor (DMS) superlattices under an in-plane magnetic field is studied within the framework of the effective-mass theory; the strain effect is also included in the calculation. The numerical results show that an increase of the in-plane magnetic field renders the DMS superlattice from the direct band-gap system to the indirect band-gap system, and spatially separates the electron and the hole by changing the type-I band alignment to a type-II band alignment. The optical transition probability changes from type I to type II and back to type I like at large magnetic field. This phenomenon arises from the interplay among the superlattice potential profile, the external magnetic field, and the sp-d exchange interaction between the carriers and the magnetic ions. The shear strain induces a strong coupling of the light- and heavy-hole states and a transition of the hole ground states from "light"-hole to "heavy"-hole-like states.

Longitudinal spin transport in diluted magnetic semiconductor superlattices: The effect of the giant Zeeman splitting

Longitudinal spin transport in diluted magnetic semiconductor superlattices is investigated theoretically. The longitudinal magnetoconductivity (MC) in such systems exhibits an oscillating behavior as function of an external magnetic field. In the weak magnetic-field region the giant Zeeman splitting plays a dominant role that leads to a large negative magnetoconductivity. In the strong magnetic-field region the MC exhibits deep dips with increasing magnetic field. The oscillating behavior is attributed to the interplay between the discrete Landau levels and the Fermi surface. The decrease of the MC at low magnetic field is caused by the s-d exchange interaction between the electron in the conduction band and the magnetic ions. The spin polarization increases rapidly with increasing magnetic field and the longitudinal current becomes spin polarized in strong magnetic field. The effect of spin-disorder scattering on MC is estimated numerically for low magnetic fields and found to be neglectible for our system.

Zero-field spin splitting in In0.52Al0.48As/InxGa1-xAs metamorphic high-electron-mobility-transistor structures on GaAs substrates using Shubnikov-de Haas measurements

Shubnikov-de Haas measurements were carried out for In0.52Al0.48As/InxGa1-xAs metamorphic high-electron-mobility-transistor structures grown on GaAs substrates with different indium contents and/or different Si delta-doping concentrations. Zero-field (B-->0) spin splitting was found in samples with stronger conduction band bending in the InGaAs well. It was shown that the dominant spin splitting mechanism is attributed to the contribution by the Rashba term. We found that zero-field spin splitting not only occurs in the ground electron subband, but also in the first excited electron subband for a sample with Si delta-doping concentration of 6x10(12) cm(-2). We propose that this In0.52Al0.48As/InxGa1-xAs metamorphic high-electron-mobility-transistor structure grown on GaAs may be a promising candidate spin-polarized field-effect transistors. (C) 2002 American Institute of Physics.

Oscillating magnetoresistance in diluted magnetic semiconductor barrier structures

Ballistic spin polarized transport through diluted magnetic semiconductor single and double barrier structures is investigated theoretically using a two-component model. The tunneling magnetoresistance (TMR) of the system exhibits oscillating behavior when the magnetic field is varied. An interesting beat pattern in the TMR and spin polarization is found for different nonmagnetic semiconductor/diluted magnetic semiconductor double barrier structures which arises from an interplay between the spin-up and spin-down electron channels which are split by the s-d exchange interaction.

Valence band structures of the InAs/GaAs quantum ring

In the framework of effective-mass envelope function theory, the valence energy subbands and optical transitions of the InAs/GaAs quantum ring are calculated by using a four-band valence band model. Our model can be used to calculate the hole states of quantum wells, quantum wires, and quantum dots. The effect of finite offset and valence band mixing are taken into account. The energy levels of the hole are calculated in the different shapes of rings. Our calculations show that the effect of the difference between effective masses of holes in different materials on the valence subband structures is significant. Our theoretical results are consistent with the conclusion of the recent experimental measurements and should be useful for researching and making low-dimensional semiconductor optoelectronic devices. (C) 2002 American Institute of Physics.

Exciton localization in In0.15Ga0.85As/GaAs quantum wire structures grown on (553)B-oriented GaAs substrate

Using time-resolved photoluminescence (PL) measurements, we have studied the exciton localization effect in InGaAs/GaAs quantum wire (QWR) structures formed in corrugated narrow InGaAs/GaAs quantum wells (QWs) grown on (553)B GaAs substrate. The PL decay time in the QWR structure was found to be independent of the temperature for T < 70 K, showing a typical dynamical behavior of the localized excitons. This result is in striking contrast to the corresponding quantum well structures, where a linear increase of the PL decay time was observed. In addition, an increase of the exciton lifetime was observed at low temperature for the QWR structure as compared to a reference InGaAs/GaAs quantum well sample (1200 vs 400 ps). The observed longer decay time was attributed to the reduction in the spatial coherence of excitons in the QWR-like structure. In PL measurements, a significant polarization anisotropy was also found in our narrow InGaAs/GaAs QWs grown on (553)B GaAs. (C) 2001 American Institute of Physics.

Experimental investigation of photoluminescence dynamics of cavity polaritons under nonresonant excitation

Low-temperature time-resolved photoluminescence (PL) experiments have been performed on a semiconductor planar microcavity, which contains two sets of three In0.13Ga0.87As/GaAs quantum wells embedded in a 3 lambda /2 GaAs cavity. The spontaneous emission dynamics of both lower- and upper-branch polaritons is investigated as a function of exciton-cavity detuning under nonresonant optical excitation. It is found that the PL decay times of both branches are independent of cavity detuning while the PL rising kinetics of the lower- and upper-branch polaritons exhibits a significant difference. The rise time of the upper polarition branch shows a strong dependence on cavity detuning, while the rise time of the lower polarition branch is less sensitive to cavity detuning. Our results can be well understood in the framework of the theoretical prediction of Tassone et al.

InxGa1-xAs/AlyGa1-yAs/AlzGa1-zAs asymmetric step quantum-well middle wavelength infrared detectors

InxGa1-xAs/AlyGa1-yAs/AlzGa1-zAs asymmetric step quantum-well middle wavelength (3-5 mum) infrared detectors are fabricated. The components display photovoltaic-type photocurrent response as well as the bias-controlled modulation of the peak wavelength of the main response, which is ascribed to the Stark shifts of the intersubband transitions from the local ground states to the extended first excited states in the quantum wells, at the 3-5.3 mum infrared atmospheric transmission window. The blackbody detectivity (D-bb*) of the detectors reaches to about 1.0x10(10) cm Hz(1/2)/W at 77 K under bias of +/-7 V. By expanding the electron wave function in terms of normalized plane wave basis within the framework of the effective-mass envelope-function theory, the linear Stark effects of the intersubband transitions between the ground and first excited states in the asymmetric step well are calculated. The obtained results agree well with the corresponding experimental measurements. (C) 2001 American Institute of Physics.

Photoluminescence of AlGaAs/InGaAs/GaAs pseudomorphic HEMTs with different thickness of spacer layer

The photoluminescence spectra of the single delta -doped AlGaAs/InGaAs/GaAs pseudomorphic HEMTs with different thickness of spacer layer were studied. There are two peaks in the PL spectra of the structure corresponding to two sub-energy levels of the InGaAs quantum well. It was found that the photoluminescence intensity ratio of the two peaks changes with the spacer thickness of the pseudomorphic HEMTs. The reasons were discussed. The possible use of this phenomenon in optimization of pseudomorphic HEMTs was also proposed. (C) 2001 Elsevier Science B.V. All rights reserved.

Longitudinal optic phonon-plasmon coupling in delta-doped metamorphic InAlAs/InGaAs high-electron-mobility transistor structures on GaAs substrates

InAlAs/InGaAs metamorphic high-electron-mobility transistor structures with different spacer layers on GaAs substrates are characterized by Raman measurements. The influence of In0.52Al0.48As spacer thickness on longitudinal optic phonon-plasmon coupling is investigated. It is found that the intensity of GaAs-like longitudinal optic phonon, which couples with collective intersubband transitions of two-dimensional electron gas, is strongly affected by the different subband energy spacings, subband electron concentrations, and wave function distributions, which are determined by different spacer thicknesses. (C) 2001 American Institute of Physics.

Photoluminescence properties of a GaN0.015As0.985/GaAs single quantum well under short pulse excitation

Under short pulse laser excitation, we have observed an extra high-energy photoluminescence (PL) emission from GaNAs/GaAs single quantum wells (QWs). It dominates the PL spectra under high excitation and/or at high temperature. By measuring the PL dependence on both temperature and excitation power and by analyzing the time-resolved PL results, we have attributed the PL peak to the recombination of delocalized excitons in QWs. Furthermore, a competition process between localized and delocalized excitons is observed in the temperature-dependent PL spectra under the short pulse excitation. This competition is believed to be responsible for the temperature-induced S-shaped PL shift often observed in the disordered alloy semiconductor system under continuous-wave excitation. (C) 2001 American Institute of Physics.

In-plane optical anisotropy in asymmetric Si1-xGex/Si/Si1-yGey superlattices

A trilayer asymmetric superlattice, Si/Si1-xGex/Si1-yGey, is proposed, in which the broken inversion symmetry makes the microstructure optically biaxial; in particular, inequivalent interfaces in this heterostructure may cause a polarization ratio as large as about 2.5% in the absence of an external field. The electronic structure and absorption spectra for two types of trilayer superlattice with different parameters are calculated by use of the tight-binding model; the findings indicate the importance of the carrier confinement for the anisotropy value. The effect of external electric field on the optical anisotropy for such structures has also been discussed, and a Pockels coefficient of 10-9 cm V-1 estimated.

Optical transitions and type-II band lineup of MBE-grown GaNAs/GaAs single-quantum-well structures

We have investigated transitions above and below band edge of GaNAs/GaAs and InGaNAs/GaAs single quantum wells (QWs) by photoluminescence (PL) as well as by absorption spectra via photovoltaic effects. The interband PL peak is observed to be dominant under high excitation intensity and at low temperature. The broad luminescence band below band edge due to the nitrogen-related potential fluctuations can be effectively suppressed by increasing indium incorporation into InGaNAs. In contrast to InGaNAs/GaAs QWs, the measured interband transition energy of GaNAs/GaAs QWs can be well fitted to the theoretical calculations if a type-II band lineup is assumed. (C) 2001 Elsevier Science B.V. All rights reserved.