This is the 2D companion to the 3D HgCdTe nanocrystal model: the same composition- and temperature-dependent bandgap, computed from the identical empirical Hansen relation used industrially to design infrared detectors, read here off four analytic plots instead of a rendered lattice.
Eg(x,T) = -0.302 + 1.93x - 0.810x² + 0.832x³ + 5.35e-4·T·(1-2x) [eV]
λc = 1.24 / Eg [μm] (cutoff wavelength, hc/e ≈ 1.24 eV·μm)
Top-left — bandgap vs composition. Eg(x) traced at the current temperature (cyan) against a 300 K reference (grey), with the live (x, Eg) point marked and the semimetal / LWIR / MWIR / SWIR+ regimes shaded by their real cutoff-wavelength ranges.
Top-right — band diagram. Valence and conduction band levels separated by Eg; fired photons cross left→right and either punch through the gap (absorbed, flash) or coast past it (transmitted) depending on whether their energy E=1.24/λ clears Eg.
Bottom-left — transmission spectrum. Transmission vs incident wavelength at the current x and T: opaque (absorbing) below the cutoff, transparent above it, with the current λ and λc both marked.
Bottom-right — cation lattice map. A top-down slice of the zinc-blende sublattice: Cd (gold) substitutes for Hg (cyan-white) on the cation sites in proportion to x, exactly as in the 3D scene, with Te anion sites (red) interleaved.
- x — Cd content. At x=0 (pure HgTe) Eg is negative: a zero-gap semimetal. Around x≈0.2-0.4 the gap opens into the long/mid-wave infrared range used by real thermal-imaging detectors.
- T — raising temperature widens the gap slightly (positive dEg/dT here) and shifts λc to shorter wavelengths; detectors are cooled mainly to suppress thermally generated dark current, which is why the illustrative D* gauge below rises sharply at low T and large Eg.
- λ slider / Fire photon — a photon of energy E = 1.24/λ eV is launched at the crystal. If E ≥ Eg it is absorbed (registered); if E < Eg it is transmitted.
- Auto-scan — sweeps λ continuously so you can watch the absorption/transmission boundary track λc live on the spectrum panel.
This composition tunability is why HgCdTe is the dominant material for cooled infrared focal-plane arrays (military, astronomy, thermal imaging): one growth recipe, continuously adjustable cutoff, from short-wave out past 14 μm.