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LaCuOSe is a wide gap (Eg = 2.8 eV) p-type semiconductor. Epitaxial films may be converted to a degenerate semiconductor with hole concentrations (n h ) > 1 × 10 21 cm -3 by doping Mg ions to the La sites. We, however, found that the Mg concentration in the highest n h film was too low (

Tin monoxide (SnO) is a stable p-type oxide semiconductor. This paper reports electrical properties, electronic structures, and thin-film transistors (TFTs) of SnO. Epitaxial films were fabricated by pulsed laser deposition. The Hall mobility and the hole density of the epitaxial films were 2.4 cm 2 V -1 S -1 and 2.5 x 10 17 , respectively. X-ray photoelectron spectroscopy (PES) indicated that the closed-shell 5s 2 orbitals of Sn 2+ ions heavily contribute to the hole conduction path in SnO. Top gate type TFTs (W/L=300/50 μm) employing 20 nm thick SnO channels exhibited field-effect mobilities μ sat = 0.7 cm 2 V -1 s -1 and μ lin = 1.3 cm 2 V -1 s -1 , which are larger by two orders of magnitude than those reported for p-channel oxide TFrs to date. On/off current ratios were ~10 2 and subthreshold voltage swings (S) ~7 V/decade. The parameters required for TFT simulations were estimated by ultraviolet PES and first-principles calculations. The TFT simulations indicated that subgap hole trap density in the SnO channel is > 10 19 cm -3 , which limits the TFT mobilities and the S values.

Copper-based chalcogenide thin films deposited at room temperature were examined for exploring an active layer material for a p-channel thin film transistor (TFT) fabricable at room temperature. The electrical conductivities of chalcopyrite and simple copper chalcogenide thin films were controlled by introducing hydrogen sulfide and oxygen gases, respectively, during the film deposition. However, no current modulation by gate bias was observed in fabricated TFTs. Optical absorption spectra showed intense subgap absorptions, and these subgap states are thought to pin the Fermi levels. Although these copper-based chalcogenides did not work as TFT channels, we found that simple copper chalcogenides deposited under a high vacuum showed p-type degenerate conduction with a high conductivity up to 7.3 × 103 S/cm and a reasonably large work function of ∼4.7 eV. These properties are rather favorable for a hole injection layer of flexible electronic devices and suggest a promising application as an anode layer in organic light emitting devices. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electronic and optical properties of widegap oxychalcogenides, LaCuOCh (Ch = chalcogen) and La 2 CdO 2 Se 2 , are reviewed with a focus on those relevant to their layered crystal structures, including high hole mobility, degenerate p-type conduction, room temperature exciton, and large third order optical nonlinearity. In particular, the widegap p-type metallic conduction was realized in Mg-doped LaCuOSe: the first demonstration among any class of widegap materials including GaN:Mg. Furthermore, we demonstrate the room temperature operation of a blue light-emitting diode using a pn hetero-junction composed of a LaCuOSe epilayer and an n-type amorphous InGaZn 5 O 8 . Those results strongly suggest that a series of the layered oxychalcogenides are applicable to the light-emitting layers in opto-electronic devices that operate in the ultraviolet-blue region as well as to transparent p-type conductors.