SBIR-STTR Award

Reliable optically activated, high gain semiconductor switches (PCSS) are being explored for multiple applications, including ground penetrating radar (GPR) and firing set switches. The ability of a PCSS to deliver fast risetime pulses suits them for their use in radars that rely on fast impulses. This type of direct time domain radar is uniquely suited for detecting buried items because it can operate at low frequency, high average power, and close to the ground, greatly increasing power on target. Utilizing wide band gap semiconductors such as SiC and GaN and its alloys, it is very likely that GaAs switch lifetime issues can be eliminated. Wide bandgap semiconductor switches can also handle much higher peak voltages and currents. This proposal seeks funding to exploit and develop switches based on nitrides and carbides. Of particular interest is AlN on SiC with a near lattice match and good interface quality. This combination is already being explored for MIS (Metal-Insulator-Semiconductor) devices in SiC. Similar approaches will be used for a lateral photoconductive switch. The proposed structure will benefit from the high thermal conductivity and robustness of SiC and AlN surface passivation, allowing large switching voltages. Using GaN for ohmic contacts on AlN with uniform current flow will prevent filamentation and premature burn out. Immediate replacement parts for commercial applications include switches for pulsed lasers, high resolution Doppler weather radar for both ground based and aircraft based instrumentation. Future applications may include ignition module switches for aircraft engines. Also, pulse forming network switches for pulsed high energy electron beams for food sterilization.

A high speed, high voltage, high current Photoconductive Semiconductor Switch (PCSS) was fabricated and tested during Phase I, demonstrating the switching of currents of up to 50 A at 1 kV for less than 10 nS, with on/off current switching ratios of 1011:1 and more. The Phase II project will build upon this success, with the goal of producing packaged PCSS capable of switching 100A at 10KV for pulse times of a few nS. During this proposed program, the following tasks will be performed: a) characterize conduction, leakage and photoconductivity of existing and new devices, b) develop processes and procedures for growth of passivating layers on SiC surfaces, such as epitaxial AlN, c) characterize current filamentation and develop processes and procedures for improved ohmic contacts to SiC substrates, and d) design and optimize packaging for devices to produce robust packages, immune to environmental stresses and capable of efficiently dissipating heat generated during operation. The technology and products developed under this SBIR program have wide applications including

Keywords:
Pulsed High Power Switch, Wide Bandwidth, Solid State Photoconductive Switch, Radar, Pulsed Laser Power Supply, Pcss