Xiaping Chen

Metal–Semiconductor–Metal Ultraviolet Photodetectors Based on

Metal-semiconductor-metal ultraviolet (UV) photodetectors (PDs) with Au electrodes, based on TiO2 thin films prepared by radio-frequency magnetron sputtering, are fabricated and characterized. The PDs exhibit a low dark current of 9.73 pA at 5-V bias and a high breakdown voltage of over 90 V, owing to the achievement of high-quality stoichiometric TiO2 films. Meanwhile, the high responsivity with a cutoff wavelength at around 380 nm and a large UV-to-visible rejection ratio (310 versus 400 nm) of more than three orders of magnitude are obtained, which suggest that the fabricated PDs are very promising in UV detection applications.

\hbox{TiO}_{2}

4H-silicon carbide (SiC) metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors with Al2O3/SiO2 (A/S) films employed as antireflection/passivation layers have been demonstrated. The devices showed a peak responsivity of 0.12 A/W at 290 nm and maximum external quantum efficiency of 50% at 280 nm under 20 V electrical bias, which were much larger than conventional MSM detectors. The redshift of peak responsivity and response restriction effect were found and analyzed. The A/S/4H-SiC MSM photodetectors were also shown to possess outstanding features including high UV to visible rejection ratio, large photocurrent, etc. These results demonstrate A/S/4H-SiC photodetectors as a promising candidate for OEIC applications

Films Deposited by Radio-Frequency Magnetron Sputtering

A 4H-SiC based separate-absorption-multiplication (SAM) avalanche photodiode with a nanoscale multiplication region and a bulk absorption region is proposed and its optoelectronic performance is modeled. The results show that the avalanche breakdown voltage of the device is found to be dependent on the illumination condition. This is attributed to the existence of an illumination-dependent hole potential well in the upper center of the absorption region. Based on the illumination-dependence of avalanche breakdown voltage, a self-quenching and an ultrahigh UV/visible rejection ratio have been realized in this structure.

High-performance 4H-SiC based metal-semiconductor-metal ultraviolet photodetectors with Al 2 O 3 SiO 2 films

The absorption coefficients of 4H-SiC at 200 – 400 nm were obtained by extrapolation and polynomial fitting methods. Considering the effect of different junction-depth on the spectral performance, the continuity equations of photo-generated minority carrier were used to theoretically calculate the responsivity of p+-n−(i)-n-n+ structure 4H-SiC ultraviolet photodetector (PD) and to find out the effect of the intrinsic layer thickness on the spectral performance. The theoretical analyses can be applied to the practical design of p-i-n structure 4H-SiC PDs.

Nanoscale avalanche photodiode with self-quenching and ultrahigh ultraviolet/visible rejection ratio

4H-SiC avalanche photodiode with a separated absorption region, a charge adjustment region and a multiplication region is proposed and its optoelectronic performance is modeled. By properly designing the doping concentration of each layer, the avalanche breakdown voltage and photo-response of the device is found to be dependent of the thickness of the multiplication region. The avalanche breakdown voltage shows a minimum and the photo-response shows a maximum at certain thickness of the multiplication region. The results are explained by the electric field distribution of the device and the impact ionization theory.

Effect of the intrinsic layer thickness on the spectral performance of p-i-n structure 4H-SiC ultraviolet photodetector

ABSTRACT Hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films were deposited by RF plasma enhanced chemical vapor deposition (PECVD) and subsequently annealed in N2 atmosphere at different temperatures. Systematic investigations of the deposition temperature and annealing effect on the films properties, including film thicknesses, optical bandgap, refractive indexes, absorption coefficient (α), chemical bond configurations, stoichiometry and crystalline structures, were performed using ellipsometry, FTIR absorbance spectroscopy, Raman spectroscopy, XPS, and XRD. All of the results indicate that the structural and optical properties of the a-Si1-xCx:H film can be effectively engineered by proper annealing conditions. Moreover, molecular vibrational level equation was introduced to explain the peak shift detected by FTIR and Raman spectroscopy.

Optimization of 4H-SiC separated-absorption-charge-multiplication (SACM) avalanche photodiode with low avalanche breakdown voltage

Effects of Al ions implantation into n-type 4H-SiC followed by annealing at various temperatures have been studied by Atomic Force Microscopy (AFM), Raman scattering, Fourier transform infrared (FTIR) reflectance spectroscopy, and Hall effect measurements. AFM experiments observed a large amount of discontinuous strips on 4H-SiC surface running along three directions after high temperature annealing. Raman scattering and FTIR spectra jointly indicated the damage and amorphization of 4H-SiC due to Al implantation and the crystal restoration after high temperature annealing. Hall effect measurements revealed that the sample annealed at 1600 °C achieved a higher activity ratio and a lower resistivity, which satisfied the application of numerous SiC-based devices.