Mohit Mehta

Simulations of “atomistic” effects in nanoscale dopant profiling

The most commonly used method for dopant profiling in semiconductors is scanning capacitance microscopy (SCM). However, the analysis on which SCM is based assumes the dopant atoms are a continuous fluid, and “atomistic” effects caused by the locations of the individual dopant atoms make this assumption invalid at a resolution finer than 10 nm for a dopant concentration of 1018cm-3 where there is an average of only 1 atom per pixel. Simulations are presented which include quantum mechanical effects such as the confinement of carriers near the dopant atoms, as well as the discrete nature of the dopant atoms. These simulations suggest that error bars should be used to show the lack of certainty in dopant profiling as such a fine resolution is approached.

Thermal relaxation in magnetic multi-layer materials with mixed hysteretic behavior

Thermal relaxation phenomena in mixed-type hysteretic systems are investigated by using recently developed mixed Preisach model and Monte Carlo technique. The anomalous hysteretic behavior observed in several heterogeneous materials, especially in nanoscale embedding, is also generating unconventional relaxation processes which may involve several steps before relaxing to the anhysteretic state. The medium-term relaxation behavior is studied under various noisy environments and applied magnetic fields, analyzing the influence of noise strength, noise bandwidth, and field values on the relaxation characteristics.

Analysis of noise spectral density and coherence resonance phenomena in mixed hysteretic systems driven by noise

In this article, the authors focus on the characterization of mixed clockwise-counterclockwise hysteretic system response to white and colored noise and prove that coherence resonance can be identified in such systems driven solely by noise . Mixed hysteretic behavior have been observed experimentally in several magnetic multi-layer and superlattices materials with antiferromagnetic interlayer coupling and positive exchange bias. Several mixed and hybrid hysteretic models based on the superposition of standard counter-clockwise hysteretic models, such as Preisach and Jiles-Atherton, and their newly developed clockwise variants have been proposed to describe this anomalous magnetic behavior. Here, we consider the mixed Preisach model obtained by linear (convex) combination of classical counter-clockwise Preisach model and the clockwise Preisach model first developed by Mayergoyz and Andrei to describe nonlinear diffusion of electromagnetic fields in conducting magnetic media with abrupt magnetic transitions. Various types of noise inputs are considered, such as white Gaussian noise, Ornstein-Uhlenbeck noise and pink Gaussian noise, and the output power spectral densities are computed, analyzed and compared for various input parameters.