Development of Precursors for Atomic Layer Deposition of p-Type Oxides

Owing to the tunable properties, high stability, and standardized fabrication process, metal oxides have become key materials in almost every electronic and energy application. In particular, oxide semiconductors possessing band gaps of 1–4 eV with controllable carrier densities and high mobilities have potentials to overcome cost, performance, and process limitations of semiconductors such as Si and GaAs. A critical obstacle in the current development of thin film transistor (TFT)-based oxide electronics is the absence of good p-type oxide semiconductors; well-known p-type oxides such as NiO and Cu2O are poor
in performance or stability when compared to n-type counterparts such as ZnO, In2O3, and Ga2O3. Because of this deficiency, practical implementations TFT circuits using oxide semiconductors are confined to unipolar (NMOS) architectures. Development of high-performance p-type components
would greatly expand the application area of oxide semiconductors by permitting, for example, energy efficient devices or sensors with new functionalities, as complementary (CMOS) architectures would be
possible. The fundamental reason underlying the scarcity of p-type oxides is well understood; firstly, valence bands of oxides are low in energy, and, therefore, holes are easily compensated by defects like oxygen vacancy and ubiquitous hydrogen, resulting in the low p-type dopability. Secondly, the valence band
maximum mainly consists of localized oxygen 2p-orbitals, which leads to a large hole effective mass. Despite this challenge materials such as tin(II) oxide (SnO) and bismuth(III) oxide (Bi2O3) and materials containing these oxides have emerged as possible p-type semiconductor materials, for the fabrication of
thin film transistors (TFTs) and complementary metal oxide semiconductors.
Atomic layer deposition (ALD) of SnO[1-4] and Bi2O3[5-6] has been reported for a range of ligand systems in conjunction with H2O. However, many of the ‘state-of-the-art’ ALD processes suffer with chemical vapor deposition (CVD) pathways or contamination of higher oxide materials or metal, negatively impacting the electronic properties. Here, we report on our continuing work on the
development potential ALD precursors for SnO and Bi2O3, with their synthesis, thermal stability and volatility discussed. The performance of devices deposited using the varying precursors, and delivery modes will also be discussed