Mehdi Saremi

Armchair Graphene Nanoribbon Resonant Tunneling Diodes Using Antidote and BN Doping

Band gap size of armchair graphene nanoribbons (AGNRs) can be tuned by implementing topological antidotes or boron/nitride (BN) atoms at the middle of ribbons. By imposing such modulated patterns on certain regions of AGNRs, double barrier quantum well structures can be produced. According to this procedure, this paper proposes a new method for constructing resonant tunneling diodes (RTDs) by using AGNRs while the widths of the ribbons remain constant. Different structures of modulated AGNR-RTDs are constructed by introducing hexagonal antidotes, hexagonal BN doping atoms, and the combination of antidotes and BN doping atoms at the middle of pristine AGNRs. It is found that in general, antidote AGNR-RTDs present negative differential resistance with better performance in comparison with other modulated AGNR-RTDs. In addition, the effects of dimensional parameters such as the length of channel, the length of barrier, and the distance between antidotes on the performance of antidote AGNR-RTDs are investigated. It is extracted that the peak to valley ratio, power dissipation, and other properties can be modified by tuning the dimensional parameters to appropriate values. Numerical tight-binding model along with nonequilibrium Greens function formalism is applied to study the electronic properties of devices.

Band Gap Tuning of Armchair Graphene Nanoribbons by Using Antidotes

The electronic properties of armchair graphene nanoribbons (AGNRs) can be changed by creating antidotes within the pristine ribbons and producing antidote super lattice AGNRs (ASL-AGNRs). In the present work, band gap tuning of ASL-AGNRs is investigated by varying the width of ribbons (dW) and the distance between antidotes (dL) for five different antidote topologies. Numerical tight-binding model is applied to obtain the band structure of the ribbons. Based on our results, it is found that the band gap of ASL-AGNRs can be increased or decreased in different cases. Furthermore, changing the width of ribbons generally results in more predictable␣band gap profiles compared to the variation of distance between antidotes. Consequently, by opting appropriate antidote topologies and dimensional parameters (dW and dL), it is possible to gain a desired band gap size. This can be considered as an alternative solution in design of electronic and optoelectronic devices where tunable band gap values are needed.

SOI LDMOSFET with Up and Down Extended Stepped Drift Region

To increase the breakdown voltage and decrease the ON resistance, a silicon-on-insulator (SOI) lateral double-diffused metal–oxide–semiconductor field-effect transistor (LDMOSFET) in which the drift region extends to the up and down oxides in a step shape is proposed. This up and down extended stepped drift SOI (UDESD-SOI) structure demonstrates a modified lateral electric field distribution with additional peaks as well as a decrease of the usual peaks near the drain and gate. Two-dimensional (2D) simulations were used to compare the characteristics of the proposed UDESD-SOI structure with those of other structures, viz. down extended stepped drift SOI (DESD-SOI), up extended stepped drift SOI (UESD-SOI), and conventional SOI (C-SOI). Under the same conditions, the breakdown voltage of the UDESD-SOI structure was nearly 35%, 117%, and 318% higher compared with the DESD-SOI, UESD-SOI, and C-SOI structure, respectively. To determine the optimum parameters for the UDESD-SOI structure leading to the highest breakdown voltage, a comparative study was performed to investigate the effect of the doping concentration in the drift region, buried oxide (BOX) thickness, and thickness of up and down extended steps (T1 and T2, respectively). In addition, the drain current (ON resistance) of the UDESD-SOI structure was found to be 13%, 43%, and 229% higher (16%, 65%, and 257% lower) than the values for the DESD-SOI, UESD-SOI, and C-SOI structure, respectively.

Analysis of the reverse I-V characteristics of diamond-based PIN diodes

Diamond is one of the most promising candidates for high power and high temperature applications, due to its large bandgap and high thermal conductivity. As a result of the growth and fabrication process of diamond-based devices, structural defects such as threading dislocations (TDs) may degrade the electrical properties of such devices. Understanding and control of such defects are important for improving device technology, particularly the reverse breakdown characteristics. Here, we show that the reverse bias current-voltage characteristics in diamond PIN diodes can be described by hopping conduction and Poole-Frenkel emission through TDs over the temperature (T) range of 323 K < T < 423 K, for typical values of the TD density found in epitaxially grown materials.

Physically Based Predictive Model for Single Event Transients in CMOS Gates

An analytical model is presented to understand the time response of an inverter to ionizing particles based on physical equations. The model divides the output voltage transient response of an inverter into three time segments, where an ionizing particle striking through the drain-body junction of the OFF-state nMOS is represented as a photocurrent pulse. If this current source is large enough, the output voltage can drop to a negative voltage. In this model, the OFF-state nMOS is represented as the parallel combination of an ideal diode and the intrinsic capacitance of the drain-body junction, while a resistance represents an ON-state pMOS. The proposed model is verified by 3-D TCAD mixed-mode device simulations. In order to investigate the flexibility of the model, the effects of important parameters, such as ON-state pMOS resistance, doping concentration of P-region in the diode, and the photocurrent pulse are scrutinized.