Large-Area 4H-SiC Ultraviolet Avalanche Photodiodes Based on Variable-Temperature Reflow Technique

In this letter, we report high-performance 4H-SiC separated absorption charge multiplication ultraviolet (UV) avalanche photodiodes (APDs) with a large active area (800-μm diameter). For the first time, a variable-temperature photoresist reflow technique is presented to obtain very smooth sidewalls for positive beveled mesa, which is very useful for suppressing the reverse leakage and premature edge breakdown. At room temperature, the dark current of our fabricated large-area APD remains at ~1-pA level (0.2 nA/cm
²
) at low reverse bias voltage, and a high multiplication gain of over 10
⁶
is achieved. The peak responsivity at the wavelength of 274 nm reaches 0.18 A/W, corresponding to a maximum external quantum efficiency of 81.5% at unity gain. Moreover, an excellent UV/visible rejection ratio of more than 10
³
is obtained. To the best of our knowledge, this is the best result reported for visible-blind UV detectors based on the large-area 4H-SiC APDs.