Ultrathin Amorphous <i>p</i> -Type Tellurium Oxide Films Enabled by Cryogenic Deposition

Amorphous <i>n</i>-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 <i>p</i>-type counterpart remains a critical bottleneck. Tellurium suboxide (TeO_<i>x</i>) has recently been shown to be a promising <i>p</i>-type semiconductor for BEOL applications. Yet, it remains to be seen if sub-10 nm TeO_<i>x</i> films, needed for practical device applications, can be achieved with acceptable hole mobilities. Here, we report ultrathin TeO_<i>x</i> 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_<i>x</i> 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 <i>p</i>-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.