Structural and Optical Characterization of InGaN Layers Grown by MOMBE
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Structural and Optical Characterization of InGaN Layers Grown by MOMBE P.Singh1, J.Aderhold2, J. Graul2, V. Yu. Davydov3, F. Gourbilleau1 and P. Ruterana1* 1 SIFCOM UMR 6176, ENSICAEN-CNRS, 6, Bd du Maréchal Juin, 14050 Caen Cedex 2 LFI, University of Hannover, Schneiderberg 32, 30167, Hannover, Germany, 3 Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia
Abstract The investigated InGaN ternary films were grown by MOMBE, with the In fraction varying from 6% to 100%. Using XRD and TEM, we determine the crystalline state, the nature of defects inside the layers and their distribution as related to the In concentration. The band gap of the alloys was studied through PL measurements, it is below 1 eV for InN.
Introduction Nitride semiconductors (AlN, GaN, InN and their alloys) have great potential for use in optical devices and high power, high frequency electronic devices. Among these nitrides, InN has the smallest effective mass and the highest electron drift velocity [1]. This sets it as a very promising material for the channel layers in high-speed electronic devices [2]. Until very recently, difficulties in growing high quality InN films have hindered the understanding of its properties and possible applications. During the past few years, the development of growth techniques, especially molecular beam epitaxy (MBE), have significantly improved the quality of InN films attaining Hall mobility beyond 1000 cm2/Vs and carrier concentration in the 1018/cm3 range. Alloying InN with AlN and/or GaN will allow the widest range in wavelength using the same family of ternary alloys (6.2-0.7 eV) [3]. However, the growth of InN and the ternary alloys is still a challenge as InN and GaN have a poor miscibility at high growth temperatures ( ~ 800°C ) probably due to the large lattice mismatch of 11% [4]. As a result, the chemical inhomogeneity gives rise to structural defects in such ternary compound [5]. Due to these defects the photoluminescence yield may be decreased. In this work, we investigate the microstructure of InGaN layers with a composition that varies from 6 to 100% (In). An attempt is made to connect the observations to the growth conditions and PL emission. Experimental The investigated layers were grown by metalorganic molecular beam epitaxy (MOMBE) from Triethylindium (TEIn), Triethylgallium (TEGa), and RF activated nitrogen, the main features of the growth for the investigated samples have been collected in table 1. The TEIn and nitrogen fluxes were kept constant at 0.3465 and 1.8 sccm, respectively. The layer composition was determined by varying the TEGa flux, during the growth the RF power was always fixed at 440 W. The PL measurements were carried out on all the samples using a He-Cd laser at low temperature (7K). X-ray diffraction allowed to measure the mosaicity of the layer first on the 0002 rocking curves, and on some layers by exploring the reciprocal lattice from 0 to 60 and 0 to 360 using ψ, χ, scans, respectively. The surface state and *
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