DX-like behavior of oxygen in GaN

The role of oxygen as a shallow donor and a DX-state in GaN is elucidated b y recent Raman experiments under hydrostatic pressure and the findings of f irst principles calculations. A pressure induced transfer of electrons from a shallow donor state to a deep DX-like state of the same donor can be cor related with vibrational gap modes by monitoring the freeze-out dynamics. B oth features are unique to oxygen doped GaN and cannot be observed in Si do ped material. The gap modes can be well explained by a linear chain model o f impurity vibrations of substitutional O on the N site. A mode variation, and switching steps in its pressure behavior, which occurs in parallel to t he carrier freeze-out are proposed to reflect three different charge states of the strongly localized states of O. This DX-type behavior as well as th e experimental threshold pressure values are in excellent agreement with th e theory results. (C) 2001 Published by Elsevier Science B.V.