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

The formation of n-p junctions by ion-implantation in Hg<inf>0.71</inf>Cd<inf>0.29</inf>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<sup>16</sup>cm<sup>-3</sup>. The implanted n-type layer is characterized by sheet electron concentration of 10<sup>14</sup>to 10<sup>15</sup>cm<sup>-2</sup>and electron mobility higher than 10<sup>3</sup>cm<sup>2</sup>. V<sup>-1</sup>. s<sup>-1</sup>, for ion doses in the range 10<sup>13</sup>-5 × 10<sup>14</sup>cm<sup>-2</sup>. 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<sup>2</sup>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.

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