A scanning laser beam is a common method used to characterise the opti
cal response of GaAs devices. Laser heating of the substrate, however,
can alter the local temperature and hence spuriously shift the values
of the electrical parameters of interest. In order to assess the magn
itude of this problem, we have solved the steady-state heat equation,
with the aid of Kirchhoffs transformation. We show for practical dimen
sions, that correct temperature prediction does not depend on the late
ral boundary conditions. We find that the variable that is most tightl
y coupled to any temperature increase is the power of the laser beam.
Usual approximations for the power dissipation density, in the substra
te, were found inadequate. A more complete model that considers power
dissipation as an exponential function of substrate depth was found to
be necessary. We conclude that for low power applications, i.e. using
lasers less than 1 mW, heating effects can be considered negligible.
For higher powers our results offer worst-case predictions of the loca
l substrate temperature rise. Published by Elsevier Science Ltd. All r
ights reserved.