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
A 1300nm, high power, vertically emitting Fabry Perot laser is presented with a monolithically integrated photodiode. The lasers use ridge waveguide technology with a 45° etched facet to create 30mW of vertically emitted light. Two types of monolithically integrated back facet monitor diodes are discussed togther with their merits for adequate collection efficiency and tracking error. HCSELs with integrated MPDs have passed over 3000 hours of reliability testing.
In the late 1980's, 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.
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.
Modern technology permits the fabrication of Kirkpatrick-Baez (KB) multilayer optics with performance close to the theoretical limit. We have constructed a KB field-imaging microscope which operates in the x-ray energy range 6-10 keV with a field of view of 40-150 micrometers . The optics perform at a reflectivity of 80% at the first Bragg peak. Using highly-collimated synchrotron radiation, we realize a resolution of 900 nm at 9 keV. The intensity and magnification are sufficient to perform real-time imaging with a CCD x-ray camera, with increases in field of view and resolution at this energy due to improvements in both data collection and image processing. The collimation of the incident radiation corresponds to Koehler illumination. The dynamic range of the images using a 12-bit camera allows us to extend the field of view at the Bragg reflection over several Kiessig fringes. We have adjusted the energy to take advantage of absorption at the excitation edges of elements and have performed imaging using circularly polarized radiation. We have used this instrument to demonstrate wide-field imaging in both absorption and diffraction. We present magnified images of multiple layers in a test integrated circuit in absorption and of a metal single crystal in diffraction.