Enhancing light emission with electric fields in polar nitride semiconductors

TL;DR

This paper shows that strong polarization fields in polar nitride semiconductors can actually enhance red light emission by increasing electron-hole overlap, challenging traditional views and enabling new LED designs.

Contribution

It introduces machine-learning surrogate models to explore heterostructure design space, revealing that larger polarization fields can improve optical transition strength in nitride quantum wells.

Findings

Larger polarization fields correlate with higher electron-hole overlap.

Quantum-confined Stark effect enables thinner wells without higher indium content.

Structural engineering of internal fields can design polychromatic LEDs.

Abstract

Significant effort has been devoted to mitigating polarization fields in nitride LEDs, as these fields are traditionally viewed as detrimental to light emission, particularly for red emission. Contrary to this prevailing notion, we demonstrate that strong polarization fields can enhance the optical-transition strength of AlInGaN quantum wells emitting in the red, which has been historically challenging to achieve. By leveraging machine-learning surrogate models trained on multi-scale quantum-mechanical simulations, we globally explore the heterostructure design space and uncover that larger fields correlate with higher electron-hole overlap. This relation arises from the quantum-confined Stark effect, which enables thinner wells without requiring higher indium compositions, thus overcoming a key limitation in nitride epitaxy. Structural and compositional engineering of internal fields offers a unique dimension for designing polychromatic nitride LEDs, crucial for miniaturizing LED pixels to the micron scale for extended-reality and biomedical applications. Broadly, our work demonstrates how machine learning can uncover unexpected paradigms for semiconductor design.