Nonpolar and semipolar GaN, optical gain and efficiency

Abstract

Crystal orientation effects on electronic and optical properties of wurtzite (WZ) InGaN/GaN quantum wells (QWs) with piezoelectric (PZ) and spontaneous (SP) polarizations are investigated using the multiband effective-mass theory and non-Markovian optical model. Also, the electron overflow in non-polar InGaN/GaN QW structures with a superlattice (SL)-like electron injector (EI) layer is investigated using a simple model. The effective mass along <i>k'_y</i> of the topmost valence band greatly decreases with increasing crystal angle while the <i>y'</i>-polarized optical matrix element significantly increases with increasing crystal angle. In particular, matrix elements of non-polar (1120)-oriented a-plane QW structure with a relatively higher In composition of 0.4 are about three and half times bigger than those of the (0001)-oriented c-plane QW structure. On the other hand, in the case of the QW structure with a relatively smaller In composition, the difference of matrix elements between the (0001)- and (1120)-oriented QW structures is smaller than that of the QW structure with a relatively higher In composition. With increasing crystal angle, the optical gain peak for the <i>x'</i>-polarization gradually decreases while that for the <i>y'</i>-polarization significantly increases. As a result, the in-plane optical anisotropy increases with increasing crystal angle. The in-plan optical anisotropy of non-polar a-plane QW structure gradually increases with increasing transition wavelength or In composition. The optical anisotropy is ranging from 0.50 at 400nm to 0.80 at 530 nm for the QW structure with <i>L_w</i> = 30 <i>&Aring;</i>. It is found that the electron overflow is found to be greatly reduced by using the SL-like EI laye and rapidly decreases with increasing the number of EI layer. Hence, we expect that the droop phenomenon can be reduced by using the EI layers.