STRAIN EFFECTS ON OPTICAL GAIN IN WURTZITE GAN

Strain effects on optical gain in hexagonal bulk GaN are calculated an d explained in terms of the change in the effective hexagonal crystal field component. Qualitatively, even unstrained wurtzite structures co rrespond to cubic crystals with a proper biaxial stress applied. Such biaxial stress results in effective tensile deformation along the c ax is ([111] direction in cubic crystals) end compressive strain in the p erpendicular plane. Therefore, the light mode with a polarization vect or parallel to the c axis is suppressed, while the mode with a perpend icular polarization is enhanced in wurtzite structures. Thus, compared to cubic structures with similar material parameters, a strong optica l anisotropy of wurtzites results in enhanced gain for certain light p olarizations, which make wurtzite structures superior for lower-thresh old lasing. These qualitative arguments are illustrated by numerical c alculations of optical gain in biaxially strained wurtzite GaN, based on a 6 x 6 envelope-function Hamiltonian. (C) 1997 American Institute of Physics.