Group III-nitrides with wurtzite crystal structure are chemically stable semiconductors with high carrier mobilities, a high internal spontaneous and piezoelectric polarization. These properties make them suitable materials for very sensitive and robust chemical sensors as wel as transistors for high frequency and high power applications. The polar GaN surfaces N-face (000-1) and Ga-face (0001) exhibit significant differences in the electrical and chemical properties. The understanding and controlling of these properties is mandatory for further successful processing for electronic devices.

We studied the properties of N-face and Ga-face GaN surfaces with X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS), atomic force microscopy (AFM), reflection of high energy electron diffraction (RHEED) as well as high resolution electron energy loss spectroscopy (HREELS).

The Ga-face GaN was grown on 6H-SiC(0001)  and the N-face GaN directly on a-Al₂O₃ (0001) by plasma assisted molecular beam epitaxy (PAMBE). The growth was controlled by in-situ RHEED measurements. After finishing the growth the samples were immediately transfered under UHV conditions to the directly attached analytic chamber (base pressure below 2x10^-10 mbar). There the samples were in-situ examined by photoelectron spectroscopy (XPS and UPS) and atomic force microscopy (AFM).

The HREELS measurements were performed after sample transfer with a high vacuum transport system (base pressure below 10^-6 mbar) into the HREELS system.

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