Growth of InN By MBE
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Abstract A series of experiments were performed to explore the growth of InN by Molecular Beam Epitaxy (MBE). The growth conditions were optimized based on the study of RHEED during growth and InN dissociation experiments. Characterization of the InN thin films were performed by various techniques such as TEM and XRD.
Introduction InN containing compounds such as the GaInN ternary are of importance for the fabrication of light emitting devices [1-3]. However, phase separation is known to prevent the homogeneous incorporation of high In-content GaInN for longer wavelength applications [4-5]. The behavior of pure InN growth might help to shed light on the mechanism of the formation of high concentration of InN in the ternary. InN has been prepared by various techniques [6-13]. However, InN normally shows poor optical properties, a high background carrier concentration and poor crystalline properties with indium clusters found from the x-ray diffraction spectrum. For the MBE technique, the most important growth parameters are the flux levels and growth temperature. In the study reported here, RHEED behavior during growth and InN thermal dissociation experiments following growth have been performed to optimize the growth parameters. The results of the characterization of InN films by various means are presented in this report.
Experiment A Perkin-Elmer 430 MBE system was used for the growth of InN. In flux was measured by a crystal monitor located at the growth sample position. An RF nitrogen plasma cell (Oxford CARS-25) was used to supply the active nitrogen. The substrates used were 2-2.5 µm thick GaN epilayers grown on c-plane sapphire by MOCVD at Sandia National Labs and, a 1µm thick molybdenum layer was evaporated on the backside of the substrates to absorb the radiation from the filament. Substrates were screw mounted on an unbonded molybdenum block. Immediately before being introduced into the growth chamber, the substrates were preheated in a preparation chamber to 350°C for 10 minutes to reduce outgassing from the block when it was heated in the growth chamber.
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The growth temperature was measured by a thermocouple on the back of the substrate and was calibrated by the eutectic point of gold-germanium at 356oC. The plasma cell was in general operated at 500W with a nitrogen flow rate of 0.8-1.2 sccm. The chamber pressure was in the 2.5-5x10-5 Torr range during growth. The nominal active nitrogen flux under this condition was measured by GaN RHEED intensity oscillations under N-limited growth conditions. The GaN growth rate was limited by the nitrogen flux at substrate temperatures lower than 750oC, above which dissociation became a factor. The available active nitrogen flux was determined to be 3.7x1014 atoms/cm2/sec which was equivalent to 0.36 ml/sec for InN if a
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