• PDF / 467,387 Bytes
• 9 Pages / 584.957 x 782.986 pts Page_size
• 28 Downloads / 257 Views

DOWNLOAD

REPORT

---

Stephen Maldonadoa) Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, USA; and Program in Applied Physics, Ann Arbor, Michigan 48109-1055, USA (Received 7 January 2015; accepted 22 June 2015)

Single-phase crystalline ZnSnP2 nanowires have been prepared via simple chemical vapor deposition method using powdered Zn and SnP3 as the precursors in a custom-built tube furnace reactor. The sublimed precursors were allowed to react with thermally evaporated Sn nanoparticles to yield ZnSnP2 nanowire films over areas of 40 mm2. The cumulative observations suggest that the Sn nanoparticles served both as the growth seed and main contributor of Sn. Prolonged growth time favored formation of Zn3P2 nanowires when the Sn supply was exhausted. For optimal growth conditions, surface and bulk elemental analyses showed homogenous elemental distribution of Zn, Sn, and P, with chemical composition close to 1:1:2 stoichiometry. Powder x-ray diffraction data and Raman scattering of the nanowire films along with single-nanowire analysis using high-resolution transmission electron microscopy indicated that the as-prepared ZnSnP2 nanowires possessed a sphalerite crystal structure, as opposed to the antisite defect-free chalcopyrite structure. Photoelectrochemical measurements in aqueous electrolyte showed that the as-prepared ZnSnP2 nanowires are capable of sustaining stable cathodic photoresponse under white light illumination. Overall, this study presented a benign and straightforward approach to prepare single-phase Zn-based phosphide nanowires suitable for energy conversion applications.

I. INTRODUCTION

Contributing Editor: Joan M. Redwing a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.195

elements and are isoelectronic with the III-V semiconductors. Moreover, the respective band structures are remarkably similar, resulting in nearly identical band gap energies and the possibility of high-charge carrier mobilities.10,11 In this report, we focus on ZnSnP2. ZnSnP2 is isoelectronic with InP and can exhibit either chalcopyrite or sphalerite crystal structure (Fig. 1). For ZnSnP2, the optoelectronic band gap energy is a function of the crystalline phase. The chalcopyrite phase of ZnSnP2 has a band gap of 1.68–1.75 eV, and the sphalerite phase of ZnSnP2 has a smaller band gap energy between 1.22 and 1.38 eV.12 In either phase, ZnSnP2 natively exhibits p-type conductivity with the capacity for good majority carrier mobilities (10–70 cm2 V
1 s
1),11,13 thus rendering ZnSnP2 amenable for solar energy capture/conversion.12,14,15 To date, the preparation of single-phase ZnSnP2 crystals has proven challenging. Based on the pseudo-binary Sn–ZnP2 phase diagram, ZnSnP2 melts incongruently and forms peritectically.11,16 Thus far, ZnSnP2 bulk crystals have been synthesized from melts,13,16,17,18 vapor phase deposition,19,20,21 and organometallic synthesis.22 The occurrence of impurity phases, such as Sn3P2, Sn4P3, and Zn3P2 in as-prepared ZnSnP2, has stymied practical interest