Transparent SnO–SnO2 p–n Junction Diodes for Electronic and Sensing Applications

Zhenwei Wang, Pradipta K. Nayak, Arwa Albar, Nini Wei, Udo Schwingenschlögl andHusam N. Alshareef*, "Transparent SnO–SnO2 p–n Junction Diodes for Electronic and Sensing Applications"
​Adv. Mater. Interfaces 2015, 1500374
Zhenwei Wang, Pradipta K. Nayak, Arwa Albar, Nini Wei, Udo Schwingenschlögl andHusam N. Alshareef*
interfacial layers;p–n diodes;temperature sensors;sensors;tin dioxide;tin monoxide
The p–n junction is a simple but versatile structure used in many electronic devices such as diodes, junction transistors, solar cells, and light-emitting diodes.[1] Apart from the rectifying effect, p–n junction devices have been widely used in sensing applications, such as thermometer, photodetector, and radiometer. Transparent all oxide-based p–n junction diodes have been attracting increasing attention due to the encouraging rectifying performance and the promise of achieving transparent circuits.[2-5] As its name suggests, a p–n junction consists of serially connected p- and n-type semiconductors, where the operation of the device strongly depends on quality of the interface between n- and p-type semiconductor layers, which may be degraded by interfacial surface roughness, third phase impurity, and the formation of interfacial layer. The interface quality is also related to the materials selection for n- or p-type transparent semiconducting oxides (TSOs). The oxide phase of metal with multivalence state is more inclined to be oxidized or reduced when exposed to higher process temperature or extended processing time,[6, 7] which would lead to the formation of third phase impurity or interfacial layer, degrading the corresponding device performance. So far, a variety of n-type TSOs with decent electrical performance and visible-range transparency are available,[8] including indium oxide (In2O3),[9] zinc oxide (ZnO),[4, 10] tin dioxide (SnO2),[11] and amorphous gallium–indium–zinc oxide (a-GIZO).[3, 5, 12] In comparison to n-type TSOs, the p-type counterparts lag in performance. The most promising p-type oxide semiconductors include ternary copper oxides[13] [which include both Cu+-based delafossites (CuMO2, M = Al, Ga, In, etc.) and nondelafossites (CuSr2O2)], binary copper oxides (CuO and Cu2O),[5, 14, 15] spinel oxides (ZnM2O4, M = Rh, Co, Ir),[3, 4, 16] and tin monoxide (SnO).[17-20] Among these, Cu2O and SnO have been reported with higher p-type Hall mobility values due to the more dispersed valence band maximum, which results from the hybridization between the O 2p and Cu 3d (or Sn 5s) orbitals.[15, 21-23] However, these two p-type oxides are known to be metastable phases, which have the tendency to be oxidized, forming stable phases with higher metal valence states.[14, 20] The p–n junctions based on these two p-type oxide always suffer from the formation of defective interfacial layers. For example, about 80 nm interfacial layer was reported by Sathyamoorthy et al. in their p-SnO/n-SnO2 junction diode, which exhibited an unexpectedly large ideality factor of 21.5, along with a small rectification ratio.[24] If the interfacial layer thickness could be reduced or its quality improved, p-SnO/n-SnO2 junctions with better performance can be realized.