Direct Measurement of Inhomogeneous Longitudinal Dopant Distribution in SiNWs Using Nano-Probe Scanning Auger Microscopy
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Direct Measurement of Inhomogeneous Longitudinal Dopant Distribution in SiNWs Using Nano-Probe Scanning Auger Microscopy. U. Givan1,2, J. K. Hyun2, E. Koren1, J. S. Hammond3, D. F. Paul3, L. J. Lauhon2, and Y. Rosenwaks1 1 Dept. of Physical Electronics, School of Electrical Engineering, Tel-Aviv University, Israel 2 Dept. of Materials Science and Engineering, Northwestern University, USA 3 Physical Electronics Inc., 18725 Lake Drive East, Chanhassen, MN, USA, 55317 ABSTRACT Controlled incorporation of dopants into semiconductors nanowires is a critical step in tailoring their physical properties and hence for their utilization in future nano electronic devices. Recently, several studies addressing this issue revealed that dopant are inhomogeneously distributed in NWs grown by the popular CVD-VLS growth technique. The majority of those studies employed indirect characterization techniques which are sensitive to the active dopants only. In order to deepen our understanding of the incorporation mechanism a direct observation of the dopant chemical concentrations is required. In addition, the comparison between direct and indirect observations can shed some light on the dopant activation mechanisms in VLS grown NWs. In this study nanoprobe scanning Auger microscopy was employed to extract the longitudinal dopant distribution along P doped SiNWs. The effect of growth conditions and postgrowth annealing on this distribution was studied and compared to previous studies which used indirect measurement techniques. In addition, dopant modulated segmented NWs were studied in order to distinguish the contribution of different mechanisms to the incorporation of dopants into VLS grown NWs. INTRODUCTION Controlled incorporation of electrically active dopants into nanowires (NWs) is essential to the development of semiconductor NW-based electronic devices. Nevertheless, the ability to engineer the electrical properties of NWs grown by the vapor-liquid-solid (VLS) process is currently limited by our incomplete understanding of the in-situ doping mechanism. Recently, several studies have shown evidence of inhomogeneous radial dopant distributions in SiNWs and demonstrated the resulting effects on the NWs electrical properties [1-3]. However, the parallel longitudinal dopant profile (which is essential for dopant incorporation study) has not been addressed to the same extent. Studies employing both indirect and direct measurement techniques (such as scanning photocurrent microscopy, Kelvin probe force microscopy and atom probe tomography) have noted inhomogeneous longitudinal P (phosphorus) dopant profiles of SiNWs and related them to excess sidewall deposition of P through vapor-solid (VS) growth mechanism [4-5]. Nevertheless, direct measurements of dopant concentrations along VLS grown NWs were not yet presented. Auger electron spectroscopy (AES) is a widely used analytical technique for high spatial resolution analysis of surface chemical composition. The surface sensitivity (0.5–2 nm), submicron lateral resolution of secondary and
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