The CdxHg1−x Te compounds are well suited to the design of semiconducting devices incorporating an optical microresonator since they display a wide variation of bandgap and refractive index with composition x, while the lattice parameter remains practically unchanged. It is then possible to create a specific optical function by stacking high quality pseudomorphic layers on a crystalline substrate.
Microcavities resonating in the 3–5 μm range have been made by growing a lower Bragg mirror (10.5 periods) and a nominally undoped cavity medium containing a 50 nm active layer (CdTe-HgTe pseudo-alloy). The upper mirror is a gold layer deposited on the cavity. The emission of these Resonant Cavity Light Emitting Diodes has been observed in the 3–4.5 μm range up to room temperature. It coincides with the cavity resonance mode (linewidth 8 meV). With the addition of a ZnS/YF3 upper mirror, a Vertical Cavity Surface Emitting Laser at 3.06 μm has also been demonstrated.
The microcavity concept appears to be very useful for designing new devices for the 3–5 μm range.