HAZUT ET AL. VOL. 6 ’ NO. 11 ’ 10311–10318 ’ 2012 www.acsnano.org 10311 October 22, 2012 C 2012 American Chemical Society Contact Doping of Silicon Wafers and Nanostructures with Phosphine Oxide Monolayers Ori Hazut, † Arunava Agarwala, † Iddo Amit, ‡ Thangavel Subramani, † Seva Zaidiner, † Yossi Rosenwaks, ‡ and Roie Yerushalmi †, * † Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram Jerusalem, 91904 Israel and ‡ Department of Physical Electronics, EE School, Faculty of Engineering, Tel-Aviv University 69978, Ramat-Aviv, Tel-Aviv, Israel C ontrolled doping of semiconductors is challenging in the context of re- cent top-down device architectures as well as for architectures based on bot- tom-up building blocks, such as semicon- ducting nanowires (NWs). 1,2 Sharp junctions and localized dopant profiles are key for fine control of the electronic structure and nano- scale properties. 3À8 Specifically, controlled surface doping may play an important role in implementing current semiconductor de- vices such as FinFETs (fin-shaped field effect transistors) and as an important tool for practical nanowire-based devices and photo- voltaic building blocks. 9À16 Conventional doping methods such as ion implantation 17,18 or solid-source di ffusion for controlled nanometer scale surface doping is challeng- ing due to limitations such as nanoscale lattice damage, dopant equilibration through- out the nanostructure, and random dopant fluctuations (RDFs). 19À21 In the context of semiconducting NWs, the commonly used in situ CVD doping method suffers from several limitations, including nonhomogen- ous longitudinal dopant distribution resulting from continuous exposure of the growing SiNW to the dopant precursor along the CVD synthesis process. 22À25 A substantial advance toward surface doping with nanometer scale control was recently introduced by the monolayer doping (MLD) method. 19,20,26À28 Important charac- teristics of the MLD approach rely on the * Address correspondence to roie.yerushalmi@mail.huji.ac.il. Received for review September 12, 2012 and accepted October 21, 2012. Published online 10.1021/nn304199w ABSTRACT Contact doping method for the controlled surface doping of silicon wafers and nanometer scale structures is presented. The method, monolayer contact doping (MLCD), utilizes the formation of a dopant-containing monolayer on a donor substrate that is brought to contact and annealed with the interface or structure intended for doping. A unique feature of the MLCD method is that the monolayer used for doping is formed on a separate substrate (termed donor substrate), which is distinct from the interface intended for doping (termed acceptor substrate). The doping process is controlled by anneal conditions, details of the interface, and molecular precursor used for the formation of the dopant-containing monolayer. The MLCD process does not involve formation and removal of SiO 2 capping layer, allowing utilization of surface chemistry details for tuning and simplifying the doping process. Surface contact doping of intrinsic Si wafers (i-Si) and intrinsic silicon nanowires (i-SiNWs) is demonstrated and characterized. Nanowire devices were formed using the i-SiNW channel and contact doped using the MLCD process, yielding highly doped SiNWs. Kelvin probe force microscopy (KPFM) was used to measure the longitudinal dopant distribution of the SiNWs and demonstrated highly uniform distribution in comparison with in situ doped wires. The MLCD process was studied for i-Si substrates with native oxide and H-terminated surface for three types of phosphorus-containing molecules. Sheet resistance measurements reveal the dependency of the doping process on the details of the surface chemistry used and relation to the different chemical environments of the PdO group. Characterization of the thermal decomposition of several monolayer types formed on SiO 2 nanoparticles (NPs) using TGA and XPS provides insight regarding the role of phosphorus surface chemistry at the SiO 2 interface in the overall MLCD process. The new MLCD process presented here for controlled surface doping provides a simple yet highly versatile means for achieving postgrowth doping of nanometer scale structures and interfaces. KEYWORDS: silicon . nanowires . monolayer doping . surface chemistry ARTICLE