GaP-ZnS Pseudobinary Alloy Nanowires Kidong Park, † Jung Ah Lee, † Hyung Soon Im, † Chan Su Jung, † Han Sung Kim, † Jeunghee Park,* ,† and Chang-Lyoul Lee ‡ † Department of Chemistry, Korea University, Jochiwon 339-700, Korea ‡ Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea * S Supporting Information ABSTRACT: Multicomponent nanowires (NWs) are of great interest for integrated nanoscale optoelectronic devices owing to their widely tunable band gaps. In this study, we synthesize a series of (GaP) 1-x (ZnS) x (0 ≤ x ≤ 1) pseudobinary alloy NWs using the vapor transport method. Compositional tuning results in the phase evolution from the zinc blende (ZB) (x < 0.4) to the wurtzite (WZ) phase (x > 0.7). A coexistence of ZB and WZ phases (x = 0.4-0.7) is also observed. In the intermediate phase coexistence range, a core-shell structure is produced with a composition of x = 0.4 and 0.7 for the core and shell, respectively. The band gap (2.4- 3.7 eV) increases nonlinearly with increasing x, showing a significant bowing phenomenon. The phase evolution leads to enhanced photoluminescence emission. Strikingly, the photo- luminescence spectrum shows a blue-shift (70 meV for x = 0.9) with increasing excitation power, and a wavelength-dependent decay time. Based on the photoluminescence data, we propose a type-II pseudobinary heterojunction band structure for the single-crystalline WZ phase ZnS-rich NWs. The slight incorporation of GaP into the ZnS induces a higher photocurrent and excellent photocurrent stability, which opens up a new strategy for enhancing the performance of photodetectors. KEYWORDS: GaPZnS nanowires, quaternary composition tuning, pseudobinary, wurtzite,-zinc blende phase evolution, band gap M ulticomposition alloying of semiconductors offers the advantages of band gap tunability, controlled conduction band gap offsets, and localized defect energy levels, which are critical for achieving high photoconversion efficiencies in photovoltaic cells. Nanowire structures have attracted consid- erable attention because they can be used as well-defined building blocks of future nanodevices with unique optical and electrical properties using bottom up approaches. Achieving compositionally tuned homogeneous alloy NWs is challenging because of the inherent differences in precursor reaction kinetics, which require adept control of the reactivity of individual precursors. Nanowires with a ternary or quaternary composition in III-V semiconductors (e.g., InGaAs, 1-7 InGaN, 8 AlGaAs, 9 GaInSb, 10 GaAsP, 11-14 AlGaP, 12 InAsP, 15 and InAsSb 16 ) or II-VI, IV-VI (e.g., CdSSe, 17-23 ZnCdS, 24,25 ZnCdSe, 26,27 ZnSSe, 28,29 PbSSe, 30 ZnCdSSe, 31 etc.) have given rise to remarkable discoveries. Nevertheless, the synthesis of NWs with an attractive quaternary composition in a pseudobinary system comprised of III-V and II-VI semi- conductors remains a great difficulty. Although the properties of such NWs can be tailored through a wide compositional range, the physical properties as a function of composition remain unknown. Recently, Liu et al. reported the synthesis of (GaP) 1-x (ZnS) x NWs at a composition x = 0.045 and 0.968. 32 The Pan group have reported (GaAs) 1-x (ZnSe) x NWs with compositions in the range of x < 0.5. 33 The GaP-ZnS system is known to form a solid solution with all four elements in the full compositional range. 34 Interestingly, however, the band gap of the solid solution was near to that of pure GaP across a very wide composition range (up to ∼70 at. % ZnS). 35,36 Recently, Hart and Allan performed ab initio calculations to explain the nonlinear dependence of the band gap on composition. 37 Remarkably, they predicted that the addition of a small amount of ZnS to GaP (or vice versa) produces a semiconductor with a significantly smaller band gap than pure GaP (or ZnS), bringing the direct band gap into the visible-light range. However, there are few works on the full compositional tuning of NWs that have different properties from the bulk phase. In the present work, we show the synthesis and composi- tional tuning of (GaP) 1-x (ZnS) x pseudobinary alloy NWs using a simple vapor transport method. The composition tuning was successfully achieved by changing the ratio of GaP and ZnS powder. The band gap (E g ) could be tuned between the UV and visible regions (E g = 2.4-3.7 eV). Compositional tuning resulted in a phase evolution from the zinc blende (ZB) (x < 0.4; GaP-rich alloy) to the wurtzite (WZ) (x > 0.7; ZnS-rich alloy) phase. In the intermediate composition range (x = 0.4- Received: July 28, 2014 Revised: September 6, 2014 Published: September 18, 2014 Letter pubs.acs.org/NanoLett © 2014 American Chemical Society 5912 dx.doi.org/10.1021/nl5028843 | Nano Lett. 2014, 14, 5912-5919