Department of Computer Science and Electrical Engineering
Abstract:
Avalanche breakdown and related phenomena induced by impact ionisation
in semiconductors have received continuous interest because their influence
on device performance. Studies have been carried both by measurement and
the numerical simulation. Numerical modelling in the past has been restricted
to one-dimensional analytical modelling and for high voltage devices. With
the proliferation of new two- and three- dimensional numerical simulators
for semiconductor devices, numerical simulation has been applied to look
at the influence of many device physical and structural parameters on avalanche
breakdown in all well-known semiconductor devices. High electric field
in devices can be due either to high applied voltage or to size reduction.
This thesis presents work on the modelling of the underlying physics of impact ionisation in semiconductor p-n junction diodes using Medici, a commercial two-dimensional device simulation software. The breakdown voltage and reverse current density as a function of dopant level, the radius of junction curvature are investigated and compared with existing information in the literature. Effect of crowding of the electric field vectors at the junction curvature is also investigated.
The work indicates that the breakdown voltage decreases as with increasing doping level and with reducing junction curvature. The reduction is due to increase in the electric field either globally in the case of dopant change or locally in the case of junction curvature change. The increase in electric field in turn increases the probability of impact ionisation and hence also the reverse leakage current density. For comparison, previous work from S. M. Sze and G. Gibbons and the present simulation work are presented.
The other well known breakdown physics of quantum mechanical tunneling is not investigated due to the fact that tunneling physics is not included in the software used in this work. The implication is that the present results of leakage currents will be lower than expected for highly doped junctions where tunneling is known to be significant.
Complete thesis:
thesis.pdf
Conference:
conference_paper.pdf