Crystallization Disruption via Atomic Layer Deposition Substitutional Dopant Scheduling: High-Mobility Amorphous Indium Zinc Tin Oxide

Abstract

Transparent conducting oxides (TCOs) are widely used in thin film transistors (TFTs), displays, window coatings, and solar energy conversion applications, with varying demands on mobility, conductivity, transparency, and roughness. We investigate supercycle atomic layer deposition (ALD) dosing strategies that achieve high electron mobility while inhibiting the crystallization of In 2 O 3 -based TCOs and producing smoother films. ALD In 2 O 3 layers (A) of varying thickness are separated by a single cycle of ALD ZnO (B) or SnO 2 (C). The resulting quaternary indium zinc tin oxide (IZTO) thin film properties depend strongly on the A N :B:A N :C structure, where "N" varies from 1 to 9 In 2 O 3 ALD cycles. The IZTO thin films remain amorphous for N < 8 or 4 sequential In 2 O 3 layers at deposition temperatures of 150 or 175 °C, respectively. The highest conductivity and carrier mobility for amorphous films, 1.6 × 10 −3 Ωcm and 50−55 cm 2 V −1 s −1 respectively, are observed nearest the crystallization transition. This dilute substitution strategy produces carrier mobilities among the highest reported for amorphous indium-based materials fabricated by ALD and comparable to those of crystalline ALD indium tin oxide (ITO).