GaAs-based room-temperature continuous-wave 1.59 mu m GaInNAsSb single-quantum-well laser diode grown by molecular-beam epitaxy

Starting from the growth of high-quality 1.3 mu m GaInNAs/GaAs quantum well (QW), the QW emission wavelength has been extended up to 1.55 mu m by a combination of lowering growth rate, using GaNAs barriers and incorporating some amount of Sb. The photoluminescence properties of 1.5 mu m range GaInNAsSb/GaNAs QWs are quite comparable to the 1.3 mu m QWs, revealing positive effect of Sb on improving the optical quality of the QWs. A 1.59 mu m lasing of a GaInNAsSb/GaNAs single-QW laser diode is obtained under continuous current injection at room temperature. The threshold current density is 2.6 kA/cm(2) with as-cleaved facet mirrors. (c) 2005 American Institute of Physics.

Time-resolved photoluminescence of sub-monolayer InGaAs/GaAs quantum-dot-quantum-well heterostructures

Time-resolved photoluminescence (PL) of sub-monolayer (SML) InGaAs/GaAs quantum-dot-quantum-well heterostructures was measured at 5 K for the first time. The radiative lifetime of SML quantum dots (QDs) increases from 500 ps to 800 ps with the increase of the size of QDs, which is related to the small confinement energy of the excitons inside SML QDs and the exciton transfer from smaller QDs to larger ones through tunneling. The rise time of quantum-dot state PL signal strongly depends on the excitation power density. At low excitation power density, the rise time is about 35 ps, the mechanism of carrier capture is dominated by the emission of longitudinal-optical phonons. At high excitation power density, the rise time decreases as the excitation density increases, and Auger process plays an important role in the carrier capture. These results are very useful for understanding the working properties of sub-monolayer quantum-dot devices.

Theoretical investigation of intersubband transition in AlxGa1-xN/GaN/AlyGa1-yN step quantum well

A modified self-consistent method is introduced for the design of AlxGa1-xN/GaN step quantum well (SQW) with the position and energy-dependent effective mass. The effects of nonparabolicity are included. It is shown that the nonparabolicity effect is minute for the lowest subband energy level and grows in size for the higher subband states. The effects of nonparabolicity have significant influence on the transition energies and the oscillator strengths and should be taken into account in the investigation of the optical transitions. The strong asymmetric property introduced by the step quantum well magnifies the weak intersubband transition from the ground state to the third state (1 -> 3). It is shown that in an appropriate scope, the intersubband transition (1 -> 3) has the comparable oscillator strength with transition from the ground state to the second one (1 -> 2), which suggests the possible application of the two-color photodetectors. The results of this work should provide useful guidance for the design of optically pumped asymmetric quantum well lasers and quantum well infrared photodetectors (QWIPs). (c) 2005 Elsevier B.V. All rights reserved.

Photoluminescence study of (GaAs1-xSbx/InyGa1-yAs)/GaAs bilayer quantum well grown by molecular beam epitaxy

Photoluminescence study of (GaAs1-xSbx/InyGa1-yAs)/GaAs bilayer quantum wells (BQWs) grown by molecular beam epitaxy (MBE) were carried out. Temperature and excitation power dependent photoluminescence (PL) study indicated that the band alignment of the BQWs is type - II. The origin of the double-peak luminescence was discussed. Under optimized growth conditions, the PL emission wavelength from the BQWs has been extend up to 1.31 mu m with a single peak at room temperature.

A new type of photoelectric response in a double barrier structure with a wide quantum well

We have calculated the photoelectric response in a specially designed double barrier structure. It has been verilied that a transfer of the internal photovoltaic effect in the quantum well to the tunnelling transport through above-barrier quasibound states of the emitter barrier may give rise to a remarkable photocurrent.

Effect of spontaneous and piezoelectric polarization on intersubband transition in AlxGa1-xN-GaN quantum well

A self-consistent solution of conduction band profile and subband energies for AlxGa1-xN-GaN quantum well is presented by solving the Schrodinger and Poisson equations. A new method is introduced to deal with the accumulation of the immobile charges at the AlxGa1-xN-GaN interface caused by spontaneous and piezoelectric polarization in the process of solving the Poisson equation. The effect of spontaneous and piezoelectric polarization is taken into account in the calculation. It also includes the effect of exchange-correlation to the one electron potential on the Coulomb interaction. Our analysis is based on the one electron effective-mass approximation and charge conservation condition. Based on this model, the electron wave functions and the conduction band structure are derived. We calculate the intersubband transition wavelength lambda(21) for different Al molar fraction of barrier and thickness of well. The calculated result can fit to the experimental data well. The dependence of the absorption coefficient a on the well width and the doping density is also investigated theoretically. (C) 2004 American Vacuum Society.

Influence of level filling on optical properties of quantum well

In a specially- designed three-barrier-double-well tunneling structure, electron injecting from the emitter in combination with escaping through a resonant-tunneling structure were used to adjust and control the filling of electrons in different subbands. It was observed that the occupation in the first-excited electron state can result in a suppression to quantum confinement Stark effect. Moreover, at very low bias, a series of intrigue photoluminescence peaks appeared as a small quantity of excess electron was filled in the ground state of the quantum well, that cannot be explained by the theory of hand-to-hand transition in the framework of single electron picture.

Weak antilocalization and beating pattern in an InGaAs/InAlAs quantum well

We have observed the weak antilocalization (WAL) and beating SdH oscillation through magnetotransport measurements performed on a heavily delta-doped In0.52Al0.48As/In0.53Ga0.47As/In0.5Al0.48As single quantum well in an applied magnetic field up to 13 T and a temperature at 1.5 K. Both effects are caused by the strong Rashba spin-orbit (SO) coupling due to high structure inversion asymmetry (SIA). The Rashba SO coupling constant alpha and zerotield spin splitting Delta(0) are estimated and the obtained values are consistent from different analysis for this sample. (c) 2007 Elsevier Ltd. All rights reserved.

High-power electroabsorption modulator using intrastep quantum well

An electroabsorption modulator using the intrastep quantum well (IQW) active region is fabricated for optical network systems. The strain-compensated InGaAsP/InGaAsP IQW shows good material quality and improved modulation properties, high extinction ratio elliciency 10 dB/V and low capacitance (< 0.42 pF), with which an ultra high frequency (> 15 GHz) can be obtained. High-speed measurement under high-power excitation shows no power saturation up to excitation power of 21 dBm. To our knowledge, the input optical power is the highest reported for multi-quantum well EAMs without heat sinks.

An n-type SiGe/Ge QC structure utilizing the deep Ge quantum well for electron at the Gamma point

In this paper, an n-type Si1-xGex/Ge (x >= 0.85) quantum cascade (QC) structure utilizing a deep Ge quantum well for electrons at the Gamma point is proposed. Based on linear interpolation, a conduction band offset at the Gamma point in a Si1-xGex/Ge ( x >= 0.85) heterostructure is presented, which is suitable for designing a QC laser. This approach has the advantages of a large conduction band offset at the Gamma point, a low lattice mismatch between the Si1-xGex/Ge ( x >= 0.85) active layers and the Si1-yGey ( y > x) virtual substrate, a small electron effective mass in the Gamma band, simple conduction energy band structures and a simple phonon scattering mechanism in the Ge quantum well. The theory predicts that if high-energy electrons are continuously injected into the Gamma band, a quasi-equilibrium distribution of electrons between the Gamma and L bands can be reached and held, i.e., electrons with a certain density will be kept in the Gamma band. This result is supported by the intervalley scattering experiments. In n-type Si1-xGex/Ge ( x >= 0.85) QC structures, population inversion between the laser's upper and lower levels is demonstrated.

Pseudospin in Si delta-doped InAlAs/InGaAs/InAlAs single quantum well

Magneto-transport measurements have been carried out on double/single-barrier-doped In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum well samples from 1.5 to 60 K in an applied magnetic field up to 13 T. Beating Shubnikov-de Haas oscillation is observed for the symmetrically double-barrier-doped sample and demonstrated due to a symmetric state and an antisymmetric state confined in two coupled self-consistent potential wells in the single quantum well. The energy separation between the symmetric and the antisymmetric states for the double-barrier-doped sample is extracted from experimental data, which is consistent with calculation. For the single-barrier-doped sample, only beating related to magneto-intersubband scattering shows up. The pesudospin property of the symmetrically double-barrier-doped single quantum well shows that it is a good candidate for fabricating quantum transistors. (c) 2007 Elsevier Ltd. All rights reserved.

Energy of a polaron in a wurtzite nitride finite parabolic quantum well

The effects of electron-phonon interaction oil energy levels of a. polaron in a wurtzite nitride finite parabolic quantum well (PQW) are studied by using a modified Lee-Low-Pines variational method. The ground state, first excited state, and transition energy of the polaron in the GaN/Al0.3Ga0.7N wurtzite PQW are calculated by taking account of the influence of confined LO(TO)-like phonon modes and the half-space LO(TO)-like phonon modes and considering the anisotropy of all kinds of phonon modes. The numerical results are given and discussed. The results show that the electron phonon interaction strongly affects the energy levels of the polaron, and the contributions from phonons to the energy of a polaron hi a wurtzite nitride PQW are greater than that in all AlGaAs PQW. This indicates that the electron-phonon interaction in a wurtzite nitride PQW is not negligible.

Metamorphic growth of 1.25-1.29 mu m InGaAs quantum well lasers on GaAs by molecular beam epitaxy

We demonstrate 1.25-1.29 mu m metamorphic laser diodes grown on GaAs by molecular beam epitaxy (MBE) using an alloy-graded buffer layer (GBL). Use of Be in the GBL is effective to reduce surface/interface roughness and improves optical quality. The RMS surface roughness of the optimized metamorphic laser is only two atomic monolayers for 1 x 1 mu m(2). Cross-sectional transmission electron microscopy (TEM) images confirm that most dislocations are blocked in the GBL. Ridge waveguide lasers with 4 mu m wide ridge were fabricated and characterized. The average threshold current under the pulsed excitation is in 170-200 mA for a cavity length of 0.9-1.5 mm. This value can be further reduced to about 100 mA by high-reflectivity coating. Lasers can work in an ambient temperature up to at least 50 degrees C. (c) 2006 Elsevier B.V. All rights reserved.

A short carrier lifetime semiconductor optical amplifier with n-type modulation-doped multiple quantum well structure

Semiconductor optical amplifiers (SOAs) with n-type modulation-doped multiple quantum well structure have been investigated. The shortened carrier lifetime is derived from the PL spectrum and electrical modulation frequency response measurement. The carrier lifetime in semiconductor optical amplifiers with any n-type-2-modulated doping multiple quantum well structure is less than 60% of that in the undoped partner. The shortest measured carrier lifetime of 236 ps in the MD-MQW SOA with sheet carrier density of 3 x 10(12) cm(-2) was only 38% of that in the undoped MQW SOA, which can increase the wavelength conversion efficiency via four wave mixing by a factor of about 7 and switching speed via XGM and XPM applications by a factor of 2.63.

The influence of internal electric fields on the transition energy of InGaN/gaN quantum well

We present a new way to meet the amount of strain relaxation in an InGaN quantum well layer grown on relaxed GaN by calculating and measuring its internal field. With perturbation theory, we also calculate the transition energy of InGaN/GaN SQWs as affected by internal fields. The newly reported experimental data by Graham et al. fit our calculations well on the assumption that the InGaN well layer suffered a 20% strain relaxation, we discuss the differences between our calculated results and the experimental data. Our calculation suggests that with the increase of indium mole fraction in the InGaN/GaN quantum well, the effect of polarization fields on the luminescence of the quantum well will increase. Moreover, our calculation also suggests that an increase in the quantum well width by only one monolayer can result in a large reduction in the transition energy. (c) 2006 Elsevier B.V. All rights reserved.