High efficiency UV emitters - theoretical investigation of GaN/AlN heterostructures

TL;DR

This study uses density functional theory to investigate GaN/AlN heterostructures, revealing their potential for high-efficiency UV emitters through analysis of quantum well properties and electrostatic effects.

Contribution

It provides a detailed theoretical analysis of GaN/AlN heterostructures, highlighting the impact of well thickness on electronic properties and UV emission potential.

Findings

Valence band offset is approximately 0.85 V.

Optimal well thickness for UV emitters is less than 8 Ga layers (~21 Å).

Quantum Confined Stark Effect influences transition energies.

Abstract

Density functional theory simulations were used to obtain physical properties of GaN/AlN system. Combination of these two compounds into multiquantum well (MQW) structure will induce strong electrostatic effect leading to emergence of high magnitude dipole layers at the AlN/GaN interfaces, which were first postulated by {Tersoff Phys. Rev. B 30(8) pp.4874 (1984)} and already identified in GaN/InN by {Romanowski et al. J. Phys. Chem C 114. 14410 (2010)}. When combining GaN and AlN in to a heterostructure a spatial projection of wavefunctions indicate that valence band offset between states becomes of order of 0.85 V. Systematic analysis of influence of number of Ga atomic layers on the properties of wells have shown that for thickness up to 4 Ga layers, GaN behave as carriers locating potential minimum rather, while for larger thickness it is a standard quantum well. In all cases wells has strongly localized quantum states close to valance band maxima (VBM) and conduction band minimum (CBM). The calculated oscillator strength values rapidly decreases for the well thickness in excess of 8 Ga layers (~21 {\AA}) which indicates that wells for UV emitters should be much thinner than these based on InGaN/GaN systems. The Quantum Confined Stark Effect (QCSE) related changes of the transition energy in function of the geometric arrangement were also obtained.