GaAs/AlGaAs multiple quantum well GRIN-SCH vertical cavity surfaceemitting laser diodes

Vertical cavity surface emitting lasers (VCSELs) with GaAs/AlGaAs multiple quantum well (20 wells) graded-index separate-confinement-heterostructure (GRIN-SCH) active regions are discussed. The VCSEL structures, which also contained two Al_xGa_1-xAs/Al_yGa_1-yAs distributed Bragg reflectors, were grown by molecular beam epitaxy and had a threshold current and current density at room temperature pulsed excitation of 16 mA and 14 kA/cm², respectively, near 0.85-μm wavelength. Both single-longitudinal and fundamental transverse mode emission characteristics were observed with a light output greater than 3 mW and a slope efficiency of 0.12 mW/mA     

Carrier-induced lasing wavelength shift for quantum well laser diodes

Lasing wavelength was analyzed for quantum well laser diodes (QW-LD's) considering both the bandgap shrinkage effect and the band-filling effect. The bandgap shrinkage effect was calculated by the local density functional method, treating both electron and hole distribution self-consistently. Assuming nok-selection rule, the band-filling effect is larger than the bandgap shrinkage effect when the carrier density is high. The lasing wavelength shifts to the short side as the threshold carrier density increases. QW-LD's with a large threshold carrier density lase at very short wavelength corresponding to the transition between the second sublevel. However, this wavelength is still longer than that expected because of the bandgap shrinkage effect.     

Improvement of GaAs/AlGaAs quantum well laser diodes by rapid thermal annealing

Post-growth annealing is shown to improve the laser diode quality of GaAs/AlGaAs graded-index separate confinement heterostructure quantum well laser diode structures grown at a nonoptimal substrate temperature lower than 680°C by molecular beam epitaxy. Reduction by a factor of up to three in the threshold current was accompanied by a reduction in the interface trap density. The reduced threshold current is still higher than that of laser diodes grown at the optimal temperatures which are between 680 and 695°C. The improvement in laser diode performance is ascribed to the reduction of interface nonradiative recombination 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.     

Energy relaxation in GaInAs/AlInAs heterojunctions and GaAs/AlGaAs multiple quantum wells

We have studied electron energy relaxation in GaInAs/AlInAs heterojunctions and GaAs/AlGaAs multiple quantum wells using mobility measurements as a function of electric field and temperature, in the range 3K to 300K. The results in the range 3 to 20K show a power loss rate which is dependent on (T_e − T_l), suggesting that the energy relaxation occurs through acoustic phonon scattering. At electron temperatures greater than 20K, the experimental results are modelled using a standard expression for polar optical phonons. This modelling yields 30meV and 31meV for the polar optical phonon energy in GaAs and InGaAs respectively.     

Dielectric properties of GaAs AlGaAs multiple quantum well waveguides

GaAs/AlGaAs multiple quantum well (MQW) waveguides are investigated using the grating coupling technique. Large polarization dependent effects of the two-dimensional excitons are seen in the TE/TM dispersion relation of single mode slab waveguides. By treating the MQW as a layered composite dielectric, we deduce the oscillator strengths of the heavy and light hole excitons, and the background dielectric constant of the MQW without the excitonic contribution, for fields polarized parallel and perpendicular to the MQW layers.     

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。     

Single-mode GaAs/AlGaAs quantum cascade microlasers

Single-mode edge emitting GaAs/A1GaAs quantum cascade microlasers at a wavelength of about 11.4 μm were realized by shortening the Fabry-P6rot cavity length. The spacing of the longitudinal resonator modes is inversely proportional to the cavity length. Stable single-mode emission with a side mode suppression ratio of about 19 dB at 85 K for a 150-μm-long device was demonstrated.     

Optimization and characterization of index-guided visible AlGaAs/GaAs graded barrier quantum well laser diodes

Index-guided, single and multiple stripe, visible laser diodes (lambda = 6950-7150Å) have been fabricated and characterized. These structures utilize a graded barrier quantum well laser structure having high aluminum composition (x = 0.60-0.85) confining layers to obtain low threshold current. The use of thin AlAs quantum well barrier layers allows short wavelengths to be obtained from the quantum size effect in binary GaAs wells without the need for alloy AlxGa1-xAs wells. Index-guiding is accomplished by use of either a complementary self-aligned structure or a shallow mesa laser structure allowing stabilized single-mode laser operation.     

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.<>     

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     

GaAs/AlGaAs多量子阱空间光调制器入射角度特性研究

研究了GaAs/AlGaAs多量子阱(MQW)空间光调制器(SLM)在不同入射角度下的调制特性。对腔模位置与入射角度的关系进行了理论计算和实验验证,两者具有较好的一致性。当入射角在0°～75°之间变化时,腔模从871nm变化至845nm,可调节范围达26nm。当入射光从垂直入射变化为约45°入射时,SLM对比度从(CR)3.8提高到16.3,调制电压从9.5V下降至6.5V。理论分析和实验结果表明,入射角度调节能够有效提高GaAs/AlGaAs MQW SLM调制性能。     

Room temperature operation of type-II GaAsSb/InGaAs quantum welllaser on GaAs substrates

A GaAsSb/InGaAs type-II quantum well laser diode on GaAs substrates was demonstrated for the first time. Threshold current density of 610 A/cm² was obtained from a 1.1 mm-long broad area laser with the emission wavelength of 1.2 μm     

单模AlGaAs／GaAs脊形波导量子阱半导体激光器

本文报道用分子束外延设备研制梯度折射率分别限制式单量子阱AlGaAs/GaAs脊形波导半导体激光器。该激光器具有良好的性能,条宽5μm器件室温阈值电流23mA,线性连续输出单模激光功率大于15mW。     

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.<>     

Room temperature excitonic nonlinear absorption and refraction in GaAs/AlGaAs multiple quantum well structures

We present detailed experimental studies and modeling of the nonlinear absorption and refraction of GaAs/AlGaAs multiple quantum well structures (MQWS) in the small signal regime. Nonlinear absorption and degenerate four-wave mixing in the vicinity of the room temperature exciton resonances are observed and analyzed. Spectra of the real and imaginary parts of the nonlinear cross section as a function of wavelength are obtained, and these are in excellent agreement with experimental data. A simple model for excitonic absorption saturation is proposed; it accounts qualitatively for the very low saturation intensities of room temperature excitons in MQWS.     

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.     

The effect of external stress on the properties of AlGaAs/GaAs single quantum well laser diodes

The change of spectrum of the AlGaAs/GaAs single quantum well laser diode is measured under the application of uniform uniaxial in-plane tensile and compressive stress. In the range of the tensile stress we apply (up to 597 MPa), the wavelength increases linearly at a rate of 5.3 nm GPa⁻¹. The energy band gap decreases with the tensile stress with the slope of −10 meV GPa⁻¹, which is close to the theoretical change of the heavy hole band edge with respect to the conduction band edge. There is a shorter wavelength peak existing on the spectrum as the tensile stress increases, suggesting a transition from the conduction band to a higher energy valence band. For the compressive stress (up to −516 MPa), the wavelength decreases with the stress, but it shows an abrupt reduction from −162 to −200 MPa. The threshold current also varies as a result of the change of the energy band structure.     

Shallow impurity levels in AlGaAs/GaAs semiconductor quantum wells

This paper reviews current knowledge of shallow impurity states (donors and acceptors) in AlGaAs/GaAs multiple-quantum-well structures. Calculations of these levels have been performed by a number of groups, most of which solved an effective-mass Schrödinger equation using the variational method. These results are generally consistent with each other, any differences being related to different approximations made in each calculation. The ground states of some of these shallow impurity levels have also been measured in several laboratories using low-temperature photoluminescence, Raman and far-infrared absorption techniques. These methods yield similar results which are consistent with the calculations. Both theoretical and experimental methods and results are discussed.     

Low-voltage phase modulation in GaAs/AlGaAs quantum well opticalwaveguides

Reports GaAs/AlGaAs quantum well waveguide phase modulators with high phase shift coefficients, as large as 520 degrees per V mm. By operating at wavelengths far below the bandedge and applying DC bias the authors achieve large electro-optic modulation with low absorption loss in device lengths on the order of 100 μm and drive voltages on the order of 1 V