טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMichael Girgel
SubjectEffect of Material Properties on Performance in Hg1-xCdxTe
based PV Infrared Photo-detectors
DepartmentDepartment of Electrical Engineering
Supervisor Professor Emeritus Bahir Gad


Abstract

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.