A new etchant system,K2Cr2O7-H2SO4-HCl,for GaAs and InP

A new K₂Cr₂O₇-H₂SO₄-HCl system has been developed that is particularly suitable for use in etching solutions of GaAs and InP. This system provides high quality etched surfaces without any undesirable roughness or etch pits. It has been found that the etching rate can be controlled by changing the etchant component proportions. This is especially the case with HCl. This leads to no change of surface quality. Vertical walls, and mesa-shaped structures have been formed on etching profiles of (001) GaAs by stripes parallel to the [110], and [¯110] directions, respectively. The mesa-shaped profiles have been formed for (001) InP in both the [110] and [¯110] directions. The solution does not erode photoresist masks and is thereby attractive for a variety of device applications.     

Influence of GaNAs strain compensation layers upon annealing of GaIn(N)As/GaAs quantum wells

GaIn(N)As/GaAs and GaIn(N)As/GaNAs/GaAs quantum well samples, with and without GaNAs strain-compensating layers (SCL), were grown on GaAs (001) substrates by molecular beam epitaxy. Photoluminescence (PL) was used to study the effects of the GaNAs SCL on the properties of the Ga(In)NAs QWs upon annealing. It is found that an extra blue-shift (ΔE = 5.2 meV) in the PL emission from the GaInNAs QW sample at the initial annealing stage (t_ann = 40 s) was induced by the GaNAs SCLs. However, for the GaInAs QW sample, the blue-shift induced by GaNAs SCL is only 1.1 meV. As the annealing time was increased, the blue-shift of both GaInNAs and GaInAs QWs showed saturations at 16 meV and 8 meV, respectively. The PL blue-shifts were much enhanced by inserting GaNAs SCLs showing a non-saturable behavior. X-ray diffractions from the strain compensated GaIn(N)As QWs before and after annealing show no N atom diffusion but Ga/In atom interdiffusion across the QW interfaces. The Ga/In atom interdiffusion caused by annealing was also confirmed by high-resolution transmission electron microscopy from the GaInNAs/GaAs QW sample.     

Site‐Controlled Single‐Photon Emitters Fabricated by Near‐Field Illumination

Many of the most advanced applications of semiconductor quantum dots (QDs) in quantum information technology require a fine control of the QDs' position and confinement potential, which cannot be achieved with conventional growth techniques. Here, a novel and versatile approach for the fabrication of site‐controlled QDs is presented. Hydrogen incorporation in GaAsN results in the formation of N–2H and N–2H–H complexes, which neutralize all the effects of N on GaAs, including the N‐induced large reduction of the bandgap energy. Starting from a fully hydrogenated GaAs/GaAsN:H/GaAs quantum well, the N? H bonds located within the light spot generated by a scanning near‐field optical microscope tip are broken, thus obtaining site‐controlled GaAsN QDs surrounded by a barrier of GaAsN:H (laterally) and GaAs (above and below). By adjusting the laser power density and exposure time, the optical properties of the QDs can be finely controlled and optimized, tuning the quantum confinement energy over more than 100 meV and resulting in the observation of single‐photon emission from both the exciton and biexciton recombinations. This novel fabrication technique reaches a position accuracy <100 nm and it can easily be applied to the realization of more complex nanostructures.     

Epitaxial growth of Ni films sputter-deposited on a GaAs(001) surface covered with a MgO film

We studied the epitaxial growth of a Ni film prepared on a GaAs(001) substrate covered with a thin epitaxial MgO buffer film, assuming that this buffer film plays a key role in the epitaxial growth of the Ni film. The MgO and Ni films were deposited by radio-frequency magnetron sputtering of the MgO and Ni targets in pure Ar gas. First, a MgO film of thickness ranging from 78 to 4.4 nm was deposited on the GaAs(001) substrate at a temperature ranging from ambient temperature to 700 °C, and then, a 136-nm-thick Ni film was deposited on the MgO/GaAs substrate at a temperature range 300-500 °C. Using transmission electron microscopy and X-ray diffractometry, we showed that the MgO film grows with the epitaxial relationship MgO(001)[001]//GaAs(001)[001] on GaAs(001) at 500 °C, and that the structure of the Ni film depends on three factors: the MgO/GaAs substrate temperature, the MgO thickness, and the annealing condition of the MgO/GaAs substrate before the Ni deposition. In conclusion, we proved that the Ni film grows with the epitaxial relationship Ni(001)[001]//MgO(001)[001]//GaAs(001)[001] on MgO/GaAs with the 4.4-nm-thick MgO film when the MgO/GaAs substrate is annealed in situ at room temperature before the Ni deposition and maintained at 300 °C during the Ni deposition.     

Chemical effect of inert argon beam on nitride nanolayer formed by ion implantation into GaAs surface

The composition of a nitride nanolayer formed on a GaAs(100) surface by the implantation of ions with an energy of E _i = 2.5 keV and the chemical state of nitrogen in this layer have been studied by the method of Auger electron spectroscopy. It is established that, in addition to GaN, a GaAsN solid solution phase is formed in the ion-implanted layer. The energies of N KVV Auger electron transitions in these phases are determined as E _A (GaN) = 379.8 ± 0.2 eV and E _A (GaAsN) = 382.8 ± 0.2 eV (relative to the Fermi level), which allowed the distribution of nitrogen between these phases to be evaluated as [N(GaN)] = 70% and [N(GaAsN)] = 30%. It is established that an argon ion beam produces a chemical effect on the nitride layer, which is related to a cascade mixing of the material. Under the action of the argon ion bombardment, the distribution of nitrogen in the indicated phases changes to opposite. As a result a nitride nanolayer is formed in which the narrow-bandgap semiconductor (GaAsN) predominates rather than the wide-bandgap component (GaN).     

Molecular beam epitaxy growth methods of wavelength control for InAs/(In)GaAsN/GaAs heterostructures

We discuss the molecular beam epitaxy (MBE) growth methods of emission wavelength control and property investigations for different types of InAs/(In)GaAsN/GaAs heterostructures containing InGaAsN quantum-size layers: (1) InGaAsN quantum wells deposited by the conventional mode in a GaAs matrix, (2) InAs quantum dots deposited in a GaAsN matrix or covered by an InGaAs(N) layer, and (3) InAs/InGaAsN/GaAsN strain-compensated superlattices with quantum wells and quantum dots. The structures under investigation have demonstrated photoluminescence emission in a wavelength range of ～1.3-1.8?μm at room temperature without essential deterioration of the radiative properties.     

Vertically standing Ge nanowires on GaAs(110) substrates

The growth of epitaxial Ge nanowires is investigated on (100), (111) B and (110) GaAs substrates in the growth temperature range from 300 to 380?°C. Unlike epitaxial Ge nanowires on Ge or Si substrates, Ge nanowires on GaAs substrates grow predominantly along the [Formula: see text] direction. Using this unique property, vertical [Formula: see text] Ge nanowires epitaxially grown on GaAs(110) surface are realized. In addition, these Ge nanowires exhibit minimal tapering and uniform diameters, regardless of growth temperatures, which is an advantageous property for device applications. Ge nanowires growing along the [Formula: see text] directions are particularly attractive candidates for forming nanobridge devices on conventional (100) surfaces.     

On the secondary droplets of self-running gallium droplets on GaAs surface

Self-running droplets by thermal evaporation GaAs (001) surface are studied and analyzed using a scanning electron microscope. The sample is prepared under high-temperature annealing in an ultrahigh vacuum molecular beam epitaxy system. Particularly, secondary droplets which formed along primary droplet running trails are investigated. The secondary droplets are found to initially move along the [1 ?10] instead of [110] direction, but these droplets tend to turn into [110] direction as they grow bigger. The scanning electron microscope also captures nanoscale footprints of secondary droplets different from the main droplets.     

Optical and Magnetic Properties of Ten-Period InGaMnAs/GaAs Quantum Wells

Ten layers of InGaMnAs/GaAs multiquantum wells (MQWs) structure were grown on high resistivity (100) p-type GaAs substrates by molecular beam epitaxy (MBE). A presence of the ferromagnetic structure was confirmed in the InGaMnAs/GaAs MQWs structure, and have ferromagnetic ordering with a Curie temperature, T _C=50 K. It is likely that the ferromagnetic exchange coupling of the sample with T _C=50 K is hole-mediated resulting in Mn substituting In or Ga sites. PL emission spectra of the InGaMnAs MQWs sample grown at a temperature of 170 °C show that an activation energy of the Mn ion on the first quantum confinement level in InGaAs QW is 32 meV and impurity Mn is partly ionized. The fact that the activation energy of 32 meV of Mn ion in the QW is lower than an activation energy of 110 meV for a substitutional Mn impurity in GaAs, indicating an impurity band existing in the bandgap due to substitutional Mn ions.     

Surface acoustic waves in a gallium arsenide-conducting layerstructure

The electron attenuation and SAW velocity versus the surface conductivity and magnetic field induction for the structure consisting of the (001) cut anisotropic GaAs substrate and an isotropic conducting layer was calculated. The SAW propagated along the [110] piezoactive direction distinguished by the greatest electromechanical coupling coefficient     

Nitrogen incorporation in GaInNAs and GaAsN near the solubility limit

The influence of nitrogen incorporation on the microstructure of GaAsN/GaAs and GaInNAs/GaAs has been investigated using cross-sectional scanning transmission electron microscopy and laser Raman spectroscopy. Energy-dispersive X-ray maps of the elemental distributions of Ga, In, N and As show that for GaAsN and GaInNAs layers containing nitrogen below the solubility limit, homogeneous compositions are obtained. These layers are of good crystalline quality near to the epilayer/GaAs interface. For GaAsN specimens with nitrogen contents above the solubility limit a graded transition from arsenide-like to nitride-like material occurs after some 50 nm of growth. This observation complements Raman spectra that show that characteristic GaN-like modes are observed in the high nitrogen content GaAsN film. The GaInNAs film containing nitrogen above the solubility limit shows a cellular microstructure consisting of gallium-depleted InGaAs cells with cell wells of a GaN-like composition.     

Orientation and temperature dependence of the tensile behavior of GaN nanowires: an atomistic study

Gallium nitride (GaN) is a high-temperature semiconductor material of considerable interest. It emits brilliant light and has been considered as a key material for the next generation of high frequency and high power transistors that are capable of operating at high temperatures. Due to its anisotropic and polar nature, GaN exhibits direction-dependent properties. Growth directions along [001], [1?10] and [110] directions have all been synthesized experimentally. In this work, molecular dynamics simulations are carried out to characterize the mechanical properties of GaN nanowires with different orientations at different temperatures. The simulation results reveal that the nanowires with different growth orientations exhibit distinct deformation behavior under tensile loading. The nanowires exhibit ductility at high deformation temperatures and brittleness at lower temperature. The brittle to ductile transition (BDT) was observed in the nanowires grown along the [001] direction. The nanowires grown along the [110] direction slip in the {010} planes, whereas the nanowires grown along the [1?10] direction fracture in a cleavage manner under tensile loading.     

Hydrogen reduction in GaAsN thin films by flow rate modulated chemical beam epitaxy

The amount of residual H in the GaAsN film grown by chemical beam epitaxy (CBE) can be decreased by flow rate modulation growth. Many H atoms in the films grown by CBE exist as N-H or N-H₂ structures. Although a higher growth temperature was required for decreasing the H concentration ([H]), it caused a decrease in the N concentration ([N]). A reduction in [H] while keeping [N] constant was necessary. By providing an intermittent supply of Ga source while continuously supplying As and N sources, [H] effectively decreased in comparison with the [H] value in the film grown at the same temperature by conventional CBE without reducing [N].     

Microstructure of Epitaxial La_(0.7)Ca_(0.3)MnO_3 Thin Films Deposited by Direct Current Magnetron Sputtering on LaAlO_3 Substrate

Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) have been used to study the microstructural properties of La0.7Ca0.3MnO3 films on (001) LaAlO3 substrates prepared by direct current magnetron sputtering technique.The as-grown thin films with different thickness are perfectly coherent with the substrates.The film suffers a tetragonal deformation in the area near the interface between the film and the substrate.With increasing thickness, the film is partially relaxed.It was found that La0.7Ca0.3MnO3 films consist of two types of oriented domains described as: (1) (110)f[001]f||(001)s[100]sand (110)f[001]f||(001)s[100]s and (2) (110)f[001]f||(001)s[010]s and (110)f[001]f//(001)s[010]s.Upon annealing, the film is relaxed by the formation of misfit dislocations.Other than misfit dislocations, two types of threading dislocations with Burgers vector of <100> and <110> were also identified.     

Sublimation growth of titanium nitride crystals

The sublimation-recondensation growth of titanium nitride crystals with N/Ti ratio of 0.99 on tungsten substrates is reported. The growth rate dependence on temperature and pressure was determined, and the calculated activation energy was 775.8 ± 29.8 kJ/mol. The lateral and vertical growth rates changed with the time of growth and the fraction of the tungsten substrate surface covered. The orientation relationship of TiN (001) || W (001) with TiN [100] || W [110], a 45° angle between TiN [100] and W [100], occurs not only for TiN crystals deposited on (001) textured tungsten but also for TiN crystals deposited on randomly orientated tungsten. This study demonstrates that this preferred orientational relationship minimizes the lattice mismatch between the TiN and tungsten.     

High Resolution Compton Scattering as a Probe of the Fermi Surface in the Iron-based Superconductor LaO1−x F x FeAs

We have carried out first-principles all-electron calculations of the (001)-projected 2D electron momentum density and the directional Compton profiles along the [100], [001] and [110] directions in the Fe-based superconductor LaOFeAs within the framework of the local density approximation. We identify Fermi surface features in the 2D electron momentum density and the directional Compton profiles, and discuss issues related to the observation of these features via Compton scattering experiments.      

Porous layers on compensated GaAs:Cr

Porous multi-layered structures on GaAs:Cr (001) were formed by anodic etching in HF acid based electrolyte. The top layer with a thickness of 0.5–1.5 μm consists mainly of As- and Ga-oxides. As–O crystallites oriented along [110]-axes were observed. Below the top layer, a porous layer of 2–10 μm thickness is formed with micro-pores of up to 2 μm in diameter. The structure and chemical composition of porous GaAs:Cr was studied by SEM, AFM and photoemission microspectroscopy. The porous GaAs:Cr samples were characterized by spectroscopic ellipsometry and modulation spectroscopy techniques. The optical response of the complex sample was analysed in terms of the pseudodielectric function.     

Atomistic Simulation of the Orientation-dependent Plastic Deformation Mechanisms of Iron Nanopillars

Tensile tests were performed on iron nanopillars oriented along [001] and [110] directions at a constant temperature of 300 K through molecular dynamics simulations with an embedded-atom interatomic potential for iron.The nanopillars were stretched until yielding to investigate the onset of their plastic deformation behaviors.Yielding was found to occur through two different mechanisms for [001] and [110] tensions.In the former case,plastic deformation is initiated by dislocation nucleation at the edges of the nanopillar,whereas in the latter case by phase transformation inside the nanopillar.The details during the onset of plastic deformation under the two different orientations were analyzed.The varying mechanisms during plastic deformation initiation are bound to influence the mechanical behavior of such nanoscale materials,especially those strongly textured.     

铜铟硒薄膜的外延生长和表面重构及其电池性能研究

在GaAs的(110)、(001)和(111)A、(111)B等极性晶面上, 通过铜铟共溅-硒蒸镀的方法, 分布外延生长出(220/204)、(001)和(112)结晶取向的单晶CIS薄膜. 系统考察了CIS薄膜外延生长的结晶取向和表面微结构, 发现了这些CIS外延薄膜均需表面重构化而形成比表面能低的CIS(112)晶面, 结合晶体结构研究了各种晶面和比表面能的相关性. 通过各种衬底下不同结晶取向的CIS薄膜的太阳能电池组装, 发现当CIS薄膜生长具有(220/204)结晶取向时电池器件性能最好、效率最高, 说明可通过控制CIS薄膜的沉积条件和选用合适取向的衬底, 增加吸收层(220/204)的结晶取向, 从而显著提高CIS薄膜太阳电池的光电性能.     

Optical gain of 1.3 /spl mu/m GaAsSbN/GaAs quantum well lasers

Optical gain of 1.3 mum GaAsSbN/GaAs quantum well (QW) structure is investigated using the multiband effective mass theory. The results are compared with those of 1.3 mum InGaNAs/GaAs and GaAsSb/GaAs QW structures. The optical gain of the GaAsSbN/GaAs QW structure is found to be similar to that of the InGaAsN/GaAs QW structure. In contrast, GaAsSbN/GaAs and InGaNAs/GaAs QW structures show significantly larger optical gain than the GaAsSb/GaAs QW structure. This is mainly attributed to the fact that the former has a larger optical matrix element than the latter. In addition, GaAsSbN/GaAs and InGaNAs/GaAs QW structures have much smaller threshold current density than the GaAsSb/GaAs QW structure. This is because the Auger recombination current density gives dominant contribution to the threshold current density and the former has smaller threshold carrier density than the latter. On the contrary, the threshold current density of the GaAsSbN/GaAs QW structure is shown to be similar to that of the InGaAsN/GaAs QW structure