Realizing GaN/Er:GaN/GaN core-cladding planar waveguide gain medium via hydride vapor phase epitaxy*

Erbium doped gallium nitride (Er:GaN) bulk crystals have been identified as a promising optical gain material for solid-state high energy lasers (HELs) operating at the 1.5 mm “retina-safe” spectral region. A highly desired design of HEL gain medium is the core-cladding planar waveguide (PWG) structure, capable of providing excellent heat dissipation and optical confinement. We report the realization of a GaN/Er:GaN/GaN core-cladding PWG structure grown by hydride vapor phase epitaxy (HVPE) and processed by mechanical and chemical-mechanical polishing. An Er doping concentration of [Er] = 3 × 10¹⁹ atoms/cm³ has been confirmed in the core layer via secondary ion mass spectrometry measurements. The structure emitted strong 1.54 μm emission under 980 nm resonant excitation. It was shown that a 96% optical confinement can be achieved in the Er:GaN core layer with a core thickness of 50 μm and [Er] = 3 × 10¹⁹ atoms/cm³. This work paves the way and marks an important progress towards the practical application of Er:GaN gain medium for “retina-safe” HELs.