Ultrathin Amorphous p-Type Tellurium Oxide Films Enabled by Cryogenic Deposition

Amorphous n-type metal oxides, such as In₂O₃ and Indium Gallium Zinc Oxide (IGZO), have shown promise as back-end-of-line (BEOL) compatible transistors, potentially offering a new paradigm for monolithic 3D stacking. However, a high-performance p-type counterpart remains a critical bottleneck. Tellurium suboxide (TeO_x) has recently been shown to be a promising p-type semiconductor for BEOL applications. Yet, it remains to be seen if sub-10 nm TeO_x films, needed for practical device applications, can be achieved with acceptable hole mobilities. Here, we report ultrathin TeO_x transistors fabricated via cryogenic thermal evaporation at a substrate temperature of -80 °C. This low-temperature process suppresses crystallization and surface diffusion, yielding ultrasmooth films with root-mean-square roughness as low as 4 Å. The back-gated TeO_x transistors achieve an on/off current ratio of 10⁵ and a field-effect mobility of 2.8 cm² V^-1 s^-1 at a channel thickness of 5.5 nm, retaining p-type switching behavior down to 2.4 nm. Selenium alloying further enhances the on/off current ratio by an order of magnitude while enabling bandgap tuning without compromising mobility.