Physics of amorphous silicon based alloy field-effect transistors

Abstract

In this paper we develop a new theory to describe the characteristics of amorphous silicon based alloy field-effect transistors. We show that the transition from below to above threshold operation occurs when the Fermi level in the accumulation region moves from the deep to tail localized states in the energy gap. The current-voltage and capacitance-voltage characteristics are related to the basic material parameters such as the distribution of localized states in the energy gap, band mobility, device geometry, channel doping, and series resistances. Our analysis shows that an on current in excess of 2×10−7 A/μm gate width can be obtained with a 10-μm gate length. We also demonstrate that even in the above threshold regime the field-effect mobility is dependent on the gate voltage. Our theory can be used to optimize the design of amorphous silicon based alloy field-effect transistors.

Trap density of states in n-channel organic transistors: variable temperature characteristics and band transport

“…The tail state has been established in a-Si transistors, where a double exponential distribution of the trap DOS has been assumed. 29 However, it is difficult to precisely determine the tail states in the present case, particularly when there are a comparatively large number of traps as in the case of DMDCNQI.…”

“…1, when V G is applied, charge Q = CV G is accumulated at the interface between the organic semiconductor and the gate insulator. In the a-Si transistors, spatial charge distribution in the accumulation layer is critical to determine the distribution of the mid-gap states, 29,30 which is generally estimated by solving Poisson's equation. 51 However, in the case of organic transistors, this process is simplified because the thickness of accumulation layer is typically shorter than the length of one monolayer.…”

“…Once such a DOS distribution is assumed, we can obtain the analytical formulas that describe the operation of a-Si transistors. 29,30 Trap DOS is sometimes considered as having two different regions, deep states and tail states. Numerous determination methods of the distribution of the trap DOS have been reported in organic transistors.…”

“…[28][29][30] The mid-gap states are studied from T-dependent transfer characteristics, and the distribution of the trap density of states is typically described as an exponential function ( Fig. 1), 31 N (E) = N G exp[(E − E C )/kT G ], (1) where N G is the trap density at the conduction band edge E C , and T G is the distribution width of the trap DOS.…”

Threshold voltage shift in organic field effect transistors by dipole monolayers on the gate insulator

“…If all deep traps are filled and the local Fermi energy in the channel is in the energy range of the transport level (the energy at which thermal activation begins to predominate) [42][43] the threshold voltage is reached [44] [45]. Horowitz and Delannoy expressed this condition as the equilibrium between trapped and mobile carriers [46] (for a refinement see [47]).…”