Molecular Beam Epitaxial Growth of Nonpolar a-plane InN/GaN Heterostructures
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Molecular Beam Epitaxial Growth of Nonpolar a-plane InN/ GaN Heterostructures Mohana K. Rajpalke1, Thirumaleshwara N. Bhat1, Basanta Roul1, 2, Mahesh Kumar1, 2, and S. B. Krupanidhi1,* 1
Materials Research Centre, Indian Institute of Science, Bangalore- 560012, INDIA Central Research Laboratory, Bharat Electronics, Bangalore-560013, INDIA E-mail:[email protected]
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ABSTRACT Nonpolar a-plane InN/GaN heterostructures were grown by plasma assisted molecular beam epitaxy. The growth of nonpolar a- plane InN / GaN heterostructures were confirmed by high resolution x-ray diffraction study. Reflection high energy electron diffraction patterns show the reasonably smooth surface of a-plane GaN and island-like growth for nonpolar a-plane InN film, which is further confirmed by scanning electron micrographs. An absorption edge in the optical spectra has the energy of 0.74 eV, showing blueshifts from the fundamental band gap of 0.7 eV. The rectifying behavior of the I-V curve indicates the existence of Schottky barrier at the InN and GaN interface. The Schottky barrier height (φb) and the ideality factor (η) for the InN/GaN heterostructures found to be 0.58 eV and 2.05 respectively. INTRODUCTION Growth of non-polar III-nitrides has been an important subject recently due to its potential improvement on the efficiency of III-nitride-based opto-electronic devices [1, 2]. The conventional c-plane GaN based optoelectronic devices suffers from spontaneous polarization effects originating from c-[0 0 0 1] polar axis of the wurtzite heterostructure [3, 4]. These polarization effects produce strong electric fields that distort the quantum well energy bands, also spatially separating the electron hole wave functions which lead to decrease in the radiative recombination efficiency. A potential approach for eliminating the effects of these polarization fields is to grow GaN along nonpolar directions (perpendicular to the c-axis). The growth of nonpolar GaN was intensively studied for improving the performance of light-emitting devices. Despite the study of non-polar GaN and GaN-based heterostructures, there are few reports on epitaxial growth of non-polar InN, which is also an important component of the III-nitride system [5, 6]. Due to narrow bandgap (~0.7 eV), InN has become attractive material for long wavelength optical devices. The large difference between the band gaps of InN and GaN suggests the existence of Schottky barrier at InN/GaN interface. The study of schottky diode based on the GaN related materials is very important from a fundamental point of view as well as forming robust Schottky diodes. Chen et al [7] reported transport studies on c-plane InN/GaN Schottky interfaces. The present work deals with the growth, structural, optical and transport properties of non-polar a-plane InN/GaN heterostructures grown on r-plane sapphire substrates.
EXPERIMENT Nonpolar a-plane InN/GaN (~200 nm / 200 nm) heterostructures were grown on rsapphire substrate by Omicron Nanotechnology plasma assisted molecular beam epitaxy (MBE) sys
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