Thin films of InN show high n-type conductivity, for which the origin is not completely identified up to date. InN layers with carrier concentrations down to 10¹⁷ cm^-3 have been prepared, however, no p-type InN could be demonstrated. Electron accumulation at the surface was verified on air [1], and on clean InN surfaces in ultrahigh vacuum [2]. It was explained as an intrinsic property of InN layers ascribed to its band structure [2]. In a previous work [3] we showed by Auger electron spectroscopy (AES) depth profiling and simultaneous conductivity measurements the correlation between the oxygen content and the electron accumulation. In this work we extend this study by analyzing the peak energy shift in AES on both undoped and Mg-doped InN. The position of the Auger peaks is sensitive to the position of the Fermi level [4]. This capability was used to obtain information about the type of conductivity and the band bending. On all InN surfaces a strong increase of the resistivity within the first 5 nm confirms the existence of a highly conductive n-type surface layer. A strong Auger peak shift of about 2 eV was observed due to the formation of a wide band gap In₂O₃. After reaching equilibrium of the peak shift after the removal of about 50 nm a difference of 0.3 eV was observed between undoped and Mg-doped InN. Consequently, Mg-doped InN layers have indeed p-type conduction; however, the high n-type surface conductivity is overlaying it and the InN layer appears to be n-type.

[1] H. Lu, W.J. Schaff, et al, Appl. Phys. Lett. 82, 1736 (2003)

[2] I. Mahboob, T.D. Veal, et al, Phys. Rev. B 69, 201307 (R) (2004).

[3] V. Cimalla, et al, phys. stat. sol (c) 2,

[4] R. Kosiba, Thesis, Technical University Ilmenau, 2004