SIMULATION OF CURRENT-VOLTAGE CHARACTERISTICS OF SPIN FIELD EFFECT TRANSISTOR USING NEMO-VN2

: We have developed a simulator for nanoelectronics devices, NEMO-VN2. In this work, we provide an overview of spin field effect transistor. We use the simulator to explore the performance of spin FET. The model of the spin FET is based on non-equilibrium Green function method and implemented by using graphic user interface of Matlab. The current-voltage characteristics such as drain current-voltage, drain current-gate voltage ones are explored. previously


INTRODUCTION
In recent years, a vigorous research effort to demonstrate spin transistors has been pursued.
One of the motivations has been that spin transistors are identified as one of the most promising alternatives to traditional MOSFET by the International Technology Roadmap for Semiconductors [1].
Simulations have predicted that spin transistors can scale in their size with smaller switching energy and less overall power dissipation than MOSFET.
The idea of spin field-effect transistor sparked after Fert et al. [2] and Grunberg et al. [3] discovered the giant magneto resistance effect in magnetic multilayer systems in 1988.
They found huge differences in current coming out of a magnetic and metallic multilayer system when the magnetic layers had the same or different scattering of electrons. Shortly thereafter room temperature magnetic field sensors were made [4] using spin property which had much better performance than previously used anisotropic magneto resistance property.
Following the preliminary realization of the potential benefits of utilizing spin property, Datta and Das proposed an electron wave analog of the electro-optic light modulator in the late 1989 [5]. Most of the today's interest in this newly born field of study is motivated by their well-known proposed device which is now known as spin field-effect transistor (spin FET).
In this work, we start with an introduction to the concepts of electron spin and proposed spin field effect transistor in the first section. In the second section, we look more into details of spin field effect transistor from a device point of view (e.g. energy band diagram, device structures    We should also note that Rashba factors are too small.

Energy band diagram of spin FET
The basic structure of a spin field-effect transistor is constructed from a metal oxide semiconductor (MOS) gate and two ferromagnetic contacts of source and drain, as it is shown in Figure 2. We also know that the existence of an insulator layer between ferromagnets and semiconductor channel so far has shown a necessity to overcome the problem of conductivity mismatch. Having said that, a variety of band diagrams for different spin field-effect transistors are shown in Figure 3.   for the source and drain contacts.

Device structures of spin FET
Two device structures for spin field-effect transistors are shown in Figure 4. We call these structures bulk spin field-effect transistor and silicon on insulator (SOI) spin field-effect transistor corresponding with their configurations. Low production cost for bulk spin field-effect transistors and excellent device performance for SOI spin field-effect transistors is expected [7]. In the bulk spin field-effect transistor, the ferromagnetic source or drain act as electrical contacts to the channel when the transistor is working in its on-state, and they work as blocking contacts for leakage current between the source and drain when the transistor is in its off-state.
We should note that in the bulk spin field-  (9) by the applied bias V: Here, E-energy, k B -Boltzmann constant, T-temperature.
The density matrix is given by The quantity T(E) appearing in the current equation (11) where H is effective mass Hamiltonian, I is an identity matrix of the same size,