Amorphous zinc tin oxide (ZTO) is a wide-band-gap (transparent) semiconductor which exhibits high electron mobilities irrespective of its disordered nature. Transient photocapacitance (TPC), drive level capacitance profiling (DLCP), and modulated photocurrent spectroscopy (MPC) were used to determine the electronic state distribution within the mobility gap of ZTO. Conduction band-tail and valence band-tail Urbach energies near 10 and 110 meV were obtained by MPC and TPC, respectively. DLCP indicated free carrier densities in the mid-1015 cm−3 range plus a 0.2eV wide band of defects 0.4eV from the conduction band. The MPC spectra for ZTO also disclosed a defect band near the conduction band-tail.

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Amorphous oxide semiconductor thin‐film transistors (TFTs) are moving towards commercialization for a variety of display applications. Invariably, display applications require a bottom‐gate TFT configuration in which passivation of the top channel layer surface is required. The objective of this work is to propose a conceptual model framework for assessing TFT passivation schemes, within the context of amorphous oxide semiconductor electronics. This model involves first estimating the energy of the charge neutrality levels (CNLs) for the channel and passivation layers. Then, an energy band diagram is drawn to establish the relative position of these CNLs prior to their establishment of intimate contact. A situation in which the passivation layer CNL is below that of the channel layer CNL is considered undesirable because interface state electronic transfer from the channel to the passivation layer leads to formation of an accumulation layer at this interface. Although the opposite case in which the passivation layer CNL is above that of the channel layer CNL is more desirable, the ideal situation would be when both CNLs align because no interface state electronic transfer would occur. This framework is then employed in a discussion of the passivation of indium gallium zinc oxide and zinc tin oxide bottom‐gate TFTs.

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