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

Area of Science:

• Semiconductor physics
• Materials science
• Device engineering

Background:

• Amorphous n-type metal oxides like Indium Gallium Zinc Oxide (IGZO) are suitable for back-end-of-line (BEOL) applications.
• A high-performance p-type semiconductor is critical for monolithic 3D integration.

Purpose of the Study:

• To investigate ultrathin tellurium suboxide (TeO_x) films for p-type transistors.
• To achieve sub-10 nm TeO_x films with acceptable hole mobilities for practical device applications.

Main Methods:

• Fabrication of TeO_x transistors using cryogenic thermal evaporation at -80 °C.
• Characterization of film properties, including surface roughness and electrical performance.
• Investigation of selenium alloying for enhanced properties.

Main Results:

• Ultrasmooth TeO_x films (RMS roughness as low as 4 Å) achieved via low-temperature processing.
• Back-gated transistors demonstrated an on/off current ratio of 10⁵ and mobility of 2.8 cm² V^-1 s^-1 at 5.5 nm thickness.
• Stable p-type switching observed down to 2.4 nm channel thickness. Selenium alloying boosted on/off ratio and allowed bandgap tuning.

Conclusions:

• Cryogenic thermal evaporation enables high-quality ultrathin TeO_x films for p-type transistors.
• TeO_x shows significant potential as a p-type semiconductor for BEOL applications.
• Selenium alloying offers a pathway for further optimization of TeO_x-based devices.