Alloying is a commonly accepted method to tailor properties of semiconductor materials for specific applications. Only a limited number of semiconductor alloys can be easily synthesized in the full composition range. Such alloys are, in general formed of component elements that are well matched in terms of ionicity, atom size and electronegativity. In contrast there is a broad class of potential semiconductor alloys formed of component materials with distinctly different properties. In most instances these mismatched alloys are immiscible under standard growth conditions. Here we report on the properties of GaN 1-x As x a highly mismatched, immiscible alloy system that was successfuly synthesized in the whole composition range using a non-equilibrium low temperature molecular beam epitaxy technique. The alloys are amorphous in the composition range of 0.170.2, and to the upward movement of the valence band for alloys with x<0.2. The unique features of the band structure offers an opportunity of using GaN 1-x As x alloys for various types of solar power conversion devices. 3 1. The Ga-N-As Alloy system Dilute alloysSemiconductor alloys formed through substitution of atoms with very different electronegativity and/or size have been known as highly mismatched alloys (HMAs).Because of large miscibility gaps, typically HMAs consist of a semiconductor matrix (elemental or compound) with the substitution of a small amount (up to several percents) of distinctly different isovalent atoms. The HMAs show large band gap reduction and their electronic structure is drastically different from their host materials. This is in contrast to conventional semiconductor alloys such as AlGaAs and GaAsP whose physical, electronic and optical properties can be deduced from a linear interpolation between their corresponding end point compounds with only a slight deviation, as predicted by the virtual crystal approximation (VCA). A most notable example of HMAs is the As-rich GaN x As 1-x in which strong band gap reduction by as much as 180 meV per mole percent of N has been observed [1,2,3,4]. The strong dependence of the band gap on the N content has made these diluted III-V nitrides important materials for a variety of applications, including long wavelength optoelectronic devices [5,6] and high efficiency hybrid solar cells [7,8].In contrast to the very extensively studied As-rich GaNAs alloys much less work has been devoted to HMAs on the N-rich side of this alloy system. It was found that GaN doped with As at low, impurity like levels shows a characteristic blue emission at room temperature. At higher As doping levels an abrupt decrease in the band gap of...

The carrier localization phenomenon has been investigated for GaBiAs by photomodulated transmittance (PT) and photoluminescence (PL). In the case of PT measurements, a decrease in the energy-gap related PT signal has been clearly observed below 180 K. In PL spectra a broad emission band very sensitive to the excitation power has been found. In comparison to the energy-gap related transition, this band is shifted to red. The recombination time for this band at low temperature decreases from 0.7 to 0.35 ns with the increase in the emission energy. All the findings are clear evidences for strong carrier localization in this alloy.

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We report the growth by molecular beam epitaxy of GaBi x As 1−x epilayers on ͑311͒B GaAs substrates. We use high-resolution x-ray diffraction ͑HRXRD͒, transmission electron microscopy, and Z-contrast imaging to characterize the structural properties of the as-grown material. We find that the incorporation of Bi into the GaBiAs alloy, as determined by HRXRD, is sizably larger in the ͑311͒B epilayers than in ͑001͒ epilayers, giving rise to reduced band-gap energies as obtained by optical transmission spectroscopy. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2827181͔ GaBi x As 1−x alloys are attracting in recent years a considerable deal of attention. [1][2][3][4][5][6] The band gap of GaAs is strongly reduced upon the addition of small amounts of Bi ͑ϳ90 meV per percent of Bi͒, with a strong enhancement of the spinorbit splitting energy.3,4 These remarkable properties make the Ga͑In͒BiAs system an attractive candidate to develop GaAs-based applications for long-wavelength optoelectronics as well as for spintronics. While the use of dilute nitrides in device applications is currently limited because the electron mobility of these compounds is abruptly reduced due to strong N-related alloy scattering, dilute bismides might exhibit improved transport properties. 6 The growth of epitaxial layers on high-index planes represents a step forward in semiconductor material engineering, as it offers an additional degree of freedom to develop applications with improved properties with respect to the conventional ͑001͒-grown devices. The interest in non-͑001͒ semiconductor structures is manifold and concerns growth, impurity incorporation, electronic properties, lasing performance, and piezoelectric effects. To mention a few examples, the use of non-͑001͒ substrates has allowed the fabrication of ultrahigh mobility two-dimensional hole gases in GaAs/ AlGaAs heterostructures, high-performance InAs/ GaAs quantum dot ͑QD͒ lasers, InGaAs/ GaAs QDs with enhanced piezoelectric effects, and GaMnAs epilayers with modified Mn incorporation and magnetic anisotropies. [7][8][9] In this study, we explore the growth by molecular beam epitaxy ͑MBE͒ of GaBiAs alloys on ͑311͒B GaAs substrates. We use a series of structural and optical techniques to characterize the as-grown material and to determine the amount of Bi incorporated into the samples. Our results reveal that the incorporation of Bi is enhanced in the ͑311͒B samples in comparison to the conventional ͑001͒ orientation.For this study, GaBi x As 1−x films were grown by MBE on semi-insulating ͑001͒ and ͑311͒B GaAs substrates at a growth temperature ͑T G ͒ of ϳ350°C with different As to Ga flux ratios. The growth was performed in a specially designed MBE reactor ͑see Ref. 10 for details͒. Atomic Ga and Bi were used as group-III and group-V sources, respectively, while As in the form of dimers ͑As 2 ͒ was produced by using a two-zone purpose made cell. In order to incorporate Bi efficiently into MBE-grown GaAs, the Ga to As flux needs to be on the brink of As shortage, close to...

Integer quantum Hall effect in single-layer graphene with tilted magnetic field