Photoluminescence studies of Mg-doped and Si-doped gallium nitride epilayers

We present time-, temperature- and intensity-dependent photoluminescence me asurements of undoped, n-type and p-type GaN epilayers. In the nominally un doped samples we observe at low temperatures the trapping of free excitons by neutral donors and subsequent radiative recombination. In the n-type Si- doped samples bound-exciton luminescence is dominant over a wide range of t emperatures. The luminescence from p-type Mg-doped samples is dominated by shallow-donor-shallow-acceptor pair recombination and by a deep blue centre s at 3.0 eV. These two emission bands show identical temperature and linear intensity dependence.