  The electrical and magnetic properties of p-type cubic (Ga,Mn)N thin films
grown by plasma-assisted molecular beam epitaxy are reported. Hole
concentrations in excess of 1018 cm-3 at room temperature are observed.
Activated behaviour is observed down to around 150K, characterised by an
acceptor ionisation energy of around 45-60meV. The dependence of hole
concentration and ionisation energy on Mn concentration indicates that the
shallow acceptor level is not simply due to unintentional co-doping.
Thermopower measurements on freestanding films, CV profilometry, and the
dependence of conductivity on thickness and growth temperature, all show that
the conduction is not due to diffusion into the substrate. We therefore
associate the p-type conductivity with the presence of the Mn in the cubic GaN
films. Magnetometry measurements indicate a small room temperature
ferromagnetic phase, and a significantly larger magnetic coupling at low
temperatures.
