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We demonstrate an unconventional near-infrared photodetector fabricated from a ZnO chip with a metallic subwavelength grating structure as a contact and optical window, which harvests hot electrons generated by plasmonic resonances introduced by incident light. The grating structure has a strong selection of the polarization of incident light, meaning that the detector is naturally polarization-sensitive. In our device, the polarization extinction ratio is as high as 64:1, much higher than that relying on crystal orientations. Since the photoresponse is introduced by plasmonic resonance, a narrow photoresponse spectrum with a linewidth of 32.1 nm at 1.201 μm is obtained. By simply changing the grating period, the spectral position can be tailored freely within the near-infrared region, i.e., wavelength-selective. Such a spectral response is not likely to be realized with conventional semiconductor photodetectors, which depend on the band edge absorption. We propose a modified Fowler's model, which well explains the line shape of photoresponse spectra of such devices.

By means of all optical characterizations, carrier dynamics of GaZn–VZn defect complex in Ga doped ZnO film has been systematically studied. It is observed that the defect complex exhibits a red emission centered at 650 nm, different from that of a reference sample containing VO only. From our observations using time-resolved photoluminescence and multiple-wavelength excitation photoluminescence measurements, the energy level of GaZn–VZn is determined to be a two-level system, which is fundamentally different from the reference sample with only a deep level in term of carrier dynamics. This work reveals that GaZn–VZn distinguished from the widely observed VO is a potential candidate for new single photon emitters.

A single-phase wurtzite MgZnO film with an optical band gap of 294.5 nm was synthesized on ZnO substrate by molecular beam epitaxy, and a photodetector was fabricated working in the ultraviolet-B spectrum region. Wurtzite BeO was adopted to restrain the substrate response as an insulating layer and provide an excellent epitaxial template for high-Mg-content MgZnO growth. In situ reflection high-energy electron diffraction observations, ex situ X-ray diffraction and reflectance spectrum indicate the achievement of high-quality single-phase wurtzite MgZnO with smooth surface and deep ultraviolet band gap. The BeO layer efficiently suppresses the photoresponse from the substrate, as the photo-detector demonstrates a sharp cutoff at 290 nm, consistent with the optical band gap. (C) 2013 Elsevier B.V. All rights reserved.

Broadband antireflection of silicon has been realized by combining black silicon, surface passivation and surface plasmons. Black silicon, fabricated by Ag assisted chemical etching, was employed here to reduce the reflection of incident light with wavelengths below 1100 nm. Due to the increased bandgap caused by the quantum confinement effect and enhanced backward-scattering in our black silicon, light trapping was diminished at the wavelengths above 1100 nm. Ag nanoparticles were deposited on black silicon to obtain the lowest reflectivity at the wavelengths above 1100 nm. Compared with traditionally textured multicrystalline silicon, the average reflectivity of passivated black multicrystalline silicon patterned with 5 nm mass thickness of Ag was decreased to 5.7% in the wavelength range from 300 nm to 1100 nm and was reduced by 20.2% in the wavelength range from 1100 nm to 1400 nm. The surface plasmon effect of the Ag nanoparticles on the black silicon was also demonstrated by surface enhanced Raman scattering, which was observed in the Ag nanoparticle patterned black silicon after being immersed in rhodamine 6g.

A unique ultraviolet photodetector based on a metal-semiconductor-metal structure was fabricated from a wurtzite MgxZn1−xO film with gradually changing Mg content, homoepitaxially grown on a BeO-buffered ZnO substrate. The BeO layer filtered out the substrate photoresponse. The cutoff wavelength of the photodetector under zero bias was 266 nm with a UV/visible light rejection ratio of greater than 2 orders of magnitude in the deep UV region. Applying a bias, the cutoff wavelength exhibited a prominent continuous redshift from 266 (0 V) to 315 nm (3 V), indicating the capability for multi-band UV detection on a monolithic chip. The bias-controlled wavelength-selective UV photoresponse mechanism occurred in the optically active area in a compositionally distributed MgxZn1−xO alloy that was achieved by molecular epitaxial growth.

We have constructed a dual-band ultraviolet photodetector by growing high quality MgxZn1−xO layers on Si substrate with molecular beam epitaxy. The device performance was studied by current-voltage, capacitance-voltage, spectra photoresponse, and time-resolved photoresponse characterizations. It demonstrates a high UV/visible light rejection ratio of more than 2 orders of magnitude and a fast response speed of less than 100 ms. The cutoff wavelength can be at solar-blind (280 nm)/visible-blind (301 nm) region by applying 1 V forward/2 V reverse bias. The working principle of the dual-band photodetector was finally investigated by interpretation of the specific carrier transport behavior with the energy band diagram.

A comparative study of n-MgZnO/p-Si UV-B photodetector performance was carried out with different device structures. The experimental results demonstrate superior photoresponse characteristics of the p-n heterojunction detector against the Schottky type metal-semiconductor-metal counterpart, including a sharper cutoff wavelength at 300 nm, a larger peak photoresponsivity of 1 A/W, and a faster response speed. The role of built-in field and low interface scattering in p-n heterojunction is explored, and the energy band diagram of n-MgZnO/p-Si is employed to interpret the efficient suppression of visible light photoresponse from Si substrate, revealing the applicability of this heterostructure in fabrication of deep ultraviolet detectors.

High-quality wurtzite MgZnO film was deposited on Si(111) substrate via a delicate interface engineering using BeO, by which solar-blind ultraviolet photodetectors were fabricated on the n-MgZnO(0001)/p-Si(111) heterojunction. A thin Be layer was deposited on clean Si surface with subsequent in situ oxidation processes, which provides an excellent template for high-Mg-content MgZnO growth. The interface controlling significantly improves the device performance, as the photodetector demonstrates a sharp cutoff wavelength at 280 nm, consistent with the optical band gap of the epilayer. Our experimental results promise potential applications of this technique in integration of solar-blind ultraviolet optoelectronic device with Si microelectronic technologies.