Junction Stability in Ion-Implanted Mercury Cadmium Telluride

Abstract

Ion implantation into HgCdTe results in the production of Hg interstitials, which can be subsequently driven into the HgCdTe by an annealing process. This diffusive drive-in of the Hg interstitials fills vacancies and kicks out group I impurities and results in the formation of an n-p junction. In this work we report on the production of interstitials during baking subsequent to the ion implantation process. Various concentrations of metal vacancies were first introduced into mid-wavelength infrared (MWIR, 3 lm to 5 lm) HgCdTe by annealing under tellurium-saturated conditions at various temperatures. Baking subsequent to planar implantation of boron produced n-p junctions whose depths were measured by defect etching. The results were modeled using a simple diffusion limited model from a fixed surface concentration. The surface concentration was allowed to decrease exponentially to zero after a time, found to be of the order of $80 h to 150 h. Exhaustion of the interstitials sources produced by the implantation was nearly complete after $400 h. The total number of mercury interstitials produced was approximately 50% of the implant dosage.

Effect of post‐implantation anneal on the current‐voltage characteristics of IR photodiodes based on p‐CdxHg1‐xTe

“…Implantation of boron ions into a vacancy p-type MCT material [7][8][9][10][11] (and subsequent annealing) forms an n + -n − -p structure as a result of Hg diffusion from a surface source located in the implanted area. The diffusing Hg atoms annihilate with mercury vacancies.…”

“…The equations of diffusion and reaction and also the numerical values of the kinetic coefficients can be found in [12]. A boundary condition [11] on the diffusing Hg concentration near the implanted region was used, which correctly describes the p-n junction extension during postimplantation annealing. Propagation of the n-p-junction inward and along the surface also depends on the boundary condition of the concentration of Hg atoms near the CdHgTe/SiO2 interface.…”