Planar n-on-p ion milled mid-wavelength and long-wavelength infrared diodes on molecular beam epitaxy vacancy-doped CdHgTe on CdZnTe

Planar mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) photodiodes were fabricated by ion milling molecular beam epitaxy (MBE) Cd_xHg_1−xTe (CMT) layers with and without compositional grading in the layer. Linear arrays with 32 and 64 diodes, as well as test diodes of varying size, were fabricated. Good quantum efficiencies were measured, and MWIR diodes, with cutoff wavelength λ_CO=4.5 μm, had zero-bias resistance-area values (R₀A) in excess of 1×10⁷ Ωcm², whereas LWIR diodes with λ_CO=8.9−9.3 μm had R₀A=3×10² Ωcm² at 77 K. Comparison between a limited number of layers indicates that in layers with a gradient the RA values are a factor of ∼10 larger, and possibly more uniform, than in layers without a gradient.