Optical isotropization of anisotropic wurtzite Al-rich AlGaN via asymmetric modulation with ultrathin (GaN) _m /(AlN) _n superlattices

Abstract

Symmetric anisotropy in wurtzite semiconductors, e.g., AlGaN, has led to the significant optical anisotropy that is rather difficult to resolve. Here, a novel scheme for achieving optical isotropization in Al‐rich AlGaN through the introduction of additional asymmetric elements is demonstrated to compensate the native asymmetry. Asymmetric modulation of alloy composition and periodicity of (GaN)m/(AlN)n superlatices was proposed with first‐principles simulations. Results showed that the compensation for the c‐axial symmetry with the asymmetric ultrathin (GaN)m/(AlN)n superlatices (m ≤ 2) could well achieve the equivalence of the ordinary and extraordinary imaginary dielectric functions ε2 at the band edge. Measurement with spectroscopic ellipsometry for this (GaN)m/(AlN)n superlatice insertion in AlGaN host confirmed the theoretical predictions of the optical isotropization. This method can be transferred to other semiconductors in anisotropic structure and with troubles of optical anisotropy.

Optical Performance of Top-Down Fabricated AlGaN Nanorod Arrays with Multi-Quantum Wells Embedded

“…One can see that for the n-type layer emission at approximately 265 nm, the LEE enhancement ratios are approximately 2.4 and 9.2 for the TE and TM polarization states, respectively. Previous investigation indicated that even for compressively grown AlGaN MQWs, strongly TE-polarized emission can be observed at wavelengths as short as 240 nm [30]. Thus, it is reasonable that the LEE enhancement of a mixture of TE and TM states is approximately 2.8.…”

Multiple fields manipulation on nitride material structures in ultraviolet light-emitting diodes

“…In previous study on the optical anisotropy in AlGaN, it was recognized that, in contrast to the Ga-rich AlGaN, the VBM is dominated by the CH band in Al-rich AlGaN instead of HH/LH bands (Fig. 8b ) 108 , 109 . With respect to c -axis, the CH band at VBM is composed of p z -orbitals with odd symmetry.…”

“… 105 , © 2011 AIP Publishing, b ref. 108 , © 2013 John Wiley and Sons; c and d : ref. 113 , © 2020 Springer Nature …”

“…Aside from the challenges at the technical level, the orbital configuration of quantum levels in MQWs should be the most fundamental, which could directly influence the probability of particle transition between the band-edge states and thus the photon behaviors. In 2013, Lin et al studied the optical anisotropy in AlGaN and recognized that the light emission polarized perpendicular to the c -axis is closely related to the near band-edge transitions occurring between the conduction bottom and the top of the valence bands 108 . The conduction band minimum (CBM) at Γ point is solely composed of s- orbitals with even symmetry along any axis going through its center.…”

“…In an attempt to couple lateral emission to the outward emission of the top surface, the photonic crystal based on nanostructure is designed with air voids, nanopillar, nanorod, and NW structures 138 – 141 . From the band engineering perspective, recent results by Lin et al addressed the compensation operation of asymmetry implemented by introducing some additional asymmetric periodicities into the matrix material to balance the intrinsic optical anisotropy in Al-rich AlGaN 108 . Specifically, the compensation of the Δ cr was successfully achieved by the superimposition of variable asymmetrical ultrathin SLs into the anisotropic AlGaN host with high Al content.…”