Crystal orientation effects on electronic properties of wurtzite InGaN/GaN quantum wells

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Abstract
Crystal orientation effects on electronic properties of wurtzite InGaN/GaN quantum wells (QWs) with piezoelectric (PZ) and spontaneous (SP) polarization are investigated using the multiband effective-mass theory. With increasing crystal angle, the internal field of the InGaN/GaN QW structure changes its sign near the crystal angle of 55° while that of the GaN/AlGaN QW structure gradually decreases without changing its sign. The interband transition energy is redshifted for crystal angles near θ=0° and gradually increases with the crystal angle due to the reduced SP and PZ polarization effects. The y′-polarized optical matrix element largely increases with increasing crystal angle. This is mainly due to the fact that the states constituting the topmost valence subband near the band edge are predominantly |Y′〉-like for QW structures with larger crystal angle. Also, it is observed that the average hole effective mass is largely reduced with increasing crystal angle. In particular, the average hole effective mass of the (101̄0)-oriented QW structure are about four times smaller than that of the (0001)-oriented QW structure.