Polarization characteristics of 480-680 nm (1 1 2¯ 2) InGaN/GaN quantum well structures with strain relaxation effects

The polarization characteristics as a function of the In composition for semipolar (1 1 2¯ 2) InGaN/GaN quantum well (QW) structures with strain relaxation effects are investigated by using the multiband effective-mass theory. We assumed that the strain relaxation ratio ∊y′y′0-∊y′y′/∊y′y′0 is linearly proportional to the difference in the lattice constants between the well and the substrate. The energy spacing between the first two subbands increases with increasing In composition, and the average hole effective mass of the first subband is reduced for a QW structure with a larger In composition. The [1¯1¯ 2 3] x′-polarized matrix elements are shown to be much larger than the [1 1¯ 0 0] y′-polarized matrix elements. As a result, the x′-polarized light emission is shown to be dominant and a weak function of the In composition. On the other hand, the light emission for y′-polarizations rapidly decreases with increasing In composition, mainly due to a decrease in the matrix elements. Thus, the absolute value of the polarization ratio rapidly increases with increasing transition wavelength.