Medium wavelength infrared HgCdTe discrete photodetectors

Abstract

The authors have developed the topology and technological fabrication route for discrete photodiodes (Θ = 0,5—1,5 mm) for the mid-wavelength infrared (MWIR) range, based on the mercury-cadmium-telluride (MCT) epitaxial layers. The paper describes technological processes of MCT photodiodes fabrication, including CdTe passivation layers growth, photolithographic processes for the formation of windows for B+ implantation, formation of metallic coatings, chemical surface treatments, cutting of the wafer on the discrete chips, assembling and bonding of the electrical contacts. Optical, photoelectrical and current-voltage characteristics of discrete MCT photodiodes for the spectral range of 3—5 microns are investigated in order to achieve the necessary operational parameters. FTIR transmission spectra were measured to evaluate samples quality and find the composition of x of Hg_1–xCd_xTe epitaxial layers grown by liquid phase epitaxy method. The limiting characteristics of photodiodes, which are determined by the magnitude of the detector current at the reverse bias and the product of the dynamic resistance at zero bias by the area of the photosensitive element R₀A_d at the operating temperature of 77 K were discussed. The requirement for the parameter R₀A_d was estimated for the operation of photodiodes of the mid wavelength infrared range in the BLIP (background limited performance) mode for the angles of view q_i = 90° and q_i = 30°: R₀A_d ≥ 5·10³ Ω·cm². It was found from dynamical resistance characteristics that without bias in these MCT MWIR photodiodes R₀A_d ≈ (0,57—1,08) Ω · 10⁵ cm² and these photodiodes can operate in BLIP mode.