Search for free holes in InN:Mg-interplay between surface layer and Mg-acceptor doped interior

We measured lateral ac transport (up to 20 MHz), thermopower, as well as resistivity and Hall effect in InN:Mg samples with various Mg content. The sign of the Hall effect for all the samples was negative (electrons), however, the thermopower (alpha) measurements have shown the p-type sign of alpha for moderate Mg content-in the window centered around 1 x 10(19) cm(-3). Further overdoping with Mg yields donor type of defects and the change of thermoelectric power sign. The ac measurements performed as a function of frequency revealed that in both samples exhibiting and nonexhibiting p-type sign of thermopower, the n-type inversion layer at the surface does not prevent the electric contact to the bulk layer. Therefore we conclude that the n-type Hall effect invariably reported for all the Mg-doped samples originates from electron domination in mobility-weighted contributions of both types of carriers. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3153942]