Rongdun Hong

Separated-absorption-multiplication 4H-SiC avalanche photodiodes with adjustable responsivity and response time

4H-SiC based avalanche photodiodes (APD) with a small multiplication region onto a large absorption region, which can be regarded as a particular separated-absorption-multiplication structure, are proposed and their optoelectronic performances are modeled. The avalanche breakdown voltage, energy band diagram, spectral responsivity and response time of the devices are found to be dependent on the area of multiplication region. The performance of the device could be similar to a conventional separated-absorption-multiplication APD or p–i–n diode by designing various multiplication areas. Characteristics of the APD are fully studied and explained by the analysis of energy band diagrams of the devices.

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

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.

TiNbO 2 -Based Photodetectors With Low Dark Current and High UV-to-Visible Rejection Ratio

We reported on metal-semiconductor-metal ultraviolet (UV) photodetector (PD) based on pulse-laser-deposited TiNbO₂ alloy film. The TiNbO₂ PD exhibited a low dark current density of ~0.46 nA/cm², a high UV-to-visible rejection ratio of ~10⁶, and a high responsivity of ~0.22 A/W under the illumination of 310-nm light (~1.86 mW/cm²). Interestingly, the TiNbO₂ alloy PD presents a blue-shift cutoff wavelength of 350 nm due to quantum size effect and alloy characteristics, which would be promising for the further research in the UV detection.

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

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.

4H-SiC Nano-Pillar Avalanche Photodiode With Illumination-Dependent Characteristics

A 4H-SiC nano-pillar-based avalanche photodiode (NAPD) with a separate absorption region and a multiplication region is proposed and its optoelectronic performance is modeled. By properly designing the device geometry and the doping concentration of each layer, the avalanche breakdown voltage (Vbr) of the NAPD is found to be dependent of the incident wavelength and power density, which are explained by the band diagrams of 4H-SiC NAPDs.

Ellipsometry, FTIR, Raman and X-Ray Spectroscopy Analysis of PECVD a-Si1-xCx:H Film

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.

Annealing effects on structural, optical and electrical properties of Al implanted 4H-SiC

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.