A-oriented GaAs Substrates Research Articles

Initial stage of InSb heteroepitaxial growth on GaAs (111)A: effect of thin InAs interlayers

MBE of InSb on the (111)A-oriented GaAs substrates has been studied using electron diffraction, X-ray diffraction, and scanning probe microscopy. The direct heteroepitaxial growth of InSb on GaAs(111)A results in a cracked morphology with flat terraces and deep gaps, which could be attributed to the extremely large lattice mismatch between InSb and GaAs (14.6%). When thin (5–30 monolayer thickness) InAs films are used as interlayers, more continuous and flat InSb films are obtained. The proposed growth technique using (111)A-oriented GaAs substrates and thin InAs interlayers are effective in improving the surface morphology and the structural quality of InSb films in highly lattice-mismatched systems.

Electrical and Photoluminescence Studies of {LT-GaAs/GaAs:Si} Superlattices Grown by MBE on (100)- and (111)A-Oriented GaAs Substrates

The results of studying semiconductor structures proposed for the first time and grown, which combine the properties of LT-GaAs with p-type conductivity upon doping with Si, are presented. The structures are {LT-GaAs/GaAs:Si} superlattices, in which the LT-GaAs layers are grown at a low temperature (in the range 280–350°C) and the GaAs:Si layers at a higher temperature (470°C). The p-type conductivity upon doping with Si is provided by the use of GaAs(111)A substrates and the choice of the growth temperature and the ratio between As4 and Ga fluxes. The hole concentration steadily decreases, as the growth temperature of LT-GaAs layers is lowered from 350 to 280°C, which is attributed to an increase in the roughness of interfaces between layers and to the formation of regions depleted of charge carriers at the interfaces between the GaAs:Si and LT-GaAS layers. The evolution of the photoluminescence spectra at 77 K under variations in the growth temperature of LT-GaAs is interpreted as a result of changes in the concentration of GaAs and VGa point defects and SiGa–VGa, VAs–SiAs, and SiAs–SiGa complexes.

Photoluminescence Studies of Si-Doped Epitaxial GaAs Films Grown on (100)- and (111)A-Oriented GaAs Substrates at Lowered Temperatures

The electrical properties and photoluminescence features of uniformly Si-doped GaAs layers grown on GaAs substrates with the (100) and (111)A crystallographic orientations of the surface are studied. The samples are grown at the same As4 pressure in the growth temperature range from 350 to 510°C. The samples grown on GaAs(100) substrates possess n-type conductivity in the entire growth temperature range, and the samples grown on GaAs(111)A substrates possess p-type conductivity in the growth temperature range from 430 to 510°C. The photoluminescence spectra of the samples exhibit an edge band and an impurity band. The edge photoluminescence band corresponds to the photoluminescence of degenerate GaAs with n- and p-type conductivity. The impurity photoluminescence band for samples on GaAs(100) substrates in the range 1.30–1.45 eV is attributed to VAs defects and SiAs–VAs defect complexes, whose concentration varies with sample growth temperature. Transformation of the impurity photoluminescence spectra of the samples on GaAs(111)A substrates is interpreted as being a result of changes in the VAs and VGa defect concentrations under variations in the growth temperature of the samples.

Structural and photoluminescence properties of low-temperature GaAs grown on GaAs(100) and GaAs(111)A substrates

Undoped, uniformly Si-doped, and δ-Si-doped GaAs layers grown by molecular-beam epitaxy on (100)- and (111)A-oriented GaAs substrates at a temperature of 230°C are studied. The As4 pressure is varied. The surface roughness of the sample is established by atomic-force microscopy; the crystal quality, by X-ray diffraction measurements; and the energy levels of different defects, by photoluminescence spectroscopy at a temperature of 79 K. It is shown that the crystal structure is more imperfect in the case of GaAs(111)A substrates. The effect of the As4 flux during growth on the structure of low-temperature GaAs grown on different types of substrates is shown as well.

Photoluminescence study of self-assembled GaAs quantum wires on (631)A-oriented GaAs substrates

The authors report a low-temperature photoluminescence (PL) study of multiple GaAs layers grown between AlAs(0.6 nm)/GaAs(0.6 nm) short-period superlattice barriers (SLBs) simultaneously grown on both GaAs(631)A and (100) substrates. Five GaAs-layers of different nominal thicknesses (LW, ranging from 12 to 2.4 nm) were grown by molecular beam epitaxy. By using (631)A-oriented substrates a self-organized and highly ordered corrugation is obtained in the growth of the GaAs layers, and at the end of the SLB growth, flat surfaces are found. Whereas, for the (100)-oriented sample, flat interfaces are confirmed after the growth of GaAs and SLB layers. By reducing LW below ∼3.6 nm in the (631) sample, strong quantum wire (QWR)-like confinement is achieved as deduced from polarized PL spectroscopy where polarization degrees as large as 0.43 are obtained. The PL emission energy of the (631)-QWRs is redshifted, as compared with the transitions of the (100)-oriented quantum wells, when LW is reduced. The authors explain this energy shift by the widening of the effective thickness of the confinement regions in the GaAs layers.

Angle-dependent magnetotransport in cubic and tetragonal ferromagnets: Application to (001)- and(113)A-oriented(Ga,Mn)As

General expressions for the longitudinal and transverse resistivities of single-crystalline cubic and tetragonal ferromagnets are derived from a series expansion of the resistivity tensor with respect to the magnetization orientation. They are applied to strained (Ga,Mn)As films, grown on (001)- and (113)A-oriented GaAs substrates, where the resistivities are theoretically and experimentally studied for magnetic fields rotated within various planes parallel and perpendicular to the sample surface. We are able to model the measured angular dependences of the resistivities within the framework of a single ferromagnetic domain, calculating the field-dependent orientation of the magnetization by numerically minimizing the free-enthalpy density. Angle-dependent magnetotransport measurements are shown to be a powerful tool for probing both anisotropic magnetoresistance and magnetic anisotropy. The anisotropy parameters of the (Ga,Mn)As films inferred from the magnetotransport measurements agree with those obtained by ferromagnetic resonance measurements within a factor of two.

The Stark Shift of the Hole States in Separate InAs∕GaAs Quantum Dots Grown on (100) and (311)A GaAs Substrates

Deep-level transient spectroscopy is used to study charge-carrier emission from the states of separate quantum dots in InAs/GaAs p-n heterostructures grown on (100)-and (311)A-oriented GaAs substrates in relation to the reverse-bias voltage U. It is established that the structures under consideration exhibit different bias-voltage dependences of the Stark shift for the energy levels of the quantum-dot states on the value of U.

MOVPE growth of highly-strained piezoelectric InGaAs/GaAs quantum wells on [1 1 1]A-oriented substrates

In this paper we present a study on the MOVPE growth and optical evaluation of strained InGaAs/GaAs quantum well (QW) structures with In contents of 17% and 22% on [111]A-oriented GaAs substrates. QW structures grown under different growth conditions were extensively analyzed by means of Photoluminescence (PL) spectroscopy. The dependence of the PL intensity and linewidth on the growth temperature and In content are investigated and compared to simultaneously grown [100]-oriented structures. It is shown that excellent QW interfaces with only ±(1–2) monolayer roughness were achieved for the [111]A-oriented structures with 17% In using a wide range of growth temperatures (550–670°C), whereas the interfacial properties of the [100] samples significantly degraded as the growth temperature was increased. For a [111]A QW structure with 22% In the PL characteristics are similar to those obtained for the 17% In sample; on the contrary, for the companion [100] sample a strong degradation of its optical properties is observed.

In 0.18 Ga 0.82 As/GaAs 1−y P y quantum wells grown on (n11)A GaAs substrates by molecular beam epitaxy

We have investigated the influence of V(As4+P2)/III(Ga) pressure ratio on interface flatness of In0.18Ga0.82As/GaAs1−yPy (2.9 nm/20 nm) single quantum wells (SQWs) (y=0.18–0.32) grown on (100)- and (n11)A-oriented GaAs substrates (n=3, 4, and 5) by molecular beam epitaxy. With decreasing V(As4+P2)/III(Ga) pressure ratio from 8 to 4, full width at half maximum (FWHM) of 11 K photoluminescence (PL) peak of the (411)A SQW was dramatically reduced to 7.8 meV, while those of the (311)A and (100) SQWs increased from their best FWHM (7.3 and 6.8 meV). This is different from those in the other SQWs. The best values of FWHM of the (311)A and (411)A SQWs were as small as those of the (100) In0.18Ga0.82As/GaAs1−yPy and In0.17Ga0.83As/Al0.3Ga0.7As QWs. The highest PL intensity was observed for the (411)A SQW grown under V(As4+P2)/III(Ga)=4. The (311)A SQWs grown under V(As4+P2)/III(Ga)=4 to 8 have 60%–70% smaller PL intensity than the (411)A SQW, but they have much higher PL intensity than the (100) and (511)A SQWs. This implies that the (311)A and (411)A In0.18Ga0.82As/GaAs1−yPy QWs have a good optical quality.

Effect of the growth parameters on the luminescence properties of high-quality GaAs/AlGaAs multiquantum wells on (1 1 1)A substrates by metal organic vapor phase epitaxy

We report on a study of the growth parameters and their effect on the structural and optical properties of GaAs/AlGaAs multiquantum well (MQW) structures grown on novel (1 1 1)A-oriented GaAs substrates by atmospheric-pressure metalorganic vapor-phase epitaxy. The MQW structures have 25 periods with well widths ranging from 25 to 45 Å and an Al fraction in the barriers of around 25% and were grown at 600°C using V/III ratios ranging from 52 to 261 and various growth rates on exact and misoriented (1 1 1)A substrates. High-resolution X-ray diffractometry was used to assess the crystal quality and obtain structural information. The growth rates for GaAs on (1 1 1)A and (1 0 0) oriented substrates are compared. The optical quality was evaluated by low-temperature photoluminescence (PL) spectroscopy. We determined the optimum growth conditions to obtain high structural quality and PL emission intensity. A PL line width of 10.5 meV was achieved, which is the lowest value reported to date for GaAs/AlGaAs MQWs on (1 1 1)A or (1 1 1)B GaAs by any growth technique, corresponding to less than a ±1 monolayer fluctuation of the well width over the 25 periods.

Growth and Characterization of Vertical-Cavity Surface-Emitting Lasers Grown on (311)A-Oriented GaAs Substrates by Molecular Beam Epitaxy

We have fabricated InGaAs/GaAs vertical-cavity surface-emitting lasers (VCSELs) grown on GaAs(311)A substrates by molecular beam epitaxy. High-quality crystals for VCSEL structures on (311)A having flat and smooth heterointerfaces were obtained by optimizing the growth conditions. It was experimentally demonstrated that the optical anisotropic gain of (311)-oriented strained-layer quantum wells is effective for polarization control. A [*BAR*2*BAR*33] polarization mode is stable against the injection currents of 3 times the threshold. In addition, the threshold current density of 80 A/(cm2·well) is achieved for a device with a laser aperture as large as 25 µ m square, which is comparable to or even lower than that of (100)-oriented VCSELs.

Optical properties of (113) GaAs/AlAs superlattices grown by molecular beam epitaxy and atomic layer molecular beam epitaxy

We have investigated the optical properties of GaAs/AlAs superlattices grown by molecular beam epitaxy (MBE) and atomic layer MBE (ALMBE) on {113}A-oriented GaAs substrates. The corrugation which appears in the samples obtained by MBE does not exhibit any periodicity. Phonon-associated replicas are only observed on the photoluminescence excitation spectra of ALMBE superlattices. It was found that the observed differences can be attributed to the growth techniques employed in the synthesis of the samples: MBE superlattices have rougher interfaces than the ALMBE ones, but a lower number of nonradiative recombination centers.

LiInSe 2 thin epitaxial films on {111} a-oriented GaAs

LiInSe 2 thin epitaxial layers were prepared by flash evaporation on {111}a-oriented GaAs substrates and investigated by reflection high energy electron diffraction. The overgrowth is characterized by one-dimensional epitaxy with preferred azimuthal orientation. In general, the LiInSe 2 thin films crystallize in the β-NaFeO 2 structure. In the substrate temperature range from 620 to 670 K a second phase with chalcopyrite structure was observed besides the β-NaFeO 2 structure.

Structural and electrical properties of CuInSe 2 epitaxial layers prepared by single-source evaporation

CuInSe 2 thin films with thicknesses in the range 1–5 μm were deposited onto glass and semi-insulating (111)A-oriented GaAs substrates by single-source evaporation. Source temperatures above 1400 K were found to be necessary to prepare single-phase and nearly stoichiometric CuInSe 2 films. Epitaxial growth on GaAs was observed in the substrate temperature range 720–870 K. From the electrical properties it follows that the films are characterized by high acceptor concentrations and high degrees of compensation.

Epitaxial layers of CuInSe 2 on GaAs

CuInSe 2 single-crystal films with (112) orientation and with thicknesses in the range 800–1200 Å were deposited onto semi-insulating (111)A-oriented GaAs substrates by flash evaporation under controlled growth conditions. Epitaxial growth began at a substrate temperature T sub = 720 K and twins in the 〈221〉 direction were detected in reflection high energy electron diffraction investigations. The twin concentration decreased with increasing growth temperature. At T sub = 870 K a change of the structure from chalcopyrite to sphalerite was observed. Films produced at T sub ⩽ 720 K showed n-type conductivity whereas at higher growth temperatures the films were always p type and showed a rapid increase in hole concentration with increasing substrate temperature. Two different acceptor levels with ionization energies of 92 meV and about meV were found.