Properties of ion-implanted junctions in mercury—cadmium—telluride

The formation of n-p junctions by ion-implantation in Hg
0.71
Cd
0.29
Te is shown to be a result of implantation damage. n-p photodiodes have been made by implantation of Ar, B, Al, and P in a p-type substrate with acceptor concentration of 4 × 10
¹⁶
cm
^-3
. The implanted n-type layer is characterized by sheet electron concentration of 10
¹⁴
to 10
¹⁵
cm
^-2
and electron mobility higher than 10
³
cm
²
. V
^-1
. s
^-1
, for ion doses in the range 10
¹³
-5 × 10
¹⁴
cm
^-2
. The photodiodes have a spectral cutoff of 5.2 µm, quantum efficiency higher than 80 percent, and differential resistance by area product above 2000 Ω . cm
²
at 77 K. The temperature dependence of the differential resistance is discussed. The junction capacitance dependence on reverse voltage fits a linearly graded junction model. Reverse current characteristics at 77 K have been investigated using gate-controlled diodes. The results suggest that reverse breakdown is dominated by interband tunneling in field-induced junctions at the surface, for both polarities of surface potential.