Ruda, Harry E.

Harry E. Ruda, Professor
BSc (Imperial College, London), PhD (MIT), FRSC

Stan Meek Chair in Advanced Nanotechnology
Director, Centre for Advanced Nanotechnology

Office: HA 204 | E: harry.ruda@utoronto.ca
Assistant & Business Officer, Ms. Millie Morris:
T: 416.978.4556 | E: ecanmpm@ecf.utoronto.ca

Other websites:
www.utoronto.ca/emg | www.utoronto.ca/ecan

Research Areas

Growth of semiconductor nanowire structures

After Wagner and Ellis demonstrated the VLS growth process in 1964 for semiconductor micron-scale whiskers, we were one of the first groups to demonstrate its use for preparing Si nanowires (i.e., diameter ~tens nm) in 1997 [JVST, B15(3),pp.554-557(1997), with 178 SCI citations]. By 1998 Lieber’s first paper was published referencing our work and interest in nanowires grew exponentially from there. Subsequently, we reported on high quality nanowires of GaAs, AlGaAs and recently, ZnSe. Most notable was our demonstration of a short period AlGaAs/GaAs superlattice within a nanowire.

Control over surface states and non-radiative recombination pathways

Our focus is on III-Vs including seminal work on influence of surface structure on surface states [JAP, 75(10), pp.5332-5338(1994)], and surface state/non-radiative recombination control using surface passivation – treatments include chlorine [e.g., APL:67(22),pp.3334-3337(1995);PRB,59(24),pp.766-771(1999); PRL, 85(7), pp.1488-1491(2000)], sulfur [e.g., JAP, 79(7), pp.3758-3762 (1996)], and oxygen [e.g., JAP, 83(11), pp.5880-884(1998)/92(5),pp.2330-2334(2002)]. We continue to collaborate strongly internationally in this area and are well recognized in this field [e.g., Ruda, Science, 283(5402), pp. 646-649(1999)].

Linear/nonlinear optical properties of semiconductor nanostructures

Excitonic effects in Type I/II quantum dots and nanowires, photoconductivity and PL response of nanowires, nonlinear optical response of nanostructures [APL, 65(25), pp.3176-3178(1994); JAP, 75, (1), pp.54-57(1994); PRB, 50(8), pp.5703-5706(1994); IEEE JQE, 31(2), pp.228-231(1995)], polarization sensitive optical properties of nanowires, plasmonic phenomena and luminescence amplification in nanostuctures.

Low dimensional photonic nanostructures

This work covers preparation of photonic crystal (PC) structures – includes inverse opals [Adv. Fun. Mater., 12(1),pp.1-8(2002)] and nanowire array based PCs; studies of properties of PCs and in particular, a proposal for a new type of resonant PC where periodic dielectric constrast media and active gain material with electronic confinement are the same material, and are represented as a nanowire array.

Transport and spin effects in semiconductor nanostructures

We presented one of the first theories of electron transport in a 2D electron gas [Phys. Rev. B30, pp.4571-4582(1984) and Phys. Rev. B29, pp.4818-4820(1984), 314 SCI citations]. This work focused on a 2D electron gas in GaAs and InGaAs, and later was supplemented by the first work on ZnSe at a ZnSTe heterointerface [APL, 49, (1), pp.35-37(1989)]. This latter work also continued to consider the role of different mechanisms as relating to confined electrons [JAP, 59, (4), pp.1220-1231(1986)] and holes [JAP, 59, (10), pp.3516-3526(1989)] in ZnSe, ZnS [JAP, 68(4),pp.1714-1719(1990)] and ZnTe [J. Phys. D, 24, 1158-1162(1991)]. This work progressed to produce one of first systematic investigations on the role of contact phenomena on carrier transport in nanowires and [JAP: 84(11), pp.5867-5872(1998); 86(9), pp.5103-5108(1999); 86(5), pp.2719-2726(1999): Physica, E6(1-4), pp.543-546(2000)]. This led to studies on nanowire carrier transport and on nanowire-based transistor behaviour. The implications of non-equilibrium carrier transport in nanostructures was also considered [Phys. Rev., B55(16), pp.10541-10548(1997); ibid, B6308(8), pp.5203-5207(2001): Nanotechnology, 12, pp.523-528(2001): Physica, A311, pp. 429-442(2002)]. In parallel with this, we initiated studies in spin effects in such low dimensional systems [e.g., JAP, 87(5), pp.2520-2525(2000)], and recently reported on the first observations of high temperature ferromagnetism in Mn-doped ZnO nanowires.

Select Publications

212 Journal Publications (internationally refereed); 1437 Citations in Science Citation Index.

Some important contibutions include:

Formation of nanostructures
Paper on understanding mechanisms for formation of nanostructures

• (1) R. Arief Budiman and Harry E. Ruda, “Smoluchowski ripening and random perlocation in epitaxial Si1-xGex/Si(001) islands”, Phys. Rev., B65, pp.045315-1– 11(2002)

One of first papers on growth of nanowires rather than microwires

• (2) J. Westwater, D.P. Gosain, S. Tomiya, S. Usui and H. Ruda, “Growth of Silicon Nanowires Via Gold/Silane Vapor-Liquid-Solid Reaction”, J. Vac.Sci. Technol., B15(3), pp.554-557(1997)

Transport properties of nanostructures

Two of first papers on so-called two dimensional electron gas structures, discussing the mobility limits for such high-mobility structures – now a backbone of the ultrafast/microwave industry

• (3) W. Walukiewicz, H. E. Ruda, J. Lagowski and H. C. Gatos, "Electron Mobility in Modulation-Doped Heterostructures", Phys. Rev. B30, (8), pp.4571-4582(1984)
• (4) W. Walukiewicz, H. E. Ruda, J. Lagowski and H. C. Gatos, "Electron Mobility Limits in a Two-Dimensional Electron Gas: GaAs-GaAlAs Heterostructures", Phys. Rev. B29, (8), pp.4818-4820(1984)
  Paper on anomalies of diffusive transport in nanostructures
• (5) A. Achoyan, S. Petrosyan, H.E. Ruda and A. Shik, “Diffusion of non-equilibrium carriers in low-dimensional structures”, Phys. Rev., B77, 085303(2008)

Paper providing fundamental understanding of non-equilibrium behavior in so-called low temperature GaAs – laying foundations for use of material in ultrafast optics and telecom

• (6) H. Ruda and A. Shik, “Nonequilibrium carriers in GaAs grown by low-temperature molecular beam epitaxy”, Phys. Rev. B6308(8), pp.5203-5207(2001)

Optical properties, focusing on nanostructures

One of first papers to present novel engineered nanostructures for nonlinear optics

• (7) X. H. Qu, D. J. Bottomley, H. E. Ruda and A. J. SpringThorpe, "Second Harmonic Generation from a GaAs/GaAlAs Asymmetric QW Structure", Phys. Rev. B50(8), pp.5703-5706(1994)

One of first papers to show giant nonlinear response in semiconductor nanowires, with exciting possibilities for applications in biological imaging

• (8) V. Barzda, R. Cisek, T.J. Spencer, U. Philipose, H.E. Ruda and A. Shik, “Giant anisotropy of second harmonic generation for single ZnSe nanowire”, Appl. Phys. Lett., 92, 113111(2008)

One of first papers to show the origins of deep and excitonic band responses in semiconductor nanowires, laying foundation for nanophotonic applications of nanowires

• (9) Saxena, S. Yang, U. Philipose and H.E. Ruda, “Excitonic and pair-related photoluminescence in ZnSe nanowires”, J. Appl. Phys., 103, 053109(2008)

One of first papers to explain polarization anisotropy in nanowires

• (10) H.E. Ruda and A. Shik, “Polarization-sensitive optical phenomena in semiconducting and metallic nanowires”, Phys. Rev., B72(11), pp. 115308-1-11(2005)

A first proposal for developing photonic crystal devices from systems of nanowires, with possibility of nanowire array cavity lasers and resonant cavity detectors

• (11) T. Xu, S. Yang, S. Nair and H.E. Ruda, “Confined modes in finite size photonic crystals”, Phys. Rev., B72(4), pp. 45126-1-11(2005)

Paper discussing anomalous dispersion/refraction effects in such photonic crystals

• (12) S. Yang, T. Xu, H.E. Ruda and M. Cowan, “Numerical study of anomalous refraction in photonic crystals”, Phys. Rev., B72(7), pp. 75128-1-6(2005)

One of first papers to show how Plasmon phenomena can be couples to emission providing strong enhancement, with important implications for sub-wavelength high resolution biological imaging

• (13) H.E. Ruda and A. Shik, “Plasmon phenomena and luminescence amplification in nanocomposite structures”, Phys. Rev., B71, pp. 245328-1 to -8(2005)

Two papers that took a well known characterization technique (SPV) used previously for minority carrier diffusion length determination, based on a limited theoretical foundation, and developed a new generalized theory for the technique, as well as showed its applicability as a deep level characterization tool.

• (14) Q. Liu, H. E. Ruda, G.M. Chen and M. Simard-Normandin, “Generalized Model for Surface Photovoltage in Semiconductors”, J. Appl. Phys., 79(10), pp.7790-7799 (1996)
• (15) Q. Liu and H.E. Ruda, “Role of Deep-Level Trapping on the Surface Photovoltage of Semi-Insulating GaAs”, Phys. Rev., B55(16), pp.10541-10548(1997)

New techniques

Similar to work on SPV (above), took an accepted technique (SCM) and formalized it and showed its wider applicability and utility.

• (16) H.E. Ruda and A. Shik, “Scanning capacitance microscopy of nanostructures”, Phys. Rev., B71, 075316-1 to -7(2005)
• (17) H.E. Ruda and A. Shik, “Theoretical analysis of SCM”, Phys. Rev.B67, 235309, pp.1-9(2003)

Semiconductor surfaces

A body of work on understanding surface and interface state formation, and influence on surface reactivity

• (18) H.E. Ruda, “Reactions on semiconductor surfaces”, Science, 283(5402), pp. 646-649(1999)
• (19) J. G. Ping and H. E. Ruda, "Influence of Chemical Character on the Reconstruction of GaAs(111) Surfaces", J. Appl. Phys. 75. (10), pp.5332-5338(1994)

New phenomena

Showed how appropriately design nanostructures could exhibit room temperature ferromagnetism for the first time – the basis of so-called “spintronics”

• (20) U. Philipose, S. V. Nair, S. Trudel, C. F. de Souza, S. Aouba, R. H. Hill and H. E. Ruda, “High temperature ferromagnetism in Mn-doped ZnO nanowires”, Appl. Phys. Lett.,88, pp.263101-263103(2006)

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