Xiaobin Xin

4H-SiC UV photo detectors with large area and very high specific detectivity

Pt/4H-SiC Schottky photodiodes have been fabricated with the device areas up to 1 cm/sup 2/. The I-V characteristics and photoresponse spectra have been measured and analyzed. For a 5 mm/spl times/5 mm area device leakage current lower than 10/sup -15/ A at zero bias and 1.2/spl times/10/sup -14/ A at -1 V have been established. The quantum efficiency is over 30% from 240 to 320 nm. The specific detectivity, D/sup */, has been calculated from the directly measured leakage current and quantum efficiency are shown to be higher than 10/sup 15/ cmHz/sup 1/2//W from 210 to 350 nm with a peak D/sup */ of 3.6/spl times/10/sup 15/ cmHz/sup 1/2//W at 300 nm.

Highly sensitive visible-blind extreme ultraviolet Ni/4H-SiC Schottky photodiodes with large detection area

Ni/4H-SiC Schottky photodiodes of 5 mm x 5 mm area have been fabricated and characterized. The photodiodes show less than 0.1 pA dark current at -4 V and an ideality factor of 1.06. A quantum efficiency (QE) between 3 and 400 nm has been calibrated and compared with Si photodiodes optimized for extreme ultraviolet (EUV) detection. In the EUV region, the QE of SiC detectors increases from 0.14 electrons/photon at 120 nm to 30 electrons/photon at 3 nm. The mean energy of electron-hole pair generation of 4H-SiC estimated from the spectral QE is found to be 7.9 eV.

4H-SiC Visible-Blind Single-Photon Avalanche Diode for Ultraviolet Detection at 280 and 350 nm

This paper reports on a 4H-SiC single-photon avalanche diode (SPAD) operating at UV wavelengths of 280 and 350 nm. The SPAD shows low dark currents of 20 and 57 fA at 80 V and 90% breakdown voltage, respectively. The quantum efficiency (QE) reaches its peak of 43% at 270 nm and is < 0.007% at 400 nm, indicating a high UV-to-visible rejection ratio of > 6100. The 4H-SiC SPAD shows a fast self-quenching and a high photon count rate of 1.44 MHz in the passive-quenching mode. At the wavelength of 280 nm, a single-photon detection efficiency (SPDE) of 2.83 % with a low dark count rate of 22 kHz is achieved at the reverse bias of 116.8 V. The SPDE at 350 nm is lower, which is 0.195%, owing to the correspondingly smaller QE. Optimization measurements were conducted on SPDE as a function of voltage bias and signal output threshold.

Demonstration of the First 4H-SiC Metal-Semiconductor-Metal Ultraviolet Photodector

Abstract. This paper demonstrates the first 4H-SiC metal-semiconductor-metal (MSM) UV photodetector. Two types of MSM photodetectors are fabricated for comparison: one in p-type 4HSiC and the other in n-type 4H-SiC. The n-type SiC photodetectors show a low dark current less than 10nA at -15V bias while the p-type ones show a lower dark current of 0.3nA at -25V. Photoresponsivity is measured from 200nm to 400nm and found to increase linearly with the increase of the bias. A very high peak responsivity of 50A/W is measured for n-type SiC MSM UV photodetector. The responsivity ratio of solar-blind UV to visible is larger than 1000, indicating a good visible-blind performance, immune to any visible and IR background noise, which is better than any Si UV detectors or other types of 4H-SiC UV detectors reported to date.

High-performance 4H-SiC single photon avalanche diode operating at solar blind wavelength

A 4H-SiC SPAD with an off-mesa bonding pad operating at 280nm is presented in this paper, with a low dark count rate of 14kHz and 27kHz at single photon detection efficiency of 3.3% and 4.5%, respectively. The device has a low breakdown voltage of 117V and a low dark current of 17fA, 49fA and 147fA at 50%, 90%, and 95% of breakdown voltage, respectively. The quantum efficiency is measured to be 28% (32%) at 280nm (270nm) with a UV to visible rejection ratio >1400 (>1600).

4H-SiC Single Photon Avalanche Diode for 280nm UV Applications

This paper reports a 4H-SiC single photo avalanche diode (SPAD) operating at the solar blind wavelength of 280 nm. The SPAD has an avalanche breakdown voltage of 114V. At 90% and 95% of the breakdown voltage, the SPAD shows a low dark current of 57.2fA and 159fA, respectively. The quantum efficiency of 29.8% at 280nm and <0.007% at 400nm indicates a high UV-to-visible rejection ratio of >4300. Single photon counting measurement at 280nm shows that a single photon detection efficiency of 2.83% with a low dark count rate of 22kHz is achieved at the avalanche breakdown voltage of 116.8V.

Demonstration of High-voltage 4H-SiC Bipolar RF Power Limiter

We present the design and fabrication of the first high-voltage 4H-SiC RF power limiter. First, Schottky and PiN diodes are compared for power limiter applications by numerical simulations. Small-signal S-parameters and large-signal operation are then simulated based on our device design. The fabrication is based on a SiC PiN diode with at least 900V blocking capability and packaged into a 50 microstrip transmission line fixture. Small signal insertion and return losses are measured in the frequency band from 100MHz to 3GHz after packaging and agree well with our simulation. The limiter has an insertion loss of only 0.6dB at 1GHz. This is believed to be the first 4H-SiC high-voltage RF power limiter, as well as one of the best SiC limiters in terms of low small-signal transmission loss up to gigahertz frequencies.

Development of Ultra High Sensitivity UV Silicon Carbide Detectors

A variety of silicon carbide (SiC) detectors have been developed to study their sensitivity, including Schottky photodiodes, p-i-n photodiodes, avalanche photodiodes (APDs), and single photon-counting APDs. Due to the very wide bandgap and thus extremely low leakage current, SiC photo-detectors show excellent sensitivity. The specific detectivity, D*, of SiC photodiodes are many orders of magnitude higher than the D* of other solid state detectors, and for the first time, comparable to that of photomultiplier tubes (PMTs). SiC APDs have also been fabricated to pursue the ultimate sensitivity. By operating the SiC APDs at a linear mode gain over 106, single photoncounting avalanche photodiodes (SPADs) in UV have been demonstrated.

Influence of band interaction on the spin prediction of superdeformed rotational bands

The influence of band interaction on the spin predictions and the J ?(2) pattern of superdeformed (SD) bands are investigated. To make a reliable spin prediction using the best-fit method, the transitions with significant band mixing should be excluded from the least-squares fitting. Spin predictions for 15 SD bands in the A ~150 region are made. In particular, the spin of the lowest level of the first discovered high-spin SD band 152 Dy(1) is predicted to be I 0 = 26. A two-band mixing model is used to describe the irregular behaviour of J ?(2) with angular momentum. Two types of J ?(2) patterns are discussed. For the band-crossing case, the J ?(2) pattern in the band-crossing region is of a V (or inverse-V) type, which has been observed in both the A ~190 and 150 regions. For the band-mixing case characterized by a relatively weak band interaction, the J ?(2) pattern in the band-mixing region is of a W (or inverse-W) type, which was observed only in some SD bands in the A ~150 region.

Proton Irradiation of Ultraviolet 4H-SiC Single Photon Avalanche Diodes

The effects of proton irradiation on ultraviolet 4H-SiC single photon avalanche photodiodes (SPADs) are investigated for the first time. The SPADs, grown by chemical vapor deposition, were designed for operation in the ultraviolet having dark count rates (DCR) of about 30 kHz and single photon detection efficiency (SPDE) of 4.89%. The SPADs were irradiated with 2 MeV protons to a fluence of 1012 cm-2. After irradiation, the avalanche breakdown voltage shifted downward 0.6 V from 113 V and the I-V characteristics show forward voltage (<; 1.9 V) generation-recombination currents 2 to 3 times higher than before irradiation. Single photon counting measurements at -114.2 V show lower voltage pulse height and a higher DCR at low threshold voltage, probably due to generation-recombination centers created in the band gap after irradiation. Yet, with the threshold voltage ranging from 23 to 26 mV, the 4H-SiC SPAD still showed low DCR (<; 54 kHz) and a reasonably high SPDE (>; 1%) after irradiation. The devices were demonstrated to show proton radiation tolerance for geosynchronous space applications.