Performance and Reliability of Deep-Etched High-Index-Contrast Ridge Waveguide Lasers

In this work, we systematically investigate the root causes of pitting during wet thermal processing of InP and analyze the resulting oxides using energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). Both dry thermal oxidation and oxygen-enhanced wet thermal oxidation (OEWTO) are studied to understand the composition and structural properties of the formed InP oxides. We also conduct time-resolved photoluminescence (TRPL) measurements on AlGaAs/GaAs heterostructures to probe surface states in regions exposed by deep etching and subsequently passivated by oxidation. From these measurements, we extract the surface recombination velocity and confirm a reduction in non-radiative recombination centers due to the OEWTO process. For the GaAs-based laser study, we begin by fabricating conventional low-index-contrast ridge waveguide (RWG) lasers to establish a performance baseline and benchmark against published data. Deep-etched RWG lasers with PECVD passivation are also fabricated to demonstrate the performance degradation caused by surface recombination at etched sidewalls, an issue that has historically hindered HIC laser development. We then introduce an advanced RWG laser design featuring deep etching, OEWTO sidewall passivation, and BCB planarization, achieving high index contrast, a low RC time constant, and a more circular beam profile. In the InP-based laser study, we first fabricate gain-guided RWG lasers to assess the as-grown heterostructure quality and lasing wavelength. We follow this by fabricating conventional index-guided RWG lasers using etch-stop layers as a baseline for performance benchmarking. Finally, we develop and demonstrate advanced InP-based deep-etched and laterally wet-etched HIC RWG lasers for telecom wavelengths. These devices exhibit low RC time constants, high differential quantum efficiency, and, most notably, a circularly symmetric, non-astigmatic output beam.