Optical characterization of disordered InxGa1−xP alloys

Abstract

We present results on the optical characterization of In x Ga 1Ϫx P layers grown by atomic layer molecular beam epitaxy on GaAs ͑001͒ substrates at a growth temperature of 420°C. Our results show that the optical characteristics of these layers, which do not show ordering effects, are strongly dependent on surface stoichiometry during growth. In this way, we can obtain either highly homogeneous alloys with a predictable band-gap energy or layers with optical properties indicative of spatial localization effects, like an anomalous behavior of photoluminescence peak energy with temperature and a large shift between the emission energy and absorption edge. © 1998 American Institute of Physics. ͓S0003-6951͑98͒01920-2͔The In x Ga 1Ϫx P alloy lattice matched to GaAs (x ϭ0.48) has enormous interest for its application in visible light emitters and as an alternative to AlGaAs in GaAs based devices. In particular, In x Ga 1Ϫx P/GaAs based tandem solar cells have reached the highest efficiency achieved at present. 1For device applications it is obviously necessary to know the band-gap energy of the alloy. However, it has been shown 2,3 that formation during growth of ordered domains with CuPt structure decreases the effective band-gap energy and broadens the absorption edge.This alloy exhibits other structural features, which are also growth dependent and are related to the existence of a miscibility gap in the range of growth temperatures used in some epitaxial techniques. 4 This means that In x Ga 1Ϫx P is thermodynamically unstable against separation into two phases of different compositions. In fact there is experimental evidence of some effects related to spinodal decomposition in layers grown by the usual nonequilibrium epitaxial techniques. For example, it is now well established that In x Ga 1Ϫx P layers show quasiperiodic variations in composition over ranges from a few nm to hundreds of nm.2,5-8 This modulated phase separation results in lattice strains which produce contrasts in transmission electron microscopy ͑TEM͒ images. CuPt-like ordering induces specific modifications in the band structure of the In x Ga 1Ϫx P layers, and the energy redshift of the photoluminescence ͑PL͒ line is currently used as a measure of the degree of ordering.2,3 To our knowledge, the effect of compositional modulation, promoted by spinodal decomposition, on the optical properties of disordered layers have not been studied.In this letter we present results on optical behavior of disordered In x Ga 1Ϫx P layers grown at low substrate temperature (T s Ϸ420°C) by atomic layer molecular beam epitaxy ͑ALMBE͒. Structural characterization of the samples was made by high resolution x-ray diffraction ͑HRXRD͒ and Raman spectroscopy, and results will be shown using PL and photoluminescence excitation ͑PLE͒.According to our previous work, 10 the In x Ga 1Ϫx P layers can show either a fine speckle structure with a size in the range 10-20 nm, or superposed to this, a long wavelength contrast (Ϸ80 nm). These features have been related to alloy clu...

Solution Phase Synthesis of Indium Gallium Phosphide Alloy Nanowires

“…Additional insight into compositional homogeneity and crystal structure was acquired with Raman spectroscopy, a technique that has been applied to In x Ga 1– x P alloys to study the presence (or lack) of long-range order and elemental composition. − We first measured the Raman spectra of InP and GaP NWs and compared them to the corresponding bulk materials (Figure S6). The Raman spectrum of the NWs matches that of the bulk and exhibits two phonon modes: one transverse optical (TO) and one longitudinal optical (LO) mode.…”

Elastic constants of InxGa1-xAs and InxGa1-xP determined using surface acoustic waves

“…We have studied two III-V systems: In x Ga 1−x As and In x Ga 1−x P with compositions around x = 0.5. Our aim was twofold: to report their elastic constant tensors, and to investigate the effect on their elastic behaviour of the observed differences in the optical [4] and relaxation [5,6] properties.…”