Enhancement of TE polarized light extraction efficiency in nanoscale (AlN)_m/(GaN)_n(m>n) superlattice substitution for Al-rich AlGaN disorder alloy: ultra-thin GaN layer modulation

Abstract

The problem of achieving high light extraction efficiency in Al-rich Al x Ga −x 1 N is of paramount importance for the realization of AlGaN-based deep ultraviolet (DUV) optoelectronic devices. To solve this problem, we investigate the microscopic mechanism of valence band inversion and light polarization, a crucial factor for enhancing light extraction efficiency, in Al-rich Al x Ga −x 1 N alloy using the Heyd-Scuseria-Ernzerhof hybrid functional, local-density approximation with 1/2 occupation, and the Perdew-Burke-Ernzerhof functional, in which the spin-orbit coupling effect is included. We find that the microscopic Ga-atom distribution can effectively modulate the valence band structure of Al-rich Al x Ga −x 1 N. Moreover, we prove that the valence band arrangement in the decreasing order of heavy hole, light hole, and crystal-field split-off hole can be realized by using nanoscale (AlN) m /(GaN) n (m>n) superlattice (SL) substituting for Al-rich Al x Ga −x 1 N disorder alloy as the active layer of optoelectronic devices due to the ultra-thin GaN layer modulation. The valence band maximum, i.e., the heavy hole band, has p x -and p y -like characteristics and is highly localized in the SL structure, which leads to the desired transverse electric (TE) polarized (E⊥c) light emission with improved light extraction efficiency in the DUV spectral region. Some important band-structure parameters and electron/hole effective masses are also given. The physical origin for the valence band inversion and TE polarization in (AlN) m /(GaN) n SL is analyzed in depth.

Experimental evidences for reducing Mg activation energy in high Al-content AlGaN alloy by MgGa δ doping in (AlN)m/(GaN)n superlattice

“…In our previous work, we have used Si Ga δ doping in Al 0.6 Ga 0.4 N alloys to increase the n-type carrier density30. Recent theoretical works predicted that the nanoscale (AlN) m /(GaN) n (m > n) SL could convert the valence-band maximum (VBM) from the crystal-field split-off hole to heavy hole band, leading to the increase of the transverse electric (TE) polarized light emission efficiency3132. The influence of the nearest and next-nearest (NN) atoms on Mg electronic structures in nanoscale (AlN) 5 /(GaN) 1 SL substitution for Al 0.83 Ga 0.17 N disorder alloy was theoretically investigated by Zhong et al 1…”

Spin transport in polarization induced two-dimensional electron gas channel in c-GaN nano-wedges

“…Conduction band minimum for wurtzite (WZ) GaN remains spin degenerate even after considering the effects of crystal field and SOC 30 . Lack of inversion symmetry in the WZ lattice results in a dependent term in the Hamiltonian, which can be expressed as 5 , 9 – 12 , 14 , 31 , 32 : where determines the strength of the k -linear Rashba like contribution.…”

Improving p-type doping efficiency in Al0.83Ga0.17N alloy substituted by nanoscale (AlN)5/(GaN)1 superlattice with MgGa-ON δ-codoping: Role of O-atom in GaN monolayer

“…5,6 However, it is extremely difficult to pursuit high efficient DUV light emitting diodes (LEDs) due to the low light extraction efficiency (∼0.1% at 230 nm) of Al-rich AlGaN active layer in these devices. 7 This overall small value is owing to the following three major reasons, i.e., the high dislocation density (10 10 cm −2 ), 7 the AlN-like valence-band maximum (VBM), 8,9 the low p-type doping efficiency. 7,10 We will here devote to improving p-type doping efficiency in Al-rich AlGaN.…”

“…26 Recent theoretical and experimental works prove that the nanoscale (AlN) m /(GaN) n (m>n) SL, substituting for the Al-rich AlGaN disorder alloy, can convert the VBM from the crystal-field split-off hole to heavy hole band, which directly leads to the increase of the desired transverse electric (TE) polarized light emission efficiency in the DUV spectral region. 9,27 Furthermore, the quantum-confinement Stark effect is minimized by decreasing the GaN thickness down to 1∼2 monolayers in the SL, 28 and the emission wavelength decreases simultaneously. Compared with Al-rich AlGaN alloy, the SL structure has an obvious advantage because it can combine the high TE polarized light emission efficiency of GaN and the wide energy gap of AlN.…”