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Insufficiently high doping in polysilicon gates of metal oxide semiconductor field effect transistor (MOSFET) becomes unavoidable due to the demands for low-energy ion implantation and limited annealing conditions to achieve ultra-shallow source and drain junctions. This results in the poly-depletion effect for ultra-thin MOSFET, loss of current drive and shift in the threshold voltage. This problem gets intense when the device is further scaled down for the gate length and thickness of gate oxide. Hence, our current work focuses on the effect of gate geometrical effect and polysilicon gate doping on scaled n-channel MOSFET(NMOS) performance. The NMOS device was constructed using TCAD ATLAS tools from SILVACO software. Six different gate lengths of 0.6 µm, 0.4 µm, 0.2 µm, 60 nm, 40 nm and 20 nm were set, and the n-type doping concentration in the polysilicon gate was varied to 1× 1018, 1× 1020 and 1 × 1021 cm-3 respectively to see their effect on the NMOS I-V and C-V performances. The findings showed that as the gate length is scaled down, the drain current increases, and as the concentration of the polysilicon doping increases, the value of the threshold voltage, VTH decreases. Based on the simulation and data collected, it can be concluded that the optimum concentration of polysilicon doping that can reduce the poly-depletion effect is 1 × 1021 cm-3, and the optimum gate length that can be used to overcome the problem is 20 nm. [ABSTRACT FROM AUTHOR]

Ge is considered to have several advantages over Si due to its high mobility and direct bandgap, which makes it ideal for optoelectronic applications. The manipulation of bulk Ge into small structures has drawn a lot of interest due to the numerous distinctive properties caused by the impact of size quantization. Porous materials are ideally suited for sensing application due to their large effective surface area beside the fabrication of porous is simple. In this work, porous Ge is investigated for potential visible to near-infrared metal semiconductor metal (MSM) photodetector. The study investigated the performance and characterization of porous Ge (P-Ge) on Si substrate at different depths of porous (1 µm, 0.25 µm and 0.01 µm) by using SILVACO Athena and Atlas device simulator. Athena process simulator was used to construct the device structure while ATLAS device simulator was used to characterize the electrical and optical characteristics' effect on the different sizes of the P-Ge fabricated on the Si substrate. The comparison of the porous devices were then made with bulk Ge devices (bulk Ge-on-Si, bulk Ge-on-Ge) to identify the exploitation of porosity resulted in a significant performance of current gains, spectral response, Schottky barrier height, and also photo and dark current. It was found that the P-Ge at 0.01 µm depth showed an improved current gain compared to other porous structures while bulk Ge-on-Si obtain greater current gain than bulk Ge-on-Ge. This evidence indicates that P-Ge produces a better performance of MSM photodetector than the bulk device. The spectral response of P-Ge shows a peak response at 800nm, which is the near-infrared (IR) region supporting the feasibility of the P-Ge to be utilized for visible to near IR photodetection. [ABSTRACT FROM AUTHOR]

In this work, an innovative porous silicon structure was utilized as an effective antireflective layer for silicon solar cell construction. Silvaco technology computer aided design tools were used to construct the three structures of the porous silicon layers which were no porous, single porous, and double porous. Athena process simulator was used to create the non-porous silicon structure (as control device) and the single porous silicon structure, while the double porous structures were created at the n-type and p-type surfaces of the silicon solar cell by using the device editor (Devedit) tools. The three simulated structures were imported to the Atlas device simulator tools to simulate the current-voltage (I-V) characteristic and the spectral response of the solar cell. The simulation results of the three structures were compared with the fabrication results obtained by Ramizy et al. Finally, the efficiency extracted from the double porous solar cell is 9.55%, the single porous is 9.32%, and the no porous structure exhibited 4.83% efficiency. The double porous silicon solar cell showed an ability to effectively trapping the light collected in the solar cell and thereby improve the efficiency of the solar cell compared to the no porous and the single porous silicon structure. [ABSTRACT FROM AUTHOR]