By combing doping and semiconductor material, many different semiconductor
junctions can be formed. If more than one type of semiconductor forms the
junction region, the semiconductor is known as a heterojunction and in many
semiconductor devices thesedifferent junctions are vital or lead to ehanced
performance of the device.
When two semiconductors with
different energy gaps are combined, a heterojunction is formed. The most
important difference between these semiconductors in heterostructure devices is
the energy gap and refractive index. Also, the threshold current density was
improved at room temperature and it was achieved by cladding the active layer
material, such as GaAs, with wider energy gap material, for instance
As has very good lattice constant matching
with GaAs. In general, heterostructure lasers will give you both good optical
current confinement, such as P-n-N or P-p-N double heterostructure laser.
The conductivity type of the smaller energy gap crystal is denoted by a lower
case n or p and that of the larger energy gap crystal is denoted by an upper
case N or P.
On these pages we shall examine more closely the theory of Heterostructures and
attempt to model their behaviour using the software developed by J. Wah. of
Essex University's Optoelectronics Research Group to run in a friendly