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Department of Physics

Terry Whall

Research Interests

Electrical properties of low dimensional semiconductor structures. SiGe devices and electronic coolers.

Biography

Terry Whall has been carrying out investigations of the electrical properties of solids and semiconductor devices since 1964. His DPhil thesis (University of Sussex) was concerned with the design and construction of a 3He cryostat and Kondo effects in dilute alloys, the latter forming the subject of a major review [1] in the prestigious series Solid State Physics.

He then turned his attention to low mobility solids and in particular magnetic oxides, looking at Mott/Anderson localisation, work which has been extensively reviewed by Mott in numerous publications [2]. During the course of this research, he carried out an effective medium calculation which gave the first satisfactory description of the Cutler-Mott thermopower minimum [3].

Between 1987 and 2006, he was joint leader, with Evan Parker, of the NanoSilicon group at Warwick University, with major responsibility for electrical characterisation and device physics. He is currently an emeritus professor in the group. The group carried out pioneering work in delta doped silicon, investigations of weak localisation phenomena and developed a delta doped MOSFET device [4] with Edinburgh and Newcastle Universities.

Most of his work, however, has been on Si/SiGe heterostructures. With UMIST, he has used CV methods to investigate band offsets and hetreointerface charge [5]. Whall first suggested that the charge has its origin in a weak piezoelectric effect [6], and this idea has been developed in some detail by a Japanese group to account fully for the carrier mobility in the SiGe 2D hole gas (2DHG). Whall has led a team which has carried out the most detailed investigations of the effective mass in the Si/SiGe/Si 2DHG, using the Shubnikov de Haas effect [7] and, with the Clarendon, cyclotron resonance [8]. Carrier mobility in the SiGe 2DHG has been a major interest, this work being undertaken with Surrey. Low temperature measurements have provided convincing evidence that the major scattering centres are screened [9] and provided a basis for an experimental and theoretical study in which it was shown that interface roughness and interface charge scattering, rather than alloy scattering, limit the carrier mobility [10]. Measurements on an Infineon Si/SiGe/Si PMOS device and theoretical analysis suggest that this also is true at room temperature [11]. With Glasgow it has been established that, whereas the equilibrium saturation velocity in SiGe is less than that in Si ,non equilibrium velocity overshoot is enhanced; this has a role to play in the increased current drive that has been observed in the Infineon MOSFET [12]. The arduous route to a fully processed device has led Warwick to refine the mobility spectrum technique [13] for extracting the room temperature 2DHG mobility in modulation doped structures, in the presence of significant amounts of parallel conduction. Terry Whall has published numerous papers on 1/f noise in SiGe MOSFETs. In a recent Applied Physics letter, he argued that a commonly used model was inadequate and that a full description of the phenomenon required the assumption of an energy dependant density of oxide trap states [14].

He is currently supervising students working on Ge MOSFETs (IMEC), Ge condensation for the fabrication of Ge on Insulator (with Imperial), surface channel high-k gated SiGe MOSFETs (with KTH, Sweden) and Schottky source/drain MOSFETs (with Spinnaker Semiconductor). Finally, he has carried out work on strained Si devices (with STMicroelectronics and Southampton) [15,16]. He contributes to the growth activity and is co-author of a number of papers on strained Ge [17,18].

  1. J. Heeger, in Solid State Physics, eds H. Ehrenreich, F. Seitz, and D. Turnbull, Vol. 23, p. 283. (Academic Press, New York, 1969)
  2. Mott N F, 1979, Advances in Solid State Physics, Festkörperproblem 19, 331
  3. T.E. Whall, An effective medium calculation of the conductivity activation energy and thermoelectric power in a Fermi Glass J.Phys. C 14, L887 (1981)
  4. A.G. O'Neill, A.C.G,. Wood, P. Phillips T.E. Whall, E.H.C. Parker, A. Gundlach and S. Taylor, A systematic investigation of n-channel delta-doped MOSFETs grown by MBE, Microelectronic Engineering 19, 743 (1992)
  5. Brighten JC, Kubiak RA, Phillips PJ, Whall TE, Parker EHC, Hawkins ID, and Peaker AR, The Electrical Assessment of P-Isotype Si/SiGe/Si Heterostructures Grown by MBE, Thin Solid Films, 222, 116 (1992)
  6. Khizhny VI, Mironov OA, Parker EHC, Phillips PJ, Whall TE, and Kearney MJ, Direct evidence for a piezoelectriclike effect in coherently strained SiGe/Si heterostructures, Appl. Phys. Lett. 69, 960 (1996)
  7. Whall TE, Plews AD, Mattey NL, Phillips PJ, Ekenberg U Effective-Mass and Band Nonparabolicity in Remote Doped Si/Si0.8Ge0.2 Quantum-Wells, Appl. Phys. Lett. 66 2724 (1995)
  8. Wong SL, Kinder D, Nicholas RJ, Whall TE, and Kubiak R , Cyclotron-Resonance Measurements on P-Type Strained-Layer Si1-xGex/Si Heterostructures, Physical Review B 51 13499 (1995)
  9. G Ansaripour, G Braithwaite, M Myronov, O A Mironov, E H C Parker and T E Whall “Energy loss rates of two-dimensional hole gases in inverted Si/Si0.8Ge0.2”, Appl.Phys.Letts., 76, 1140 (2000).
  10. Emeleus CJ, Whall TE, Smith DW, Kubiak RA, Parker EHC, Kearney MJ Scattering Mechanisms Affecting Hole Transport in Remote-Doped Si/SiGe Heterostructures, J. Appl. Phys. 73, 3852 (1993)
  11. D R Leadley, H Fischer, L Risch, M J Kearney, A I Horrell, E H C Parker and T E Whall Performance enhancement in Si/Si0.5Ge0.5/Si strained alloy p-channel metal oxide semiconductor field effect transistors, Semicond. Sci. Technol. 18, 945 (2003)
  12. D R Leadley, M J Kearney, A I Horrell, H Fischer, L Risch, E H C Parker and T E Whall Analysis of hole mobility and strain in a Si/Si0.5Ge0.5/Si metal oxide semiconductor field effect transistor, Semicond. Sci. Technol. 17, 708 (2002)
  13. S Kiatgamolchai, O A Mironov, V G Kantser, M Myronov, E H C Parker and T E Whall, "Maximum Entropy Mobility Spectrum Analysis for electron Transport in Layered Semiconductor Structures", Phys. Rev. E, 66, 36705 (2002).
  14. Prest MJ, Bacon AR, Fulgoni DJF, Grasby TJ, Parker EHC, Whall TE, and Waite AM, Low-frequency noise mechanisms in Si and pseudomorphic SiGe p-channel field-effect transistors, Applied Physics Letters 85 6019 (2004)
  15. Nicholas G, Grasby TJ, Parker EHC, Whall TE, and Skotnicki T Evidence of reduced self heating in strained silicon MOSFETs, Electron Device Letters (accepted 2005)
  16. Nicholas G, Grasby TJ, Parker EHC, Whall TE, Paul DJ, Evans GR, von Kanel H, Investigation of the injection velocity of holes in strained Si pMOSFETs, Semicond. Sci. Technol. 20, L20 (2005)
  17. R.J.H. Morris, D.R. Leadley, T.J. Grasby, T.E. Whall, and E.H.C. Parker, Influence of regrowth conditions on the hole mobility in strained Ge heterostructures grown using hybrid epitaxy, Journal of Applied Physics 96, 6470 (2004)
  18. R.J.H. Morris, T.J. Grasby, R. Hammond, M. Myronov, D.R. Leadley, T.E. Whall, E.H.C. Parker, M.T. Currie, C.W. Leitz, and E.A. Fitzgerald, High conductance Ge p-channel heterostructures realised by hybrid epitaxial growth, Semicond. Sci. Technol. 19, L106 (2004)

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Department of Physics, University of Warwick, Coventry, CV4 7AL

Contact Details:

Office: P557

Telephone:
+44 (0)2476 522258

Fax:
+44 (0)2476 150897

E-Mail:
T.E.Whall@warwick.ac.uk

Links:

Nano Silicon Group