Trapped Carrier Scattering and Charge Transport in High‐Mobility Amorphous Metal Oxide Thin‐Film Transistors

Abstract

The multiple trap and release (MTR) model is extended to more completely and accurately describe charge transport in high-mobility amorphous metal oxide thin-film transistors (TFTs). In addition to trapping and release of charges, other scattering mechanisms that influence mobility are considered along with screening by free carriers. The mobility for each of the dominant scattering mechanisms is calculated using the Boltzmann transport equation (BTE) in the relaxation time approximation. It is found that trapped carriers very effectively scatter the charges that move in extended states. This type of scattering is unique to TFTs. Experimental data from high-mobility amorphous metal oxide TFTs are compared with calculations with very good agreement. At high temperatures, scattering by longitudinal optical phonons and surface phonons becomes significant. This work represents the first successful combination of charge carrier scattering and the BTE with thermally activated MTR transport in a disordered semiconductor. Charge transport in amorphous metal oxide transistors is quantitatively described for the first time and the factors that influence the mobility at various temperatures and charge carrier densities are clearly described. This approach can be used for describing transport in several amorphous and polycrystalline semiconductors with significant disorder and trapping.

Effectively modulating thermal activated charge transport in organic semiconductors by precise potential barrier engineering

“…Figure 1a shows the energy-level diagram including band bending at GB of p-type organic semiconductor. The positive charges trapped at GB repel other charges of the same sign, and are screened by bared negative charges to remain macroscopic electrical neutrality, which results in a build-in potential ∅ B [36][37][38][39][40] . The SCR of hole depletion is thus formed, which produces a downward band bending of local energy level at GB, just like two back-to-back Schottky barriers 22,27,39 .…”

Redefining the Mobility Edge in Thin-Film Transistors

“…In the case of disordered semiconductors such as polymers and amorphous oxides, however, this condition is not generally satisfied. Only in a few instances with relatively high mobilities [1], can the RTA be used. In most other cases, the mean free path is equal to or slightly less than the lattice constant or intermolecular distance.…”

“…Band transport in the extended multiple trap and release model [1] has several dominant scattering mechanisms. The main scattering mechanisms for this semiconductor system are trapped carrier (TC) scattering, polar optical phonon (LO) scattering, optical deformation potential (ODP) scattering and acoustic phonon (AC) scattering.…”

“…These are very efficient scattering centers due to the high degree of special overlap with mobile carriers. The trapped carrier scattering rate is evaluated as [1,34]:…”

“…The mean free path can be considered to be the average distance charge carriers travel between scattering events. When carrier mobilities are more than about 20 cm 2 /(Vs), the mean free paths exceed typical lattice constants/intermolecular distances [1,2]. At these mobility values and beyond, charge transport theories based on the Boltzmann Transport Equation (BTE) can be applied.…”