GaAs MESFET的热电子应力退化

进行GaAs MESFET的热电子应力试验,在24V≤VDS≤28V,-5．5≤VGS≤-4V的应力条件下,热电子效应将导致GaAs MESFET直流参数的严重退化。退化模式主要表现为饱和漏电流如s减小,跨导gn减小,夹断电压Vp增大,击穿电压增大。从微波性能方面来看,热电子效应器件的输出功率增益大幅度下降。退化机理主要是栅漏区表面及栅边缘俘获负电荷。     

Hot-electron magnetophonon resonances in doped and undoped GaAs/(Ga,Al)As quantum wells studied using photoluminescence

Hot-electron magnetophonon resonances in the effective temperature T_eff of photo-excited carriers in GaAs/Al_xGa_1-xAs quantum wells have been observed using photoluminescence for the first time. The technique has been demonstrated to be applicable to both doped and undoped structures, allowing the hot-electron magnetophonon effect in the latter to be studied. The experimental data are in good agreement with values of T_eff=T_eff(B) calculated using a modell or the energy relaxation of hot two-dimensional carriers in a strong magnetic field.     

The influence of composition and unintentional doping on the two-dimensional electron gas density in AlGaN/GaN heterostructures

We have studied the influence of Al content, AlGaN layer thickness, and unintentional background doping by oxygen on the two-dimensional electron gas (2DEG) density in AlGaN/GaN heterostructures. Hall measurements were made on samples grown with molecular beam epitaxy. The 2DEG densities in the range 2–3×10¹³ cm^?2 were measured. A one-dimensional Schrödinger-Poisson model was used to describe the heterostructure. The calculations gave two-dimensional electron densities in accordance with measured values. The electron density is very sensitive to the Al concentration in the AlGaN layer, whereas the sensitivity to layer thickness is small. Our simulations also showed that the two-dimensional concentration increased 50% when the free-carrier concentration changed from 10¹⁵ cm^?3 to 10¹⁸ cm^?3. The relation between donor concentration and free-carrier concentration was found to agree when using oxygen ionization energy as a parameter.     

偏置电压驱动下AlGaN/GaN二维电子气的宽谱太赫兹波发射

本文介绍了低温（6 K）下偏置电压加速AlGaN/GaN二维电子气产生的宽谱太赫兹波发射。根据“浅水波”等离子体波失稳理论和史密斯-珀塞尔理论,分别设计了两种器件结构。实验结果表明所观测到的太赫兹辐射与电子浓度无明显依赖关系,得到的而是自于晶格和热电子的黑体辐射。通过考虑湿度和衬底法布里-珀罗谐振腔作用,计算得到的热电子发射光谱与实验光谱良好吻合。研究结果表明通过电流驱动二维电子气产生太赫兹辐射的器件将不可避免地产生强烈的电子气加热和晶格加热问题,很难实现理论预言的等离子体波失稳与高效太赫兹发射。因此,需要设计更加精巧的器件结构才能实现高效的等离子体波激发和太赫兹发射。     

Tunable cyclotron resonance laser based on hot holes in germanium applied to FIR spectroscopy of GaAs/AlGaAs heterostructures

We have studied the stimulated far infrared (FIR) cyclotron resonance emission from the heavy holes in germanium. The emission spectrum consists of a single line which is linearly tunable by the magnetic field. We have measured the cyclotron resonance absorption of a GaAs/AlGaAs heterostructure using the stimulated cyclotron resonance emission as a light source for the first time. The photoconductive response of the GaAs/AlGaAs heterostructure is studied as a function of the magnetic field. We found that the photoconductive signal depends strongly on the filling factor.     

Full dynamic screening calculation of hot electron scattering rates in multicomponent semiconductor plasmas

The total scattering rate of a single energetic electron in the conduction band of GaAs in the presence of a non-equilibrium electron-hole plasma is calculated using different approximations for the screening effects of the free carriers. The best agreement with recent experimental results is obtained when full dynamic screening is taken account of (exactly within the random phase approximation), including the lattice polarizability.     

Interplay between the hot phonon effect and intervalley scattering on the cooling rate of hot carriers in GaAs and InP

The influence of hot phonon effect and intervalley scattering on the hot carrier cooling rate was investigated using femtosecond time‐resolved photoluminescence spectroscopy in bulk GaAs and InP, two electronically similar but vibrationally distinct semiconductors. In both materials, a broad photoluminescence signal that extends from the band gap energy to values larger than the pump pulse energy was observed during the first few picoseconds after photoexcitation, for different excitation energies (1.7, 1.88, and 2.4 eV) at high carrier densities (>10¹⁹ cm⁻³). Different hot carrier relaxation times were observed in GaAs and InP for different excitation energies, demonstrating the influence of intervalley scattering phenomena in GaAs. When electrons were not energetic enough to access satellite valleys, longer decay transients were observed for InP compared with GaAs. This provides experimental evidence of the hot phonon effect in InP. Temperature transients were calculated by analyzing the topography of the two‐dimensional spectra. Copyright © 2011 John Wiley & Sons, Ltd.     

Deposition of diamond from alcohol precursors in an electron cyclotron resonance plasma system

Microstructural control is a critical issue in the use of diamond films in a variety of engineering applications. Using a novel, electrostatic-based particle seeding process, we have investigated the deposition of diamond films with varying areal nucleation densities. Depositions were performed at low pressures (1.000 and 1.500 Torr) in a modified electron cyclotron resonance plasma system. Methyl alcohol was the primary diamond precursor species. Scanning electron microscopy and Raman spectroscopy were used to evaluate microstructure and composition characteristics. Comparisons in deposition characteristics were made based on relative nucleation density and gas-phase composition.     

Rashba spin splitting and cyclotron resonance in strained InGaAs/InP heterostructures with a two-dimensional electron gas

Cyclotron resonance and magnetic transport in InP/InGaAs/InP heterostructures with axially symmetric quantum wells are studied experimentally at 4.2 K. An increase in the cyclotron mass at the Fermi level from 0.047m ₀ to 0.057m ₀ with an increase in the concentration of two-dimensional electrons from 5.5 × 10¹¹ to 2.1 × 10¹² cm^?3 is shown. The values of the Rashba spin splitting at the Fermi level are determined from Fourier analysis of the beats of Shubnikov-de Haas oscillations. The obtained experimental data are compared with the theoretical results of self-consistent calculations of the energy spectrum and cyclotron masses of 2D electrons performed using the eight-band k · p Hamiltonian.     

Effects of electrode geometry and polarity on the occurrence of negative peaks in optical transient current spectroscopy applied to semi-insulating gallium arsenide

Optical transient current spectroscopy (OTCS) involves observing the transient decay of “photoconductivity” and is of interest as a means of characterizing semi-insulating GaAs wafers. We report experimental results which show that the OTCS spectrum and, in particular, the occurrence of negative peaks is strongly dependent on the shape, size and electrode configuration of the specimen, as well as on the magnitude of the applied voltage and (with asymmetric electrodes) its polarity. A negative peak sometimes changes to a current oscillation with increasing voltage, probably indicating field enhanced trapping. Negative peaks may be observed with sandwich structures with a transparent electrode covering the illuminated surface. This shows that a recent proposal that surface states are involved is at least not always correct. It is suggested that several mechanisms can give negative peaks, and probably more than one has done so under the various experimental conditions which have been used. The present work shows that any practical application of OTCS for ingot qualification will be dependent on standardization of specimen geometry, electrodes and operating parameters.     

Suppression of phonon‐mediated hot carrier relaxation in type‐II InAs/AlAsxSb1 − x quantum wells: a practical route to hot carrier solar cells

InAs/AlAs_xSb_{1 − x} quantum wells are investigated for their potential as hot carrier solar cells. Continuous wave power and temperature‐dependent photoluminescence indicate a transition in the dominant hot carrier relaxation process from conventional phonon‐mediated carrier relaxation below 90 K to a regime where inhibited radiative recombination dominates the hot carrier relaxation at elevated temperatures. At temperatures below 90 K, photoluminescence measurements are consistent with type‐I quantum wells that exhibit hole localization associated with alloy/interface fluctuations. At elevated temperatures, hole delocalization reveals the true type‐II band alignment, where it is observed that inhibited radiative recombination due to the spatial separation of the charge carriers dominates hot carrier relaxation. This decoupling of phonon‐mediated relaxation results in robust hot carriers at higher temperatures, even at lower excitation powers. These results indicate type‐II quantum wells offer potential as practical hot carrier systems. Copyright © 2016 John Wiley & Sons, Ltd.     

Electron mobility in two-dimensional electron gas in AIGaN/GaN heterostructures and in bulk GaN

We report on temperature dependencies of the electron mobility in the two-dimensional electron gas (2DEG) in AIGaN/GaN heterostructures and in doped bulk GaN. Calculations and experimental data show that the polar optical scattering and ionized impurity scattering are the two dominant scattering mechanisms in bulk GaN for temperatures between 77 and 500K. In the 2DEG in AIGaN/GaN heterostructures, the piezoelectric scattering also plays an important role. Even for doped GaN, with a significant concentration of ionized impurities, a large volume electron concentration in the 2DEG significantly enhances the electron mobility, and the mobility values close to 1700 cm²/Vs may be obtained in the GaN 2DEG at room temperature. The maximum measured Hall mobility at 80K is nearly 5000 cm²/Vs compared to approximately 1200 cm²/Vs in a bulk GaN layer. With a change in temperature from 300 to 80K, the 2DEG in our samples changes from nondegenerate and weakly degenerate to degenerate. Therefore, in order to interpret the experimental data, we propose a new interpolation formula for low field mobility limited by the ionized impurity scattering. This formula is valid for an arbitrary degree of the electron gas degeneracy. Based on our theory, we show that the mobility enhancement in the 2DEG is related to a much higher volume electron concentration in the 2DEG, and, hence, to a more effective screening.     

Liquid-phase deposition of thin Si and Ge films based on ballistic hot electron incidence

Using the reducing activity of ballistic hot electrons emitted from a nanocrystalline silicon (nc-Si) diode, it is demonstrated that thin Si and Ge films can be deposited under a situation that output electrons directly impinge upon a SiCl₄ or GeCl₄ solution-coated target substrate located in close proximity to the nc-Si emitter. After the electron incidence, uniform deposition of thin Si or Ge films was clearly observed in the irradiated area. In accordance with spectroscopic characterizations, no signs of contaminations were detected in deposited thin Si and Ge films, and those films exhibit features as oxidized nano-clusters. It is also shown that from a thermodynamic viewpoint, the output electron energy of the nc-Si emitter is suitable for promoting preferential reduction of target ions within the penetration depth in solutions followed by the nuclei formation.     

The role of oxygen in electron cyclotron resonance etching of silicon carbide

The electron cyclotron resonance (ECR) etching of silicon carbide (SiC) was studied using SF₆ + O₂ based plasma. The role of O₂ was studied by varying the O₂ flow rate while keeping the total gas flow constant. It was found that oxygen enhances the etch rate at low O₂ fraction through releasing more fluorine atoms, while lowers the etch rate at high O₂ fraction by diluting fluorine atoms and forming an oxide-like layer. The etched surface roughness was found to be affected by the surface oxidation and oxygen ion related physical ion bombardment. The role of oxygen in chemical etching of carbon was found to be insignificant. In general, the etched surface is smooth and free of micromasking effect that can arise from Al contamination and C rich layer.     

强场物理中超热电子能量沉积特性的实验研究

报道了在100 Tw超短脉冲掺钛蓝宝石激光装置上,完成的飞秒激光-固体靶相互作用中超热电子的能量沉积实验,获得了靶后激光传播方向超热电子的能谱、产额、注量和总能量.结果表明,超热电子的注量和总能量随靶厚的增加而减少,超热电子约80%的能量主要沉积在靶内的前10μm,分析其原因是由于静电场的影响所致.     

自由电子激光光导效应数值研究

本文对喇曼型自由电子激光光导效应进行了理论研究和数值模拟。我们编写了轴对称的二维计算机程序(FELOG),用来研究无波导和有波导情况下的光导效应。对光场分布、光场半径、填充因子及等效折射率等进行了模拟。根据实验参数进行的模拟结果与实验结果进行比较,它们符合很好。并对影响光导效应的因素进行了分析。     

Dry etching of III-V semiconductors in IBr/Ar electron cyclotron resonance plasmas

IBr/Ar plasmas were found to be promising candidates for room temperature dry etch processing of the III-V semiconductors GaAs, AlGaAs, GaSb, InP, InGaAs, and InSb. Results showed fast etch rates (～3,000Å/min) at high microwave power (1000W) and good surface morphology (typical root mean square roughness ～2 nm), while retaining the near-surface stoichiometry. There was little variation of surface smoothness over a wide range of plasma compositions for Gacontaining materials. By contrast, there was a plasma composition window of about 25–50% of IBr in IBr/Ar plasmas for maintaining good morphology of Incontaining semiconductors like InP. Etch rates of the semiconductors generally increased with microwave power (400-1000 W) and rf power (50-250 W), whereas there was little dependence of the rates on the increasing percentage of IBr in the IBr/Ar plasma composition above 30% IBr for In-based, and 50% IBr for Ga-based materials. Those results show the etch rates over 30% of IBr in IBr/ Ar are desorption-limited. Photoresist masks do not hold up well to the IBr under ECR conditions, resulting in poor profile control, whereas SiN_x offers much better etch resistance.     

Hot electron energy relaxation via acoustic phonon emission in GaAs/Al0.24Ga0.76As single and multiple quantum wells

The energy relaxation associated with acoustic phonons has been investigated in a series of modulation doped GaAs/AlGaAs single and multiple quantum wells grown by molecular beam epitaxy, using the hot electron Shubnikov — de Haas effect. The power loss is shown to be proportional to (T_e² − T_L²) for electron temperatures 2.2K < T_e < 8K and proportional to (T_e³ − T_L³) for 8K < T_e < 20K. The energy loss rates due to acoustic phonon scattering via both deformation potential coupling and piezoelectric coupling have been calculated. The total energy loss rate as a function of electron temperature is compared with the experimental results. Good agreement is obtained for 2.2K < T_e < 8K. Above 8K the energy loss rate is seen to rise above the predicted values, indicating the onset of an extra energy relaxation mechanism. The application of a high electric field (E = 3kV/cm) at low lattice temperatures is shown to induce persistent parallel conduction and a subsequent reduction of the low field well mobility.     

基于智能电子自旋共振仪的信号测量与监控系统

在研究基于智能电子自旋共振仪的普通高校近代物理实验上,设计了一种适合智能电子自旋共振仪的基于单片机和PC机的数据传输系统,并实现串口与嵌入式单片机数据透明传输的硬件连接和软件编程,实际效果表明该系统数据采集准确,并达到了实时监测实验数据的目的,同时系统自动生成图文并茂的实验报告,避免了手工输入时产生的误差。     

Polar optical phonon scattering of charge carriers in alloy semiconductors: Effects of phonon localization

The effects of spatial localization of phonons or their correlation functions to finite distances in alloy semiconductors on polar optical phonon scattering of hot carriers are modeled analytically. Despite the possibility of increased numbers of carrier-scattering-active phonon modes, it is demonstrated that phonon localization in alloys should have little if any effect on the total polar optical scattering rate for charge carriers coupled to equilibrium phonon populations. Further, it is demonstrated that phonon localization may have a beneficial effect on hot carrier transport by reducing the possibility of exciting nonequilibrium phonon populations. These results are obtained without assuming any specific functional form or degree of phonon localization; rather, calculations rely on the inherent orthogonality and mathematical completeness of the classical vibrational modes over the crystal lattice degrees of freedom.