This letter reports a technique for increasing the carrier concentration and the conductivity of the p-type CuAlO2 through doping the material with nitrogen. The x-ray photoelectron spectroscopy and the optical band gap analyses suggested that the nitrogen atoms occupying the interstitial sites of the delafossite structure provided the p-type CuAlO2 with an impurity energy level in the energy gap. It was also found that the N-doped CuAlO2 film had its optimum conduction properties when the dopant level reached 1.1 at. %. Here, the carrier concentration was raised from 4.81x10(16) in the undoped film to 2.13x10(17) cm(-3) in the doped film, and the corresponding film's conductivity was increased from 3.8x10(-2) to 5.4x10(-2) (Omega cm)(-1), as compared with the undoped CuAlO2 film. (C) 2007 American Institute of Physics
A visible-blind UV photodetector (PD) using a double heterojunction of n-ZnO/LaAlO3 (LAO)/p-Si was demonstrated. Inserted LAO layers exhibit electrical insulating properties and serve as blocking layers for photoexcited electrons from p-Si to n-ZnO, leading to an enhanced rectification ratio and a visible-blind UV detectivity of the n-ZnO/LAO/p-Si PDs due to the high potential barrier between LAO and p-Si layers (~2.0 eV). These results support the use of n-ZnO/LAO/p-Si PDs in the visible-blind UV PDs in a visible-light environment.
Annealed Cu-Al-O films showed marked structural changes and differing optoelectronic properties with varying annealing temperature. Results of X-ray diffraction ͑XRD͒ demonstrated that CuO and CuAl 2 O 4 were the intermediate reaction phases. XRD also showed that the phase grown above 800°C annealing temperature was pure CuAlO 2 phase. Cross-sectional high-resolution transmission electron microscopy revealed that the crystallization behavior of the Cu-Al-O films belonged to an outward model. The optimum properties of delafossite structure CuAlO 2 film was attained after annealing at 800°C. The surface morphology of CuAlO 2 had a cell-like surface appearance and the grain sizes were approximately 20-100 nm. The optical direct bandgap of the CuAlO 2 film was estimated to be 3.11 eV. Hall effect measurements revealed that the CuAlO 2 film belonged to the p-type conduction category, with a carrier concentration of 4.81 ϫ 10 16 cm −3 and the conductivity of 3.8 ϫ 10 −2 ͑⍀ cm͒ −1 . The optoelectronic properties of the Cu-Al-O system are dominated by the delafossite CuAlO 2 .The n-type transparent conducting oxides ͑TCOs͒, such as In 2 O 3 , 1 ZnO, 2-4 and SnO 2 , 5,6 have been extensively studied and widely used in flat panel displays, touch panels, and solar cells. p-Type TCOs are neither well studied nor thoroughly explored yet. Recently, a series of p-type TCOs such as CuAlO 2 , 7,8 CuGaO 2 , 9 and SrCu 2 O 2 10 have been successfully produced by various techniques. The p-type CuAlO 2 film of delafossite structure in particular has been attracting an immense research interest because of its attractive properties, which have great potential for practical applications. One of the main applications proposed for CuAlO 2 film is in the transparent p-n junction semiconductor device, which is the structure that combines the two types of TCO materials in the form of a p-n junction. The device is capable of absorbing ultraviolet light but transmitting the visible light. As such, it can be used as a transparent functional window in microelectronic devices. [11][12][13] So far, little research has been devoted to the study of microstructure and associated optoelectronic properties of the CuAlO 2 film. The present paper reports the study on the CuAlO 2 film prepared by the dc reactive sputtering technique and annealed under controlled Ar atmosphere. In particular, properties of the CuAlO 2 thin films characterized by X-ray diffraction ͑XRD͒, field-emission scanning microscope ͑FESEM͒, high-resolution transmission electron microscope ͑HRTEM͒, X-ray photoelectron spectroscopy ͑XPS͒, UV-visible ͑UV-vis͒ spectroscopy, and Hall effect measurement are presented. In addition, the structural, optical, and electrical properties of the p-type CuAlO 2 are discussed. ExperimentalThe Si wafer and quartz substrates used for the film were thoroughly cleaned by ultrasonic vibration in baths of hot degreasing solvent, acid solution, and deionizer water sequentially. Deposition of the CuAlO 2 films was carried out by a dc reactive sputtering sys...
The anisotropic relaxation behavior of the compressive residual stress of delafossite CuAlO2 film was identified to take place on silicon substrate, on which the film was grown. Experimental results suggest that in order to release the internal compressive residual stress of the CuAlO2 film, CuO hillocks would be favored to grow on the film surface. It was also proposed that because of the structural anisotropic nature associated with the delafossite CuAlO2 , the compressive residual stress was released first by breaking the O–Cu–O bonds of the dumbbell layers and subsequently by the diffusion of Cu and O atoms along the a -axis direction on the close-packed Cu layers, suggesting that the c -axis direction across the AlO6 octahedral layers has a greater resistance to compressive residual stress.
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