Growth and fabrication of GaN/Er:GaN/GaN core-cladding planar waveguides

Abstract

Erbium doped gallium nitride (Er:GaN) bulk crystals have emerged as a promising optical gain material for high energy lasers (HELs) operating at the 1.5 lm "retina-safe" spectral region. Among the many designs of HEL gain medium, the core-cladding planar waveguide (PWG) structure is highly desired due to its abilities to provide excellent optical confinement and heat dissipation. We report the realization of a GaN/Er:GaN/GaN core-cladding PWG structure synthesized by hydride vapor phase epitaxy and processed by mechanical and chemical-mechanical polishing. An Er doping concentration of [Er] ¼ 3 Â 10 19 atoms/cm 3 has been attained in the core layer, as confirmed by secondary ion mass spectrometry measurements. A strong 1.54 lm emission line was detected from the structure under 980 nm resonant excitation. It was shown that these PWGs can achieve a 96% optical confinement in the Er:GaN core layer having a thickness of 50 lm and [Er] ¼ 3 Â 10 19 atoms/cm 3 . This work represents an important step toward the realization of practical Er:GaN gain medium for retina-safe HEL applications.

Vibrational Spectrum and Thermal Conductivity of Rare‐Earth Semiconducting Erbium Nitride Thin Films

“…[11] Even though research on ErN has been gaining attention in the last few years, Er-doped semiconductors have been studied for over 20 years for various applications. For example, due to the intra-4f electronic transitions, Er-doped semiconductors such as GaN, [12,13] InGaN, [14] Si, [15] ZnO, [16] etc. exhibit emission at the retina-safe, fiber-optical telecommunication window of 1.54 μm that is explored for the use in solid-state lasers, amplifiers, and light-emitting devices.…”

Optical properties of GaN/Er:GaN/GaN core–cladding planar waveguides

“…2, we carried out HVPE growth for a core-cladding structure with a targeted N Er = 3 × 10 19 cm −3 in the core. 25) Figure 1(a) shows a schematic diagram of the GaN/Er:GaN/GaN PWG structure of this study. The undoped GaN cladding layer has a refractive index n = 2.2735 at 1.54 μm, whereas the refractive index of the Er:GaN core layer is n = 2.2752 at 1.54 μm with an Er doping concentration of 3 × 10 19 atoms cm -3 .…”

“…After HVPE growth, the top doped Er:GaN layer of the Er:GaN/GaN structure was subjected to mechanical and chemical-mechanical polishing (CMP) to bring it down to a thickness of 50 μm. 25) The quality of surface finishing is critical to providing low surface…”