THERMOPOWER INVESTIGATION OF N-TYPE AND P-TYPE GAN

A comparative investigation of the Hall effect, conductivity, and ther mopower properties of molecular-beam-epitaxy-grown GaN is presented. I n unintentionally doped n-rype GaN, a negligible thermal activation of the thermopower is observed above 300 K. In as-grown GaN:Mg, a thermo power activation energy of 280 meV is observed at high temperatures, a s well as a scattering factor A = 3. At temperatures below 120 K, the Seebeck coefficient of p-type GaN changes sign and indicates n-type co nductivity. These results show that hopping in the acceptor band contr ibutes significantly to the electronic transport properties. After hyd rogenation of GaN:Mg, both conductivity and thermopower have an activa tion energy of 520 meV, which is at variance with the presence of pote ntial fluctuations in the material. This demonstrates hat hydrogen pas sivates Mg-doped GaN by the formation of electrically inactive Mg-H co mplexes, in contrast to the formation of compensating H-related donors , which should lead to noticeable potential fluctuations. [S0163-1829( 98)00335-X].