Alfred T. Schremer

Progress in etched facet technology for GaN and blue lasers

We report recent progress in chemically assisted ion beam etching (CAIBE) of GaN/AlGaN materials leading to improved performance of 405nm blue lasers fabricated with etched mirrors. Using a proprietary Etched Facet Technology (EFT) designed for GaN, we have fabricated ridge lasers in conventional GaN/sapphire material. Typical 3&mgr;m ridge lasers with 600&mgr;m cavity lengths exhibit threshold currents of 150mA with high yield and cross wafer uniformity. This represents a factor of five reduction in threshold current over previous results. Additional processing (such as FIB) was not required to improve the mirror verticality and smoothness as in previous work. Continuing improvements in laser performance are anticipated with further optimization of facet smoothness, laser design, and improved epitaxial material. We are also investigating the benefits of shorter cavity lasers, made feasible by etching, to realize improvements in laser reliability and yield. The yield advantage is based on the concept that shorter cavity devices will intercept fewer defects per device. Combined with EFT advantages like low cost wafer-scale testing and monolithic integration, this is a promising approach for next generation blue lasers for optical storage applications.

Horizontal cavity surface-emitting laser (HCSEL) devices

A horizontal cavity surface-emitting laser (HCSEL) has been demonstrated at 1310nm. The HCSEL incorporates a 45-degree etched facet that produces total internal reflection within the laser cavity. The laser light leaves the cavity at an angle perpendicular to the substrate.

Etched facet technology for GaN and blue lasers

In the late 1980s, etched facet lasers were demonstrated at Cornell University using a process based on chemically assisted ion beam etching (CAIBE). These etched facets allowed, for the first time, mirror reflectivities to be obtained that were equal to those of cleaved facets. Over the past few years, BinOptics Corporation has used this proprietary Etched Facet Technology (EFT) in fabricating InP based lasers with a quality equal to those of cleaved facets. Etched facets allow mirrors to be placed on the epitaxial substrate with very high precision. EFT eliminates losses that result from mechanical facet cleaving, allows wafer-scale testing and coating, and enables monolithic integration. BinOptics Corporation has now developed a modified version of its EFT for GaN materials and blue lasers where mechanical cleaving losses can be even more problematic. The relatively high defect density of currently available GaN materials creates an additional yield advantage for EFT: it allows the formation of shorter cavity devices with fewer defects per device. The first etched facet GaN devices are Fabry-Perot type ridge waveguide lasers emitting at 405nm for optical storage applications. However, as demonstrated in InP, it is planned to extend the technology to horizontal-cavity surface-emitting lasers (HCSELs) with integrated monitoring photodetectors (MPDs). A surface-emitting blue laser will allow two-dimensional arrays for high power applications and monolithic integration of additional functions. For example, the integration of a blue HCSEL with a receive detector will enable the creation of a compact optical head.