24.12.14

You are invited to attend a lecture

By

Iddo Amit

PhD student under the supervision of Prof. Yossi Rosenwaks

Department of Physical Electronics, School of Electrical Engineering

Tel Aviv University

On the subject:

Functional Imaging of In-situ and Ex-situ Doped Silicon Nanowires

Semiconductor Nanowire-based electronics offers the opportunity to achieve tight control over a precisely defined component, often comprised of the nanowire (NW) itself, which in turn, enables the enhancement of the device performance. Currently, one of the main challenges facing the fabrication process of NW-based electronics is the formation of well-defined doping profiles which are crucial for the fine-tuning of the device behavior.

However, the conventional doping mechanism, where dopants are introduced in-situ during growth, results in both axial and radial inhomogeneous doping profiles which stem from a surface doping mechanism known as vapor-solid (VS) doping. Moreover, in interfaces between different doping types, a region of diffuse boundaries is formed rather than an abrupt transition between the two segments.

We use quantitative Kelvin probe force microscopy (KPFM) and nano-probe scanning Auger spectroscopy to measure both the longitudinal and the radial doping distribution in doped Si nanowires (SiNWs). Our findings shed light on the underlying mechanisms that produce these inhomogeneities by studying P doping profiles of axially modulation-doped SiNWs. We find that both the VLS and the VS mechanisms result in radially inhomogeneous doping, specifically, a lightly doped core surrounded by a heavily doped shell structure. By designing a modulated doping profile, the effects of the two mechanisms can be distinguished. We also discuss the influence of the reservoir effect that significantly broadens the axial doping junctions.

These results are compared to measurements conducted on monolayer contact doped (MLCD) NWs. This ex-situ doping process takes advantage of the precision of electron beam lithography as well as the selectivity and controllability of chemical monolayer formation to produce tailor-made dopant profiles by post-growth doping through the surface.

24 December 2014, at 14:00,

Room 031, Engineering Labs Building