Vapor-Transport Synthesis and Annealing Study of Zn_xMg_1–xO Nanowire Arrays for Selective, Solar-Blind UV-C Detection

Abstract

This work uniquely reports the synthesis of Zn x Mg 1– x O nanowires and submicron columns by utilizing a traditional carbothermal reduction process toward forming ZnO nanowire ultraviolet detectors, while simultaneously utilizing Mg 3 N 2 as the source of Mg. To investigate the relationship between Mg content in the ZnO lattice and the cutoff wavelength for high spectral responsivity, the nanowires were annealed in a series of designed conditions, whereas chemical, nanostructural, and optoelectronic characteristics were compared before and after treatment. Postanneal scanning electron micrographs revealed a reduction of the average ensemble nanowire dimensions, which was correlated to the modification of ZnO lattice parameters stemming from Zn 2+ dissociation and Mg 2+ substitution (confirmed via Raman spectroscopy). The analysis of cathodoluminescence spectra revealed a blueshift of the peak alloy band-edge emission along with a redshift of the ZnO band-edge emission; and both were found to be strong functions of the annealing temperature. The conversion of Zn 2 SiO 4 to Mg 2 SiO 4 (in O 2 ) and MgSiO 3 (in Ar) was found to correspond to transformations (shifting and scaling) of high-energy luminescence peaks and was confirmed with X-ray diffraction analysis. The tunability of the cutoff photodetection wavelength was evaluated as the nanowire arrays exhibited selective absorption by retaining elevated conduction under high-energy UV-C irradiation after thermal treatment but exhibiting suppressed conductivity and a single order of magnitude reduction in both spectral responsivity ( R λ ) and photoconductive gain ( G ) under UV-A illumination. Noise analysis revealed that the variation of detectivity ( D *) depended on the regime of ultraviolet irradiation, and that these variations are related to thermal noise resulting from oxygen-related defects on both nanowire and substrate surfaces. These results suggest a minor design tradeoff between the noise characteristics of thermally treated ZnMgO nanowire array UV detectors and the tunability of their spectral sensitivity.

Ga2O3 Field-Effect-Transistor-Based Solar-Blind Photodetector With Fast Response and High Photo-to-Dark Current Ratio

“…ECAUSE of the absence of radiation in the solar-blind region (240-280 nm) at the surface of the Earth, the so-called solar-blind photodetectors have advantages of high signal-tonoise ratios, low false alarm rates and ability of weak signal detection in many applications including ozone monitoring, flame detection, and missile tracking [1]- [5]. In recent years, a large variety of semiconductors like AlxGa1-xN, ZnxMg1-xO, and ZnxGa1-xO have been explored for solar-blind photodetectors [6,7]. However, their complex growth processes and difficulties in achieving high material quality are still challenging.…”

“…Furthermore, the crystal growth of Ga2O3 bulk single crystals and the material quality have progressed rapidly in recent years [8,9]. Compared with previous multi-element alloy materials [6,7], Ga2O3 is not an alloy, and hence has a lower defect density which is critical to achieve a low dark current [10]. Ga2O3 active layers in photodetectors have already been achieved via several methods, including hot-wall chemical vapor deposition [2], metalorganic vapor phase epitaxy [11], molecular beam epitaxy [12], magnetron sputtering [13,14], and mechanical exfoliation from bulk single crystals [15,16].…”

Non‐Ultrawide Bandgap Semiconductor GaSe Nanobelts for Sensitive Deep Ultraviolet Light Photodetector Application

“…The lowest NEP and the highest D* are calculated to be 1.51 × 10 −15 W Hz −1/2 and 6.01 × 10 11 Jones, respectively, demonstrating the ability to detect a weak light signal (Figure S5, Supporting Information). It is worth noting that the present GaSe nanobelt displays much better photoelectric performance than previously reported GaSe nanosheet, including mechanically exfoliated GaSe nanosheets [ 20,39 ] and gas‐phase grown GaSe nanosheets, [ 40 ] which is comparable to or even better than that of traditional UWBG DUV photodetectors [ 12–15 ] (shown in Table 1 ), making it a promising candidate for application in future high‐performance DUV photodetector‐based devices and systems.…”

“…[4][5][6][7][8][9] Currently, commercially available DUV photodetectors (e.g., photomultiplier tubes and Si photodetectors) normally operate at high bias voltage or adopt elaborate filters to eliminate the effect of visible and near infrared spectra. [10,11] To overcome the drawbacks of high power consumption as well as costly and complicated fabrication, a variety of ultrawide-bandgap (UWBG) semiconductors with bandgaps larger than 3.4 eV (the bandgap of GaN), such as Al x Ga 1-x N, [12] Zn x Mg 1-x O, [13] Ga 2 O 3 , [14] and diamond, [15] have been extensively explored. Various studies have shown that their relatively high radiation hardness and intrinsic visible blindness have indeed made them prominent candidates for highly sensitive DUV photodetection applications.…”

Inkjet-Printed Imbedded Graphene Nanoplatelet/Zinc Oxide Bulk Heterojunctions Nanocomposite Films for Ultraviolet Photodetection

“…Zinc oxide (ZnO) and graphene, especially their nanohybrids, have been extensively studied for a wide variety of applications ranging from photodetectors, − gas sensors, , and stress/strain sensors. ,− The appeal of ZnO and graphene for these applications is that ZnO is a wide direct bandgap (3.4 eV) material, piezoelectric, biocompatible, and inexpensive, while graphene has high charge mobility, transparent, environmentally stable, and chemically inert. − Nanohybrids of ZnO and graphene are typically fabricated by predepositing graphene first via chemical vapor deposition (CVD) and then incorporating the ZnO on the top through hydrothermal growth, , sputtering, atomic layer deposition (ALD), spin-coating sol–gel precursors, electrochemical deposition, vapor transport, and dropcasting prefabricated ZnO nanostructures . However, synthesis methods such as CVD require high temperatures and a controlled gaseous environment and other methods such as sputtering and ALD require expensive high-vacuum systems. ,, In addition, these methods deposit a film everywhere and require additional steps of advanced lithography to define the active channels for devices.…”