Quantitative characterization of AlAs/GaAs interfaces by high-resolution transmission electron microscopy along the 〈100〉 and the 〈110〉 projection

The interface microstructure of AlAs/GaAs quantum wells grown by molecular beam epitaxy (MBE) was investigated by transmission electron microscopy (TEM). High-resolution transmission electron microscopy (HRTEM) yields information about the width of the chemical transition between the binary components and about the lateral step distances along the interface. The chemical composition is quantitatively determined by the application of a pattern recognition procedure based on the Fourier transformation of image unit cells. Along the 100 zone axis the composition across the interfaces is obtained with a precision of ±10 atomic percent and with a spatial resolution of 0.28 nm. Despite a lower chemical sensitivity a quantitative chemical analysis was also carried out for images along the 110 projection.     

Damage created by high-current-density implants of phosphorus into 〈100〉 and 〈111〉 silicon wafers

The damage left by high-current-density, 9 A/cm², implants of 120 keV phosphorus into 100 and 111 silicon oriented substrates was investigated as a function of the fluence in the range 4×10¹⁵–1.5×10¹⁶/cm². The samples were analyzed by 2 MeV He⁺ channeling and transmission electron microscopy. Initially a buried amorphous layer forms at low fluences until the wafer temperature saturates at 450 °C at a fluence of 4.5×10¹⁵/cm². As the fluence is further increased ion-assisted regrowth of this initial buried amorphous layer takes place and is 2 to 2.5 times faster (with respect to ion fluence) for 100 substrates than for 111 substrates. At higher fluences, most of the residual damage is located at a depth equal to the sum of the projected range and of the straggling. In the regrown layers twins are found in both orientations, and in some cases a hexagonal silicon phase is present at high fluences. The results are compared with the ion assisted regrowth of amorphous layers at well defined temperatures in the 250°–400 °C range.     

Effects of annealing temperature on the alloying behavior of the AuGe-GaAs〈100〉 interface

UV(He I) and X-ray photoelectron spectroscopies (UPS and XPS) were used to examine the alloying behavior of AuGe ohmic contacts to silicon-doped 100 oriented n-type GaAs substrates. The reacted interface was then revealed by Ar ion sputter depth profiling at room temperature and after annealing in ultra high vacuum at 300°, 500°, or 700°C. The indiffusion of Au and the outdiffusion of Ga and As are evident. Instead of obtaining a maximum peak of the Ge profile on annealing in forming gas, we observed an increase of Ge indiffusion with temperature. The Au indiffusion results in a decrease in the Au 5d splitting and a shift of both levels to higher binding energy. Au-Ga alloy formation is indicated by the Au 4f levels, and is further supported by the observation of the metallic Ga peak. It has been concluded that the sample annealed at 500°C forms the Au-Ga alloy and the compound of As containing Ge more easily than the samples annealed at 300° or 700°C. This result is consistent with the observations of low contact resistance at the annealing temperature of 500°C for AuNiGe ohmic contacts to n-type GaAs.     

Observation of compensation effects during the thermal dissolution of aluminum oxide layers on tungsten and molybdenum 〈111〉 and on tungsten {110} in the presence of electric fields

Aluminum oxide layer dissolution was studied between 700 and 1200 K in the substrate areas of W〈111〉, Mo〈111〉, and on W{110} by means of FEM. Varying the electric field strength, F, between +45 and $\text{+105}\text{MV}\text{cm}$, two types of dissolution could be observed: dissolution by surface diffusion (low F's) and dissolution by ion desorption (high F's). It is assumed that aluminum suboxides — preferentially AlO — are involved in the dissolution processes. The preexponential factors, A_F, of an Arrhenius-Frenkel type equation were measured as a function of F. The field dependence of A_F is determined by the dissolution mechanism: (a) dissolution by diffusion: $\text{log}\text{A}{}^0{}_{\mathrm{F}}\text{=}\text{log}\text{A}{}^0{}_0\text{?}\text{ΔμF}\text{2.3k}{}^1\text{T}$ (μ  molecular dipole moment, ¹T ≡ isokinetic for W〈111〉, log A⁰₀ = ? 6.0 and ${}^1\text{T = 940}\text{K}$; for Mo〈111〉, log A⁰₀ = ? 3.1 and ${}^1\text{T = 860}\text{K}$; and (b) dissolution by ion desorption: $\text{log}\text{A}{}^{\mathrm{+}}{}_{\mathrm{F}}\text{=}\text{log}\text{A}{}^{\mathrm{+}}{}_0\text{+}\text{n}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{e}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{F}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{2.3k}{}^1\text{T}$; for A⁺₀ = ? 22 and ${}^1\text{T = 1200}\text{K}$; for W〈111〉, log A⁺₀ = ? 21 and ${}^1\text{T = 1200}\text{K}$. Using earlier proposed safeguards, isokinetic relationships (compensation effects) could be established for each of the two dissolution processes. The coordinates of the isokinetic points have the following average values: $\text{log}{}^1\text{A}{}^0{}_0\text{= 2.5}$ and ${}^1\text{T = 920}\text{K}$ for diffusion; $\text{log}{}^1\text{A}{}^{\mathrm{+}}{}_0\text{= ? 1}$ and ${}^1\text{T = 1240}\text{K}$ for ion desorption. The entropy changes (at $\text{T =}{}^1\text{T}$, zero field strength, and unit pressure) for the phase changes: solid layer → diffusion layer and solid layer → ion gas, are of the order of $\text{30}\text{cal}\text{K}$ · mol and $\text{90}\text{cal}\text{K}$ · mol, respectively. The two dissolution mechanisms can be described by the following Arrhenius-Frenkel type equations:

$\text{τ}{}^0{}_{\mathrm{F}}\text{=}{}^1\text{A}{}^0{}_0\text{exp}\text{[}\text{? (E}{}^0{}_0\text{+ ΔμF)}\text{k}{}^1\text{T}\text{]}\text{exp}\text{[(}\text{E}{}^0{}_0\text{+ ΔμF)}\text{kT}\text{]}$

for diffusion and

$\text{τ}{}^{\mathrm{+}}{}_{\mathrm{F}}\text{=}{}^1\text{A}{}^{\mathrm{+}}{}_0\text{exp}\text{[}\text{? (E}{}^{\mathrm{+}}{}_0\text{? n}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{e}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{F}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}\text{k}{}^1\text{T}\text{]}\text{exp}\text{[(}\text{E}{}^{\mathrm{+}}{}_0\text{? n}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{e}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{F}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}\text{kT}\text{]}$

for ion desorption.     

Microstructure evolution and passivation quality of hydrogenated amorphous silicon oxide(a-SiOx:H) on〈100〉- and 〈111〉-orientated c-Si wafers

Hydrogenated amorphous silicon oxide(a-SiOx:H) is an attractive passivation material to suppress epitaxial growth and reduce the parasitic absorption loss in silicon heterojunction(SHJ) solar cells. In this paper, a-SiOx:H layers on different orientated c-Si substrates are fabricated. An optimal effective lifetime(τ(eff)) of 4743 μs and corresponding implied opencircuit voltage(iV(oc)) of 724 mV are obtained on〈100〉-orientated c-Si wafers. While τ(eff) of 2429 μs and iV_oc of 699 mV are achieved on 111-orientated substrate. The FTIR and XPS results indicate that the a-SiOx:H network consists of SiOx(Si-rich), Si–OH, Si–O–SiHx, SiO2 ≡ Si–Si, and O3 ≡ Si–Si. A passivation evolution mechanism is proposed to explain the different passivation results on different c-Si wafers. By modulating the a-SiOx:H layer, the planar silicon heterojunction solar cell can achieve an efficiency of 18.15%.     

Control of circular polarization of electroluminescence in spin light-emitting diodes based on InGaAs/GaAs/δ〈Mn〉 heterostructures

Circularly polarized luminescence of light-emitting InGaAs/GaAs structures with a delta-doped Mn layer in a GaAs barrier was studied. The structural parameters were varied by different ways, among them are homogeneous and delta-doping with acceptor impurity, and removal of donor doping from the technological process. As it was found, the magnitude and polarity of the degree of circular polarization of luminescence strongly depend on the technological mode chosen. Simultaneous modeling of wave functions of structures highlights a good agreement between the parameters of circularly polarized luminescence and spatial distribution of wave functions of heavy holes relative to the Mn delta-layer.     

Influence of delta〈Mn〉 doping parameters of the GaAs barrier on circularly polarized luminescence of GaAs/InGaAs heterostructures

The circular polarization of low-temperature electroluminescence of diodes based on heterostructures with an undoped quantum well InGaAs/GaAs and a delta〈Mn〉 layer in the GaAs barrier has been investigated. The possibility of changing the degree of circular polarization of the electroluminescence by varying the main structural parameters of diodes (spacer layer thickness, i.e., the distance between the delta〈Mn〉 layer and the quantum well, atomic concentration in the delta〈Mn〉 layer, and introduction of an additional acceptor delta layer) has been analyzed. It has been revealed that the variation in the spacer layer thickness is the most effective method for controlling the degree of circular polarization of the electroluminescence.     

On the core structure and mobility of the 〈100〉{010} and 〈100〉{01^-1} dislocations in B2 structure YAg and YCu

Dislocations are thought to be the principal mechanism of high ductility of the novel B2 structure intermetallic compounds YAg and YCu.In this paper,the edge dislocation core structures of two primary slip systems 〈100 〉{010} and 〈100 〉 {011} for YAg and YCu are presented theoretically within the lattice theory of dislocation.The governing dislocation equation is a nonlinear integro-differential equation and the variational method is applied to solve the equation.Peierls stresses for 〈100 〉 {010} and 〈100 〉 {011} slip systems are calculated taking into consideration the contribution of the elastic strain energy.The core width and Peierls stress of a typical transition-metal aluminide NiAl is also reported for the purpose of verification and comparison.The Peierls stress of NiAl obtained here is in agreement with numerical results,which verifies the correctness of the results obtained for YAg and YCu.Peierls stresses of the 〈100 〉 {011} slip system are smaller than those of〈100 〉 {010} for the same intermetallic compounds originating from the smaller unstable stacking fault energy.The obvious high unstable stacking fault energy of NiAl results in a larger Peierls stress than those of YAg and YCu although they have the same B2 structure.The results show that the core structure and Peierls stress depend monotonically on the unstable stacking fault energy.     

Properties of the Schottky Barriers on compensated PbTe〈Ga〉

C-V, I-V and photoelectric characteristics were investigated for some metals with different work functions, deposited onto compensated PbTe〈Ga〉 substrates with low carrier concentrations N, P ⩽ 10¹⁶cm⁻³. The surfaces of the PbTe〈Ga〉 substrates were prepared by anode-mechanical polishing, that results in enriching of the surface by Te. It was shown that the heights of the potential barriers Ø_B of the Schottky contacts prepared by oxidization in air anode-mechanically polished PbTe surfaces do not depend on the metal work function of Cu, Ag, Au and In. The highest values of resistance-area product were obtained for the Cu/p-PbTe〈Ga〉 contacts (R₀A≅ 1 × 10⁴Ωcm²) and were slightly lower than the R₀A value limited by the thermoemission current.     

An investigation of the anomalous surface phonon softening on noble metal 〈111〉 surfaces using the embedded atom method

The problem of the anomalous softening of the surface phonons on noble metal 〈111〉 surfaces is addressed using the embedded atom method. The results indicate that the observed decrease in the force constant between atoms in the surface layer can be attributed to a slight increase in the electron density in the surface layer ( ∼ 7% of the free electron density).     

Diagnostic and characterization of the VCSEL diodes based on GaSb

Vertical-Cavity Surface-Emitting Laser (VCSEL) diodes are among the youngest members of the semiconductor laser diode family. The main aim of our work focuses on the measurement of the basic properties (the spectral range of the laser emission, temperature and current tunability) of experimental VCSEL diode lasers based on GaSb operating in the infrared region around 4250 cm^?1. A high-resolution FTIR Bruker IFS 120 HR spectrometer with a maximum resolution of 0.0035 cm^?1 was used in the emission setup for the laser diagnostic research. The absorption spectra of atmospheric pollutants like methane, carbon monoxide and ammonia have been measured using these VCSELs for the first time.     

Magnetic properties of GaAs/δ〈Mn〉/GaAs/In x Ga1 − x As/GaAs quantum wells

The field and temperature dependences of the magnetization of GaAs/δ〈Mn〉/GaAs/In _x Ga_{1 ? x} As/GaAs quantum wells with the δ〈Mn〉 layer separated from the well by a 3-nm GaAs spacer have been studied in the temperature range of 3–300 K in a magnetic field up to 6 T. An external magnetic-field-induced phase transition to a ferromagnetic state with a magnetization hysteresis loop shifted from a zero magnetic field has been found to occur at a temperature below 40 K. A theoretical model is proposed that implies the coexistence of ferromagnetically and antiferromagnetically ordered regions within the GaAs layers.     

Studies on the properties of flow-induced oscillation and sound radiation in streamlined protuberant special cavities

I.IntroductionAsanuidpassingthroughthecavityatcertainflowrate,themediuminthemouthandthccavityisoscillatingandsoundisradiated.Noton1ystochasticturbu1encenoiscispossi-blyproducedbutsinglefrequencysoundofspecia1lydesignatedpitchisalsoproduced.Andthusthespcctrumofthcradiatedsoundisshownascontinuousspectrumandcharacteristiclinespcctrum.Inthiscascwcmaycallitflow-inducedosci1lation.Flow-inducedoscillationandsoundradiationcanbeproducedasafluid(waterorgas)passingthroughthecavitybysinkingcavityunderint…     

Exciton mechanism of the formation of an N-section on the volt-ampere characteristic of GaSe 〈Cu〉

The photoelectric properties of gallium selenide doped with copper are investigated. An N section is observed on the volt-ampere characteristic (VAC) of samples illuminated by a laser beam at a wavelength of 0.63 m. The influence of white and monochromatic light and the contact material on the VAC is considered over a broad temperature range. It is established that, together with existing mechanisms, N-section formation on the VAC of GaSe Cu single crystals is associated with thermofield quenching of the exciton photoconduction.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 90–93, November, 1984.     

Dissociation of a 〈100〉 edge superdislocations in the γ ′-phase of nickel-base superalloys

Dissociation of a〈100〉 edge superdislocations in Ni₃Al, the hardening γ′-phase of nickel-base superalloys, was investigated using molecular dynamics simulations and theory of elasticity. It was shown that these dislocations dissociate either symmetrically or asymmetrically when they are close to the 〈011〉 orientation. The symmetric dissociation, called Hirth lock, has the lowest energy. The reasons for the dissociation are the strong energy reduction due to the core splitting and the relaxation of elastic strains within the dissociation area. The dissociation of a〈100〉 edge superdislocations is the reason for their alignment in 〈011〉 orientation in the γ′-rafts of superalloys. However, the dissociation does not block the movement of the dislocation because they penetrate the γ′-rafts by climbing. Under loading conditions, typical for creep tests of nickel-base superalloys at high temperatures (≥1000°C), the Hirth lock slightly expands but remains stable. The asymmetric configuration is less stable and can transform into the lower energy Hirth lock.     

Effect of growth parameters on the structure and magnetic properties of thin polycrystalline Fe films fabricated on Si〈1 0 0〉 substrates

This paper deals with the experimental investigation of the structure and magnetic properties of thin polycrystalline Fe films. Two sets of 50 ± 2 nm thick Fe films were fabricated on Si〈1 0 0〉 substrates with native oxides in place by varying (i) the sputter pressure p_Ar and (ii) the Fe sputter power P_Fe. X-ray diffraction (XRD) study revealed that all films grew with strong 〈1 1 0〉 texture normal to the film plane. No higher order peaks were observed in any of the films studied. For both film sets, the lattice constant (a) was less than the bulk Fe lattice constant (a₀ = 2.866 Å), which suggested the existence of compressive strain in all films. Two regions of homogeneous strain were observed over the range of p_Ar studied. Magneto-optical Kerr effect (MOKE) measurements showed that all films exhibited magnetically isotropic behaviour. The magnetic properties were observed to be influenced strongly by p_Ar. The film grown at p_Ar = 4 μbar was the most softest (H_s = 100 ± 8 kA m⁻¹, M_r/M_s = 0.87 ± 0.02) film among all the films studied. The magnetic properties were found to be independent of P_Fe. The effective saturation magnetostriction constant λ_eff determined (using the Villari method) was positive (4 ± 1 ppm) and observed to vary within the calculated error.     

Studies on the growth,structural, optical,SHG and thermal properties of γ-glycine single crystal: An organic nonlinear optical crystal

Single crystals of the organic nonlinear optical material γ-glycine have been grown in the presence of Zinc sulphate by slow evaporation technique at ambient temperature for the first time. Bulk growth of γ-glycine single crystals was grown by Top-seeded solution growth method. The γ-phase of glycine was confirmed by powder X-ray diffraction and the FTIR analysis. Elemental analysis CHN was performed to confirm the non-inclusion of zinc sulphate species into the solution. Inductively coupled plasma optical emission spectrometry study (ICP-OES) was employed to quantify the concentration of Zinc element in the grown γ-glycine single crystals. The optical transmission was ascertained from UV–Vis–NIR spectrum. The optical band gap was estimated for γ-glycine single crystal using UV–Vis–NIR study. Differential scanning calorimetry analysis was employed to explore information about thermal stability, phase transition and melting point of the grown crystal. The second harmonic generation relative efficiency was measured by Kurtz and Perry powder technique.     

Evolution of Photocurrent during Coadsorption of Cs and O on GaAs （100）

The photocurrent and spectral response characteristics of gallium arsenide （GaAs） are obtained by a multiinformation measurement system, and the evolution of the photocurrent versus the Cs：O flux ratio is investigated. The experimental results show that the photocurrent increases approximately exponentially after the first exposure to Cs until a maximum sensitivity is reached, the detailed evolution process and the ultimate photocurrent are different for different samples. These differences are analysed, and according to the process of coadsorption of Cs and oxygen on GaAs, an equation is presented to explain the increase of photocurrent.