Wide bandgap nitride components for silicon-based integrated ultraviolet photodetection

Abstract

The wide bandgap semiconductor AlxGal-p is desired for applications as a solar-blind ultraviolet photodetector for endoatmospheric sensing of jet or rocket plumes and exoatmospheric sensing of solar uv rays reflected from orbiting craft. Recent success in producing epitaxial AlN and GaN on Si [ 11 leads to the present work, which demonstrates at a proof-of-concept level the cointegration of nitride-based photodetectors and Si microelectronics. Development of this concept can lead to unique "solar-blind / solar-sighted'' uv / visible imaging arrays. The materials synthesis is based on an N2 beam excited in an electron cyclotron resonance plasma in a molecular beam epitaxy process. The Si (1 1 1) face provides a commensurate though highly mismatched growth substrate. Microstructure of the AlN and GaN layers is analyzed by x-ray diffractometty and electron microscopy. Two demonstrations are offered to establish the feasibility of the device concepts. In the fist, a GaN photoconductive sensor is produced on a thin A1N buffer layer on Si (1 11). A similar demonstration has previously been made for GaN on sapphire [2]. In the present case, however, the use of Si as the substrate opens up an opportunity to enhance the detector functionality and combine the optoelectronic components with Si-based signal conditioning and read-out circuitry. To integrate nitride- based photodetector architectures with Si electronics, MISFET structures using AN as the gate insulator are demonstrated. Electronic-grade AlN/Si interfaces appear to be a realistic goal.