Frensley, William R.

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William Frensley is a Professor of Electrical Engineering. His research interests include:

  • Electron transport in semiconductor devices, high-performance devices, quantum devices.
  • Quantum transport theory, kinetic theories.
  • Physics of semiconductor heterostructures, band lineup, size quantization, resonant tunneling, electron waveguides.
  • Device simulation techniques, development of interactive modeling tools.
  • Application of computer graphics and object-oriented software design.
Learn more about Dr. Frensley on his Home and Research Explorer pages.

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    Electrical Design of InAs-Sb/GaSb Superlattices for Optical Detectors using Full Bandstructure Sp³s* Tight-Binding Method and Bloch Boundary Conditions
    Mir, Raja N.; Frensley, William R.; 0000 0000 3595 8922 (Frensley, WR); 93078927 (Frensley)
    InAs-Sb/GaSb type-II strain compensated superlattices (SLS) are currently being used in mid-wave and long-wave infrared photodetectors. The electronic bandstructure of InSb and GaSb shows very strong anisotropy and non-parabolicity close to the Γ-point for the conduction band (CB) minimum and the valence band (VB) maximum. Particularly around the energy range of 45-80 meV from band-edge we observe strong non-parabolicity in the CB and light hole VB. The band-edge dispersion determines the electrical properties of a material. When the bulk materials are combined to form a superlattice we need a model of bandstructure which takes into account the full bandstructure details of the constituents and also the strong interaction between the conduction band of InAs and valence bands of GaSb. There can also be contact potentials near the interface between two dissimilar superlattices which will not be captured unless a full bandstructure calculation is done. In this study, we have done a calculation using second nearest neighbor tight binding model in order to accurately reproduce the effective masses. The calculation of mini-band structure is done by finding the wavefunctions within one SL period subject to Bloch boundary conditions ψ(L) = ψ(0) e(ikL). We demonstrate in this paper how a calculation of carrier concentration as a function of the position of the Fermi level (EF) within bandgap(Eg) should be done in order to take into account the full bandstructure of broken-bandgap material systems. This calculation is key for determining electron transport particularly when we have an interface between two dissimilar superlattices.

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