微微秒Al_xGa_(1-x)As双异质结激光器

用宽度为300微微秒的电脉冲驱动质子轰击条形的Al_xGa_(1-x)As双异质结激光器,产生12微微秒光脉冲。并已经用来检测快速光电二极管的响应速率。     

Strained-insulatorInxAl1-xAs/n+-In0.53Ga0.47As heterostructure field-effect transistors

In an effort to enhance the conduction band discontinuity between channel and insulator, In_xAl_1-xAs/n⁺-In _0.53Ga_0.47As heterostructure field-effect transistors (HFETs) were fabricated with InAs mole fractions in the In _xAl_1-xAs gate insulator of x=0.52 (lattice matching), 0.48, 0.40, and 0.30. Decreasing the InAs mole fraction in the insulator results in reduced forward- and reverse-bias gate currents, increased reverse gate breakdown voltage, and reduced real-space transfer of hot electrons from channel to gate. Down to x =0.40, these improvements trade off with a slightly reduced transconductance, but the gain in gate bias swing results in an increase in maximum current drivability. From x=0.40 to x=0.30, there is a drastic decrease in transconductance, coincident with a high density of misfit dislocations     

Modeling of short-pulse threshold voltage shifts due to DX centersin AlxGa1-xAs/GaAs and AlxGa1-xAs/InyGa1-yAs MODFET's

The DX-center-related short-pulse threshold voltage shifts (SPTVS) in Al_xGa_1-xAs-based MODFETs is modeled using CBAND, a simulator that solves Poisson equations self-consistently with Schrodinger equations and donor statistics. Using values given in the literature for the DX energy level in Al_xGa_1-xAs this technique gives good agreement between measured and simulated SPTVS for Al_0.3Ga_0.7As/GaAs and Al_0.3Ga_0.7As/In_0.2Ga_0.8As MODFETs. Both simulation and experiment show that the use of Al_0.2 Ga_0.8As in the donor layer reduces the SPTVS relative to the structures using Al_0.3Ga_0.7As. However, the measured shifts at this composition are considerably lower than the simulated values, indicating a DX energy level that may be higher than the value extrapolated from the literature, possibly due to the existence of multiple trap levels. Despite this discrepancy, these results support the use of strained-channel layers and lower Al_x Ga_1-xAs compositions in MODFETs for digital and other large-signal applications requiring good threshold stability     

Short pulse transfer characteristics of AlxGa1-xAs/GaAs andAlxGa1-xAs/InyGa1-yAsmodulation-doped heterojunction FET's

Short-pulse drain current versus gate voltage transfer characteristics measured for modulation-doped HFETs (MODFETs) with four donor-layer-channel-layer combinations-(1) Al_0.3Ga_0.7 As-GaAs, (2) Al_0.2Ga_0.8As-GaAs, (3) Al_0.3Ga_0.7As-In_0.2Ga_0.8As, and (4) Al_0.2Ga_0.8As-In_0.2 a_0.8 As-are compared with the DC transfer characteristics. The measurements are relevant to high-speed switching in HFET circuits. Significant shifts in threshold voltage are observed between the DC and short-pulse characteristics for the structures with n⁺-Al_0.3Ga_0.7As donor layers, while the corresponding shifts for structures with n⁺-Al_0.2Ga_0.8As donor layers are relatively small or virtually nonexistent     

Monte Carlo study of GaAs/Alx Ga1-xAsMODFETs: effects of AlxGa1-xAs composition

Monte Carlo methods are used to compare electronic transport and device behavior in n⁺-Al_xGa_1-xAs/GaAs modulation-doped field-effect transistors (MODFETs) at 300 K for x =0.10, 0.15, 0.22, 0.30, 0.35, and 0.40. The differences between the x=0.22 and x=0.30 MODFETs with respect to parasitic conduction in Al_xGa_1-xAs, gate currents, and switching times, are of particular interest. The donor-related deep levels in Al_xGa_1-xAs, are disregarded by assuming all donors to be fully ionized, and the focus is only on the confinement and transport of the carriers. The following quantities are studied in detail: transfer characteristics (I_D versus V _G), transconductance (g_m), switching speeds (τ_ON), parasitic conduction in Al_xGa _1-xAs, gate current (I_G), average electron velocities and energies in GaAs and Al_xGa_1-x As, electron concentration in the device domain, k-space transfer (to low mobility L and X valleys), and details of the real-space transfer process     

Temperature dependence of the ionization coefficients of AlxGa1-xAs

As Al_xGa_1-xAs alloys are increasingly used for microwave and millimeter wave power devices and circuits that work under high electric field intensities and junction temperatures; understanding the temperature dependence of impact ionization and related properties in this material system becomes more and more important. Measurements of the multiplication gain and noise of avalanche photodiodes (APDs) provide insight to the avalanche characteristics of semiconductors. Previously, we have reported the characteristics of GaAs and Al_0.2Ga_0.8As APD's at room temperature. In this paper, the gain and noise of a series of homojunction Al_xGa_1-xAs APD's were investigated over a wide temperature range from 29°C to 125°C, and the temperature dependence of their ionization coefficients was extracted     

A study of wet oxidized AlxGa1-xAs forintegrated optics

An investigation of wet oxidized Al_xGa_1-xAs layers in integrated optical applications is reported. Refractive index and thickness shrinkage of wet oxidized Al_xGa_1-xAs layers are measured using spectroscopic ellipsometry. A Cauchy fit to the refractive index is found in the wavelength range between 0.3 and 1.6 μm. The refractive index at 1.55 μm is found to be 1.66±0.01 with little dispersion around 1.55 μm. Very low loss single-mode waveguides with metal electrodes showing very low polarization dependence of loss coefficient are fabricated using wet oxidized Al_xGa_1-xAs layers as upper cladding. Optical polarization splitters are also designed and fabricated from the same type of waveguides taking advantage of increased birefringence. Designs utilizing wet oxidized Al_xGa_1-xAs are compared with conventional designs using only compound semiconductor heterostructures     

Femtosecond studies of intervalley scattering in GaAs and AlxGa1-xAs

Results are presented from ensemble Monte Carlo simulations of the relaxation of photoexcited electrons and holes. The results are compared directly with three types of femtosecond optical experiments: transient absorption saturation, pump and continuum probe, and tunable pump-probe experiments. For these experiments we find that intervalley scattering has a dominant effect for the first several hundred femtoseconds, and that electron-electron scattering is only important at later times.     

Fabrication of high-performance AlxGa1-xAs/InyGa1-yAs/GaAs resonant tunneling diodes using amicrowave-compatible technology

A microwave-compatible process for fabricating planar integrated resonant tunneling diodes (RTDs) is described. High-performance RTDs have been fabricated using Al_xGa_1-xAs/In_y Ga_1-yAs/GaAs strained layers. Peak-to-valley current ratios (PVRs) of 4.8:1 with simultaneous peak current densities of 4×10⁴ A/cm² have been achieved at room temperature for diodes of area 9 μm². Accurate measurements of reflection gain versus frequency between 1.5 and 26.5 GHz in the negative differential region indicate that the present technology is promising for millimeter-wave integrated circuits including self-oscillating mixers, frequency multipliers, and detectors     

Calculation of gain and noise with dead space for GaAs and AlxGa1-xAs avalanche photodiode

It is well known that, as a result of the nonlocal nature of impact ionization, the noise of avalanche photodiodes decreases as the thickness of the multiplication region is reduced. In this paper, we present an alternative technique to calculate the gain distribution, including the dead-space effect, by numerical solution of the recursive equations. This method yields the average gain, the multiplication noise, and gain distribution curves. The results are compared with simple Monte Carlo simulation and the Z-transform technique     

AlxGa1-xAs/GaAs异质结中电子迁移率的压力效应

对Al_xGa_1-xAs/GaAs半导体单异质结系统,引入有限高势垒与考虑导带弯曲的真实势，同时计入电子对异质结势垒的隧穿，利用变分法和记忆函数方法讨论在界面光学声子和体纵光学声子的散射下，异质结界面附近电子迁移率随温度的变化关系及其压力效应.结果显示：电子迁移率随温度、压力的增加而减小；且两种声子的散射作用均随压力增强，界面光学声子的变化幅度更大.因此，在讨论压力的情形下，界面光学声子的作用不容忽略.     

AlxGa1—xAs Solar Cell Grown by Multi—substrate Liquid Phase Epitaxy

A novel horizontal push-pull multi-substrate epitaxy boat with three separate cells is introduced in this article, with multi-substrate LPE processing is feasible in horizontal LPE furnace. The processes of LPE Alx Ga1-xAs/GaAs solar cells are studied and the efficiency of the solar cells achieved 19.8%(AM0,25℃,120mW/cm^2).     

Behavior of exciton in direct-indirect band gap AlxGa1-xAs crystal lattice quantum wells

Excitons have significant impacts on the properties of semiconductors.They exhibit significantly different properties when a direct semiconductor turns in to an indirect one by doping.Huybrecht variational method is also found to influence the study of exciton ground state energy and ground state binding energy in Al_xGa_1-xAs semiconductor spherical quantum dots.The Al_xGa_1-xAs is considered to be a direct semiconductor at AI concentration below 0.45,and...     

Rectification in AlxGa1-xAs-GaAs N-n heterojunction devices

The previously unsolved problem of rectification at Al_xGa_1-xAs-GaAs N-n heterojunction is found to originate from a vague concept regarding the maximum junction grading width which can sustain rectification. The theoretical current density vs voltage characteristics of this heterojunction system are derived from thermionic emission theory. It is found that, unless the impurity concentration of the AlGaAs layer (prepared by LPE techniques) is less than 10¹⁶ cm^?3, typical 90–200 Å metallurgical grading widths at the N-n heterojunction interface produce either ohmic or poorly rectifying characteristics. These results explain (1) the lack of rectification in most N-n Al_xGa_1-xAs-GaAs heterojunctions reported in the literature and (2) the recent observation of significant rectification in high purity (N)Al_0.3Ga_0.7As-(n)GaAs heterojunctions reported by Chandra and Eastman.     

Dislocation scattering in n-type modulation dopedAl0.3Ga0.7As/InxGa1-xAs/Al0.3Ga0.7As quantum wells

The mobility due to misfit dislocation scattering in n-type modulation doped Al_0.3Ga_0.7As/In_xGa_1-xAs/Al _0.3Ga_0.7As quantum wells is discussed. Initially, the dislocations are modeled as an array of orthogonal charged lines. The scattering potential is introduced, including both the coulombic and piezoelectric components. The expression for the mobility limited by dislocation scattering is established, and the anisotropic characteristics of mobility and its variation with various material and device parameters are presented and discussed     

60-GHz noise performance of ion-implanted InxGa1-xAs MESFET's

The authors report the 60-GHz noise performance of low-noise ion-implanted In_xGa_1-xAs MESFETs with 0.25 μm T-shaped gates and amplifiers using these devices. The device noise figure was 2.8 dB with an associated gain of 5.6 dB at 60 GHz. A hybrid two-state amplifier using these ion-implanted In_xGa_1-x As MESFETs achieved a noise figure of 4.6 dB with an associated gain of 10.1 dB at 60 GHz. When this amplifier was biased at 100% I _dss, it achieved 11.5-dB gain at 60 GHz. These results, achieved using low-cost ion-implantation techniques, are the best reported noise figures for ion-implanted MESFETs     

Minority electron transport anisotropy in p-type AlxGa1-xN/GaN superlattices

The minority electron diffusion length, L, in Mg-doped molecular beam epitaxy (MBE) grown p-type Al_xGa_1-xN/GaN superlattices with aluminum content x=0.1 and 0.2 was measured perpendicular and parallel to the superlattice planes by the electron beam induced current technique. A large anisotropy in the transport properties was observed with the effect varying from 1:3 to 1:6. We attribute an experimentally observed diffusion length anisotropy to minority electron scattering during transport across the potential barriers of the superlattice. Reference p-GaN samples were also investigated, and the diffusion length was observed to be isotropic in both MOCVD (L=0.5 μm) and MBE (L=0.27 μm) grown samples     

Numerical modeling of energy balance equations in quantum well AlxGa1-xAs/GaAs p-i-n photodiodes

The energy balance equations coupled with drift diffusion transport equations in heterojunction semiconductor devices are solved modeling hot electron effects in single quantum well p-i-n photodiodes. The transports across the heterojunction boundary and through quantum wells are modeled by thermionic emission theory. The simulation and experimental current-voltage characteristics of a single p-i-n GaAs/Al _xGa_1-xAs quantum well agree over a wide range of current and voltage, The GaAs/Al_xGa_1-xAs p-i-n structures with multi quantum wells are simulated and the dark current voltage characteristics, short circuit current, and open circuit voltage results are compared with the available experimental data, In agreement with the experimental data, simulated results show that by adding GaAs quantum wells to the conventional cell made of wider bandgap Al_x Ga_1-xAs, short circuit current is improved, but there is a loss of the voltage of the host cell, In the limit of radiative recombination, the maximum power point of an Al_0.35Ga_0.65As/GaAs p-i-n photodiode with 30-quantum-well periods is higher than the maximum power point of similar conventional bulk p-i-n cells made out of either host Al_0.35Ga_0.65As or bulk GaAs material     

Doping dependence of the properties of GaAsAlxGa1-xAs single heterostructure luminescent diodes

GaAs luminescent diodes with single heterostructure have been fabricated. The dependence of light power output and time behaviour on doping of the active layer has been investigated. An optimal doping of p = 2.5 × 10¹⁸ cm^?3 with respect to light power and 8 × 10¹⁸ cm^?3 with respect to the power bandwidth product has been achieved.