# Q factor limitation at short wavelength (around 300 nm) in III-nitride-on-silicon photonic crystal cavities

## TL;DR

This paper investigates the decline in quality factors of III-nitride-on-silicon photonic crystal cavities at wavelengths around 300 nm, identifying residual absorption in AlN layers as a key limiting factor.

## Contribution

It provides the first detailed analysis of the wavelength-dependent Q factor limitation in III-nitride-on-silicon cavities, highlighting residual AlN absorption as a major factor.

## Key findings

- Q factors up to 1085 at 337 nm achieved
- Residual AlN absorption limits Q to around 2000 at 300 nm
- Quantum well absorption contributes to Q reduction below 340 nm

## Abstract

III-nitride-on-silicon L3 photonic crystal cavities with resonances down to 315 nm and quality factors (Q) up to 1085 at 337 nm have been demonstrated. The reduction of the quality factor with decreasing wavelength is investigated. Besides the quantum well absorption below 340 nm, a noteworthy contribution is attributed to the residual absorption present in thin AlN layers grown on silicon, as measured by spectroscopic ellipsometry. This residual absorption ultimately limits the Q factor to around 2000 at 300 nm when no active layer is present.