Heterojunction bipolar transistor
The heterojunction bipolar transistor (HBT) is a type of
Materials
The principal difference between the BJT and HBT is in the use of differing semiconductor materials for the emitter-base junction and the base-collector junction, creating a heterojunction. The effect is to limit the injection of holes from the base into the emitter region, since the potential barrier in the valence band is higher than in the conduction band. Unlike BJT technology, this allows a high doping density to be used in the base, reducing the base resistance while maintaining gain. The efficiency of the heterojunction is measured by the Kroemer factor.[3] Kroemer was awarded a Nobel Prize in 2000 for his work in this field at the University of California, Santa Barbara.
Materials used for the substrate include silicon, gallium arsenide, and
In
Fabrication
Due to the need to manufacture HBT devices with extremely high-doped thin base layers,
Other techniques are used depending on the material system. IBM and others use
Normally the epitaxial layers are lattice matched (which restricts the choice of bandgap etc.). If they are near-lattice-matched the device is pseudomorphic, and if the layers are unmatched (often separated by a thin buffer layer) it is metamorphic.
Limits
A pseudomorphic heterojunction bipolar transistor developed at the
Besides being record breakers in terms of speed, HBTs made of
See also
References
- ^ W. Shockley: 'Circuit Element Utilizing Semiconductive Material', United States Patent 2,569,347, 1951.
- S2CID 51651950.
- ^ The phototransistor effect: "The Kroemer factor is a function of the physical parameters of the materials making up the heterojunction, and can be expressed in the following way [formula given]"
- ^ Indium Phosphide: Transcending frequency and integration limits. Semiconductor Today. Vol 1 Issue 3. Sept 2006
External links
- NCSR HBT at the Wayback Machine (archived April 4, 2008)
- HBT Optoelectronic Circuits developed in the Technion (15Mb, 230p)
- New Material Structure Produces World's Fastest Transistor 604 GHz Early 2005