Enhanced screening on remote phonon scattering in InGaZnO thin-film transistor by using Ge gate electrode

Abstract

Room-temperature-processed amorphous InGaZnO thin-film transistors (TFTs) with three different semiconductors (Si, GaAs, and Ge) of various doping concentrations as gate electrodes are fabricated. Like the conventional Si gate devices, both their GaAs and Ge counterparts show carrier mobility increasing with increasing gate doping concentration, further supporting that the holes at/near the surface of a p-type gate electrode can have a screening effect on the remote phonon scattering caused by the surface phonons of their high-k gate dielectrics. Moreover, for the same gate doping concentration, the Ge gate device has a carrier mobility about three times that of its conventional Si gate counterpart. This implies that lower-mass charge carriers in the gate electrode could have a stronger screening effect on remote phonon scattering. As a result, even with a moderate gate doping concentration of 1.0 × 1018 cm−3, the room-temperature-processed Ge gate device shows a high carrier mobility of 60.8 cm2/V s. The enhanced screening effect of the Ge gate electrode should be due to its higher-energy plasmons, which could couple more strongly with the phonons of the gate dielectric to result in weaker gate-dielectric vibration.