Polar optic phonon scattering of two dimensional electron gas in a rectangular potential well

The mobility of a two-dimensional electron gas (2DEG) in a rectangular potential well formed in a AlGaAs/GaAs/AlGaAs structure scattered by polar-optic phonon is calculated by an iterative solution of Boltzmann equation. The values are significantly different from those calculated by using a relaxation time. The polar-optic mobility is found to dominate over acoustic mobility over a temperature range of 100–300 K when the well thickness is about 10 nm. The mobility values for 2DEG are, however, found to be lower than the bulk values.     

Electron mobility in a modulation doped AlGaN/GaN quantum well

We consider a two dimensional electron gas confined to a modulation doped AlGaN/GaN quantum well and study the dependence of low field mobility on various parameters such as composition, well width, remote impurity and interface roughness as a function of temperature. GaN is assumed to be in the zincblende structure. Acoustic and optical phonon, ionized remote impurity and interface roughness scatterings are taken into account in mobility calculations. The scattering rates are calculated using the self-consistently calculated wave functions obtained from the numerical solution of Poisson and Schr?dinger equations. Also found from the self-consistent solutions are the potential profile at the junction, the energy levels in the well and electron concentrations in each level. Ensemble Monte Carlo method is used to find the drift velocities of the two dimensional electrons along the interface under an applied field. The mobility of two dimensional electrons is obtained from the drift velocity of electrons. It is found that while remote impurity scattering is very effective for small values of spacer layer and doping concentrations, increasing Al concentration reduces the mobility of electrons. The effect of surface roughness, on the other hand, on mobility is almost independent of well width. The results of our simulations are compatible with the existing experimental data.     

Determination of the LO phonon energy by using electronic and optical methods in AlGaN/GaN

The longitudinal optical (LO) phonon energy in AlGaN/GaN heterostructures is determined from temperature-dependent Hall effect measurements and also from Infrared (IR) spectroscopy and Raman spectroscopy. The Hall effect measurements on AlGaN/GaN heterostructures grown by MOCVD have been carried out as a function of temperature in the range 1.8-275 K at a fixed magnetic field. The IR and Raman spectroscopy measurements have been carried out at room temperature. The experimental data for the temperature dependence of the Hall mobility were compared with the calculated electron mobility. In the calculations of electron mobility, polar optical phonon scattering, ionized impurity scattering, background impurity scattering, interface roughness, piezoelectric scattering, acoustic phonon scattering and dislocation scattering were taken into account at all temperatures. The result is that at low temperatures interface roughness scattering is the dominant scattering mechanism and at high temperatures polar optical phonon scattering is dominant.     

Surface roughness scattering limited mobility of one dimensional electron gas in a narrow channel FET

An expression has been derived for the relaxation time due to surface roughness scattering of a one dimensional electron gas (1DEG) in a narrow channel FET. The bumps in the interface are assumed to have Gaussian autocorrelation. The values of mobility at low temperature are calculated for the 1DEG in GaAs HEMTs for different 1D densities and are compared with the values limited by phonon and impurity scattering. For moderate values of 1D density, surface roughness scattering is as important as the impurity scattering. A rough estimate of the effect of screening on the values of mobilities is also made.     

Electron mobility variance in the presence of an electric field: Electron–phonon field-induced tunnel scattering

The problem of electron mobility variance is discussed. It is established that in equilibrium semiconductors the mobility variance is infinite. It is revealed that the cause of the mobility variance infinity is the threshold of phonon emission. The electron–phonon interaction theory in the presence of an electric field is developed. A new mechanism of electron scattering, called electron–phonon field-induced tunnel (FIT) scattering, is observed. The effect of the electron–phonon FIT scattering is explained in terms of penetration of the electron wave function into the semiconductor band gap in the presence of an electric field. New and more general expressions for the electron–non-polar optical phonon scattering probability and relaxation time are obtained. The results show that FIT transitions have principle meaning for the mobility fluctuation theory: mobility variance becomes finite.     

Phonon Limited Electron Mobility in Germanium FinFETs:Fin Direction Dependence

We investigate the phonon limited electron mobility in germanium(Ge) fin field-effect transistors(FinFETs)with fin rotating within(001),(110),and(111)-oriented wafers. The coupled Schrodinger-Poisson equations are solved self-consistently to calculate the electronic structures for the two-dimensional electron gas, and Fermi's golden rule is used to calculate the phonon scattering rate. It is concluded that the intra-valley acoustic phonon scattering is the dominant mechanism limiting the electron mobility in Ge FinFETs. The phonon limited electron motilities are influenced by wafer orientation, channel direction, in thickness Wfin, and inversion charge density Ninv. With the fixed Wfin, fin directions of(110),(112) and(110) within(001),(110), and(111)-oriented wafers provide the maximum values of electron mobility. The optimized for mobility is also dependent on wafer orientation and channel direction. As Ninv, increases, phonon limited mobility degrades, which is attributed to electron repopulation from a higher mobility valley to a lower mobility valley as Ninv increases.     

Relaxation processes and mobility of electrons in a semiconductor quantum well with the modified Pöschl-teller confining potential

Relaxation processes and mobility of electrons in a semiconductor quantum well are studied. The modified Pöschl-Teller potential is used as a confining potential. Scattering rates due to impurity ions, acoustic and piezoacoustic phonons are calculated taking into account the screening of scattering potentials by charge carriers. It is shown that when degenerate electrons are scattered by acoustic phonons, the dependence of scattering rate on electron wave number ν_ac(k) is almost linear. At small k, the acoustic phonon piezoelectric scattering rate of degenerate electrons increases with k, and then it decreases slightly when k > 8 × 10⁷ m⁻¹. The ionized impurity scattering rate of degenerate electrons does not depend on temperature, is directly proportional to the electron density, and decreases with increasing k. Dependences of electron mobility on surface ion density and temperature are studied. It is shown that in the case of non-degenerate or slightly degenerate electron gas, a maximum appears in the temperature dependence of the mobility, and the screening effect is negligible. The screening significantly increases the mobility of electrons in the case of high degeneration. Obtained results are applied to GaAs-based quantum wells.     

The frequency dependence of phonon interactions at Terahertz-frequencies studied by time-resolved phonon spectroscopy

Phonon properties concerning propagation, frequency spectrum and lifetime in the Terahertz range have been investigated. The phonons have been produced by square wave Joule heating of thin constantan films evaporated onto a strongly doped ruby. Cross sections for phonon scattering at the Cr³⁺ impurity ions of the ruby were determined as a function of frequency. The theoretical estimate for mass defect scattering given by Klemens [9] is found to agree reasonably with the experimental results. Lifetime measurements indicate that phonons in ruby preferentially propagate in the transversal mode. Phonon frequency spectra in the constantan films were measured under experimental conditions, where the strength of electron phonon coupling is significant; thus electron-phonon relaxation times could be obtained as a function of frequency.     

Fang–Howard wave function modelling of electron mobility in AlInGaN/AlN/InGaN/GaN double heterostructures

To study the electron transport properties in InGaN channel-based heterostructures,a revised Fang-Howard wave function is proposed by combining the effect of GaN back barrier.Various scattering mechanisms,such as dislocation impurity(DIS) scattering,polar optical phonon(POP) scattering,piezoelectric field(PE) scattering,interface roughness(IFR) scattering,deformation potential(DP) scattering,alloy disorder(ADO) scattering from InGaN channel layer,and temperature-dependent energy bandgaps are considered in the calculation model.A contrast of AlInGaN/AlN/InGaN/GaN double heterostructure(DH) to the theoretical AlInGaN/AlN/InGaN single heterostructure(SH) is made and analyzed with a full range of barrier alloy composition.The effect of channel alloy composition on InGaN channel-based DH with technologically important Al(In,Ga)N barrier is estimated and optimal indium mole fraction is 0.04 for higher mobility in DH with Al_(0.4)In_(0.07)Ga_(0.53)N barrier.Finally,the temperature-dependent two-dimensional electron gas(2 DEG) density and mobility in InGaN channel-based DH with Al_(0.83)In_(0.13)Ga_(0.0)4 N and Al_(0.4)In_(0.07)Ga_(0.53)N barrier are investigated.Our results are expected to conduce to the practical application of InGaN channel-based heterostructures.     

Polaronic Effects on the Impurity Binding Energy in a Polar Crystal Slab Within an Electric Field

The effects of the interaction between electron and bulk longitudinal optical (LO) phonon and surface optical (SO) phonon on the impurity binding energy of the ground state in a polar crystal slab within an external electric field are derived by using the method of a variational wavefunction. The binding energy of the bound polaron is obtained as a function of the impurity position, the slab thickness and the electric field strength. It is found that the polaronic correction to the impurity binding energy by the SO phonon may be enhanced and that by the LO phonon may be reduced with increasing electric field strength. And the effect of the electron-phonon interaction is quite important in increasing the values of binding energy.     

应变Si/(001)Si1-xGex电子迁移率

依据离化杂质散射、声学声子散射和谷间散射的散射模型,在考虑电子谷间占有率的基础上,通过求解玻尔兹曼方程计算了不同锗组分下,不同杂质浓度时应变Si/(001)Si_1-xGe_x的电子迁移率.结果表明:当锗组分达到0.2时,电子几乎全部占据Δ₂能谷;低掺杂时,锗组分为0.4的应变Si电子迁移率与体硅相比增加约64%;对于张应变Si NMOS器件,从电子迁移率角度来考虑不适合做垂直沟道.选择相应的参数,该方 关键词： 电子谷间占有率 散射模型 锗组分 电子迁移率     

SiC电子输运特性的Monte Carlo数值模拟

利用系综MonteCarlo法研究了2H ,4H和6HSiC的电子输运特性.在模拟中考虑了对其输运过程有着重要影响的声学声子形变势散射、极化光学声子散射、谷间声子散射、电离杂质散射以及中性杂质散射.通过计算,获得了低场下这几种不同SiC多型电子迁移率同温度的关系,并以4H SiC为例,重点分析了中性杂质散射的影响.最后对高场下电子漂移速度的稳态和瞬态变化规律进行了研究.将模拟结果同已有的实验数据进行了比较,发现当阶跃电场强度为10×106V·cm-1时,4H Sic电子横向瞬态速度峰值接近33×107cm·s^-1,6H Sic接近30×107cm·s^-1.     

The effect of interface roughness scattering on low field mobility of 2D electron gas in GaN/AlGaN heterostructure

We report the results of our experimental and theoretical studies concerning the temperature dependence of electron mobility in a two dimensional electron gas (2DEG) confined at the GaN/AlGaN interface. Experimental mobility of about at 3.8 K remains almost constant up to lattice temperature , it then decreases rapidly down to about at . The results are discussed using a theoretical model that takes into account the most important scattering mechanisms contributing to determine the mobility of electrons in 2DEG. We show that the polar optical phonon scattering is the dominant mechanism at high temperatures and the acoustic deformation potential and piezoelectric scatterings are dominant at the intermediate temperatures. At low temperatures, the Hall mobility is confined by both the interface roughness (IFR) and ionised impurity scattering. The correlation length (Λ) and lateral size (Δ) of roughness at the GaN/AlGaN heterointerface have been determined by fitting best to our low-temperature experimental data.     

Electron mobility for a model Al<Subscript>x</Subscript> Ga<Subscript>1-x</Subscript> As/GaAs heterojunction under pressure

A variational method and a memory function approach are adopted to investigate the electron mobility parallel to the interface for a model Al_xGa_1-xAs/GaAs heterojunction and its pressure effect by considering optical phonon modes (including both of the bulk longitudinal optical (LO) in the channel side and interface optical (IO) phonons). The influence of a realistic interface heterojunction potential with a finite barrier and conduction band bending are taken into account. The properties of electron mobility versus Al concentration, electronic density and pressure are given and discussed, respectively. The results show that the electron mobility increases with Al concentration and electronic density, whereas decreases with pressure from 0 to 40 kbar obviously. The Al concentration dependent and the electron density dependent contributions to the electron mobility from the scattering of IO phonons under pressure becomes more obvious. The variation of electron mobility with the Al concentration and electron density are dominated by the properties of IO and LO phonons, respectively. The effect of IO phonon modes can not be neglected especially for higher pressure and electronic density.     

纤锌矿相GaN空穴输运特性的Monte Carlo模拟研究

用全带多粒子Monte Carlo方法模拟纤锌矿相(Wurtzite)GaN空穴输运特性的结果. 用经验赝势法计算得到能带结构数据. 模拟包含了声学声子散射，光学声子散射，极性光学声子散射，压电散射，电离杂质散射及带间散射等散射机理. 计算得到了空穴沿3个主要对称方向上的空穴平均漂移速度和平均能量与电场强度的关系曲线，室温下漂移速度呈现饱和特性. 在所研究的电场范围内，最大平均漂移速度约为6×10⁶cm s^-1，最大空穴平均能量约为0.12eV, 这些值均比电子的相应参数低很多. 还给出了空穴的扩散迁移率与杂质浓度关系的模拟结果. 关键词： 蒙特卡罗 氮化镓 输运特性 能带结构     

Lattice-controlled electron transport characteristics in quantized surface layers at low temperature

A theory of intravalley acoustic scattering of the carriers in a non-degenerate two-dimensional electron gas is developed here under the condition of low lattice temperature when the assumptions of the well-known traditional theory are not valid. The scattering rates thus obtained are then used to estimate the zero-field mobility characteristics in an n-channel Si inversion layer. It is found that the finite energy of the phonons makes the energy and lattice temperature dependence of the scattering rate, and consequently the lattice temperature dependence of the mobility, significantly different from what follows, in the light of traditional theory which assumes equipartition law for the phonon distribution and neglects the phonon energy in comparison to the carrier energy.     

Electron transport in wurtzite InN

Using ensemble Monte Carlo simulation technique, we have calculated the transport properties of InN such as the drift velocity, the drift mobility, the average electron, energy relaxation times and momentum relaxation times at high electric field. The scattering mechanisms included scattering mechanisms are polar optical phonon, ionized impurity, acoustic phonon and intervalley phonon. It is found that the maximum peak velocity only occurs when the electric field is increased to a value above a certain critical field. This critical field is strongly dependent on InN parameters. The steady-state transport parameters are in fair agreement with other recent calculations.     

Electron scattering in CdxHg1−xTe

Experimental studies of the electron mobility in Cdinx,Hgin1?xTe/0x/0.33, 10¹⁵ cm^?3n10¹⁸ cm^?3, 4.2 K ?T ?300 K/and of the thermoelectric power of intrinsic HgTe from 300 K down to 5 K are reported. These results are interpreted in terms of calculations based on the variational solution of the Boltzmann equation. Analysis shows that in pure samples at low temperatures, the electron mobility is limited by ionized donors, heavy holes, and, in some cases, unresolved defect scattering. In the doped samples with x0&#x0306;.1, disorder scattering also becomes significant. Polar-optical phonon scattering is dominant at high temperatures. The sharp decrease of mobility in the region 20–40 K, which occurs for pure samples with x0&#x030C;.14, is explained by interband optical phonon scattering. The thermoelectric power of intrinsic HgTe is strongly affected by phonon-drag of holes at low temperatures and by electron-electron scattering at high temperatures.     

Variational treatment for the dynamical pseudo Jahn-Teller system

We present a variational treatment for the E × e pseudo Jahn-Teller system. Through canonical transformation the electron and phonon states are decoupled. An analytical form is obtained for the ground state energy by scaling transformation. Including both the dynamical displacement of phonon modes and the softening of phonon frequency, this approach yields fairly accurate results for the ground state energy. The energy splitting and Ham's reduction factor are calculated, which also generates fairly good results compared with other perturbation results. We argue that our variational wave function is valid for the weak and intermediate coupling range.     

Carrier mobility and relaxation time in BiCuSeO

To obtain thermoelectric properties of materials, a constant relaxation time approximation is generally employed. By employing deformation potential theory, a derivation of relaxation time and carrier mobility of BiCuSeO system is proposed combining with density functional theory calculation. And the inter-valley scattering, acoustic phonon scattering and ionized impurity scattering were considered in the model. The calculated values of relaxation time and carrier mobility in BiCuSeO are in good agreement with the results of experiment. The results suggest that acoustic phonon scattering is in dominant and the constant relaxation time approximation is reasonable in lightly doped sample, and the ionized impurity scattering play a significant role in heavily doped system.