The optical properties of wurtzite-structured InN grown on sapphire substrates by molecular beam epitaxy have been characterized by optical absorption, photoluminescence, and photo-modulated reflectance techniques. All these three characterization techniques show an energy gap for InN between 0.7 and 0.8 eV, much lower than the commonly accepted value of 1.9 eV. The photoluminescence peak energy is found to be sensitive to the free electron concentration of the sample. The peak energy exhibits very weak hydrostatic pressure dependence, and a small, anomalous blueshift with increasing temperature.Electronic Mail: w_walukiewicz@lbl.gov

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We succeeded in growing InN films two-dimensionally by radio-frequency plasma-excited molecular beam epitaxy (RF-MBE), using a low-temperature-grown InN buffer layer. From the results of reflection high-energy electron diffraction (RHEED) observation and X-ray diffraction (XRD) measurement, it was found that a single crystal of InN films with a wurtzite structure was obtained. Moreover, from the results of Hall effect measurement, it was found that the InN films had quite high electron mobilities. The best electron mobility at room temperature obtained in this study was 760 cm2/V·s and the corresponding carrier density was 3.0×1019 cm-3. To our knowledge, this electron mobility is the highest value ever reported for single crystal InN films.

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