ELASTIC STRAIN RELAXATION AND PIEZOEFFECT IN GAN-ALN, GAN-ALGAN AND GAN-INGAN SUPERLATTICES

We calculated the elastic strain relaxation in (GaN)(n)-(AlN)(n), (GaN )(n)(AlxGa1-xN)(n) and (GaN)(n)(InxGa1-xN)(n) superlattices where n is the number of layers in the superlattice cell. This calculation and a similar calculation for a semiconductor-insulator-semiconductor struc ture allowed us to determine the lower and upper bounds for the elasti c strain relaxation in (GaN)(m)(AlN)(n) superlattices with arbitrary n /m ratios, i.e., we determine a full range of the critical thicknesses for GaNm(AlN)(n) superlattices. The obtained theoretical results can also be applied to other superlattices based on III nitrides and their solid solutions. Our theory agrees with the experimental data for GaN -AlN superlattices. Also, we shaw that the piezoelectric effect may ca use a large shift of the absorption edge in defect-free GaNm(AlxGa1-xN )(n) superlattices. (C) 1997 American Institute of Physics.