THERMOMIGRATION OF TE PRECIPITATES AND IMPROVEMENT OF (CD,ZN)TE SUBSTRATE CHARACTERISTICS FOR THE FABRICATION OF LWIR (HG,CD)TE PHOTODIODES

(Cd,Zn)Te wafers containing Te precipitates have been annealed under w ell defined thermodynamic conditions at temperatures below and above t he melting of Te. Results of the examination of the wafers with infrar ed microscopy before and after the anneals indicate a substantial redu ction of the Te precipitates in wafers annealed at temperatures in exc ess of the melting point of Te compared with those annealed at tempera tures below the melting point of Te. These results confirm the thermom igration of liquid Te precipitates to be the principally operative mec hanism during annealing in the elimination of these precipitates in (C d,Zn)Te wafers. The occurrence of Te precipitates in (Hg,Cd)Te epitaxi al layers grown on (Cd,Zn)Te substrates containing Te precipitates is also explained on the basis of thermomigration of these precipitates d uring LPE growth from the substrates to the epilayers. Absence of occu rrence of Te precipitates in (Hg,Cd)Te epilayers grown on annealed (Cd ,Zn)Te substrates with negligible Te precipitates is also confirmed. U sefulness of annealing (Cd,Zn)Te substrates-to eliminate Te precipitat es -prior to epilayer growth is confirmed via demonstration of improve d long wavelength infrared (Hg,Cd)Te device array performance uniformi ty in epitaxial layers grown on (Cd,Zn)Te substrates with negligible T e precipitates after annealing.