Binding Energies of Screened Excitons in a Strained(111)-Oriented Zinc-Blende GaN/AlGaN Quantum Well Under Hydrostatic Pressure

We investigate the binding energies of excitons in a strained （111）-oriented zinc-blende GaN/Al0.3 Ga0.7 N quantum well screened by the electron-hole （e-h） gas under hydrostatic pressure by combining a variational method and a selfconsistent procedure. A built-in electric field produced by the strain-induced piezoelectric polarization is considered in our calculations. The result indicates that the binding energies of excitons increase nearly linearly with pressure,even though the modification of strain with hydrostatic pressure is considered, and the influence of pressure is more apparent under higher e-h densities. It is also found that as the density of an e-h gas increases,the binding energies first increase slowly to a maximum and then decrease rapidly when the e-h density is larger than about 1 ×10^11 cm^-2. The excitonic binding energies increase obviously as the barrier thickness decreases due to the decrease of the built-in electric field.

Screening influence on the Stark effect of impurity states in strained wurtzite GaN/Al_xGa_(1-x)N heterojunctions under pressure

The screening effect of the random-phase-approximation on the states of shallow donor impurities in free strained wurtzite GaN/AlxGa1-xN heterojunctions under hydrostatic pressure and an external electric field is investigated by using a variational method and a simplified coherent potential approximation. The variations of Stark energy shift with electric field, impurity position, A1 component and areal electron density are discussed. Our results show that the screening dramatically reduces both the blue and red shifts as well as the binding energies of impurity states. For a given impurity position, the change in binding energy is more sensitive to the increase in hydrostatic pressure in the presence of the screening effect than that in the absence of the screening effect. The weakening of the blue and red shifts, induced by the screening effect, strengthens gradually with the increase of electric field. Furthermore, the screening effect weakens the mixture crystal effect, thereby influencing the Stark effect. The screening effect strengthens the influence of energy band bending on binding energy due to the areal electron density.

Study on Valence Band Offsets atStrained Heterojunctions

A method, which can predict the valence band offsets at strained layer heterojunctions under different strain situations only by calculating band structures and deformation parameters of the bulk materials, is suggested. The applicability of this method is verified by calculation of the valence band offsets at strained layer heterojuntions ,such as InP/InAs, InP/GaP, GaAs/InAs, GaP/GaAs and AlAs/InAs with various strain conditions.

Strain-Modulated Photoelectric Responses from a Flexibleα-In_(2)Se_(3)/3R MoS_(2)Heterojunction

Semiconducting piezoelectricα-In_(2)Se_(3) and 3R MoS_(2) have attracted tremendous attention due to their unique electronic properties.Artificial van der Waals(vdWs)hetero-structures constructed withα-In_(2)Se_(3)and 3R MoS_(2)flakes have shown promising applications in optoelectronics and photocatal-ysis.Here,we present the first flexibleα-In_(2)Se_(3)/3R MoS_(2)vdWs p-n heterojunction devices for photodetection from the visible to near infrared region.These heterojunction devices exhibit an ultrahigh photoresponsivity of 2.9×10^(3)A W^(−1) and a substantial specific detectivity of 6.2×10^(10) Jones under a compressive strain of−0.26%.The photocurrent can be increased by 64%under a tensile strain of+0.35%,due to the heterojunction energy band modulation by piezoelectric polarization charges at the hetero-junction interface.This work demonstrates a feasible approach to enhancement of α-In_(2)Se_(3)/3R MoS_(2) photoelectric response through an appropriate mechanical stimulus.

Modulation of Schottky barrier in XSi_(2)N_(4)/graphene(X=Mo and W)heterojunctions by biaxial strain

Reducing the Schottky barrier height(SBH)and even achieving the transition from Schottky contacts to Ohmic contacts are key challenges of achieving high energy efficiency and high-performance power devices.In this paper,the modulation effects of biaxial strain on the electronic properties and Schottky barrier of Mo Si_(2)N_(4)(MSN)/graphene and WSi_(2)N_(4)(WSN)/graphene heterojunctions are examined by using first principles calculations.After the construction of heterojunctions,the electronic structures of MSN,WSN,and graphene are well preserved.Herein,we show that by applying suitable external strain to a heterojunction stacked by MSN or WSN—an emerging two-dimensional(2D)semiconductor family with excellent mechanical properties—and graphene,the heterojunction can be transformed from Schottky ptype contacts into n-type contacts,even highly efficient Ohmic contacts,making it of critical importance to unleash the tremendous potentials of graphene-based van der Waals(vd W)heterojunctions.Not only are these findings invaluable for designing high-performance graphene-based electronic devices,but also they provide an effective route to realizing dynamic switching either between n-type and p-type Schottky contacts,or between Schottky contacts and Ohmic contacts.

Temperature effects on interface polarons in a strained(111)-oriented zinc-blende GaN/AlGaN heterojunction under pressure

The properties of interface polarons in a strained （111）-oriented zinc-blende GaN/AlxGa1-xN heterojunction at finite temperature under hydrostatic pressure are investigated by adopting a modified LLP variational method and a simplified coherent potential approximation. Considering the effect of hydrostatic pressure on the bulk longitudinal optical phonon mode, two branches interface-optical phonon modes and strain, respectively, we calculated the polaronic self-trapping energy and effective mass as functions of temperature, pressure and areal electron density. The numerical result shows that both of them near linearly increase with pressure but the self-trapping energies are nonlinear monotone increasing with increasing of the areal electron density. They are near constants below a range of temperature whereas decrease dramatically with increasing temperature beyond the range. The contributions from the bulk longitudinal optical phonon mode and one branch of interface optical phonon mode with higher frequency are important whereas the contribution from another branch of interface optical phonon mode with lower frequency is extremely small so that it can be neglected in the further discussion.

PHOTOLUMINESCENCE STUDIES OF In_(0.25)Ga_(0.75)As-GaAs STRAINED QUANTUM WELLS UNDER HIGH PRESSURE

We report the results of the photoluminescence(PL)studies of the Ino.jsGao.r$As-GaAs strained quantum wells(QW’s)at 77K and at high pressures up to 5Okbar.The pressure coefficients of the T valley of(InGa)As-GaAs strained QW’s are presented for the first time.The crossover between the energy level in the well and the X valley in the barrier GaAs has been observed.The ratio of the conduction band offset to valence band offset in In_(0.25)Ga_(0.75)As-GaAs heterojunction was determined to be Qc=ΔEc:ΔEv=0.68:0.32.Some discussions about GaAs-Al0.3Ga0.7As QW’s are also presented.

Epitaxial quasi-2D/3D hybrid perovskite heterojunctions for photodetector with enhanced detectivity and stability

Although numerous metal halide perovskite materials have been investigated in the field of optoelectronic,the development of perovskite heterojunctions with exotic structures is still rare.Herein,we report the epitaxial growth of quasi-two-dimensional(Q-2D)perovskites on methylammonium lead iodide(MAPbI_(3))single crystals to form perovskite heterojunctions with interfacial bonding.The MAPbI_(3)adjacent to epitaxial Q-2D perovskite shows blue shifted photoluminescence with shortened lifetime,which becomes significant with the reduced layer number of the Q-2D perovskites.Our findings suggest the presence of an interfacial strain gradient leading to enhanced photocarrier separation.Accordingly,compared to the MAPbI_(3)single crystal detector,the BA_(2)MAPb_(2)I_(7)/MAPbI_(3)(BA:n-butylamine)heterojunction-based photodetector demonstrates a bandpass detecting property and exhibits 5 times enhanced external quantum efficiency and 83 times enhanced specific detectivity(D*=3.26×10^(11)Jones).Remarkably,the unencapsulated BA_(2)MAPb_(2)I_(7)/MAPbI_(3)heterojunction is stable in ambient condition for>300 days.The Q-2D/3D heterojunction shows suppressed ion inter-diffusion due to the presence of Q-2D phase.

应变诱导二维SnSe/SnS范德华异质结的光电性质

二维材料具有非常优异的性能,这使其在材料物理领域具有广泛的研究价值.该文基于第一性原理方法研究计算了单层SnSe和单层SnS以及SnSe/SnS范德华异质结的电子性质和光学性质.单层SnSe和单层SnS的带隙分别为0.95 eV和1.46 eV间接带隙半导体,而SnSe/SnS异质结的带隙为0.47 eV间接带隙半导体,带隙明显低于其单层材料.SnSe/SnS异质结与其单层材料相比,具有更优异的光学性质,其介电函数虚部和光吸收系数远远大于单层材料.该文还研究了在不同类型应变下SnSe/SnS异质结的电子性质和光学性质的变化规律.单轴应变和双轴应变能够有效地调控SnSe/SnS的光电性质.研究表明,相较于a轴应变和b轴应变,双轴应变的调控效果更为显著.在双轴应变下,SnSe/SnS异质结的能带有从间接带隙到直接带隙的转变.通过应变调控可以增强SnSe/SnS异质结的光吸收系数.该研究为获得更好的电子和光学特性的材料提供了思路.研究证明SnSe/SnS范德华异质结在光电器件领域具有潜在的应用价值.

Influence of optical phonons on the electronic mobility in a strained wurtzite AlN/GaN heterojunction under hydrostatic pressure

A variational method combined with solving the force balance equation is adopted to investigate the influence of strain and hydrostatic pressure on electronic mobility in a strained wurtzite AlN/GaN heterojunction by considering the scattering of optical-phonons in a temperature ranges from 250 to 600 K. The effects of conduction band bending and an interface barrier are also considered in our calculation. The results show that electronic mobility decreases with increasing hydrostatic pressure when the electronic density varies from 1.0 × 1012 to 6.5 × 1012 cm-2. The strain at the heterojunction interface also reduces the electronic mobility, whereas the pressure influence becomes weaker when strain is taken into account. The effect of strain and pressure becomes more obvious as temperature increases. The mobility first increases and then decreases significantly, whereas the strain and hydrostatic pressure reduce this trend as the electronic density increases at a given temperature （300 K）. The results also indicate that scattering from half space phonon modes in the channel side plays a dominant role in mobility.

Skyrmion transport driven by pure voltage generated strain gradient

The magnetic skyrmion transport driven by pure voltage-induced strain gradient is proposed and studied via micromagnetic simulation.Through combining the skyrmion with multiferroic heterojunction,a voltage-induced uniaxial strain gradient is adjusted to move skyrmions.In the system,a pair of short-circuited trapezoidal top electrodes can generate the symmetric strain.Due to the symmetry of strain,the magnetic skyrmion can be driven with a linear motion in the middle of the nanostrip without deviation.We calculate the strain distribution generated by the trapezoidal top electrodes pair,and further investigate the influence of the strain intensity as well as the strain gradient on the skyrmion velocity.Our findings provide a stable and low-energy regulation method for skyrmion transport.

Pressure influence on bound polarons in a strained wurtzite GaN/Al_xGa_(1_x)N heterojunction under an electric field

The binding energies of bound polarons near the interface of a strained wurtzite GaN/Al_xGa_（1-x）N het-erojunction are studied by using a modified LLP variational method and a simplified coherent potential approximation under hydrostatic pressure and an external electric field.Considering the biaxial strain due to lattice mismatch or epitaxial growth,the uniaxial strain effects and the influences of the electron-phonon interaction as well as impurity-phonon interaction including the effects of interface-optical phonon modes and half-space phonon modes,the binding energies as functions of pressure,the impurity position,areal electron density and the phonon effect on the Stark energy shift are investigated.The numerical result shows that the contributions from the interface optical phonon mode with higher frequency and the LO-like half space mode to the binding energy and the Stark energy shift are important and obviously increase with increasing hydrostatic pressure,whereas the interface optical phonon mode with lower frequency and the TO-like half space mode are extremely small and are insensitive to the impurity position and hydrostatic pressure.It is also shown that the conductive band bending should not be neglected.

Si／SiGe／Si双异质结晶体管异质结势垒效应（HBE）研究

本文研究了不同温度下Ｓｉ／ＳｉＧｅ／Ｓｉ双异质结晶体管（ＤＨＢＴ）异质结势垒效应（ＨＢＥ），研究发现，集电结（ＢＣ）处价带能量差△Ｅｖ越大，ＨＢＥ越明显，在给定的△Ｅｖ下，随着温度的降低，ＨＢＥ越显著。在低温下ＨＢＥ比常温下更严重地退化器件参数；基于以上研究结果，我们指出了减弱ＨＢＥ的有效方法，本研究结果对设计开发Ｓｉ／ＳｉＧｅ／ＳｉＨＢＴ，尤其对设计开发低温工作的微波功率Ｓｉ／ＳｉＧｅ／ＳｉＨＢＴ是非常重要的。

Ge_xSi_（1－x）／Si超晶格红外探测器最佳结构

通过对ＧｅｘＳｉ１－ｘ／Ｓｉ超晶格机理的研究，算出了ＧｅｘＳｉ１－ｘ／Ｓｉ超晶格红外探测器的最佳结构参数，以对１．３μｍ红外光有最大的利用率。

基于应变Si/SiGe的CMOS电特性模拟研究

提出了一种应变Si/SiGe异质结CMOS结构,采用张应变Si作n-MOSFET沟道,压应变SiGe作p-MOSFET沟道,n-MOSFET与p-MOSFET采用垂直层叠结构,二者共用一个多晶SiGe栅电极。分析了该结构的电学特性与器件的几何结构参数和材料物理参数的关系,而且还给出了这种器件结构作为反相器的一个应用,模拟了其传输特性。结果表明所设计的垂直层叠共栅结构应变Si/SiGe HCMOS结构合理、器件性能提高。

双应变SiGe/Si异质结CMOS的设计及其电学特性的Medici模拟(英文)

本文提出一种沟道长度为0.125μm的异质结CMOS(HCMOS)器件结构。在该结构中,压应变的SiGe与张应变的Si分别作为异质结PMOS(HPMOS)与异质结NMOS(HNMOS)的沟道材料,且HPMOS与HNMOS为垂直层叠结构;为了精确地模拟该器件的电学特性,修正了应变SiGe与应变Si的空穴与电子的迁移率模型;利用Medici软件对该器件的直流与交流特性,以及输入输出特性进行了模拟与分析。模拟结果表明,相对于体SiCMOS器件,该器件具有更好的电学特性,正确的逻辑功能,且具有更短的延迟时间,同时,采用垂直层叠的结构此类器件还可节省约50%的版图面积,有利于电路的进一步集成。

AIN、GaN立方晶体的静态性质和AIN/GaN异质结的价带偏移

采用LMTO能带从头计算方法，计算了闪锌矿（立方）结构AIN和GaN的静态性质；用平均键能方法，预言了AlN与GaN自由应变生长、以AlN为衬底和以GaN为衬底等三种不同应变状态下AlN／GaN应变层异质结的△Ev值；最后，采用超原胞（AIN）n（GaN）n（001），（n=1，3，5）界面自洽计算方法，考察了超晶格中平均键能Em的“对齐”程度和验证了价带偏移△Ev计算结果的准确性。

线性缓变SiGe HBT低温基区滚越时间的研究

提出了线性缓交ＳＩＧｅＨＢＴ的基区滚越时间τｂ的解析模型，基于该模型研究了基区渡越时问的低温行为。研究发现，τｂ随温度的降低而迅速减小，虽然大的基区Ｇｅ组份级变有利于τｂ的减少，但对小的基区缓变的ＨＢＴ，通过降低温度，也能使τｂ有较大的减小，改善其频率特性。

硅锗基区异质结双极型晶体管的研究进展

本文综述了SiGe-HBT工艺及性能研究的最新进展,提出了若干重要的研究课题.

硅基低维材料的可见光发射机理探讨

Si的可见光发射是半导体发光材料研究中的一个新课题。文中从能带工程的角度出发，着重讨论了SiGe应变层异质结、Si量子细线、Si纳米团簇以及Si－O化合物年维体系的可见光发射机理，并进而探讨了提高这些娃基低线材料发光效率的可能途径。