Radial modulation doping in core–shell nanowires

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Abstract

Semiconductor nanowires are potential candidates for applications in quantum information processing1,2, Josephson junctions3,4 and field-effect transistors5,6,7,8 and provide a unique test bed for low-dimensional physical phenomena9. The ability to fabricate nanowire heterostructures with atomically flat, defect-free interfaces enables energy band engineering in both axial10,11,12 and radial13,14,15,16 directions. The design of radial, or core–shell, nanowire heterostructures relies on energy band offsets that confine charge carriers into the core region, potentially reducing scattering from charged impurities on the nanowire surface13,14,15,16. Key to the design of such nanoscale heterostructures is a fundamental understanding of the heterointerface properties, particularly energy band offsets and strain. The charge-transfer and confinement mechanism can be used to achieve modulation doping17,18,19 in core–shell structures20,21. By selectively doping the shell, which has a larger bandgap, charge carriers are donated and confined in the core, generating a quasi-one-dimensional electron system with higher mobility. Here, we demonstrate radial modulation doping in coherently strained Ge–SixGe1−x core–shell nanowires and a technique to directly measure their valence band offset. Radial modulation doping is achieved by incorporating a B-doped layer during epitaxial shell growth. In contrast to previous work showing site-selective doping in Ge–Si core–shell nanowires13,22, we find both an enhancement in peak hole mobility compared with undoped nanowires and observe a decoupling of electron transport in the core and shell regions. This decoupling stems from the higher carrier mobility in the core than in the shell and allows a direct measurement of the valence band offset for nanowires of various shell compositions.

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Figure 1: Nanowire growth and structural characterization.
Figure 2: Modulation-doped core–shell nanowire FETs.
Figure 3: Decoupled core and shell transport in modulation-doped nanowires.
Figure 4: Valence band offset extraction.

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Acknowledgements

This work was supported by the National Science Foundation (grants DMR-0846573 and DMR-0819860) and by the Norman Hackerman Advanced Research Program. The authors thank K. Varahramyan for technical discussions and assistance.

Author information

D.C.D. performed nanowire sample growth, nanowire device fabrication and characterization, with assistance from K.K. and E-S.L. D.C.D. and E.T. analysed the data and wrote the paper, with input from all authors.

Correspondence to Emanuel Tutuc.

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The authors declare no competing financial interests.

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Dillen, D., Kim, K., Liu, E. et al. Radial modulation doping in core–shell nanowires. Nature Nanotech 9, 116–120 (2014). https://doi.org/10.1038/nnano.2013.301

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