# Wafer Scale III‐Nitride Deep‐Ultraviolet Vertical‐Cavity Surface‐Emitting Lasers Featuring Nanometer‐Class Control of Cavity Length

## TL;DR

Researchers developed a new method to precisely control the cavity length in deep-ultraviolet lasers, improving their performance and consistency.

## Contribution

A wafer-scale strategy for nanometer-precision cavity length control in DUV VCSELs is introduced.

## Key findings

- DUV VCSELs achieved a record low threshold of 0.38 MW cm−2 and a narrow linewidth of 0.11 nm.
- The lasing wavelength varied by only 1.9 nm across a 4-in wafer, indicating minimal cavity length variation.
- A self-terminated etching process with 100:1 selectivity enabled precise cavity length determination.

## Abstract

AlGaN‐based deep‐ultraviolet vertical‐cavity surface‐emitting lasers (DUV VCSELs) have shown a great application potential in optical atomic clocks, maskless photolithography, etc. Nevertheless, the uncontrolled cavity length‐induced detuning issue, i.e., the difference between the resonance wavelength and gain peak, severely impairs the device performance. Herein, a DUV‐VCSEL strategy featuring the uniform nanometer‐class control of the cavity length in a 4‐in wafer is proposed in the DUV framework based on GaN templates, which ensures the wafer‐scale removal of sapphire substrates by laser lift‐off, and then provides space for the subsequent deposition of dielectric distributed Bragg reflector (DBR). It is more significant that the strategy brings about a GaN/AlGaN sharp interface with an Al composition difference up to 80%, whereby self‐terminated etching with an ultrahigh selectivity of 100:1 is achieved. The cavity length is hence accurately determined by epitaxy itself instead of the fabrication process, so as to minimize the detuning. As such, 285.6‐nm optically pumped DUV VCSELs with double dielectric DBRs are fabricated, exhibiting a record low threshold of 0.38 MW cm−2 and a narrow linewidth of 0.11 nm. What's more, the lasing wavelength varies within 1.9 nm across the 4‐in wafer, indicating a cavity length variation of only 0.81%.

A DUV‐VCSEL strategy featuring the nanometer‐class control of the cavity length is proposed in the DUV optoelectronic framework based on GaN templates. After the sapphire removal, a self‐terminated etching technology is developed, whereby the cavity length can be accurately determined by epitaxy instead of the fabrication process. As such, a record low threshold is realized in 285.6‐nm optically pumped DUV VCSELs.