Ultraviolet (UV) detectors are important for their applications in flame detection, furnace gas control systems, plume monitoring etc. Due to their wide band-gap, 4H-SiC (Eg=3.26eV) and III-V semiconductors such as GaN (Eg=3.4eV), AlxGa1-xN (Eg=3.4eV to 6.2eV) etc., are excellent candidates for visible(lambdacut-0ff =400nm) and solar blind(lambdacut-0ff=290nm) UV detectors. Conventional SiC UV detectors suffer from poor UV responsivities due to reflection/absorption/transmission losses caused by the metal electrodes used in those detector.

In the first part, a novel bipolar transistor with epitaxial graphene(EG)/p-SiC (30microm)/n+-SiC substrate was fabricated and characterized. The 2-3 ML thick, transparent and conducting, EG used in this work was grown by using thermal sublimation of SiC. Under 0.43 microW 365nm UV illumination, this device showed a responsivity(R) of 7.1A/W better than or comparable to the state of the art SiC Schottky and PiN diodes, and a bipolar current gain of 113, when operated in the Schottky emitter(SE) mode. Further, a UV-visible rejection (R365: R444) >103 is estimated for this device.

In the second part, EG/p-SiC(13microm)/ n+-SiC bipolar transistor device structures were fabricated, where EG was grown by selectively etching Si from SiC using a novel Tetrafluorosilane(SiF4) precursor. The photo-transistor showed responsivity as high as 25 A/W at 250 nm in the SE mode. The SC mode showed a responsivity of 17A/W at 270nm with a visible rejection (R270: R400)>103. The fastest response was seen in the SC-mode, with 10ms turn-on and 47ms turn-off, with a noise equivalent power(NEP) of 2.3fW at 20 Hz and a specific detectivity of 4.4x1013 Jones.

In the final part, HEMT devices with Al0.85Ga0.15N/Al 0.65Ga0.35N as barrier and channel layers, were fabricated and characterized. These devices showed a photo-responsivity ~1x10 6A/W at 220nm, with solar and visible rejection ~102 limited by sub-bandgap states in the AlGaN. The lowest NEP was observed near the threshold voltage, 4.7fW at 220nm and ~4.4fW at 260nm, with a responsivity of ~103A/W. A measured slow response time of ~20s is attributed to trapping at the AlN/AlGaN growth interface. Potential solutions to reduce the trapping responsible for the increased response times are discussed.