High-power lasers (λ = 940–980 nm) based on asymmetric GaInAs/GaInAsP/AlGaAs separate-confinement heterostructure

Asymmetric GaInAs/GaInAsP/AlGaAs heterostructures with the emission wavelength of 940 and 980 nm were grown by MOCVD. The composition of solid solution in the waveguide layer, Ga_0.74In_0.26As_0.47P_0.53, was chosen based on the calculations of the escape energy of electrons from the quantum well of the active region into the waveguide. Semiconductor lasers with the emission aperture of 100 μm were fabricated from these heterostructures. The CW output optical power of 12 W was achieved at room temperature. The internal optical loss was 0.6 and 0.3 cm^?1 for 940 and 980 nm wavelengths, respectively.     

Effect of the built-in electric field on optical and electrical properties of AlGaAs/InGaAs/GaAs P-HEMT nanoheterostructures

This study is concerned with the photoluminescence spectra and electrical parameters of AlGaAs/InGaAs/GaAs pseudomorphic high-electron-mobility transistor (P-HEMT) structures with a quantum well grown at different depths L _b with respect to the surface. The samples are produced so as to make the concentration of electrons in the quantum well unchanged, as the barrier layer thickness L _b is reduced. It is established that the photoluminescence spectra of all of the samples exhibit peaks at the photon energies ħ _ω = 1.28−1.30 and 1.35–1.38 eV. The ratio between the intensities of these peaks increases as L _b is decreased. Calculations of the band structure show that variations in the spectra are due to the fact that the built-in electric field increases as the quantum well is set closer to the surface.     

The effect of spacer-layer growth temperature on mobility in a two-dimensional electron gas in PHEMT structures

The effect of growth temperature of the AlGaAs spacer layer on mobility in a two-dimensional electron gas μ _e in single-side δ-doped pseudomorphic AlGaAs/InGaAs/GaAs transistor structures with a high electron mobility is studied experimentally. The energy-band diagram is analyzed using a self-consistent calculation. In order to study the electronic transport properties, an optimized structure in which there is no parallel conduction over the doped layer was chosen. It is shown that, in optimized structures, the mobility μ _e increases by 53% at T = 300 K and by 69% at T = 77 K as the growth temperature increases from 590 to 610°C, with the other parameters and the growth conditions remaining the same. It is assumed that this behavior is related to an improvement in the structural quality of the AlGaAs spacer layer and the AlGaAs/InGaAs/GaAs heteroboundary.     

Super-flat (411)A interfaces and uniformly corrugated (775)B interfaces in GaAs/AlGaAs and InGaAs/InAlAs heterostructures grown by molecular beam epitaxy

Extremely flat interfaces, i.e. effectively atomically flat interfaces over a wafer-size area were realized in GaAs/AlGaAs quantum wells (QWs) grown on (411)A GaAs substrates by molecular beam epitaxy (MBE). These flat interfaces are called as “(411)A super-flat interfaces”. Besides in GaAs/AlGaAs QWs, the (411)A super-flat interfaces were formed in pseudomorphic InGaAs/AlGaAs QWs on GaAs substrates and in pseudomorphic and lattice-matched InGaAs/InAlAs QWs on InP substrates. GaAs/AlGaAs resonant tunneling diodes and InGaAs/InAlAs HEMT structures with the (411)A super-flat interfaces were confirmed to exhibit improved characteristics, indicating high potential of applications of the (411)A super-flat interfaces. High density, high uniformity and good optical quality were achieved in (775)B GaAs/(GaAs)_m(AlAs)_n quantum wires (QWRs) self-organized in a GaAs/(GaAs)_m(AlAs)_n QW grown on (775)B GaAs substrates by MBE. The QWRs were successfully applied to QWR lasers, which oscillated at room temperature for the first time as QWR lasers with a self-organized QWR structure in its active region. These results suggest that MBE growth on high index crystal plane such as (411)A or (775)B is very promising for developing novel semiconductor materials for future electron devices.     

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.     

Electrical and structural properties of PHEMT heterostructures based on AlGaAs/InGaAs/AlGaAs and δ-doped on two sides

The pseudomorphic AlGaAs/InGaAs/AlGaAs heterostructure δ-doped with silicon on both sides and used for fabrication of high-power transistors is optimized to obtain a high concentration n _s and mobility of two-dimensional electron gas in the quantum well (n _s ≈ 3 × 10¹² cm^?2). Electrical and structural characteristics of the samples grown by molecular-beam epitaxy with various doping levels are studied. It is shown that the mobility and concentration of electrons varies as doping level is increased and the subbands of dimensional quantization are sequentially filled. In order to analyze the distribution of electrons in subbands of the heterostructure, the Shubnikov-de Haas oscillations at the liquid helium temperature were studied. The quality of the heterostructure layers was assessed using the method of X-ray diffraction. The data of photoluminescence spectroscopy are in good agreement with the results of calculations of the band structure.     

Drift velocity of electrons in quantum wells in high electric fields

It is experimentally found that the maximum drift velocity of electrons in quantum wells of differently arranged AlGaAs/GaAs heterostructures and pseudoamorphous Al_0.36Ga_0.64As/In_0.15Ga_0.85 As heterostructures is higher than the maximum drift velocity of electrons in bulk materials. It is established that no negative differential conductivity is exhibited by the field dependence of the drift velocity of two-dimensional electrons in GaAs and In_0.15Ga_0.85As. The drift velocity in the GaAs quantum well is saturated in fields several times higher than the field corresponding to the Γ-L intervalley transitions of electrons in bulk GaAs.     

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.     

InGaAs/GaAs/AlGaAs应变量子阱激光器

优化设计了既能实现较小垂直方向远场发散角,又能降低腔面光功率密度的ＩｎＧａＡｓ／ＧａＡｓ／ＡｌＧａＡｓ应变层量子阱激光器,并计算了该结构激光器实现基横模工作的脊形波导结构参数。利用分子束外延生长了ＩｎＧａＡｓ／ＧａＡｓ／ＡｌＧａＡｓ应变量子阱激光器材料并研制出基横模输出功率大于１４０ｍＷ,激射波长为９８０ｎｍ的脊形波导应变量子阱激光器,其微分量子效率为０．８Ｗ／Ａ,垂直和平行结平面方向远场发散角分别为２８°和６．８°     

Resonance Coulomb scattering at shallow donors in AlGaAs/n-GaAs/AlGaAs quantum wells

The characteristics of the Coulomb scattering of conduction electrons at shallow donor centers in Al _x Ga_{1 ? x} As/n-GaAs/Al _x Ga_{1 ? x} As quantum well heterostructures are studied theoretically with consideration for the influence of resonance states. The resonance states emerge below the excited quantum-confinement subbands because of the presence of donors. It is found that the spectra of total and transport Coulomb-scattering cross sections exhibit asymmetric resonance features in the vicinity of resonance energies. It is shown that these features do not exhibit a small effect: in the vicinity of resonance energies, the cross sections can differ from the corresponding quantities in the nonresonance case several times.     

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).     

MOCVD-grown InGaAs/GaAs/AlGaAs laser structures with a broad-area contact

A metal-organic chemical vapor deposition (MOCVD) technique is developed for a diode laser heterostructure in a system of InGaAs/GaAs/AlGaAs solid solutions; the optimal sizes and the doping profile of the structure are determined to minimize the internal optical losses. Mesa-strip diode lasers with a threshold density of current J _th=150–200 A/cm², internal optical loss factor α_i=1.6–1.9 cm^?1, and an internal quantum yield η_i=85–95% were fabricated. In the continuous lasing mode of a diode laser with a 100-µm-wide aperture and a wavelength of 0.98 µm, the optical power output was as high as 6.5 W and was limited by the catastrophic optical degradation of mirrors. The radiation divergence in the plane normal to the p-n junction amounts to θ_⊥. The use of wide-gap waveguide layers, which deepens the potential electron well in the active region, is shown to reduce the temperature sensitivity of the InGaAs/GaAs/AlGaAs laser heterostructures in the temperature range from 0 to 70°C.     

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量子阱红外探测器特性非对称性分析

在分子束外处生长量子阱材料过程中,分析了在不同的GaAs/AlGaAs异质结生长次序中Ga的解吸附速率不同和量子阱中掺杂的扩散造成量子阱结构的不对称,讨论了GaAs/AlGaAs最子红外探测器的性能参数相对于正负偏压的不对称性,并与金属有机化合物汽相沉淀法生长的最子阱材料和相应器件进行了比较,发现,采用分子束外延方法生长器件的不对称性更明显。     

反射各向异性谱在线监测852nm半导体激光器AlGaInAs/AlGaAs量子阱的MOCVD外延生长

研究了生长温度和中断时间对AlGaInAs/AlGaAs量子阱外延质量的影响,并使用金属有机化合物汽相沉积(MOCVD)外延生长了AlGaInAs/AlGaAs量子阱和852nm半导体激光器。通过使用反射各向异性谱(RAS)和光致发光谱在线监测和研究了AlGaInAs/AlGaAs界面的外延质量。研究结果表明高温生长可以导致从AlGaInAs量子阱层到AlGaAs势垒层的In析出现象。通过优化生长温度和在AlGaInAs/AlGaAs界面处使用中断时间,可以有效抑制In析出,从而获得AlGaInAs/AlGaAs陡峭界面。使用优化后的外延生长条件,外延生长了整个852nm半导体激光器,使用RAS在线监测了激光器的外延生长过程,可以有效地分辨出不同外延层和生长阶段。     

Vertical integration of a GaAs/AlGaAs quantum-well laser and along-wavelength quantum-well infra-red photodetector

A short-wavelength (~0.8 μm) GaAs/AlGaAs graded-index separate-confinement heterostructure quantum-well laser has been monolithically integrated with a long-wavelength (~8 μm) GaAs/AlGaAs multiple-quantum-well infra-red photodetector on a semi-insulating GaAs substrate by molecular beam epitaxy. The vertical integration method is used and the combined structure is a pinin structure. Both the laser and detector exhibit excellent characteristics. At room temperature, the ridge waveguide laser has an extremely low threshold current of 25 mA and a differential quantum efficiency above 65% with a stripe width of 20 μm. The quantum-well detector has a peak response at 8 μm and a responsivity of 0.7 A/W     

A cascade laser on shallow-donor transitions in δ-Doped GaAs/AlGaAs superlattices

The possibility of amplification of terahertz-range electromagnetic waves due to optical transitions between a two-dimensional continuum and shallow-level donor states in GaAs/AlGaAs superlattices with selectively δ-doped quantum wells is analyzed theoretically. The population inversion required for the gain is attained under the conditions of vertical transport in the superlattice due to the hybridization of states in neighboring quantum wells coupled via electron tunneling through the barrier. It is shown that, at a doping level of 5 × 10¹⁰ cm^?2 per period, the gain can be as high as 50 cm^?1 at wavelengths 100–120 μm. The current density under operating conditions is ～50 A/cm².     

Photoreflectance spectroscopy of low-dimensional GaAs/AlGaAs structures

Results of room-temperature photoreflectance measurements on three GaAs/Al_0.33Ga_0.67As multiquantum well (MQW) structures with three different widths of wells and on two GaAs/Al_0.33Ga_0.67As high-electron-mobility transistor (HEMT) structures are presented. Energy-gap-related transitions in GaAs and AlGaAs were observed. The Al content in AlGaAs was determined. MQW transition energies were determined using the first derivative of a Gaussian profile of the measured resonances. In order to identify the transitions in the MQS, the experimentally observed energies were compared with results of the envelope function calculation method for a rectangular quantum well. The Franz–Keldysh oscillation (FKO) model was also used to determine the built-in electric field in various parts of the investigated structures. The values of the electric fields allow us to hypothesise about the origin of these fields. © 1997 John Wiley & Sons, Ltd.     

Changes in the density of nonradiative recombination centers in GaAs/AlGaAs quantum-well structures as a result of treatment in CF4 plasma

The effect of low-energy CF₄ plasma treatment on the stationary photoluminescence (PL) spectra and PL kinetics in GaAs/AlGaAs quantum-well (QW) structures is investigated. Intensity of the PL from QWs located deeper than the surface layer damaged by plasma treatment increases. It is established that this is accompanied by an increase in the PL decay time at temperatures above 30 K. It is shown that the density of nonradiative recombination centers in the QW located below the damaged surface layer decreases by a factor of 30 after 40-s exposure to plasma.     

MOCVD of AlGaAs/GaAs with novel group III compounds

The MOCVD of AlGaAs and GaAs from coordinatively saturated group III source materialsi.e. 1–3-dimethyl-aminopropyl-l-galla-cyclohexane ((C₅H₁₀)Ga(C₂N(CH_{3 2}) and the corresponding Al compound) was investigated. It was demonstrated that these precursors, which are inherently free of alkoxy contamination, are suitable for epitaxial growth of GaAs layers and structures of GaAs/AlGaAs. For comparison, data achieved with TEA (Al(C₂H₅)₃) or TⁱBA (Alⁱ(C₄H₉)₃) and TEG (Ga(C₂H₅)₃) are presented. A basic finding of this study is that due to the low thermal stability of TEA, TⁱBA and TEG the layers grown from these compounds suffer from insufficient homogeneity of layer thickness and composition. In contrast, the coordinatively saturated compounds show a reactivity suitable for large area growth. Additionally, intrinsic impurity (N, C) uptake appears to be low and electrical as well as PL data show the satisfactory quality of GaAs and AlGaAs layers grown from this new type of precursors. Specifically, a reduction of oxygen incorporation compared to growth from the standard trialkyls is indicated by PL measurements on layers grown at different temperatures.