Abstract
? 2022 Elsevier B.V.Reliable bipolar carrier transport remains a challenge in most wide-gap oxide semiconductors, and this limits the extensive adoption of oxides in transparent optoelectronic devices. For instance, it has been difficult to efficiently dope ZnO p-type in its hexagonal wurtzite polymorph. However, metastable octahedral rocksalt (RS) polymorph of ZnO has been predicted to be p-type dopable. Previously, we showed that RS-ZnO can be stabilized by alloying with octahedral RS- NiO forming Zn-rich RS-NixZn1-xO alloys which exhibit p-type conductivity due to their much higher valence band maximum with respect to vacuum. Here, we compare experimental results with computations by first-principles methods based on density functional theory (DFT) and Green's function-based Koringa-Kohn-Rostoker (KKR), and confirm that NixZn1-xO alloy assumes the octahedral rocksalt structure at alloy composition concentration x ~ 0.32. We further explore the electrical and optical properties of RS-NixZn1-xO (0.3≤x≤1.0) alloys with Li doping synthesized by magnetron sputtering under different growth conditions. Our data show that Li doping in O-rich RS alloys (NixZn1-xO1+δ) can lead to reliable p-type conductivity. In the Zn-rich NixZn1-xO1+δ (0.3≤x≤0.5) region, with Li doping the electrical resistivity, ρ decreases from 397 Ω-cm (x = 0.3) to 108 Ω-cm (x = 0.5), and the hole concentration increased from 1.1 × 1017 cm?3 to 3.8 × 1018 cm?3. The electrical properties of these alloys further improve as the Ni content x increases. This can be attributed to the higher Li doping and upward lifting of the valence band maximum (VBM), making the Li acceptor level shallower. These p-type Li doped Zn-rich alloy oxides are desirable for the formation of “quasi-homojunction” in ZnO-based devices for potential transparent optoelectronic applications.
NSTL
Elsevier