Photovoltaic infrared sensor arrays in monolithic lead chalcogenides on silicon

TLDR

IV‑VI on‑Si infrared sensors offer a low‑cost route to large focal‑plane arrays for 3–5 µm and 8–12 µm, with reduced uniformity issues due to a weaker band‑gap composition dependence than CdHgTe. This work reviews the MBE growth of epitaxial IV‑VI lead‑salt layers on Si(111) and the fabrication of photovoltaic infrared devices within those layers. Sensor arrays are fabricated in 2–4 µm thick PbTe, PbS₁₋ₓSeₓ, and Pb₁₋ₓEuₓSe for 3–5 µm, and in Pb₁₋ₓSnₓSe for 8–12 µm, with a 0.2 µm CaF₂–BaF₂ bilayer to mitigate lattice and thermal mismatch with Si. The arrays exhibit atomically smooth surfaces with defect densities below 10³ cm⁻², rocking‑curve widths of ~150 arcsec, and were produced in 66‑ and 256‑pixel configurations on standard Si chips with Al metallization.

Abstract

MBE growth of epitaxial IV-VI lead salt layers on Si (111) substrates and fabrication of photovoltaic infrared devices in the layers is reviewed. IV-VI on Si IR sensors have potential as a low-cost technique of fabrication of large IR focal plane arrays for both the 3-5 mu m and 8-12 mu m ranges because of the easy fabrication procedure and because uniformity problems are much less severe in IV-VIs due to the weaker composition dependence of the bandgap compared with Cd1-xHgxTe. Sensor arrays are fabricated in 2-4 mu m thick PbTe, PbS1-xSex and Pb1-xEuxSe for 3-5 mu m and in Pb1-xSnxSe for 8-12 mu m cut-off. An intermediate epitaxial stacked 0.2 mu m thick CaF2-BaF2 bilayer serves for compatibility and helps to overcome the large lattice and thermal expansion mismatch between the Si substrate and the IV-VI layer. Perfectly smooth surfaces with surface defect concentrations down to 103 cm-2, and X-ray rocking-curve linewidth of approximately=150 arcsec are obtained. Sensor arrays with 66 and 256 elements are described, the latter having been grown on standard Si chips with Al metallization.