Optical anisotropy modulation in nonpolar a-plane AlGaN by manipulating the anisotropic in-plane strains through SiNx interlayers engineering

The achievement of high polarization nonpolar III-nitrides has been hindered by high density of defects, large surface fluctuations and in-plane strains. Here, we show that these critical challenges can be improved by manipulating the growth time of SiNx interlayers. The discolation density of nonpolar a-plane Al0.1Ga0.9N has been effectively reduced by introducing the in-situ deposited SiNx interlayer, as the nonpolar a-plane Al0.1Ga0.9N can only nucleate at open pores of SiNx nanomask. During the growth process, the lateral overgrowth will occur from the openings with the dislocation bending and annihilation. Furthermore, the strip distributed nanomask can change the anisotropy of in-plane strains and optical properties of nonpolar a-plane Al0.1Ga0.9N. When the growth time of SiNx increased from 0 min to 2 min, the in-plane strain along m-axis and c-axis direction changed from -0.2250% and -0.5145% to -0.0638% and -0.2728%, respectively. More importantly, the optical degree of polarization of nonpolar a-plane Al0.1Ga0.9N has been changed from 0.4385 to 0.8129 along with the increase SiNx deposition time by polarized photoluminescence. By simplely changing the SiNx growth time, high polarization nonpolar a-plane devices may be fabricated on this high quality strain-modulatable nonpolar AlGaN template, which is desirable for high efficiency liquid crystal displays or other polarization sensitive photodetectors. (c) 2018 Elsevier B.V. All rights reserved.