Photoluminescence characterization of the effects of rapid thermal annealing on AlGaAs/GaAs modulation-doped quantum wells

In this study, we describe the effects of rapid thermal annealing on the electrical and optical properties of modulation-doped quantum wells (MDQWs). The sheet carrier concentration in MDQW structures which have been annealed in contact with a piece of GaAs tends to decrease with increasing annealing time due to Si auto-compensation in the doped AlGaAs regions. The high energy cut-off point of 4.2 K PL spectra, which occurs at the Fermi energy, and the 77 K PL linewidth are accurate measures of sheet carrier density. These two parameters track variations in carrier density produced by annealing. Photoluminescence spectra also provide additional insight into annealing-induced changes such as Si migration, which causes a degradation in the mobility of the two-dimensional electron gas.     

Photoluminescence characterization of AlGaN-GaN pseudomorphic quantum wells and calculation of strain induced bandgap shifts

The low temperature (77 K) photoluminescence characteristics of Al _x Ga_1-x N-GaN strained layer quantum wells with differentx values grown by metalorganic chemical vapor deposition (MOCVD) were investigated. The photoluminescence spectra were useful in analyzing both quantum confinement effects and strain induced energy shifts. The strain induced shifts were found to be a strong function of aluminum compositionx. A model was developed to calculate the strain induced bandgap shifts atk = 0. The values predicted by this model which took into account the wurtzite crystal structure of the material system, were in good agreement with (i.e. within 2 meV of) the experimentally measured shifts.     

Photoluminescence in n and p modulation-doped GaInNAs/GaAs quantum wells

Experimental results concerning the steady-state photoluminescence (PL) studies in n and p modulation doped and undoped GaInNAs/GaAs quantum wells are presented. The effects of modulation, type of doping and nitrogen concentration on the PL and the temperature dependence of the band gap, carrier localization and non-radiative recombination are investigated. Increasing the nitrogen composition decreases energy band gap as expected. The n-type modulation doping eliminates most of the defect-related effects and blue shifts the energy band gap. However, the p-type doping gives rise to additional features in the PL spectra and red shifts energy band gap further compared to the n-type-doped material.     

Contactless electroreflectance study of a GaAIAs/lnGaAs/ GaAs/GaAIAs step quantum well structure

Using contactless electroreflectance at 300 and 77K, we have studied the inter-subband transitions from a GaAlAs/InGaAs/GaAs/GaALAs step quantum well structure (small well inside a large well) consisting of two layers A (In_xGa_1−xAs) and B (GaAs) with widths L_A and L_B, respectively, bounded by two thick barrier regions of Ga_x Al_yAs. By comparison of the observed spectral features with an envelope function calculation, including the effects of strain, we have been able to characterize the potential profile of the structure, i.e., L_A, L_B, x, and y. There is very good agreement between experiment and the intended materials param-eters. Such configurations are of considerable importance since (a) they form the basis for pseudomorphic high electron mobility transistors, and (b) also have applications in optoelectronics due to their large Stark shifts.     

Characterization of InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistors

High-performance pseudomorphic InyGa1-yAs/Al0.15- Ga0.85As (0.05 le y le 0.2) MODFET's grown by MBE have been characterized at dc (300 and 77 K) and RF frequencies. Transconductances as high as 310 and 380 mS/mm and drain currents as high as 290 and 310 mA/mm were obtained at 300 and 77 K, respectively, for 1-µm gate lengths and 3-µm source-drain spacing devices. Lack of persistent trapping effects,I-Vcollapse, and threshold voltage shifts observed with these devices are attributed to the use of low mole fraction AlxGa1-xAs while still maintaining 2DEG concentrations of about 1.3 × 10¹²cm^-2. Detailed microwave S-parameter measurements indicate a current gain cut-off frequency Of 24.5 GHz Wheny = 0.20, which is as much as 100 percent better than similar GaAs/AlGaAs MODFET structures, and a maximum frequency of oscillation of 40 GHz. These superior results are in part due to the higher electron velocity of InGaAs as compared with GaAs. Velocity field measurement performed up to 3 kV/cm using the magnetoresistance method indicates an electron saturation velocity of greater than 1.7 × 10⁷cm/s at 77 K fory = 0.15, which is 20 percent higher than GaAs/AlGaAs MODFET's of similar structure.     

GaInAs/AlGaAs应变量子阱结构的荧光特性

本文报道了4—300K温度范围内量子阱宽度分别为20、40、90和130A的GaInAs/AlGaAs应变量子阱结构的光荧光特性。我们考虑量子尺寸对载流子子能带的影响和弹性应变引起带隙的移动,计算了量子阱中本征激子发光的能量位置,计算值与实验结果基本吻合。还研究了荧光峰强度随阱宽的变化以及不同温度下荧光峰的半高宽度。     

Optimization of buffer layers for AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors by atmospheric pressure metalorganic chemical vapor deposition

Pseudomorphic AlGaAs/InGaAs/GaAs high electron mobility transistors (HEMT) incorporating various types of buffer layers were fabricated (D = 0.50 × 100μm) and characterized by Hall-effect measurements, low temperature photoluminescence (PL), and room temperature IV characteristics. The devices fabricated with a thick (5000Å) undoped high purity GaAs buffer layer grown at 650° C showed poor pinch-off characteristics, high output conductance and large leakage currents (>2 mA at pinch-off). Devices incorporating an undoped high purity GaAs (3000Å) buffer layer grown at 550° C showed sharp pinch-off characteristics, low output conductance, and low leakage currents (1.3 mA at pinch-off). Low temperature growth of GaAs (550° C) enhanced carbon incorporation resulting in increasedp-type characteristics. This type of buffer layer provided additional barrier height between the active layer and the substrate reducing the injection of electrons into the substrate.     

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。     

Cathodoluminescence characteristics of pseudomorphic modulation-doped quantum well AlGaAs/InGaAs/AlGaAs heterostructures at high carrier densities and their radiation damaging

Cathodoluminescence characteristics of modulation-doped transistor heterostructures AlGaAs/InGaAs/AlGaAs with the width of quantum well ∼12 nm are investigated in this work. The investigation was conducted by means of cathodoluminescence generation depth changing; the depth depends on electron energy. This fact allows us to obtain cathodoluminescence characteristics from different depth of the investigated structure. The influence of γ-radiation with several doses on the cathodoluminescence spectra was examined. The text was submitted by the authors in English.     

Critical thickness of GaAs/InGaAs and AlGaAs/GaAsP strained quantum wells grown by organometallic chemical vapor deposition

In this paper we describe a study of strained quantum wells (QWs) as a means to experimentally observe the critical thickness (h _c) for the formation of interfacial misfit dislocations. Two material systems were investigated: GaAs/In_0.11Ga_0.89As, in which the QW layers are under biaxialcompression, and Al_0.35Ga_0.65As/GaAs_0.82P_0.18, in which the QW layers are under biaxialtension. Samples were grown by atmospheric pressure organometallic chemical vapor deposition, and characterized by low-temperature photoluminescence (PL), x-ray diffraction, optical microscopy, and Hall measurements. For both material systems, the observed onset of dislocation formation agrees well with the force-balance model assuming a double-kink mechanism. However, overall results indicate that the relaxation is inhomogeneous. Annealing at 800–850° C had no significant effect on the PL spectra, signifying that even layers that have exceededh _c and have undergone partial relaxation are thermodynamically stable against further dislocation propagation.     

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.     

Low-Temperature photoluminescence of SiGe/Si disordered multiple quantum wells and quantum well wires

Low-temperature photoluminescence from disordered SiGe/Si quantum wells and quantum wires made from periodic quantum wells by electron beam lithography and reactive ion etching has been measured. No enhancement in luminescence is seen, compared to that in periodic quantum wells, in the disordered wells or quantum wires. New transitions are observed in the wire luminescence, including a possible no-phonon transition exhibiting a 32 meV blue shift compared to the same transition in the wells.     

InGaAs/GaAs量子阱中自组装InAs量子点的光学性质

在InGaAs/GaAs量子阱中生长了两组InAs量子点样品,用扫描电子显微镜(SEM)测量发现,量子点呈棱状结构,而不是通常的金字塔结构,这是由多层结构的应力传递及InGaAs应变层的各向异性引起的.采用变温光致发光谱(TDPL)和时间分辨谱(TRPL)研究了其光致发光稳态和瞬态特性.研究发现,InGaAs量子阱层可以有效地缓冲InAs量子点中的应变,提高量子点的生长质量,可以在室温下探测到较强的发光峰.在量子阱中生长量子点可以获得室温下1 318 nm的发光,并且使其PL谱的半高宽减小到25 meV.     

GaAs／ALGaAs和InGaAs／GaAs窄量子阱中激子线宽与温度的关系

研究了具有不同阱宽的ＧａＡｓ／ＡｌＧａＡｓ和ＩｎＧａＡｓ／ＡｌＧａＡｓ窄量子阱结构中激子线宽与温度的关系，发现在低温范围内，声学声子的线性散射系统随着阱宽的减小而增加，对实验结果作了讨论。     

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.     

Critical layer thickness of strained-layer InGaAs/GaAs multiple quantum wells determined by double-crystal x-ray diffraction

Double-crystal x-ray diffraction (DCXD) is shown to reveal the onset of relaxation in strained-layer InGaAs/GaAs multiple quantum well (MQW) structures. The MQW structures contain 10 nm thick In_0.16Ga_0.84As quantum wells and 55 nm thick GaAs barrier layers. As the number of periods in the structure was increased from to 3 to 15, the x-ray rocking curves were characterized by increasing distortion of superlattice interference fringes, broadening of superlattice peaks, and reduction in peak intensity. The x-ray diffraction data are correlated with an asymmetric crosshatched surface pattern as observed under Nomarski contrast microscopy. By using DCXD and Nomarski microscopy, the onset of strain relaxation in InGaAs/GaAs MQW structures was established for samples with various GaAs barrier layer thicknesses. For MQW structures in which the thickness of the barrier layers is the same or greater than that of the strained quantum wells, the critical layer thickness can be calculated according to the Matthews and Blakeslee force-balance model with dislocation formation by the single-kink mechanism.     

Photoluminescence study of AlGaAs/GaAs/AlGaAs double quantum wells separated by a thin AlAs layer

Photoluminescence (PL) spectra of Al_0.21Ga_0.79As/GaAs/Al_0.21Ga_0.79As double quantum wells (DQWs) separated by a thin AlAs barrier have been studied in the temperature range 77–300 K. The well width was varied from 65 to 175 Å, and the thickness of the AlAs barrier was 5, 10, or 20 Å. In the case of a sufficiently thin (5, 10 Å) AlAs barrier, the energy spectrum of QW states is considerably modified by coupling between the QWs. This effect shifts the main spectral peak of PL, and specific features associated with the splitting of the ground state into symmetric and asymmetric states are observed in the spectra at higher temperatures. The DQW structure with a 20-Å-thick AlAs barrier is a system of two uncoupled asymmetric Al_0.21Ga_0.79As/GaAs/AlAs QWs. The energy levels in double coupled QWs were calculated as functions of the well width and AlAs barrier thickness, and good correlation with the experimentally observed energies of optical transitions was obtained.     

量子阱无序的窗口结构InGaAs/GaAs/AlGaAs量子阱激光器

对ＳｉＯ２薄膜在快速热退火条件下引起的空位诱导ＩｎＧａＡｓ／ＧａＡｓ应变量子阱无序和ＳｒＦ２薄膜抑制其量子阱无序的方法进行了实验研究。并将这两种技术的结合（称为选择区域量子阱无序技术）应用于脊形波导ＩｎＧａＡｓ／ＧａＡｓ／ＡｌＧａＡｓ应变量子阱激光器，研制出具有无吸收镜面的窗口结构脊形波导量子阱激光器。该结构３μｍ条宽激光器的最大输出功率为３４０ｍＷ，和没有窗口的同样结构的量子阱激光器相比，最大输出功率提高了３６％。在１００ｍＷ输出功率下，发射光谱中心波长为９７８ｎｍ，光谱半宽为１．２ｎｍ。平行和垂直方向远场发散角分别为７．２°和３０°     

Optical studies of acceptor centre doped GaAs/AlGaAs quantum wells

We present a theoretical and experimental study of the optical properties of acceptor centre doped quantum wells. We have performed theoretical calculations for the dependence of the band structure with doping level. Steady state photoluminescence and photoluminescence excitation results are compared with theoretical calculations involving exchange and correlation effects for the electron-hole system and the interaction between charge carriers and acceptor ions. We have studied the intensity, energy peak position, and broadening effects for excitons at doping level between 10⁸ and 10¹³ cm⁻². Theoretical calculations that only consider band filling effects are not sufficient to describe the effect on the band structure due to the doping. A much better agreement is achieved when exchange and correlation effects for the electron-hole system are taken into account. Excitons can still be detected at high hole concentrations, above the degenerated limit. They survive due to the inefficiency of screening in the two-dimensional system.