Influence of Nitrogen Species on InN Grown by PAMBE
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Influence of Nitrogen Species on InN Grown by PAMBE P.A. Anderson1, R.J. Kinsey1, C.E. Kendrick1, I. Farrell2, D. Carder2, R.J.Reeves2 and S.M. Durbin1 1 Department of Electrical and Computer Engineering, MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Canterbury, Christchurch, New Zealand. 2 Department of Physics and Astronomy, MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Canterbury, Christchurch, New Zealand. ABSTRACT Active nitrogen species produced by an Oxford Applied Research HD-25 plasma source have been monitored by optical emission spectroscopy and quadrapole mass spectroscopy. Both techniques confirmed that at higher RF powers and lower flow rates the efficiency of atomic nitrogen production increased; emission spectroscopy confirmed that this was at the expense of active molecular nitrogen (N2*). InN films grown on (0001) sapphire/GaN with higher relative molecular content were found to have lower carrier concentrations than the corresponding films grown with higher atomic content. However, electrical properties of films grown on (111) YSZ showed insensitivity to the active nitrogen content. Etching experiments revealed that films grown on sapphire/GaN were nitrogen-polar, while films grown on YSZ were In-polar, suggesting that film polarity can greatly influence the effect active species have on growth. Lattice relaxation, as measured by reflection high-energy electron diffraction, revealed that the N-polar films grown under high relative molecular flux relaxed fully after ~60 nm of growth, while the corresponding In-polar film relaxed fully within the first several nm of growth. INTRODUCTION Despite the success of molecular beam epitaxy (MBE) in growing commercial arsenide and phosphide semiconductors, the nitride industry depends entirely on metal organic chemical vapour deposition (MOCVD) for production. MBE has proved a useful technique for nitrides research but the film quality achieved by the technique has always lagged slightly behind that of MOCVD [1]. A key difference between the two techniques is how the growth constituents are supplied to the substrate surface. MOCVD typically uses trimethylgallium, trimethylindium and trimethylaluminium as the group-III sources, and ammonia as the nitrogen source. MBE normally utilises elemental group-III sources, and while the radio frequency inductively coupled plasma source (RF-ICP) is the most common nitrogen source [2, 3], ammonia is also widely used. The different sources clearly play a critical role in the growth dynamics as MOCVD growth of GaN can be sustained at temperatures several hundred degrees higher than MBE. It is this higher sustainable growth temperature which is widely believed to result in the superior properties of MOCVD grown films. In the case of MBE, the elemental group-III flux is well understood and easily quantified by devices such as a quartz crystal oscillator. However, the nitrogen RF-ICP source produces many different active species [4-6]; a detailed
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