Study On Performance And Stability Of 4H-SiC Schottky-barrier Ultraviolet Photodiodes

Ultraviolet (UV) detectors have drawn extensive attention due to their many important applications including UV communication, chemical/biological agent detection, solar physics and flame detection. Due to its advantages of large bandgap energy, superior thermal conductivity, high electron saturation velocity and mature substrate, SiC has been an attractive candidate semiconductor material for UV photodiodes (PDs). Recently, UV PDs with various structures and excellent performance based on SiC have been demonstrated.However, in practical applications, the further improvement of long-time stability is still required to ensure the tolerance in high temperature harsh environment, especially when UV PDs are applied as flame detectors in turbine engine or gamma-ray detectors for down-hole natural gas/petroleum exploration.In addition, UV detectors with "solar blind" feature are necessary for the applications in missile warning system and ultraviolet communications, in which sensitivity and accuracy is highly required.In this work, we focus investigation on the high-temperature performance and stability of vertical type 4H-SiC Schottky-barrier UV PDs, as well as the "solar blind" feature of PDs. The main results are highlighted as below:1. Based on 4H-SiC, a vertical type Schottky-barrier photodiode with 1mm×1mm in size is designed and fabricated. The photodiode exhibits very low dark current and high quantum efficiency in the entire temperature range from 25 to 200℃. The high temperature reliability characteristics are evaluated by high temperature storage at 200℃ and high temperature spike annealing up to 550℃.2. We propose an innovative approach to realize UV PDs with "solar blind" feature by directly integrating the filter into SiC detectors. The filter is formed by alternatively depositing high and low refractive index materials, which acts as not only a passivation layer to protect the device, but also a distributed Bragg reflector with resonances to filter out UV light selectively. In this work, two 4H-SiC Schottky-barrier UV detectors with different dielectric thickness are fabricated. The test results indicate that their filtering function covers different solar-blind spectral region. As compared to the traditional way to install expensive filters on the detectors, the proposed method is easier and cheaper.