Mobility of nondegenerate two-dimensional electrons in scattering by a correlated distribution of impurity ions

The temperature dependences of the inverse mobility of nondegenerate two-dimensional electrons in scattering by impurity ions in heterostructures with a narrow spacer have been investigated using the Al _x Ga_{1 ? x} As/GaAs heterostructure as an example. Correlations in the arrangement of impurity ions have been taken into account in the model of hard spheres on a plane. The influence of the form of the structure factor in the electron mobility has been considered.     

Influence of correlations in a flat distribution of impurity ions on the mobility of two-dimensional electrons at low temperatures

The temperature dependences of the electrical resistivity of degenerate two-dimensional electrons in scattering by impurity ions in heterostructures with a spacer of arbitrary width have been investigated using the Al _x Ga_{1 ? x} As/GaAs heterostructure as an example. Correlations in the arrangement of impurity ions have been taken into account in the model of hard spheres on a plane.     

Temperature features of electrical resistivity of two-dimensional electrons in scattering by a correlated distribution of impurity ions in doped thin layers

Spatial correlations of impurity ions in doped thin layers at finite temperatures have been considered in the model of hard spheres on a plane. It has been shown that, in systems with separate doping, the correlations in the arrangement of impurity ions are weakened by thermal motion of electrons at sufficiently low temperatures (below the liquid-helium temperature). The temperature dependences of the electrical resistivity of degenerate two-dimensional electrons in heterostructures with separate doping have been investigated using the Al _x Ga_{1 − x} As/GaAs heterostructure as an example.     

Mobility of two-dimensional electrons upon scattering by a correlated distribution of impurity ions

Correlation effects in the mobility of two-dimensional electrons upon scattering by a correlated distribution of impurity ions are described in the framework of the hard-sphere model. The theory is developed for the case of partially ionized impurity centers when correlations in the distribution of impurity ions are weakened as the result of a deficit of free positions for impurity holes. The calculations are performed for heterostructures with a wide spacer when small-angle scattering of electrons dominates.     

Density of states in the impurity d band and inelastic electron scattering by a system of mixed-valence iron ions in HgSe: Fe crystals

The resistivity and the Hall coefficient of HgSe: Fe crystals with various iron content are experimentally studied in the temperature range 1.3≤T≤300 K and in magnetic fields up to 60 kOe. The temperature dependences of the density and mobility of conduction electrons in these crystals are determined. The influence of spatial charge ordering in the system of mixed-valence iron ions on impurity states in HgSe: Fe crystals is considered. The density of states in the impurity d band is theoretically analyzed, and inelastic electron scattering in which bi-and trivalent iron ions are recharged is discussed. It is shown that the experimentally detected features in the dependence of the density and mobility of electrons on temperature and iron impurity content can be explained by the influence of Coulomb correlations in the mixed-valence iron ion system on the structure of the impurity d band.

     

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.     

n-Hg0.80Mg0.20Te界面积累层中二维电子气的输运特性研究

通过变磁场霍耳测量研究了MBE生长的Hg_0.80Mg_0.20Te薄膜在15 —250K温度范围内的输运特性.采用迁移率谱(MS)和多载流子拟合过程(MCF)相结合的方法对 实验数据进行了分析,由该方法获得的结果和Shubnikov de Hass(SdH)振荡测量的结果都证 明材料中存在二维(2D)电子和三维(3D)电子.其中2D电子主要来自于Hg_1-xMgxTe-CdTe的界面积累层或Hg_1-x关键词： 变磁场霍耳测量 界面积累层 二维电子气 1-xMg_xTe')" href="#">Hg_1-xMg_xTe     

ZnO高掺杂Ga的浓度对导电性能和红移效应影响的第一性原理研究

采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法,在相同环境条件下建立了浓度不同的由Ga原子取代Zn原子的Zn_1-xGa_xO模型.对低温高掺杂Ga原子的Zn_1-xGa_xO半导体的能带结构、态密度和吸收光谱进行了计算.结果表明:Ga原子浓度越大,进入导带的相对电子数越多,但是电子迁移率反而减小.通过对掺杂和未掺杂ZnO的电导率以及最小间隙带宽度分别进行了比较 关键词： ZnO高掺杂Ga 电导率 红移 第一性原理     

Impact of pressure on transport properties of AlGaN/GaN high electron mobility transistor

The properties of Al_xGa_1−xN/GaN high electron mobility transistor (HEMT) impacted by pressure are characterized quantitatively. The results indicate that the dislocation density increases as the critical thickness decreases with increasing pressure. The two-dimensional electron gas density was found to be linearly changeable with the pressure. A simulation has been completed to verify the influence of electron mobility. The results show that the misfit dislocation scattering induced by the pressure is a major limiting factor for the properties of HEMT.     

Mobility of 2D-electrons in scattering on a correlated distribution of impurity ions in doped thin layers

The spatial correlations of impurity ions in doped thin layers have been considered. A model of hard spheres on the plane has been developed for describing the correlations. In this model, an analytical expression has been obtained for the structure factor of 2D-electrons. The concentration dependences of the mobility of 2D-electrons in heterostructures with separate doping have been investigated using Al _x Ga_{1 − x} As/GaAs as an example.     

Raman scattering from the ferroelectric mode in the Pb5(Ge1−x,Six)3O11 system

We have observed the temperature dependence of the ferroelectric soft mode in the single crystals of Pb₅(Ge_1?x,Si_x)₃O₁₁ (x = 0.05 and 0.10) by means of the Raman scattering technique. The increasing of the amount of the silicon impurity lowers the soft mode frequency and influences the small change on the damping. The damping constant seems to be dominantly dependent upon the frequency. The experimental results have been well explained by considering the change of the short range harmonic force due to the silicon impurity.     

Alloy disorder scattering limited mobility of two-dimensional electron gas in the quaternary AlInGaN/GaN heterojunctions

Nitride heterojunction field effect transistors (HFETs) with quaternary AlInGaN barrier layers have achieved remarkable successes in recent years based on highly improved mobility of the two-dimensional electron gases (2DEGs) and greatly changed AlInGaN compositions. To investigate the influence of the AlInGaN composition on the 2DEG mobility, the quaternary alloy disorder (ADO) scattering to 2DEGs in AlInGaN/GaN heterojunctions is modeled using virtual crystal approximation. The calculated mobility as a function of AlInGaN alloy composition is shown to be a triangular-scarf-like curved surface for both cases of fixed thickness of AlInGaN layer and fixed 2DEG density. Though the two mobility surfaces are quite different in shape, both of them manifest the smooth transition of the strength of ADO scattering from quaternary AlInGaN to ternary AlGaN or AlInN. Some useful principles to estimate the mobility change with the Al(In,Ga)N composition in Al(In,Ga)N/GaN heterojunctions with a fixed 2DEG density are given. The comparison between some highest Hall mobility data reported for Al_xGa_1−xN/GaN heterojunctions (x=0.06~0.2) at very low temperature (0.3~13 K) and the calculated 2DEG mobility considering ADO scattering and interface roughness scattering verifies the influence of ADO scattering. Moreover, the room temperature Hall mobility data of Al(In,Ga)N/AlN/GaN heterojunctions with ADO scattering eliminated are summarized from literatures. The data show continuous dependence on Hall electron density but independence of the Al(In,Ga)N composition, which also supports our theoretical results. The feasibility of quaternary AlInGaN barrier layer in high conductivity nitride HFET structures is demonstrated.     

Influence of the Miniband Width on the Relaxation Time of Superlattice Electrons Scattered by Impurity Ions

Based on the Boltzmann equation, the influence of the miniband width on the relaxation time of nondegenerate electrons scattered by impurity ions in the GaAs/Al _x Ga_1–x As superlattice with doped quantum wells is numerically analyzed. The wave function being the eigenfunction of the ground state of the lower miniband of the superlattice is used to calculate the scattering probability. The dispersion of the longitudinal and transverse relaxation times versus the longitudinal wave vector is investigated.     

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     

Low temperature electron mobility in a coupled quantum well system

We study low temperature electron mobility μ_nin a GaAs/Al_x Ga _1 − xAs coupled double quantum well structure. Both the extreme barriers are δ -doped with Si so that the electrons diffuse into the adjacent wells forming two sheets of two-dimensional electron gas (2DEG) separated by a thin central barrier. The subband electron wavefunctions and energy levels are numerically obtained as a function of the well width, barrier width and doping concentration. The screening of ionized impurity potential by the 2D-electrons is obtained in terms of the static dielectric response function within the random phase approximation (RPA). μ_nis calculated by solving the coupled Boltzmann equation in the relaxation time approximation. The coupling of wavefunctions through the barrier, screening of ionized impurities and intersubband scattering effects on μ_nare investigated.     

Electron Transport Properties of Two-Dimensional Electron Gas in BexZn1−xO/ZnO Heterostructures

In this study, we have numerically investigated the conduction band structures, the carrier densities and the electron probability densities of pseudomorphic grown Be_xZn_1?xO/ZnO heterostructures using self-consistent solutions of one-dimensional, non linear Schrödinger–Poisson equations. In the calculations, two-dimensional electron gas (2DEG) formations were observed in the studied heterostructures and the effects of layer thickness and Be-mole fraction (x) of Be_xZn_1?xO barrier layer on 2DEG were described. For possible transistor device applications, 10 nm Be_xZn_1?xO barrier layer structure with x = 0.08 has been suggested. For this structure, we examined the variation of electron mobility with temperature using analytical calculations. Because of the polarization-induced low carrier densities, we found that the background impurity scattering has a strong effect on total electron mobility even at room temperature.     

Evidence for the spin-dependent scattering of conduction electrons on Mn2+ ions in Hg1−xMnxTe and Cd1−xMnxSe mixed crystals

Changes in the resistivity of Hg_1?xMn_xTe and Cd_1?xMn_xSe mixed crystals associated with paramagnetic resonance of the Mn²⁺ ions have been observed at liquid helium temperature in a strong magnetic field. The effect was recorded by monitoring the submillimeter radiation induced photoconductivity in a swept magnetic field. An increase in the resistivity associated with EPR of the Mn²⁺ ions is interpreted in terms of the spin- dependent scattering of electrons on magnetic impurities, the spins of which are selectively depolarised by means of paramagnetic resonance. Some additional effects influencing the experiments are also discussed.     

EPR study of exchange interactions in the nonmagnetic Kondo system La1−x CexCu6

The EPR of paramagnetic impurities Gd³⁺ and Mn²⁺ was studied in nonmagnetic Kondo system La_1−x Ce_xCu₆ containing in the 1.6–200 K range. The exchange interaction parameters of gadolinium and manganese ions with conduction electrons, of cerium ions with conduction electrons and with one another, the Kondo temperature of cerium ions, and the temperature behavior of cerium-ion spin-fluctuation rate have been determined. A pseudogap in the density of states at the Fermi level has been detected in the CeCu₆ regular system, which is apparently due to s-f hybridization. This pseudogap can be destroyed by introducing an aluminum impurity, which induces strong conduction-electron scattering. It was also found that RKKY interaction among manganese ions in CeCu_6−y Mn_y is considerably stronger than it is in LaCu_6−y Mn_y, which implies enhancement of nonlocal spin susceptibility due to an f band contribution to conduction-electron states. Fiz. Tverd. Tela (St. Petersburg) 40, 593–599 (April 1998)     

Observation of plasma and magnetoplasma resonances of two-dimensional electrons in a single MgZnO/ZnO heterojunction

The magnetoluminescence of the two-dimensional electron system in a single Mg _x Zn_{1 ? x} O/ZnO hetero-junction (x = 0.02) at a temperature of 0.3 K in magnetic fields up to 14 T has been studied. The concentration of two-dimensional electrons in the structure under study has been determined from the oscillations of the luminescence intensity as a function of the magnetic field. The value thus obtained is close to the one derived from transport measurements. The resonance corresponding to plasma excitations of two-dimensional electrons has been observed using optical detection of microwave absorption. In a magnetic field, the lower branch of magnetoplasma excitations, which corresponds to the propagation of edge magnetoplasmons in a structure with nearly square geometry, has been observed and investigated.     

Barrier D − complexes in a high-mobility two-dimensional electron system

The cyclotron excitation spectrum of selectively doped AlGaAs/GaAs quantum wells with a high (up to 2 × 10⁷ cm²/(V s)) mobility of electrons has been studied by means of the Raman scattering. The lines of the Raman scattering by the excitations of D ^? complexes, the objects in which two electrons localized in a quantum well are coupled to a charged impurity in a barrier, have been detected and identified. Spin-singlet D ^? complexes have been shown to exist in the entire range of the electron filling factor, from v → 0 to v = 2, owing to the specificity of the Coulomb interaction in two-dimensional systems. The excitation energies of the singlet D ^? complexes have been studied as functions of the electron density, quantum well width, and magnetic field.