ABSTRACT
Low temperature photoluminescence spectra of strained InxGa1-xAs/GaAs quantum wells grown by metalorganic vapour phase epitaxy at 700° C reveal significantly higher PL line widths on substrates with 2° off-orientation than on (100) just oriented ones. Additionally, the PL intensity drops earlier when the In-supply is increased. X-ray diffraction measurements show that the higher PL line widths are related to In carry-over from the QW to the following GaAs cap. Segregation is stronger for the off-oriented InGaAs QWs leading to lower In concentration XS in the QW. These differences vanish at higher In concentrations (XS > 0.2). For high In supply (XV > 0.3) In segregation leads to the formation of dark spot defects visible in cathodoluminescence which cause a drastic decrease of the PL intensity and increase of the PL peak width. The stronger segregation effect on off-oriented substrates leads to the earlier formation of an In-rich wetting layer at the surface, as a precondition for the defect formation. So the critical layer thickness for the defect formation on the off-oriented samples is smaller than for the just oriented ones. The reduced segregation on just oriented GaAs makes the (100) orientation the preferred one for the growth of lasers with emission wavelengths above 1000 nm that require a high total In content in the InGaAs QWs.
