Anisotropic structural and optical properties of semi-polar (20–21) InGaN/GaN multiple quantum wells grown on patterned sapphire substrates

Abstract

Semi-polar orientation owns the advantage of reduced internal piezoelectric fields by tilting the growth direction away from the conventional c-direction. The crystal symmetry and the balanced biaxial stress in growth plane are inevitably broken in the semi-polar orientation, leading to the appearance of anisotropic properties in both structural and optical performance. This report has investigated the structural and optical properties of semi-polar (20–21) InGaN/GaN multiple quantum wells overgrown on patterned sapphire substrates with a wide wavelength range from 415 nm to 521 nm. Polarization switching was not observed on these semi-polar (20–21) samples. The polarization ratio monotonically increases from 0.18 to 0.43 with increasing the emission wavelength, and the energy difference simultaneously increases from 17 meV to 29 meV. As increasing the excitation laser power, the polarization ratio drops slightly while the energy difference remains stable, indicating a saturation of the recombination to the topmost valence subband. These results help exploit the anisotropic structural and optical properties of semi-polar nitrides and promote the development of highly polarized light source for the application in the fields of display and communication.