MBE Growth of Cubic InN
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0955-I08-03
MBE Growth of Cubic InN Jörg Schörmann, Donat Josef As, and Klaus Lischka Department of Physics, University of Paderborn, Warburger Strasse 100, Paderborn, 33095, Germany
ABSTRACT Cubic InN films were grown on top of a c-GaN buffer layer by rf-plasma assisted MBE at different growth temperatures. X-Ray diffraction investigations show that the c-InN layers consist of a nearly phase-pure zinc blende (cubic) structure with a small fraction of the wurtzite (hexagonal) phase grown on the (111) facets of the cubic layer. The content of hexagonal inclusions is decreasing with decreasing growth temperature. The full-width at half-maximum (FWHM) of c-InN (002) rocking curve is about 50 arcmin. Low temperature photoluminescence measurements reveal a band gap of about 0.61eV for cubic InN. INTRODUCTION Among nitride semiconductors, InN is the least investigated of all and is expected to be a promising material for high frequency electronic devices [1,2]. The most important recent discovery about InN is that it has a much narrower band-gap than reported previously. For hInN values between 0.6 eV and 0.7 eV are measured [3,4]. Group III-nitrides with cubic crystal structure are expected to have even lower band gaps and can be grown on substrates with cubic structure. However, the zincblende polytype is metastable and only a very narrow growth window is available for the process conditions [5]. The use of nearly lattice matched, free standing high quality 3C-SiC (001) substrates let to substantial improvements of the crystal quality of c-III-nitrides [6] and the absence of polarization fields [7] is advantageous for many device applications. So far little has been reported on the growth of cubic InN [8, 9]. EXPERIMENT Cubic InN films were grown on top of a c-GaN buffer layer (600 nm) by rf-plasma assisted molecular beam epitaxy (MBE). The c-GaN buffer layer was deposited on free standing 3C-SiC (001) substrates at growth temperatures of 720 °C. For the InN growth the temperature was reduced and varied in the range of 419°C to 490°C, respectively. InN growth was started under In rich conditions at an In-BEP of 6.8*10-8 mbar and was decreased to 3.1*10-8 mbar after two minutes of growth. The thicknesses of the InN layers were at least 130 nm and the growth was continuously monitored by reflection high energy electron diffraction (RHEED). Structural characterization was carried out by high resolution X-Ray diffraction (HRXRD). Photoluminescence (PL) measurements at 10 K were performed using the 488 nm line of an Ar+ laser and PL-signal was detected with an InAs photodiode.
RESULTS AND DISCUSSION
3.0 3C-SiC
HRXRD investigations were performed to determine the phase purity of our c-InN layers. All ω-2Θ-scans confirmed the 2.6 formation of the cubic phase of InN. c-InN Bragg peaks observed at 35.8 °, 39.9 ° and 2.4 41.3 ° correspond to c-InN (002), c-GaN (002) and 3C-SiC (002), respectively. No h-InN (10-11) additional reflexion of h-InN grown in 2.2 -0.2 0.0 0.2 (0002) direction was detected. The full q [Å ] width at
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