Zhenguang Shao

Trap-assisted tunneling in AlGaN avalanche photodiodes

We fabricated AlGaN solar-blind avalanche photodiodes (APDs) that were based on separate absorption and multiplication (SAM) structures. It was determined experimentally that the dark current in these APDs is rapidly enhanced when the applied voltage exceeds 52 V. Theoretical analyses demonstrated that the breakdown voltage at 52 V is mainly related to the local trap-assisted tunneling effect. Because the dark current is mainly dependent on the trap states as a result of modification of the lifetimes of the electrons in the trap states, the tunneling processes can be modulated effectively by tuning the trap energy level, the trap density, and the tunnel mass.

Metal-Free Half-Metallicity in B-Doped gh-C 3 N 4 Systems

Half-metallicity rising from the s/p electrons has been one of the hot topics in spintronics. Based on the first-principles of calculation, we explore the magnetic properties of the B-doped graphitic heptazine carbon nitride (gh-C3N4) system. Ferromagnetism is observed in the B-doped gh-C3N4 system. Interestingly, its ground state phase (BC1@gh-C3N4) presents a strong half-metal property. Furthermore, the half-metallicity in BC1@gh-C3N4 can sustain up to 5% compressive strain and 1.5% tensile strain. It will lose its half-metallicity, however, when the doping concentration is below 6.25%. Our results show that such a metal-free half-metallic system has promising spintronic applications.

Interface state density effect on the performance of graphene silicon heterojunction solar cell

A planar structure consisting of graphene layer as the hole transport material, and n-type silicon as substrate is simulated. The degradation of this cell caused by high interface state density has been carried out. The simulated results match published experimental results indicating the accuracy of the physics-based model. Using this model, the effect of interface state density as zero, 1×1016cm-2, 1×1017cm-2 on the photovoltaic performance has been studied. The obtained IV and EQE characteristic based on realistic parameters shows that the interface state playing a prominent role in graphene silicon schottky contact.

Numerical simulation study of graphene silicon solar cell with boron diffusion layer

Two dimensional model of graphene silicon heterojunction solar cell with an boron doped surface layer is structured using Silvaco TCAD tools by accurate control of diffusion process. The introduction of inverse doped layer obviously improved the efficiency of heterojunction photovoltaic cell.

Light absorption enhancement by embedding aluminum nanodisk arrays in rear dielectric of ultra-thin film solar cells

In this work, in order to enhance the light absorption in one micron thick crystalline silicon solar cells, a back reflecting and plasmonic nanodisk scheme is proposed. We investigate the scattering properties of aluminum nanostructures located at the back side and optimize them for enhancing absorption in the silicon layer by using finite difference time domain simulations. The results indicate that the period and diameters nanoparticles, spacer layer have a strong impact on short circuit current enhancements. This finding could lead to improved light trapping within a thin silicon solar cell device.