Use of high-k encapsulation to improve mobility in trap-limited metal-oxide semiconductors

Abstract

Low-temperature spray-deposited ZnO films are encapsulated by insulating Ga2O3 films and the resulting electronic properties of heterostructure films and transistors are analyzed and compared to un-encapsulated ZnO as a function of processing temperature. An enhancement in Hall mobility and field-effect mobility is observed similar to when high-k dielectrics are used as gate-dielectrics in transparent conductive oxide thin-film transistors except without the presence of undesirable device behavior such as gate-leakage and hysteresis. Based on a recently proposed theory consisting of electron donation from high-k dielectrics, work function measurements show that conditions for electron transfer from Ga2O3 to ZnO can be met by optimally-tuning the deposition temperature of the respective films resulting in an effective doping which is qualitatively similar to modulation doping. As a result, TFTs composed of ZnO/Ga2O3 heterostructures exhibit greatly improved switching characteristics and electron transport relative to the otherwise poor performance of low-temperature processed ZnO achieved through a simple modification to TFT device structure.