We compared the
performance of Hg(1-x)Cd(x)Te based PV infrared photodetectors implemented on
SCD and Fermionics wafers. Both undoped and Au-doped samples were examined. It
is known that Hg vacancies can create double ionized acceptors and
recombination centers, and that Te antisites can create donor states and
additional recombination centers. Based on the results of structural
characterization (HRXRD, EDS, and transmission using FTIR) we have determined
that the density of Te antisites in significantly larger in SCD samples than in
Fermionics'. We examined the influence of this difference on the structure
parameters using temperature dependent Hall measurements, light modulated Hall
effect, and modified photo-electro-magnetic (PEM) technique. Electrical
measurements show that all samples have p-type conductivity. Increasing lifetime
with increased temperature indicates that S.R.H is the dominant mechanism.
Recombination centers are associated with electrically active Te antisites and
Hg vacancies. Au and Te fill vacancies of Hg, thus Au doping decreases the
number of recombination centers. This process affectivity is proportional to
the number of recombination centers. In Fermionics undoped samples the dominant
recombination center is double charged Hg vacancies (Er= 40meV), while in
undoped SCD samples the dominant recombination center is multi charged Te
antisites (Er=30meV). In doped Fermionics samples Au doping results in a very
large decrease in the concentration of electrically active Hg vacancies thus
the dominant recombination mechanism is due to Te antisites centers (Er=30meV)
rather than Hg vacancies. In doped SCD samples the dominant recombination
center remains Te antisites (Er=30meV) but their concentration is lower than in
undoped material due to Au doping. The short lifetime in SCD sample is due to
excess Te antisites. Device characterization of temperature dependence of
reveres bias I-V characteristics reveals that SCD samples have discrete trap
levels while Fermionics samples have continues spectra of traps. Nevertheless,
for working temperatures (77K), the dark current is limited by thermally
generated currents, for all diodes. R0A was found to be larger in
Fermionics diodes, consistent with lifetime measurements. Excess of Te
antisites in SCD samples (both doped and undoped) is the main reason for
inferior detectors quality.
