Abstract:
In practical optical devices one of the most important parameter which determines
the performance of the device is the quantum efficiency. Generally, an optical device is
fabricated using a junction between two semiconductors or a junction between a metal
and a semiconductor. However, in practice formation of unwanted junctions during the
fabrication stage of the optical devices is a major problem and it will result in the reduction
of the overall performance of the device. In this investigation, a theoretical study was carried
out on an optical device made by using a semiconductor/ metal junction to study this eff�ct.
The formation of an additional junction at the back contact was considered as the reason for
the formation of a double junction.
In the study, photoinduced charge separation at the two space charge layers was
considered as the main contribution to the photocurrents. Both drift current and diffusion
current of the majority and minority carriers are considered in the continuity equation
for calculating the total current produced by the device. Absorption of photons in the
semiconductor was calculated using the variation of the absorption coefficient with the
wavelength of the direct band gap semiconductor Cu20. In solving the continuity equation,
the absorption of light in both space charge regions and creation of electron- hole pairs and
the motion of the carriers in opposite directions were considered.
The computed variation of the quantum efficiency with the wavelength of the
incident light agreed well with the reported experimental results. We could observe that
the efficiency of the device is drastically reduced as a result of the double junction effect.
Further, with our model it was possible to explain the observation of the variation of direction
of photocurrent with the wavelength, as a result of the existence of a double junction. In
conclusion, using the computed quantum efficiency variation with the wavelength it was
possible to obtain the junction parameters of an optical device using experimental data.
