Papers by Author: Alexey V. Vert

Abstract: We report measurements and modeling of silicon carbide (SiC) based ultraviolet photodetectors for the detection of light in the mid-to-short ultraviolet range where SiC’s absorption coefficients are high and the corresponding penetration depths are low. These large absorption coefficients result in increased susceptibility of photo-generated electron and holes to surface recombination and therefore give rise to lower quantum efficiencies. To increase responsivity and extend the detection capability of these photodetectors to short ultraviolet wavelengths (or UVC), we measure an existing silicon carbide avalanche photodiode (APD) designed and fabricated for 280 nm operation by General Electric Global Research Center, and then develop models and techniques to increase their operation range to lower UV wavelengths. The measurements aid the development and calibration of a silicon carbide modeling and design suite that is currently being used to assist the design of a new silicon carbide APD for UVC detection. Here the design considerations require low operating voltages, low noise, low dark count rate and high responsivity. We plan to satisfy design criteria by engineering thickness and doping of stacked layers as well as by designing an APD surface that gives rise to minimal recombination of electrons and holes generated by the incident light.

Abstract: Silicon carbide based integrated circuits (ICs) have the potential to operate at temperatures exceeding that of conventional semiconductors such as silicon and silicon on insulator. Analog and digital silicon carbide (SiC) based circuits were fabricated and characterized at room temperature and 300°C. An operational amplifier and a ring oscillator were tested for prolonged period of time to evaluate their stability and reliability at 300°C. More than 1,000 hours was achieved with the operational amplifier without failures and the ring oscillator operated for almost 300 hours.

Abstract: We present overview of achieved results on 4H-SiC avalanche photodiodes (APDs) and arrays. Cost-effective solar-blind optical filter allows achieving high solar photon rejection ratio of more than 106 in combination with more than 40% single photon detection efficiency at 266nm. Three iterations of devices were fabricated and evaluated to compare their optical and electrical properties. Dark count rates and single photon detection efficiencies are the main characteristics compared for these three iterations of device designs.

Abstract: We present recent results on 4H-SiC avalanche photodiode arrays and SiC-based solid-state photomultiplier arrays suitable for ultraviolet and solar-blind light detection. A novel SiC-based photomultiplier array was demonstrated. An additional solar-blind filter enabled a solar photon rejection ratio of more than 106 in combination with 40% quantum efficiency at 280 nm.

Abstract: 4H-SiC single photon avalanche diodes are reported. A separate absorption and multiplication non-reach through device structure was optimized for operation in Geiger mode. An estimated dark current at a gain of 1000 was ranging between 0.4 pA (0.75 nA/cm2) and 20nA (38 A/cm2) on devices with an effective mesa diameter of 260 m. The electron beam induced current technique was used to image defects in the active region of studied devices. Increased reverse bias leakage current and increased Geiger mode dark count probability were correlated with the presence of large number of defects. Single photon detection efficiencies of up to 11% were measured at a wavelength of 266 nm in Geiger mode.

Abstract: In this work, solar-blind UV 4H-SiC avalanche photodetectors were fabricated and tested in linear and Geiger modes. APDs with both PIN and separate absorption and multiplication (SAM) structures were investigated. PIN structures demonstrated higher quantum efficiencies while the SAM structure exhibit lower leakage currents. Deposition of a thin film optical filter on top of the devices was used to provide a high photon rejection ratio of (Stas add value here). However, an external filter showed a better photon rejection ratio compared to the deposited one by about one order of magnitude.

Abstract: We report on the fabrication and testing of SiC p-i-n avalanche photodiodes. APDs of 0.25 mm2 area on a-plane (1120) 6H-SiC as well as off-axis Si face 6H and 4H-SiC were successfully fabricated. A beveled mesa was used as edge termination. Recessed windows were formed using reactive ion etching to enhance low-wavelength UV performance. We performed current-voltage tests with and without UV illumination to determine dark current, photocurrent, and gain on selected devices. Dark current was less than 1 pA at 0.5Vbr on multiple devices. Quantum efficiency of 40% or greater was observed for all orientations and polytypes.

Abstract: In this work, avalanche photodiodes (APDs) were fabricated using a-plane 6H- and 4H-SiC materials to investigate their electrical and optical properties. Temperature dependence of avalanche breakdown was measured. The diode structures were fabricated with positive angle beveling and oxide passivation to ensure a uniform breakdown across the device area. Despite the apparent presence of micro-plasmas, we observed that the breakdown voltage of a-plane 6H-SiC APDs increased with temperature suggesting a positive temperature coefficient.