Controlling the Pd Metal Contact Polarity to Trigonal Tellurium by Atomic Hydrogen-Removal of the Native Tellurium Oxide

Palladium (Pd) electrodes have enabled superior performance in Te-based devices. Theory predicts strong Fermi level (EF) pinning near the Te valence band, which likely explains the predominant p-type conduction in Te transistors. The effects of the native TeOx on the contact polarity has not been explored. In this work, X-ray and ultraviolet photoelectron spectra (XPS and UPS, respectively) reveal the native surface oxide de-pins the EF between Pd and trigonal Te (t-Te) and can reduce contact resistance of hole and electron contacts to Te for back end of line-compatible complementary logic circuits. Atomic hydrogen reduces the native t-Te oxide below the XPS detection limit, after which, the EF resides near the t-Te conduction band edge. Therefore, an n-type band alignment is formed between Pd and t-Te via an atomic hydrogen treatment. Furthermore, UPS shows the EF is pinned near the t-Te conduction band edge. XPS indicates the formation of a PdTex intermetallic at the Pd-t-Te interface also affects the electrostatics of the interface. The concentration of PdTex is 40% higher when TeOx is removed from the t-Te surface before Pd metallization, likely the root cause of the low (pinned) work function when the native oxide is absent.

Automated summary

Pd electrodes have shown superior performance in Te-based devices, with native TeOx impacting contact polarity and resistance, and atomic hydrogen treatment affecting band alignment and electrostatics between Pd and Te. The presence or absence of TeOx also influences the formation of PdTex intermetallic, ultimately affecting the work function.