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It is the optimum wavelength band for detecting the natural glow of the night sky. Meaning, it is sensitive to the wavelengths of light that suffer the least signal dispersion and transmit furthest down a glass fiber (1.3 µm and 1.55 µm), therefore detecting "eye-safe" lasers (wavelengths longer than 1.4 µm). Standard InGaAs has a long wavelength cutoff of 1.68 µm. InxGa1-xAs with 53% InAs is often called "standard InGaAs" without bothering to note the values of "x" or "1-x" because it has the same lattice constant as InP and therefore the combination leads to very high quality thin films. High quality InP substrates are available with diameters as large as 100 mm.

If the thin film and the substrate do not have the same lattice constant, then the properties of the thin film will be severely degraded.įor lots of reasons, the most convenient substrate for InxGa1-xAs is InP. The challenge is that while it's possible to make thin films of InxGa1-xAs by a number of techniques, a substrate is required to hold up the thin film. The lattice constants and long wavelength cutoffs of these alloys are depicted as the red lines in Figure 1. The InAs/GaAs alloy is referred to as InxGa1-xAs where x is the proportion of InAs and 1-x is the proportion of GaAs. The relationship between the lattice constant and the long wavelength cutoff of the 4 ternary alloys in the InGaAsP family are shown in Figure 1 For our four friends, the lattice constants range from 5.4505 Å (GaP) to 6.0585 Å (InAs) with GaAs at 5.6534 Å and InP at 5.8688 Å. The challenge is that not only does the energy bandgap depend on the alloy composition, so also does the resulting lattice constant. This "long wavelength cutoff" works out to 3.75 µm for InAs and 0.55 µm for GaP with InP at 0.96 µm and GaAs at 0.87 µm.īy mixing two or more of the binary compounds, the properties of the resulting ternary and quaternary semiconductors can be tuned to intermediate values. A semiconductor will only detect light with photon energy larger than the bandgap, or put another way, with a wavelength shorter than the cutoff wavelength associated with the bandgap. At SUI we emphasize photodetectors, so we care most about the optical properties of semiconductors. To a large extent, the electrical and optical properties of a semiconductor depend on its energy bandgap and whether the bandgap is "direct" or "indirect." The energy bandgaps of the 4 binary members of the InGaAsP quaternary system range from 0.33 eV (InAs) to 2.25 eV (GaP), with InP (1.29 eV) and GaAs (1.43 eV) falling in between.