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Low-Dislocation-Density GaN from a Single Growth on a Textured Substrate

Description: The density of threading dislocations (TD) in GaN grown directly on flat sapphire substrates is typically greater than 10{sup 9}/cm{sup 2}. Such high dislocation densities degrade both the electronic and photonic properties of the material. The density of dislocations can be decreased by orders of magnitude using cantilever epitaxy (CE), which employs prepatterned sapphire substrates to provide reduced-dimension mesa regions for nucleation and etched trenches between them for suspended lateral growth of GaN or AlGaN. The substrate is prepatterned with narrow lines and etched to a depth that permits coalescence of laterally growing III-N nucleated on the mesa surfaces before vertical growth fills the etched trench. Low dislocation densities typical of epitaxial lateral overgrowth (ELO) are obtained in the cantilever regions and the TD density is also reduced up to 1 micrometer from the edge of the support regions.
Date: July 31, 2000
Creator: ASHBY,CAROL I.; WILLAN,CHRISTINE C.; HAN,JUNG; MISSERT,NANCY A.; PROVENCIO,PAULA P.; FOLLSTAEDT,DAVID M. et al.
Partner: UNT Libraries Government Documents Department

Developments in Pursuit of a Micro-Optic Gyroscope

Description: Rotation sensors (gyros) and accelerometers are essential components for all precision-guided weapons and autonomous mobile surveillance platforms. MEMS gyro development has been based primarily on the properties of moving mass to sense rotation and has failed to keep pace with the concurrent development of MEMS accelerometers because the reduction of size and therefore mass is substantially more detrimental to the performance of gyros than to accelerometers. A small ({approx}0.2 cu in), robust ({approx}20,000g), inexpensive ({approx}$500), tactical grade performance ({approx}10-20 deg/hr.) gyro is vital for the successful implementation of the next generation of ''smart'' weapons and surveillance apparatus. The range of applications (relevant to Sandia's mission) that are substantially enhanced in capability or enabled by the availability of a gyro possessing the above attributes includes nuclear weapon guidance, fuzing, and safing; synthetic aperture radar (SAR) motion compensation; autonomous air and ground vehicles; gun-launched munitions; satellite control; and personnel tracking. For example, a gyro of this capability would open for consideration more fuzing options for earth-penetration weapons. The MEMS gyros currently available are lacking in one or more of the aforementioned attributes. An integrated optical gyro, however, possesses the potential of achieving all desired attributes. Optical gyros use the properties of light to sense rotation and require no moving mass. Only the individual optical elements required for the generation, detection, and control of light are susceptible to shock. Integrating these elements immensely enhances the gyro's robustness while achieving size and cost reduction. This project's goal, a joint effort between organizations 2300 and 1700, was to demonstrate an RMOG produced from a monolithic photonic integrated circuit coupled with a SiON waveguide resonator. During this LDRD program, we have developed the photonic elements necessary for a resonant micro-optical gyro. We individually designed an AlGaAs distributed Bragg reflector laser; GaAs phase modulator and GaAs photodiode ...
Date: March 1, 2003
Creator: VAWTER, GREGORY A.; ZUBRZYCKI, WALTER J.; PEAKE, GREGORY M.; ALFORD, CHARLES; HARGETT, TERRY; SALTERS, BETTY et al.
Partner: UNT Libraries Government Documents Department

GaAs MOEMS Technology

Description: Many MEMS-based components require optical monitoring techniques using optoelectronic devices for converting mechanical position information into useful electronic signals. While the constituent piece-parts of such hybrid opto-MEMS components can be separately optimized, the resulting component performance, size, ruggedness and cost are substantially compromised due to assembly and packaging limitations. GaAs MOEMS offers the possibility of monolithically integrating high-performance optoelectronics with simple mechanical structures built in very low-stress epitaxial layers with a resulting component performance determined only by GaAs microfabrication technology limitations. GaAs MOEMS implicitly integrates the capability for radiation-hardened optical communications into the MEMS sensor or actuator component, a vital step towards rugged integrated autonomous microsystems that sense, act, and communicate. This project establishes a new foundational technology that monolithically combines GaAs optoelectronics with simple mechanics. Critical process issues addressed include selectivity, electrochemical characteristics, and anisotropy of the release chemistry, and post-release drying and coating processes. Several types of devices incorporating this novel technology are demonstrated.
Date: March 1, 2003
Creator: SPAHN, OLGA B.; GROSSETETE, GRANT D.; CICH, MICHAEL J.; TIGGES, CHRIS P.; RENO, JOHN L.; PEAKE, GREGORY M. et al.
Partner: UNT Libraries Government Documents Department

Final Report on LDRD Project: High-Bandwidth Optical Data Interconnects for Satellite Applications

Description: This report describes the research accomplishments achieved under the LDRD Project ''High-Bandwidth Optical Data Interconnects for Satellite Applications.'' The goal of this LDRD has been to address the future needs of focal-plane-array (FPA) sensors by exploring the use of high-bandwidth fiber-optic interconnects to transmit FPA signals within a satellite. We have focused primarily on vertical-cavity surface-emitting laser (VCSEL) based transmitters, due to the previously demonstrated immunity of VCSELs to total radiation doses up to 1 Mrad. In addition, VCSELs offer high modulation bandwidth (roughly 10 GHz), low power consumption (roughly 5 mW), and high coupling efficiency (greater than -3dB) to optical fibers. In the first year of this LDRD, we concentrated on the task of transmitting analog signals from a cryogenic FPA to a remote analog-to-digital converter. In the second year, we considered the transmission of digital signals produced by the analog-to-digital converter to a remote computer on the satellite. Specifically, we considered the situation in which the FPA, analog-to-digital converter, and VCSEL-based transmitter were all cooled to cryogenic temperatures. This situation requires VCSELs that operate at cryogenic temperature, dissipate minimal heat, and meet the electrical drive requirements in terms of voltage, current, and bandwidth.
Date: April 1, 2003
Creator: SERKLAND, DARWIN K.; GEIB, KENT M.; BLANSETT, ETHAN L.; KARPEN, GARY D.; PEAKE, GREGORY M.; HARGETT, TERRY et al.
Partner: UNT Libraries Government Documents Department