Strained alloy InGaAsGaAs multiple quantum well structures MQWs, on GaAs substrates, are being investigated for use in optical modulators, low-threshold diode lasers, photodetectors and other opto-electronic devices operating near 1 um. Attempts are being made to cover the 0.9-1.1 am spectral range by varying well-widths andor alloy mole-fraction and by growing such structures on superlattice or alloy buffer layers. Special problems, however, are posed in growing these strained ternary alloy quantum wells with high quality by epitaxial techniques. Alloy concentration is difficult to reproduce, and alloy-disorder introduces an additional line-broadening contribution and non-uniformity into the materials. The critical thickness parameter places an upper limit on the indium mole-fraction and thereby the strain for growth directly on GaAs, restricting the flexibility in varying the well width for increased spectral coverage. Typically, this mole-fraction must be less than 0.2, and the lattice-parameter mismatch below 2, for well-widths -10 nm. Here, we focus on structures in which each quantum well consists of an ordered InAsGaAs short-period superlattice as an attractive alternative to the random InGaAs alloy structures. These all-binary MQWs are highly-strained 7 lattice parameter mismatch and can accommodate high average indium mole-fraction 30-40 in wide wells 10-20 nm without evidence of strain relaxation due to misfit dislocation formation.
This article is from 'Organization of the Optical Society of America Photonic Science Topical Meeting Series. Volume 7. Quantum Optoelectronics Held in Salt Lake City, Utah on 11-13 March 1991,' AD-253 823, p49-52.