Single-Crystalline Branched Zinc Phosphide Nanostructures:  Synthesis, Properties, and Optoelectronic Devices

Abstract

Hierarchical tree-shaped nanostructures, nanobelts, and nanowires of Zn 3 P 2 were synthesized in a thermal assisted laser ablation process. All nanostructures are tetragonal phased Zn 3 P 2 with excellent crystallinity and are free from an oxidization layer according to electron microscopy and X-ray diffraction analyses. Optical measurement revealed a strong absorption from the ultraviolet to near-infrared regions. Optoelectronic devices fabricated using individual nanowires demonstrate a high sensitivity and rapid response to impinging light. A crossed heterojunction of an n-type ZnO nanowire and a p-type Zn 3 P 2 nanowire has been characterized, and it offers a great potential for a high efficient spatial resolved photon detector.Being a novel optoelectronic material, Zn 3 P 2 has the following advantages over some other materials. It has a direct band gap in the range of 1.4-1.6 eV, which is the optimum range for solar energy conversion. The large optical absorption coefficient (>10 4 cm -1 ) and a long minority diffusion length (∼13 µm) of Zn 3 P 2 permit high current collection efficiency. 1 In addition, the constituent materials are abundant and cheap and would allow the large scale deployment of such devices as solar cells, infrared (IR) and ultraviolet (UV) sensors, lasers, and light polarization step indicators. 2,3 In order to investigate the potential applications of Zn 3 P 2 , several kinds of heterojunctions have been designed, such as InP/Zn 3 P 2 , 4 Mg/Zn 3 P 2 , 5 Zn 3 P 2 /ZnSe, 2,6 ITO/ Zn 3 P 2 , 7 and ZnO/Zn 3 P 2 . 8 However, the majority of research on Zn 3 P 2 has been limited to thin films, and very little work has been done in the nanoscale range except for very few reports on the synthesis of Zn 3 P 2 nanoparticles 9-11 and on the synthesis of nanotrumpets with an unavoidable ZnO layer coated on the surface. 12 Because of the large excitonic radii, Zn 3 P 2 is expected to exhibit pronounced quantum size effect, which has been observed for Zn 3 P 2 nanoparticles. 10 To the best of our knowledge, the electric property and photoresponse of Zn 3 P 2 nanostructures, and heterojunctions made from Zn 3 P 2 nanostructures, have not been reported thus far.In this paper we report for the first time the synthesis of single crystalline tree-shape Zn 3 P 2 structure arrays, nanowires, and nanobelts. The morphology and crystal structure were determined by electron microscopy and analytical techniques. In addition, the optical property of the synthesized nanostructures has been measured through photoluminescence (PL). Furthermore, we also present the crossed heterojunction made using a ZnO nanowire and a Zn 3 P 2 nanowire. Optoelectronic measurements of single Zn 3 P 2 nanowire and the crossed heterojunction indicate that Zn 3 P 2 was very sensitive to light and the heterojunction exhibits enhanced performance, which implies that the Zn 3 P 2 nanostructures have promising applications in optoelectronics.

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Hierarchical silver indium tungsten oxide mesocrystals with morphology-, pressure-, and temperature-dependent luminescence properties

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