Dual-Application-Mode Buried-Gate GaN OPFET for Ultraviolet Communication

Cost and area are important constraints in the sensor industry. In this regard, we adopt a dual-application-mode buried-gate GaN Optical Field Effect Transistor (OPFET) device for Ultraviolet (UV) Communication functioning in the diode or the transistor mode depending upon the bias conditions. The diode mode (Schottky junction mode) caters to high background light immunity applications whereas the transistor mode (OPFET mode) serves in applications in which the same optical source is used for imaging/treatment as well as communication. The parameters of interest are responsivity, bandwidth, unity-gain cut-off frequency, and dark current. The OPFET surpasses the Schottky diode bandwidth performance at lower intensities whereas at higher intensities, the diode shows improved frequency response. Non-saturation of photocurrent is observed in both cases. Both devices offer high responsivities with OPFET device exhibiting higher sensitivity than the Schottky device. The dark current is very low in the Schottky detector whereas the OPFET detector shows considerable dark current. The amplification bandwidth of the diode device is much higher that of the transistor device. The results have been analyzed and explained by the photoconductive and the photovoltaic effects, and the effect of illumination on the minority carrier lifetime. The device shows great potential for high date rate UV communication applications.