Indium gallium arsenide

Indium gallium arsenide (InGaAs) (alternatively gallium indium arsenide, GaInAs) is a ternary alloy (chemical compound) of indium arsenide (InAs) and gallium arsenide (GaAs). Indium and gallium are (group III) elements of the periodic table while arsenic is a (group V) element. Alloys made of these chemical groups are referred to as 'III-V' compounds. InGaAs has properties intermediate between those of GaAs and InAs. InGaAs is a room-temperature semiconductor with applications in electronics and photonics. The principal importance of GaInAs is its application as a high-speed, high sensitivity photodetector of choice for optical fiber telecommunications. Indium gallium arsenide (InGaAs) and gallium-indium arsenide (GaInAs) are used interchangeably. According to IUPAC standards the preferred nomenclature for the alloy is GaxIn1-xAs where the group-III elements appear in order of increasing atomic number, as in the related alloy system AlxGa1-xAs. By far, the most important alloy composition from technological and commercial standpoints is Ga0.47In0.53As, which can be deposited in single crystal form on indium phosphide (InP). GaInAs is not a naturally-occurring material. Single crystal material is required for electronic and photonic device applications. Pearsall and co-workers were the first to describe single-crystal epitaxial growth of In0.53Ga0.47As on (111)-oriented and on (100)-oriented InP substrates.Single crystal material in thin-film form can be grown by epitaxy from the liquid-phase (LPE), vapour-phase (VPE), by molecular beam epitaxy (MBE), and by metalorganic chemical vapour deposition (MO-CVD). Today, most commercial devices are produced by MO-CVD or by MBE. The optical and mechanical properties of InGaAs can be varied by changing the ratio of InAs and GaAs, In1-xGaxAs. Most InGaAs devices are grown on indium phosphide (InP) substrates. In order to match the lattice constant of InP and avoid mechanical strain, In0.53Ga0.47As is used. This composition has an optical absorption edge at 0.75 eV, corresponding to a cut-off wavelength of λ=1.68 μm at 295 K. By increasing the mole fraction of InAs further compared to GaAs, it is possible to extend the cut-off wavelength up to about λ=2.6 µm. In that case special measures have to be taken to avoid mechanical strain from differences in lattice constants. GaAs is lattice-mismatched to germanium (Ge) by 0.08%. With the addition of 1.5% InAs to the alloy, In0.015Ga0.985As becomes latticed-matched to the Ge substrate, reducing stress in subsequent deposition of GaAs. InGaAs has a lattice parameter that increases linearly with the concentration of InAs in the alloy. The liquid-solid phase diagram shows that during solidification from a solution containing GaAs and InAs, GaAs is taken up at a much higher rate than InAs, depleting the solution of GaAs. During growth from solution, the composition of first material to solidify is rich in GaAs while the last material to solidify is richer in InAs. This feature has been exploited to produce ingots of InGaAs with graded composition along the length of the ingot. However, the strain introduced by the changing lattice constant causes the ingot to be polycrystalline and limits the characterization to a few parameters, such as bandgap and lattice constant with uncertainty due to the continuous compositional grading in these samples.