Basudev Nag Chowdhury

Estimation of step-by-step induced stress in a sequential process integration of nano-scale SOS MOSFETs with high-k gate dielectrics

The current work proposes a novel technique to incorporate process-induced uni-axial stress for significant mobility boosting in high-performance metal–oxide–semiconductor field-effect-transistors. It has been shown that two existing standard techniques, namely, silicon-on-sapphire and high-k gate dielectrics can be combined to develop such technology. Sapphire has very high elastic constant and thermal expansion coefficient, thereby capable of inducing a significant amount of stress which is observed to be biaxial in nature. However, with the incorporation of different materials during process integration, such biaxial stress is gradually changed to uni-axial nature. The high-k gate dielectric plays the key role in converting the biaxial stress to uni-axial. Several high-k gate dielectrics have been studied and titanium oxide (TiO2) is observed to maximize the induced stress and also effective to convert it to uni-axial. A final average longitudinal channel stress of 0.73 GPa has been obtained.

Investigation of the electrical switching and rectification characteristics of a single standalone n-type ZnO-nanowire/p-Si junction diode

In this work, n-ZnO-nanowire/p-Si junction diodes have been fabricated and characterized both physically as well as electrically. The measurements are performed on a single standalone nanowire diode for the investigation of electrical transport through the nano-junction. The rectification properties of the single n-ZnO nanowire/p-Si diode have been studied for various input waveforms and frequencies. The diodes exhibit very promising rectification as well as switching behavior with no charge storage effect and consequently, a switching time as small as ∼1 ms has been achieved.

Investigating the impact of source/drain doping dependent effective masses on the transport characteristics of ballistic Si-nanowire field-effect-transistors

This article studies the impact of doping dependent carrier effective masses of the source/drain regions on transport properties of Si-nanowire field effect transistors within ballistic limit. The difference of carrier effective mass in channel and that in the source/drain regions leads to a misalignment of respective sub-bands and forms non-ideal contacts. Such non-idealities are incorporated by modifying the relevant self-energies which control the effective electronic transport from source to drain through the channel. Non-ideality also arises in the nature of local density of states in the channel due to sub-band misalignment, resulting to a reduction of drain current by almost 50%. The highest values of drain current, leakage current, and their ratio are obtained for the S/D doping concentrations of 3 × 1020 cm−3, 8 × 1020 cm−3, and 2 × 1020 cm−3, respectively, for the nanowire of length 10 nm and diameter of 3 nm. Interestingly, the maximum of sub-threshold swing, minimum of threshold voltage, and t...

Analytical Modeling of Vertically Oriented Standalone Si-Nanowire Metal-Oxide-Semiconductor Capacitors for Wavelength Selective Near-Infrared Sensing Applications

In the current work, photogeneration in a vertically oriented standalone Si-nanowire metal-oxide-semiconductor (MOS) capacitor has been investigated by developing a theoretical model that incorporates phase-breaking phenomena such as electron-photon interaction. For this purpose, a set of quantum field equations associated with second quantization electron and photon field operators have been solved through non-equilibrium Green’s function (NEGF) formalism by achieving self-consistency with Poisson’s equation. The obtained photocapacitance profile shows sharp peaks at specific wavelengths, detected by their relevant diameter-voltage combinations in the near-infrared region. Such peaks are observed to be shifted towards shorter wavelengths with increasing the applied voltage. Thus, the proposed device scheme can contribute significantly to wavelength selective photosensing applications with high selectivity.

Optimization of cross-sectional aspect ratio of ballistic Si nanobar MOSFETs for superior current-voltage characteristics

Si nanobar field effect transistors (Si-NBFETs) have emerged as one of the potential candidates in the present era of nano-structured electronic devices. In the current work, the carrier transport in ballistic Si-NBFETs is modeled by constructing a relevant Hamitonian matrix, where the coupling of source and drain with the channel is incorporated by the corresponding self-energy matrices. The Hamiltonian is solved by non-equilibrium Green’s function formalism. The current-voltage characteristics for different width and thickness of the nanobar channel are investigated in detail. Comparative study on drive current and leakage current for various transverse dimensions suggests a cross-sectional design window with an aspect ratio in the range of 1.3-1.6 to be appropriate for superior performance.

Modeling of transport behavior of the ballistic Silicon nanowire gate-all-around field-effect-transistors (Si NWFETs) with Si/SiO 2 interface roughness

In the current work, the contribution of gate oxide/channel interface roughness has been estimated and incorporated into the transport models of a Si nanowire field-effect-transistor (Si NWFET). This has been incorporated by modifying the relevant energy sub-bands taking into account the roughness in both transverse and longitudinal directions. Accordingly, the channel Hamiltonian matrix elements related to energy sub-bands are modified. It has been observed from the study that such interface roughness has significant effect on the device performance in terms of transfer and output characteristics. The transfer characteristics show that the current decreases up to 40% for an increase in interface roughness up to 25%.