Xenics has developed InGaAs detectors that offer a spectral range of 0.9 – 1.7 µm, 1.0 – 2.2 µm and 1.0 - 2.5 µm. The very beneficial extension from 1.7 µm to 2.2 µm and 2.5 µm is accomplished by varying the fraction of indium in the ternary compound. Introducing indium into GaAs decreases the bandgap of the compound and enables the detection of infrared radiation of longer wavelengths. The graph below illustrates how the bandgap will change when the composition of the III-V compound changes. However, changing the composition of a compound material will also change the lattice constant of the material. Most IR materials are fabricated lattice-matched, meaning: on a substrate that has the same lattice constant as the IR material itself. For III-V compounds, the most commonly used substrates are GaAs, InP, InAs, GaSb and InSb. The InGaAs alloy with a 1.7 µm cut-off wavelength is lattice matched to InP. Therefore it is generally fabricated on InP substrates. In order to extend its sensibility to longer wavelengths, the alloy has to be fabricated on a lattice-mismatched substrate. This can be done on an InP substrate or on a standard GaAs substrate.
Using the lattice matched and mismatched technology, state of the art InGaAs linear arrays as well as focal-plane-array (FPA) detectors have been fabricated.