Overcoming
Difficulties in Photoreflectance Measurements on Product HBTs
Kopin
Corporation
Photoreflectance
(PR) is an optical measurement technique used to study material properties and
device structures. It is uniquely able
to non-destructively measure electric fields within devices. Some device structures such as HBTs have a
rough highly doped InGaAs surface layer.
In some cases the surface roughness is sufficient to produce light
scattering that impedes optical measurements such as PR. We have developed a new measurement
configuration separating the pump laser, which causes the light scattering,
from the probe laser. Rapid,
non-destructive measurements of the emitter and collector depletion regions are
possible with this configuration on product wafers with rough surface layers