Features of the spatial distribution of indium in InGaN epitaxial layers grown by plasma-assisted molecular beam epitaxy
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ICATION, TREATMENT, AND TESTING OF MATERIALS AND STRUCTURES
Features of the Spatial Distribution of Indium in InGaN Epitaxial Layers Grown by Plasma-Assisted Molecular Beam Epitaxy V. N. Jmerik^, A. M. Mizerov, T. V. Shubina, D. S. Plotnikov, M. V. Zamoryanskaya, M. A. Yagovkina, Ya. V. Domracheva, A. A. Sitnikova, and S. V. Ivanov Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia ^e-mail: [email protected] Submitted September 25, 2007; accepted for publication October 17, 2007
Abstract—The processes leading to the formation of a spatially nonuniform distribution of indium in the InxGa1 – xN layers with x = 0–0.6 grown by molecular beam epitaxy with plasma activation of nitrogen at relatively low growth temperatures (590–630°C) are studied. It is found that at low values of x < 0.1, the growth proceeds pseudomorphically at least to a thickness of 70 nm, and these layers are characterized by a high uniformity of the In distribution, which confirms their thermodynamic stability. Upon increasing x up to ~0.3, the signs of a nonuniform In distribution are observed, which is associated with the stress relaxation facilitating the development of phase separation. It is shown that layers with In distribution of lower uniformity feature more intense photoluminescence in the energy range 2.0–2.5 eV. For the layers with x ≈ 0.6, complete phase separation is observed with the formation of several phases with a wide range of compositions, including the region in the vicinity of the InN binary compound. PACS numbers: 81.40.Tv, 81.05.Ee, 81.15.Gh DOI: 10.1134/S1063782608050229
1. INTRODUCTION In recent decades, the mass production of light-emitting and laser diodes based on wide-gap III–V compounds has become an important segment of the semiconductor industry. It is considered that a key role in the development of technologies of these devices was played by the unique properties of the InxGa1 – xN/GaN heterostructures used in the active region of lasers. These properties are first of all associated with the existence of the localization effect of charge carriers in the InGaN compound, which emerges due to a spatially nonuniform In distribution in the layers (aggregation of In) with respect to the average In content (x) [1]. The development of the potential profile observed in this case restricts the lateral transport of nonequilibrium charge carriers, which leads to an increase in the efficiency of radiative recombination in device structures even at a relatively high density of grown-in dislocations (as high as ~109 cm–2), which are the centers of nonradiative recombination. Commercial III–N based light-emitting diodes (LEDs) are produced with a maximum working emission wavelength (λmax) as high as 525 nm [2]. In the literature are reports on the fabrication of pilot samples of LEDs with λmax = 645 nm. However, these devices had substantially smaller values of quantum efficiency and output optical power [3, 4]. For commercial laser diodes, the value of λmax
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