单模GaAs/AlGaAs短腔长量子级联激光器

通过缩短Fabry-Pérot腔量子级联激光器的腔长,得到了激射波长为11.4μm的单模GaAs/AlGaAs量子级联激光器。纵模间距与F-P腔腔长成反比,腔长为150μm的器件实现了稳定单模激射,在85K时边模抑制比达到19dB。     

GaAs/AlGaAs quantum cascade microlasers based on monolithic semiconductor-air Bragg mirrors

Edge emitting GaAs-based quantum cascade microlasers at a wavelength of 9 /spl mu/m were realised by monolithic integration of photonic bandgap mirrors based on deeply etched air-semiconductor Bragg gratings. The shortest operating device with Bragg mirrors on both sides has a cavity length of 180 /spl mu/m.     

Intervalley scattering in GaAs/AlGaAs quantum wells and quantum cascade lasers

The results of simulations of Γ−X scattering in GaAs/AlGaAs quantum wells are presented, discussing the importance of the mole fraction, doping density, and lattice and electron temperatures in determining the scattering rates. A systematic study of Γ−X scattering in GaAs/Al_xGa_1−xAs heterostructures, using a single quantum well to determine the importance of well width, molar concentration x, lattice temperature, and doping density, has been performed. After this we consider a double quantum well to determine the role of intervalley scattering in the transport through single-layer heterostructures, i.e. Γ−X−Γ scattering compared with Γ−Γ scattering. Finally, we estimate the relative importance of intervalley scattering in a GaAs-based quantum-cascade laser device and compare it with other relevant scattering mechanisms important to describe carrier dynamics in the structure. Our simulations suggest that Γ−X scattering can be significant at room temperature but falls off rapidly at lower temperatures.     

GaAs/AlGaAs太赫兹量子级联激光器的热分析

为研究太赫兹量子级联激光器(THz QCLs)中的热传输及有效散热方法,建立了二维/三维有限元热分析模型,模拟计算了GaAs/AlGaAs THz QCLs低温工作时的温度及热流分布;并讨论了源区结构参数、热沉材料及散热膜层对器件热传输的影响规律。研究结果表明,器件源区温度水平方向分布较均匀,垂直方向温差大,源区热量主要依靠热沉导出;减小源区厚度、增加腔长与减小脊宽均有利于促进热传导并降低源区温度;在器件顶部增加AlN薄膜具有显著的辅助散热效果,当薄膜厚度大于8 μm时,源区温降趋于缓慢。     

Electroluminescence from AlGaAs/GaAs quantum-cascade structures in the terahertz range

Electroluminescence from a quantum-cascade structure comprising 40 periods of GaAs/Al_0.15Ga_0.85As tunnel-coupled quantum wells (QW) was studied. A terahertz emission band in the range 1.0–1.8 THz is observed under bias exceeding 1.5–2.0 V. The emission band peak shifts linearly to higher frequency with the increasing bias. The effect is accounted for by spatially indirect electron transitions between states in the neighboring QWs.     

Diagnostics of quantum cascade structures by optical methods in the near infrared region

The spectra and kinetics of the low-temperature interband photoluminescence of epitaxial structures of terahertz quantum cascade lasers is studied under conditions of strong pulsed excitation. Photoluminescence corresponding to transitions between both the ground and excited states of two tunnel-coupled wells is observed at high excitation levels (600 mW; spot diameter ??200 ??m). Kinetic measurements show that the rise and decay times significantly decrease up to the time resolution of the measuring system at wavelengths <770 nm with decreasing photoluminescence observation wavelength.     

Manifestation of A(+) centers in the luminescence of two-dimensional GaAs/AlGaAs structures

Photoluminescence of GaAs/AlGaAs multiple-quantum-well structures incorporating positively charged beryllium-impurity shallow-level acceptors (the so-called A(+) centers) was investigated. A novel luminescence line, which originated from radiative recombination of free electrons with A(+) centers, was observed. It was shown that its spectral position is determined uniquely by the binding energy of A(+) centers. It was also ascertained that the binding energy of A(+) centers increases with a decrease in the quantum-well width when the latter is comparable to the radius of A(+) centers.     

Electron mobility in a AlGaAs/GaAs/AlGaAs quantum well

An oscillatory dependence of the electron mobility on the quantum well (QW) thickness in a AlGaAs/GaAs/AlGaAs heterostructure with double-sided modulation doping has been observed experimentally. A steep decrease in mobility with increasing electron concentration in the QW is established. The conditions for an increase in mobility on introducing a thin barrier into the QW are determined. The first experimental observation of an increase in mobility by a factor of 1.3 in a QW of thickness L=26 nm upon introducing a thin (1–1.5 nm) AlAs barrier is reported.     

Electron nonelastic scattering by confined and interface polar optical phonons in a modulation-doped AlGaAs/GaAs/AlGaAs quantum well

The calculations of electron scattering rates by polar optical (PO) phonons in an AlGaAs/GaAs/AlGaAs quantum well (QW) with a different width and doping level are performed. The electron-and PO-phonon scattering mechanisms which are responsible for the alternate dependence of electron mobility on a QW width, as well as for the decrease of conductivity in the QW with increasing sheet electron concentration, are determined. It is shown that the enhancement of the scattering rate by PO-phonon absorption when the lower subband electron gas is degenerated is responsible for the decrease of QW conductivity with increasing sheet electron concentration. The competition between the decrease of the intrasubband scattering and the increase of the intersubband scattering by PO-phonon absorption is responsible for the alternate changes of the mobility with a QW width.     

Degradation of AlGaAs/GaAs HBTs induced by hot carriers

In AlGaAs/GaAs HBTs, the instability of the surface states of the extrinsic base, which is revealed by mesa-etching and passivated by Si₃N₄, affects reliability. In this study the reverse constant current stress in an avalanche regime is applied across the emitter–base junction in order to test the stability of the heterojunction and the surface state of the extrinsic base. It has been identified that the surface of the extrinsic base is vulnerable to hot carriers. A new degradation mechanism is suggested and verified by numerical simulation. In addition, a way to improve the reliability is proposed based on the experimental results.     

Scattering of hot electrons by neutral acceptors in GaAs/AlAs quantum well structures

The optical alignment of hot electrons and its destruction in a magnetic field under conditions when electron scattering by neutral acceptors plays a large role is investigated. This makes it possible to determine the probability of the scattering of hot electrons from an initial photoexcited state, as well as the times characterizing the energy and momentum relaxation of hot electrons on scattering by neutral acceptors. The experimental results are compared with calculations. Fiz. Tekh. Poluprovodn. 32, 866–875 (July 1998)     

Single-pulse pump-probe measurement of optical nonlinear propertiesin GaAs/AlGaAs multiple quantum wells

Single-pulse ps-pump and ns-probe nonlinear transmission measurements provide carrier-density-dependent optical nonlinear spectra in GaAs/AlGaAs multiple quantum wells grown by metalorganic chemical vapor deposition. The use of the ps pump eliminates the need to know carrier lifetime to determine carrier density. The saturation behavior of changes in absorption coefficient and refractive index are modeled by a simple saturation equation to obtain saturation carrier density. The saturation spectra for different well thicknesses are obtained. The minimum saturation carrier density appears around 150 Å     

Low-loss single-mode GaAs/AlGaAs miniature optical waveguides withstraight and bending structures

Low-loss single-mode GaAs/AlGaAs miniature optical waveguides fabricated for use in monolithically integrated optical circuits are discussed. The propagation characteristics of these waveguides with straight and S-bending structures have been investigated at wavelengths of 1.30 and 1.55 μm. The lowest propagation losses are estimated to be 0.58 dB/cm and 0.69 dB/cm at wavelengths of 1.30 and 1.55 μm, respectively. The total loss of an S-bending waveguide with a curvature radius of 2 mm and with a lateral displacement of 200 μm was 0.61 dB and 0.46 dB at wavelengths of 1.30 and 1.55 μm. The fabricated single-mode strip-loaded waveguides proved to be suitable for application of the semiconductor waveguide into monolithically integrated optical circuits     

Ion beam milling-induced damage in AlGaAs/GaAs/AlGaAs single quantum well

Ion beam milling-induced damage in a 500 AA AlGaAs/40 AA GaAs/500 AA AlGaAs single quantum well structure was investigated using low temperature cathodoluminescence spectroscopy. The ion beam energy (500-1500 eV) dependence of luminescence intensity indicated that minimum damage is introduced at a beam energy of 500 eV. Most (80-85%) of the original luminescence intensity was recovered on annealing at 400 degrees C for 5 min.<>     

Birefringence of disordered AlGaAs/GaAs quantum wells

Birefringence at room temperature is analysed for interdiffusion induced (disordered) Al/sub 0.3/Ga/sub 0.7/As/GaAs single quantum well structures in the wavelength range 0.5 mu m to 1.0 mu m. The confinement profile for the disordered QW is modelled by an error function and the refractive index model includes excitonic effects and contributions from the Gamma , X and L Brillouin zones. Results show that at longer wavelengths the birefringence is small and varies from positive to negative before reducing to zero as interdiffusion proceeds. For wavelengths between the QW and barrier band-edges, the birefringence is large and reduces with increasing interdiffusion.<>     

Determination of the heterojunction type in structures with GaAsSb/GaAs quantum wells with various antimony fractions by optical methods

The type of heterojunction in the GaAs_{1 ? x} Sb _x /GaAs heterostructure at x = 0.36 is studied by photoluminescence spectroscopy and time-resolved photoluminescence. A GaAsSb/GaAs heterostructure with an Sb fraction of 15%, for which we can confidently state is a type-I heterojunction, was studied for comparison. It was established from the blue shift of the photoluminescence line depending on the excitation power and relaxation time of the photoluminescence signal from the GaAs_{1 ? x} Sb _x /GaAs quantum well, which was ??11 ns, that the GaAs_{1 ? x} Sb _x /GaAs structure at an Sb content of 36% clearly constitutes a type II heterojunction. This was additionally evidenced by the data obtained for structures with an Sb content of 15%, in which case no shift of the location of the photoluminescence line on the pump power was observed, while the relaxation time of photoluminescence in the region of the signal from the quantum well was ??1.5 ns.     

Modulation of optical absorption of GaAs/AlGaAs quantum wells in a transverse electric field

Results of experimental investigations of the transformation of intraband light absorption spectra by the quantum-well electrons in a transverse electric field are presented. In addition to the familiar Stark effect, absorption oscillations in the photoionization band are detected. These oscillations are caused by electron transitions from the ground state in a quantum well to quasidiscrete levels arising in the continuum of states above the well due to the linear potential of the external electric field. Fiz. Tekh. Poluprovodn. 32, 849–851 (July 1998)     

Bend losses in GaAs/AlGaAs optical waveguides

Circular bends with low excess bend loss (? l dB) and radii of a few millimetres were fabricated using GaAs/AlGaAs single-heterostructure rib waveguides with propagation loss ? 1 dB/cm. The effect of rib geometry and roughness due to bend pattern quantisation on the excess bend loss at 1.52/?i was investigated.     

Photoluminescence of anti-modulation-doped GaAs/AlGaAs single quantum well structures exposed to hydrogen plasma

Techniques of low-temperature photoluminescence (PL), photoluminescence excitation, and photoreflectance were used to study the effect of hydrogen plasma treatment at 260°C on antimodulation Si-doped GaAs/AlGaAs heterostructures with near-surface single quantum wells (QWs) grown by molecular-beam epitaxy. It was found that, in the case of excitation below the AlGaAs band gap, exciton PL from the QW is quenched due to an increase in the electric field in the structure. The reason for this is that the passivation of surface states by hydrogen results in the Fermi level depinning from the midgap of the nominally undoped p-type GaAs cap layer, while shallow-level impurities present in the layers of the structure are not neutralized (their complexes with hydrogen dissociate under the influence of illumination and strong electric fields).     

Low-loss GaAs/AlGaAs optical waveguides on InP substrates

It is shown that the waveguide losses in lattice-mismatched GaAs-on-InP structures can be significantly reduced using an appropriate buffer layer. An AlGaAs buffer layer sequence was used for this purpose. A thin (400 nm) layer of Al_0.7Ga_0.3As, with an index below that of InP, was placed adjacent to the GaAs guiding layer both to maximize optical confinement in the guide and to increase the allowable guide dimensions for a single planar waveguide mode. Additional separation between guide and mismatched interface was achieved by inserting an Al_0.5Ga_0.5As layer with an index nearly equal to that of InP between the low-index buffer and InP. The final waveguide structure also included a thin (<40 nm) GaAs layer which was used to initiate growth and did not affect waveguide performance. Low losses (typically 3 dB/cm, with best results below 1 dB/cm) were achieved at a 1.52-μm wavelength for samples grown by organometallic chemical vapor deposition