Oxide electronics, which together with amorphous semiconductors could become a rapid‐growth field, have come a step closer with the first report of a p‐type amorphous oxide semiconductor, ZnO·Rh2O3. The thin‐film deposition of this material at room temperature and the fabrication of p–n heterojunction diodes on flexible plastic sheets (see Figure) are demonstrated.

No abstract

A reactive solid-phase epitaxy technique was applied to fabricate all-oxide transparent p-n heterojunctions composed of p-ZnRh2O4 and n-ZnO thin layers. Polycrystalline ZnRh2O4 was deposited on a ZnO epitaxial layer at room temperature. Thermal annealing of the bilayer sample at 950 °C in air converts the polycrystalline ZnRh2O4 layer to an epitaxial single-crystalline layer. The resultant p-n heterojunctions have an abrupt interface and exhibit a distinct rectifying I–V characteristic. The threshold voltage is ∼2 V, agreeing well with the band-gap energy of ZnRh2O4. It also exhibits photovoltage with UV-light illumination, which originates mainly from the n-ZnO layer.

p‐Type conduction in amorphous oxide was firstly found in zinc rhodium oxide (ZnO·Rh2O3) (Adv. Mater. 2003, 15, 1409), and it is still the only p‐type amorphous oxide to date. It was reported that an ordered structure at the nanometer scale was contained and its electronic structure is not clear yet. In this paper, optoelectronic and structural properties are reported in detail for xZnO·Rh2O3 thin films (x = 0.5–2.0) in relation to the chemical composition x. All the films exhibit positive Seebeck coefficients, confirming p‐type conduction. Local network structure strongly depends on the chemical composition. Transmission electron microscopic observations reveal that lattice‐like structures made of edge‐sharing RhO6 network exist in 2–3 nm sized grains for rhodium‐rich films (x = 0.5 and 1.0), while the zinc‐rich film (x = 2) is completely amorphous. This result indicates that excess Zn assists to form an amorphous network in the ZnO–Rh2O3 system since Zn ions tend to form corner‐sharing networks. The electronic structure of an all‐amorphous oxide p‐ZnO·Rh2O3/n‐InGaZnO4 junction is discussed with reference to electrical characteristics and results of photoelectron emission measurements, suggesting that the p/n junction has large band offsets at the conduction and valence bands, respectively.

No abstract