Browse Prior Art Database

Multi-quantum Well Base Theta Semiconductor Device

IP.com Disclosure Number: IPCOM000122695D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

Heiblum, M: AUTHOR

Abstract

Described is a multi-quantum-well semiconductor structure whose base is relatively thick and is designed to replace the thin base in THETA devices. The thicker base remains quasi two-dimensional with the expected reduced scattering and higher transfer ratio.

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Multi-quantum Well Base Theta Semiconductor Device

      Described is a multi-quantum-well semiconductor structure
whose base is relatively thick and is designed to replace the thin
base in THETA devices.  The thicker base remains quasi
two-dimensional with the expected reduced scattering and higher
transfer ratio.

      As the base in THETA devices gets narrower, quantization
effects take place due to the electron confinement in the direction
normal to the base layer.  The 'cold' electrons that reside in the
base are, in effect, quasi two-dimensional, occupying a new subband
in the base, similar to a potential well.  One of the most important
scattering mechanisms, expected to dominate hot electron scattering
in heavily doped bulk materials, is due to the coupled modes of
plasmons and longitudinal optical phonons. In bulk GaAs materials,
n-type doped to a level of 1x1018cm-3, a mean free path of
approximately 30 nm is expected for hot electrons with a kinetic
energy of approximately 0.25 eV.  However, due to the quantization
effects mentioned above, the plasmon and phonon modes are mostly
longitudinal in the base plane, namely, their k is in the plane of
the layer: perpendicular to the k of the ballistic hot electrons that
traverses the base.  In this case, the coupling between the hot
electrons and the ballistic electrons is expected to be small.
Moreover, the number of states to scatter into is restricted because
of the size quantization effects.

      As a result, mfp in THETA type structures (60-100 nm) are no
longer found.  Therefore, it is expected that as the base width gets
narrower, the longer will be the mfp. However, with the reduction of
the base width, the total number of carriers in the base reduces and
the...