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Rectifying contacts to n-type GaN formed with sputter deposited films of Au, Cu, Cr, Ni and Pt were studied using current–voltage and capacitance–voltage measurements. These rectifying contacts were non-ideal as seen from the non-linearity of the semilogarithmic plots of the forward characteristics. Also, the high ideality factors as determined from the approximately linear region of the plots were much greater than one. The non-ideal behavior cannot be understood in terms of thermionic emission simply by excluding the effects of a series resistance and recombination current. This deviation from thermionic emission has been interpreted to be due to space charge limited current conduction in the presence of deep-level states. A simple analysis of these characteristics has been used to identify the deep-level states in the energy range 0.27–0.43 eV below the conduction band minimum and with an approximate concentration between 1015 and 1016/cm3. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]