Strain-driven light polarization switching in deep ultraviolet nitride emitters

TL;DR

This paper investigates how residual strain influences the band structure and polarization properties of deep ultraviolet nitride emitters, enabling polarization switching and improved emission characteristics for UV LEDs.

Contribution

It reveals strain-induced valence band anti-crossing and demonstrates strain engineering to achieve vertical light emission and polarization control in deep UV nitride quantum wells.

Findings

Compressive strain causes valence band anti-crossing at high Al compositions.

Strain supports vertical emission from AlxGa1-xN quantum wells up to x≈0.80.

Strain engineering enables polarization switching in deep UV emitters.

Abstract

Residual strain plays a critical role in determining the crystalline quality of nitride epitaxial layers and in modifying their band structure; this often leads to several interesting physical phenomena. It is found, for example, that compressive strain in AlxGa1-xN layers grown on AlyGa1-yN (x<y) templates results in an anti-crossing of the valence bands at considerably much higher Al composition than expected. This happens even in the presence of large and negative crystal field splitting energy for AlxGa1-xN layers. A judicious magnitude of the compressive strain can support vertical light emission (out of the c-plane) from AlxGa1-xN quantum wells up to x\approx 0.80, which is desirable for the development of deep ultraviolet light-emitting diodes designed to operate below 250nm with transverse electric polarization characteristics.