Development of Ultra-High Sensivity Silicon Carbide Detectors

A variety of silicon carbide (SiC) detectors have been developed to study the sensitivity of SiC ultraviolet (UV) detectors, including Schottky photodiodes, p-i-n photodiodes, avalanche photodiodes (APDs), and single photon-counting APDs. Due to the very wide bandgap and thus extremely low leakage current, Sic photo-detectors showed excellent sensitivity. The specific detectivity, D*, of SiC photodiodes are orders of magnitude higher than that of their competitors, such as Si photodiodes, and comparable to the D* of photomultiplier tubes (PMTs). To pursue the ultimate detection sensitivity, SiC APDs and single photon-counting avalanche diodes (SPADs) have also been fabricated. By operating the SiC APDs at a linear mode gain over 10(exp 6), SPADs in UV have been demonstrated. SiC UV detectors have great potential for use in solar blind UV detection and biosensing. Moreover, SiC detectors have excellent radiation hardness and high temperature tolerance which makes them ideal for extreme environment applications such as in space or on the surface of the Moon or Mars

Development of 4H-SiC high voltage unipolar power switching devices:

4H-SiC is a promising material for switching high power and high temperature device applications. The superior properties of SiC, such as wider band-gap and higher value of critical electric field allow significant reduction in device on-resistance compared to Si power devices of similar voltage ratings. In addition the excellent thermal conductivity of SiC alleviates the device cooling requirements and allows design of smaller and more efficient systems. Several advantages of the unipolar power switches over the bipolar switches make them desirable for fast switching applications. Voltage-controlled normally-off devices are particularly attractive for practical applications because of simpler gate-drive circuitry. The advantages of the vertical JFET device being free of the problems related to oxide reliability, as compared to the MOSFET, recognize it as an excellent candidate for high power, high temperature switching applications. Device designs for normally-off and normally-on unipolar switches with blocking voltages from 400V to 11kV are proposed, based on a pure vertical trenched and implanted structure. Two different junction termination structures (junction termination extension and guard rings) are designed and successfully implemented. A fabrication process is designed to achieve a simple and reliable self-aligned fabrication process. The fabrication challenges are discussed and ways to improve the process are identified. Three different devices were designed and fabricated. The world’s first normally-off 4H-SiC TIVJFET with a blocking voltage of 11kV was demonstrated, showing low specific on-resistance of 124mOhm.cm2. Normally-off and normally-on 4H-SiC High Frequency TIVJFETs with blocking voltages up to 400V were demonstrated. 3.3A-397V normally-off capability was achieved for a single die, corresponding to a high power of 1310 W/die. This corresponds to a class B operation RF power of 164W for a single die. Cut-off frequency fT= 0.9 to 1.5 GHz was reached. In the 1200V class devices a normally-on 4H-SiC TIVJFET with guard ring termination and substantially simplified processing was also demonstrated. The highest blocking voltage achieved was 1562V with a specific on-resistance of 2.8mOhm.cm2 at VDS=0.5V and VGS=2.5V and a current gain of 1495. The lowest specific on resistance achieved was 2.2mOhm.cm2 at VDS=0.5V and VGS=2.5V with a current gain of 1454 and a blocking voltage of 1232V.Ph.D.Includes bibliographical references (p. 131-133)by Petre Alexandro