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

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%.