Phase separation suppression due to external biaxial strain is observed in InxGa1−xN alloy layers by Raman scattering spectroscopy. The effect is taking place in thin epitaxial layers pseudomorphically grown by molecular-beam epitaxy on unstrained GaN(001) buffers. Ab initio calculations carried out for the alloy free energy predict and Raman measurements confirm that biaxial strain suppress the formation of phase-separated In-rich quantum dots in the InxGa1−xN layers. Since quantum dots are effective radiative recombination centers in InGaN, we conclude that strain quenches an important channel of light emission in optoelectronic devices based on pseudobinary group-III nitride semiconductors.

Metal Organic Chemical Vapor Deposition (MOCVD) is nowadays the most frequently used industrial method for growing III‐nitrides. The possible spectrum of in‐situ diagnostic tools is quite narrow because the MOCVD growth process excludes all techniques based on ultra high vacuum conditions. Therefore, only optical methods like spectroscopic ellipsometry and X‐ray diffraction give the possibility to observe and analyse the growing surface in‐situ. We attached simultaneously a multi wavelength spectroscopic ellipsometer and a X‐ray diffraction system to our reactor and could determine parameters like growth rate and layer composition from both techniques. On the one hand the optical measurement gives surface sensitive information about the sample. On the other hand the measurement of the diffraction peak of hexagonal GaN and related alloys during growth gives additional information about the entire structure and the crystal quality. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The energetics and thermodynamic properties of cubic (c-)InxGa1−xN alloys are investigated by combining first-principles total energy calculations, a concentration-dependent cluster-based model, and Monte Carlo simulations. The search for the ground-state energies leads to the conclusion that biaxial strain suppresses phase separation, and acts as a driving force for chemical ordering in c-InxGa1−xN alloys. Ordered superlattice structures, with composition x≅0.5 and stable up to T=1000 K, arises as the relevant thermodynamic property of the strained alloy. We suggest that the In-rich phases recently observed by us in c-GaN/InxGa1−xN/GaN double heterostructures are ordered domains formed in the alloy layers due to biaxial strain.

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We present an x-ray diffractometer for the analysis of epitaxial layers during ͑in situ͒ metal-organic chemical vapor deposition ͑MOCVD͒. Our diffractometer has a conventional x-ray source, does not need a goniometer stage, and is not sensitive to precise adjustment of the samples before measurement. It allows us to perform measurements within a few seconds even from rotating and wobbling samples. The first results of laboratory tests performed with our x-ray diffraction system show that it is well suited for in situ and real-time monitoring of the MOCVD growth process. We were able to measure the growth rate of a cubic GaN layer and the intensity and peak position of Bragg reflections of the growing layer in less than 20 s only.