平均键能方法在应变层异质结带阶研究中的应用

将平均键能方法推广应用于应变层异质结的带阶研究.通过流体静压力应变和单轴应变对带阶参量E_mv作用的仔细研究,发现平均带阶参量E_mv,av=E_m-E_v,av在不同应变状态下基本上保持不变.因此,在应变层带阶参量E_mv的计算中,只需计算其发生应变前体材料的带阶参量E_mv,o值并引用形变势b和SO裂距Δ₀的实验值,通过简便的代数运算得到应变层的E_{mv 关键词： 异质结 平均键能方法 价带偏移}     

InxGa1-xAs-GaAs应变层量子阱结构的流体静压光荧光研究

本文报道了对分子束外延(MBE)生长的In_0.25Ga_0.75As-GaAs应变层量子阱结构在77K下的压力光荧光(PL)研究的结果。流体静压力从0到50kbar.,给出了In_0.25Ga_0.75As-GaAs应变层量子阱的Γ谷压力系数,实验观察到了量子阱中能级与势垒GaAs中X谷的能级交叉。通过对其压力行为的分析,给出了In_0.25Ga_0.75As-GaAs异质结的导带与价带跃变比:Q_c=△E_c:△E_v=0.68:0.32。对(InGa)As-GaAs应变量子阱常压下的理论分析与实验符合很好。本文也对Al_0.3Ga_0.70As-GaAs量子阱进行了讨论。 关键词：     

Piezoreflectance measurements on GaxIn1−x Sb alloys

Piezoreflective experiments between 77 and 300°K are performed on Ga_x, In_1?x Sb alloys. E_o and E_o + Δ_o transition energies, vs composition are determined. Band gap E_o variations, are obtained in good agreement with the two band dielectric model. The Δ_o splitting is observed to be linear with composition.The fundamental edge temperature coefficient β is also determined, it is found to vary linearly with composition.E_o and E_o + Δ_o energy determination permit one to deduce effective mass and g_e value variation with composition.     

Structure and optical analysis of Ta2O5 deposited on infrasil substrate

Electron beam gun technique was used to prepare Ta₂O₅ thin films onto infrasil substrates of thicknesses 333 and 666 nm. The structure characterization was investigated using X-ray diffraction patterns. Transmittance measurements in the wavelength range (240-2000 nm) were used to calculate the refractive index n and the absorption index k depending on Swanepole's method. The dispersion curve of the refractive index shows an anomalous dispersion in the absorption region and a normal one in the transparent region. The analysis of the optical absorption data revealed that the optical band gap E_g was indirect transition. It was found that the refractive index dispersion data obeyed the single oscillator of the Wemple-DiDomenico model, from which the dispersion parameters (E_o and E_d) and the high frequency dielectric constant were determined. The electric free carrier susceptibility and the carrier concentration to the effective mass ratio were estimated according to the model of Spitzer and Fan. Graphical representation of the relaxation time as a function of photon energy was also presented.     

On the structure of wave fields in the region of linear interaction between ordinary and extraordinary waves in two-dimensionally inhomogeneous magnetoactive plasmas

The spectra of the low-temperature photodissociation (photoionization) of Landau-Pekar polarons are calculated using the theory of quantum-coherent states and a new method of variation with respect to the parameters of phonon vacuum deformation. It is shown that the final polaron states upon photodissociation may have different numbers of phonons produced in a single dissociation event and different momenta of charge carriers. The spectrum of optical absorption related to the photodissociation of polarons exhibits a superposition of bands corresponding to various numbers of phonons formed as a result of dissociation of a single polaron. Due to a large width of the energy region corresponding to the final states of charge carriers, the halfwidth of each band is on the order of the energy of polaron coupling and is much greater than the phonon energy. For this reason, the individual phonon bands exhibit strong overlap. The very broad and, probably, structureless band formed as a result of the superposition of all these components begins at an energy equal to the sum of the polaron coupling energy (E _p) and the phonon energy. This band has a maximum at a frequency of about 5.6E _p/? and a halfwidth on the order of 5.6E _p/? at a unit effective mass (m* = m _e) of band electrons. For an effective charge carrier mass within m* = (1–3)m _e, the energy of the polaron band maximum can be estimated as 5E _p with an error of about 10%, and the halfwidth falls within 3.4E _p < ?Ω_1/2 < 5.6E _p. The multiphonon character of this band is related to a decay of the phonon condensate after the escape of charge carrier from a polaron. Such polarons are likely to be observed in the spectra of complex metal oxides, including high-temperature superconductors. Examples of such polaron bands in the reported absorption and photoconductivity spectra of nonstoichiometric cuprates, manganites, nickelates, and titanates are presented. A theory of the formation of Landau-Pekar polarons with the participation of branches of the polarization oscillations of the medium is developed. It is shown that, under certain conditions, such a multiphonon-dressed polaron can possess a coupling energy on the order of 0.2–0.3 eV, so that the maximum of the corresponding absorption band may occur at 1–1.5 eV.     

Optical absorption and dispersion characterizations of CuGaSe2 thin films prepared by flash evaporation technique

Thin films of CuGaSe₂ have been prepared by flash evaporation technique. The optical properties of the prepared films were investigated using spectrophotometric measurements of the transmittance and reflectance at normal incidence of light in the wavelength range from 400 to 2500 nm. The optical constants as refractive index, n, and absorption index, k, were calculated and found to be independent of film thickness in the range of the film thickness 132–423 nm. The analysis of the photon energy against the absorption coefficient showed three direct optical transitions (one of them is allowed while the others are forbidden). This direct transition was ascribed to the crystal field and spin orbital splitting of the upper most valence band. The crystal field and spin orbital splitting of CuGaSe₂ were found to be ? 0.15 eV and 0.45 eV, respectively. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple–DiDomenico (WD) model. The single oscillator energy (E_o), the dispersion energy (E_d), the high frequency dielectric constant (ε_∞), the lattice dielectric constant (ε_L) and the ratio of free charge carrier concentration to the effective mass (N / m*) were estimated. The capacitance–voltage measurements of CuGaSe₂/p-Si heterojunction showed that the diode is abrupt junction diode. The carrier concentration and the built-in voltage were estimated. The current–voltage characteristics of the device under illumination were investigated and photovoltaic properties of the device were evaluated.     

分子束外延生长Si/GaP(111)异质结的界面特性

本文研究了分子束外延(MBE)生长的n-N型Si/GaP(111)异质结的界面特性。采用C-V法测量Si/GaP(111)异质结的表观载流子浓度分布n(x),从中导出了异质界面的导带失配值和界面电荷密度。实验结果表明,n-N型Si/GaP(111)是一种弱整流结构。导带失配△E_c=0.10eV,界面电荷密度σ_i=8.8×10¹⁰cm^-2。通过表现载流子浓度n(x)的理论计算曲线与实验曲线符合较好,说明了实验结果的可靠性 关键词：     

Hydrostatic pressure dependence of excitonic optical transitions in strained wurtzite GaN/AlN quantum disks

In the framework of the effective mass approximation, the effects of hydrostatic pressure on optical transitions associated with the excitons confined in strained wurtzite (WZ) GaN/AlN quantum disks (QDisks) with the confinement potential of finite depth are investigated by using a variational technique, with considering the influences of the built-in electric field (BEF) and the biaxial strain dependence of material parameters. The Schrödinger equation via the proper choice of the exciton trial wave function is solved. The behaviors of the excitonic optical transition are examined at different pressures for different QDisk sizes. In our calculations, the effective masses of electron and hole, dielectric constants, phonon frequencies, energy gaps, and piezoelectric polarizations are taken into account as functions of biaxial strain and hydrostatic pressure. Numerical results show that the hydrostatic pressure and the QDisk size have a remarkable influence on exciton states. The calculated pressure coefficient of optical transition energy shows a negative value if the QDisk height L > 3.2 nm, in contrast with the positive pressure coefficient of the GaN band gap. The peculiar pressure behavior is related to the pressure-induced increase of the built-in electric field. For a fixed pressure, the optical transition energy has a red-shift if the QDisk height and radius increase and QDisk height has a more obvious influence on E_ph than QDisk radius. Furthermore, the relationship between the radiative decay time and hydrostatic pressure (QDisk height) is also investigated. It is found that the radiative decay time increases with pressure and the increment tendency is more prominent for the large height QDisks. The radiative decay time strongly increases by three orders of magnitude reaching microsecond order if the QDisk height increases from 1 nm to 3 nm.     

流体静压力对高简并砷化镓P-N结某些参数的影响

本文报导了在流体静压力18000kg/cm²范围内,高简并砷化镓P-N结峯值电流l_p,谷值电流l_v,峯值电压V_p,谷值电压V_v,指数过剩电流I_x等参数随压力变化的实验结果。分析了峯值电压V_p随压力P的增加按指数规律显著减小,以及指数过剩电流I_x的斜率S=(dlnI_x)/dV随压力P的增加而增加等实验结果。分析的     

Photoreflectance spectroscopy of semiconductor structures at hydrostatic pressure: A comparison of GaInAs/GaAs and GaInNAs/GaAs single quantum wells

The pressure dependence of optical transitions in Ga_0.64In_0.36As/GaAs and Ga_0.64In_0.36N_0.01As_0.99/GaAs single quantum well (SQW) structures were studied in photoreflectance (PR) spectroscopy. In order to apply high hydrostatic pressure, up to ∼11 kbar, the liquid-filled clamp-pressure cell with a sapphire window for optical access has been adopted in the PR set-up with the so called ‘bright configuration’. It has been found that the linear hydrostatic pressure coefficient for the ground state transition are equal to 8.6 and 7.3 meV/kbar for the GaInAs/GaAs and GaInNAs/GaAs SQWs, respectively. This result shows that the incorporation of only 1% of N atoms into GaInAs/GaAs leads to ∼15% decrease in the pressure coefficient. In addition, a non-linearity in the pressure dependence of the ground state transition has been resolved for the GaInNAs/GaAs SQW.     

Excitation of theΔ (1232)-resonance in proton-nucleus collisions

The excitation of theΔ resonance is observed in proton collisions on C, Nb and Pb targets at 0.8 and 1.6 GeV incident energies. The mass E₀ and widthΓ of the resonance are determined from the invariant mass spectra of correlated (p, π^±)-pairs in the final state of the collision: The mass E₀ is smaller than that of the free resonance, however by comparing to intra-nuclear cascade calculations, this reduction is traced back to the effects of Fermi motion, NN scattering and pion reabsorption in nuclear matter.     

压力下GaN/Ga1-xAlxN量子点中杂质态的界面效应

考虑界面处导带弯曲,流体静压力以及有效质量随量子点位置的依赖性,采用变分法以及简化相干势近似,研究了无限高势垒GaN/Ga_1-xAl_xN球形量子点中杂质态的界面效应,计算了杂质态结合能随量子点尺寸、电子面密度以及压力的变化关系。结果表明,结合能随压力的增大呈线性增加的趋势,有效质量位置的依赖性以及导带弯曲对结合能有不容忽视的影响。     

First principles investigation of magnesium antimonite semiconductor compound in two different phases under hydrostatic pressure

We investigate the electronic and the structural properties of Mg₃Sb₂ in cubic and hexagonal phases using the full potential-linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory. The effects of hydrostatic pressure on band gap, bandwidths of bands under Fermi energy labeled by B1 and B2 from the top, the energy gap between B1 and B2 (anti-symmetry gap) and also effective masses of electrons and holes are studied using optimized lattice parameters. We observe that the hydrostatic pressure decreases the band gap and the anti-symmetry gap while it increases the bandwidths of all bands below the Fermi energy. The effective masses of electrons and holes for the hexagonal phase depend on pressure in the Γ→Λ direction. In the cubic phase the effective mass of electrons is independent of pressure and the effective mass of holes depend on the pressure in the Γ→N direction.     

Deep level states and negative photoconductivity in n-ZnO/p-Si hetero-junction diodes

Negative photoconductivity (NPC) was observed in n-ZnO/p-Si heterojunction diode grown by ultra-high vacuum sputtering method under nitrogen ambient. Under the illumination of ultra-violet light, positive photoconductivity was observed at low bias voltages, whereas NPC was observed at high bias voltages. The defect states in the ZnO layers grown on Si were analyzed by photoluminescence and deep level transient spectroscopy measurements. Two deep levels were measured at E_c-0.51 eV and E_c-0.54 eV, which might be originated from oxygen vacancy and nitrogen atom related defects, respectively. Based on the simulation of band diagram, the defect states were located below Fermi level at zero bias voltage. However, as increasing the bias voltages, NPC was observed due to the increase of empty defect states. This analysis allowed us to consider the possibility that the NPC phenomenon in n-ZnO/p-Si heterojunction diode is originated dominantly from the defect states as a carrier recombination center in ZnO layer.     

Effect of conduction band nonparabolicity on the optical properties in a single quantum well under hydrostatic pressure and electric field

The effect of conduction band nonparabolicity on the linear and nonlinear optical properties such as absorption coefficients, and changes in the refractive index are calculated in the Al_0.3Ga_0.7As/GaAs heterostructure-based symmetric rectangular quantum well under applied hydrostatic pressure and electric field. The electron envelope functions and energies are calculated in the effective mass equation including the conduction band nonparabolicity. The linear and nonlinear optical properties have been calculated in the density matrix formalism with two-level approximation. The conduction band nonparabolicity shifts the positions of the optical properties and decreases their strength compared to those without this correction. Both the optical properties are enhanced with the applied hydrostatic pressure. While the absorption coefficients are bleached under the combined effect of high pressure and electric field, the bleaching effect is reduced when nonparabolicity is included.     

Electronic transport in strained p-modulation Be-doped Ga0.8In0.2As/GaAs single quantum well

We report on the electronic transport properties of p-modulation Be-doped Ga_0.8In_0.2As/GaAs single quantum well. The experiments included the spectral photoluminescence between 8 and 300?K, and Hall effect measurements at temperatures between 14 and 300?K. The effect of strain which induces splitting of the valence band as light and heavy hole bands on transport is discussed. The calculated band alignment of the GaInAs sample using model-solid theory including strain effects indicates large conduction band discontinuities and a much smaller valance band discontinuity in GaInAs. The effect of the conduction and valance band discontinuity on the electronic transport properties is also discussed.     

High power splitting of the cyclotron resonance induced photoconductivity in n-GaAs

Conclusion In summary our results show that photoconductivity and optical absorption under cyclotron resonance conditions in high purity n-GaAs are more complex than it has been assumed previously. As cyclotron resonance can only be measured with non zero free electron concentration, and because the 2p _– shallow donor level remains below the N=0 Landau level for all magnetic field strengths, a certain population of 2p _– states must be present and thus the interference between both absorption processes is unavoidable as long as 2p _–2p ₊ electric dipole transitions are activated by ionized impuritics. This interference gets most drastically manifest at high intensities causing an apparent splitting of the photoconductivity line. Even at lower intensities however when the dip in the photoconductivity line is not observable, all optical characteristics previously attributed to cyclotron resonance are affected by the shallow donor absorption. The energy separationE _2p+–E _2p– of shallow donors in a magnetic field is exactly equal to w _CR only for isolated impurities in the effective mass approximation. The same electric stray field of ionized impurities which cause the activation of 2p _–2p ₊ absorption may shift the donor energy levels due to stark effect. For magnetic field strengthsB<1 T a field dependent deviation ofE _{2 +}–E _{1p –} from the cyclotron resonance quantum energy was observed [15] amounting up to 8 pc. In this case we expect that the peak positions of photoconductivity and absorption do not spectrally coincide and do not occur at the resonance magnetic field strength of 01 Landau level transitions. Thus effective masses determined by standard cyclotron resonance methods at low magnetic fields may be incorrect by a few percent.     

Quantum properties of two-dimensional electron gas in the inversion layer of Hg1−xCdxTe bicyrstals

The electronic and magnetotransport properties of conduction electrons in the grain boundary interface of p-type Hg_1−xCd_xTe bicrystals are investigated. The results clearly demonstrate the existence of a two-dimensional degenerate n-type inversion layer in the vicinity of the grain boundary. Hydrostatic pressure up to 10³ MPa is used to characterize the properties of the two-dimensional electron gas in the inversion layer. At atmospheric pressure three series of quantum oscillations are revealled, indicating that tthree electric subbands are occupied. From quantum oscilations of the magnetoresistivity the characteristics parameters of the electric subbands (subband populations n_si, subband energies E_F−E_i, effective electron masses m^*_ci) and their pressure dependences are established. A strong decrease of the carrier concentration in the inversion layer and of the corresponding subband population is observed when pressure is applied A simple theoretical model based on the triangular-well approximation and taking into account the pressure dependence of the energy band structure of Hg_1−xCd_xTe is use to calculate the energy band diagram of the quantum well and the pressure dependence of the subband parameters.     

Deep traps in GaAs under hydrostatic pressure

The influence of hydrostatic pressure on the energy levels of eight different deep traps in GaAs is determined by means of a transient capacitance technique. Hydrostatic pressure coefficients are shown to be decisive parameters in order to distinguish isoenergetic traps of different origin. For the EL6-, the M3- and the E3-traps (E_c?0.31eV), strongly different pressure coefficients are found. The HK1- and HK2- hole traps exhibit only small pressure coefficients relative to the valence band edge.     

The effects of pressure and hydrogenic donor impurity on the linear and nonlinear optical properties of a GaAs/GaAlAs nanowire superlattice

The combined effects of hydrostatic pressure, presence and absence of hydrogenic donor impurity are investigated on the linear and nonlinear optical absorption coefficients and refractive index changes of a GaAs/Ga_1−xAl_xAs nanowire superlattice. The wave functions and corresponding eigenvalues are calculated using finite difference method in the framework of effective mass approximation. Analytical expressions for the linear and third order nonlinear optical absorption coefficients and refractive index changes are obtained by means of compact-density matrix formalism. The linear and third order nonlinear absorption coefficient and refractive index changes are presented as a function of photon energy for different values of hydrostatic pressure, incident photon intensity and relaxation time in the presence and absence of hydrogenic donor impurity. It is found that the linear and third order nonlinear absorption coefficients, refractive index changes and resonance energy are quite sensitive to the presence of impurity and applied hydrostatic pressure. Moreover, the saturation in optical spectrum and relaxation time can be adjusted by increasing pressure in presence of impurity whereas the effect of hydrostatic pressure is negligible in the case of absence of hydrogenic impurity.