Phonon-limited mobility in two-dimensional semiconductors with spin-orbit coupling

The authors demonstrate that the Rashba spin-orbit interaction in low-dimensional semiconductors can enhance or reduce the electron-phonon scattering rate by as much as 25%. The underlying mechanism is that the electron-phonon scattering phase space for the upper (lower) Rashba band is significantly enhanced (suppressed) by the spin-orbit interaction. While the scattering time decreases for the upper level, the mobility of the level increases due to an additional term in the electron velocity. (C) 2007 American Institute of Physics.

THEORETICAL INVESTIGATION OF THE DYNAMIC PROCESS OF THE ILLUMINATION OF GAAS

The dynamic process of light illumination of GaAs is studied numerically in this paper to understand the photoquenching characteristics of the material. This peculiar behavior of GaAs is usally ascribed to the existence of EL2 states and their photodriven metastable states. To understand the conductivity quenching, we have introduced nonlinear terms describing the recombination of the nonequilibrium free electrons and holes into the calculation. Though some photoquenching such as photocapacitance, infrared absorption, and electron-paramagnetic-resonance quenching can be explained qualitatively by only considering the internal transfer between the EL2 state and its metastability, it is essential to take the recombination into consideration for a clear understanding of the photoquenching process. The numerical results and approximate analytical approach are presented in this paper for the first time to our knowledge. The calculation gives quite a reasonable explanation for n-type semiconducting GaAs to have infrared absorption quenching while lacking photoconductance quenching. Also, the calculation results have allowed us to interpret the enhanced photoconductance phenomenon following the conductance quenching in typical semi-insulating GaAs and have shown the expected thermal recovery temperature of about 120 K. The numerical results are in agreement with the reported experiments and have diminished some ambiguities in previous works.

EXCIMER-LASER DOPING OF SPIN-ON DOPANT IN SILICON

Solid films containing phosphorus impurities were formed on p-type silicon wafer surface by traditional spin-on of commercially available dopants. The doping process is accomplished by irradiating the sample with a 308 nm XeCl pulsed excimer laser. Shallow junctions with a high concentration of doped impurities were obtained. The measured impurity profile was ''box-like'', and is very suitable for use in VLSI devices. The characteristics of the doping profile against laser fluence (energy density) and number of laser pulses were studied. From these results, it is found that the sheet resistance decreases with the laser fluence above a certain threshold, but it saturates as the energy density is further increased. The junction depth increases with the number of pulses and the laser energy density. The results suggest that this simple spin-on dopant pre-deposition technique can be used to obtain a well controlled doping profile similar to the technique using chemical vapor in pulsed laser doping process.

CALCULATION OF SPIN-REORIENTATION TEMPERATURE IN ND2FE14B

The spin-reorientation phenomenon in Nd2Fe14B has been investigated using an angular dependent free energy approach. A magnetic Hamiltonian which includes the crystal electric field term and the exchange term has been established using realistic band structure results. The temperature dependence of the molecular field is accounted for by introducing the Brillouin function and the magnetic Hamiltonian is diagonalized within the ground state multiplet of the Nd ion. The eigenstates are then used to form the partition function for the free energy. At each temperature, the direction of the molecular field is obtained by searching for the minimum in the angular parameter space of the free energy. Our calculations show that for Nd2Fe14B, the net magnetic anisotropy direction is canted away from the c axis at a temperature close to the experimentally reported spin-reorientation temperature of 150 K. The temperature dependence of the magnetic structure is found to be very sensitive to the size of the second order crystal field parameter B20.

Characteristics of InAs epilayers for Hall effect devices grown on GaAs substrates by MBE

InAs thin films with good characteristics were grown on GaAs (0 0 1) substrates by molecular beam epitaxy. Cross-sectional transmission electron microscopy indicated that most of the threading dislocations formed by the interaction of misfit dislocations are annihilated above a small thickness. The high electron mobility and small temperature dependence of InAs epilayers are useful for magnetic sensors which is demonstrated by the properties of Hall effect devices.

Cyclotron resonance and quantum Hall effect studies of the two-dimensional electron gas confined at the GaN/AlGaN interface

We report on high magnetic fields (up to 40 T) cyclotron resonance, quantum Hall effect and Shubnikov-de-Hass measurements in high frequency transistors based on Si-doped GaN-AlGaN heterojunctions. A simple way of precise modelling of the cyclotron absorption in these heterojunctions is presented, We clearly establish two-dimensional electrons to be the dominant conducting carriers and determine precisely their in-plane effective mass to be 0.230 +/- 0.005 of the free electron effective mass. The increase of the effective mass with an increase of two-dimensional carrier density is observed and explained by the nonparabolicity effect. (C) 1997 American Institute of Physics.

Effect of a step quantum well structure and an electric-field on the Rashba spin splitting

Spin splitting of conduction subbands in Al_(0.3)Ga_(0.7)As/GaAs/Al_xGa_(1-x)As/Al_(0.3)Ga_(0.7)As step quantum wells induced by interface and electric field related Rashba effects is investigated theoretically by the method of finite difference. The dependence of the spin splitting on the electric field and the well structure, which is controlled by the well width and the step width, is investigated in detail. Without an external electric field, the spin splitting is induced by an in terface related Rashba term due to the built-in structure inversion asymmetry. Applying the external electric field to the step QW, the Rashba effect can be enhanced or weakened, depending on the well structure as well as the direction and the magnitude of the electric field. The spin splitting is mainly controlled by the interface related Rashba term under a negative and a stronger positive electric field, and the contribution of the electric field related Rashba term dominates in a small range of a weaker positive electric field.A method to determine the interface parameter is proposed.The results show that the step QWs might be used as spin switches.

高线性度外延及注入GaAs Hall器件

讨论了外延及注入制作的薄层GaAs Hall器件如何获得高的磁线性度。GaAs Hall器件的磁线性度在高磁场下会有偏离，但可以通过外延及注入的过渡层对有源区进行补偿，在合适的有源区和过渡区的浓度和厚度分布中，可以得到在2.5T的强磁场下，±0.04%的高磁线性度。

半绝缘砷化镓Hall测量中的若干问题

建立了绝缘电阻大于10~(13)Ω和温度起伏小于0.1℃的半绝缘砷化镓Hall测量装置。研究了环境温度、湿度、漏电流、数据读取时间、测量电压、样品尺寸等因素对电阻率与迁移率的影响，并讨论了各种因素所引起的测量误差。