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MOVPE growth and characterization of InN and related heterostructures
Tata Institute of Fundamental Research (TIFR), 1, Homi Bhabha Road, Mumbai, Mumbai 400005, India
|Among the Group III-nitrides, InN has been an enigma, with excellent material properties predicted theoretically, which have been difficult to realize experimentally, primarily limited by poor material quality. I will present an overview of research at TIFR into the synthesis and characterization of InN epilayers.
We have performed a detailed investigation of the microstructure of InN deposited under various MOVPE conditions in a showerhead reactor, allowing us to optimize the InN epilayers. We obtain InN layers that are highly mosaic, with an intrinsic bandgap of ~ 0.7eV, whose measured absorption edge is strongly influenced by background carrier concentration and residual stress. By a careful evaluation of the lattice constants we find that the films are under primarily hydrostatic stress which results in a shift in the band edge to higher energy. The key factor influencing the microstructure is the total amount of ammonia dissociation which is governed by a combination of growth parameters. Inserting an InGaN interlayer between the GaN buffer layer and InN films is helpful in reducing the edge dislocation density, which is otherwise not very sensitive to the growth parameters for a given layer thickness.
We found signatures of superconductivity in a few of our InN samples. However, by a careful correlation of the temperature dependences of both resistivity and magnetic susceptibility with structural information, we conclusively established that the superconductivity seen is not intrinsic to the InN, and arises from the presence of trace amounts of indium oxide impurity in the sample.
We have grown GaN/InN/GaN single- and multi-quantum well structures by MOVPE, although with very rough interfaces. From internal photoemission measurements we can determine the band offsets at the GaN/InN heterojunction. Recently, we have also synthesized a-plane InN layers via MOVPE, and are in the process of optimizing the layer quality.
Presentation: Invited oral at E-MRS Fall Meeting 2009, Symposium A, by Arnab Bhattacharya
See On-line Journal of E-MRS Fall Meeting 2009
Submitted: 2009-05-25 02:51 Revised: 2009-06-07 00:48