Role of Strain-Induced Microscale Compositional Pulling on Optical Properties of High Al Content AlGaN Quantum Wells for Deep-Ultraviolet LED

Abstract

A systematic study was carried out for strain-induced microscale compositional pulling effect on the structural and optical properties of high Al content AlGaN multiple quantum wells (MQWs). Investigations reveal that a large tensile strain is introduced during the epitaxial growth of AlGaN MQWs, due to the grain boundary formation, coalescence and growth. The presence of this tensile strain results in the microscale inhomogeneous compositional pulling and Ga segregation, which is further confirmed by the lower formation enthalpy of Ga atom than Al atom on AlGaN slab using first principle simulations. The strain-induced microscale compositional pulling leads to an asymmetrical feature of emission spectra and local variation in emission energy of AlGaN MQWs. Because of a stronger three-dimensional carrier localization, the area of Ga segregation shows a higher emission efficiency compared with the intrinsic area of MQWs, which is benefit for fabricating efficient AlGaN-based deep-ultraviolet light-emitting diode.

Why and how In composition fluctuations appear in InGaN?

“…In intermediate cases, we simply interpolate and the elastic energy calculated in ( 2) is multiplied by NNN/9. At the end, we find an elastic energy which is on the order of 0.4-0.5 eV for an isolated atom on a surface, similar to the value calculated by DFT for the case of AlN and GaN [39].…”

“…Surface reconstruction also occurs in order to minimize the related elastic energy [37,38]. The effect of strain on the formation enthalpy of an isolated Ga or Al atom on a surface as a function of strain has been estimated, showing that the strain modifies this energy by about 0.4 eV [39]. Lymperakis and coworkers [40] have calculated by Density Functional Theory (DFT) the energies of the associated reconstructed surface for a 1 ML of InN grown on GaN.…”