Investigation of effect of strain-compensated structure and compensation limit in strained-layer multiple quantum wells

We investigated the effect of the strain-compensated structure of InGaAs(+)/InGaAs(-) multiple quantum wells (MQWs). Photoluminescence (PL) spectroscopy and thickness fringes by a transmission electron microscopy were used to evaluated the optical and structural crystal quality. For the +0.5/ −0.5% strain-compensated cases, lattice distortion was not observed, and PL intensity increased when the number of periods increased from 5 to 15. Crystal quality was improved by using the +0.5/ −0.5% strain-compensated MQW instead of the +0.5/0% compressively strained MQW. It was possible to increase the stack thickness of the strained MQWs. However, crystal quality was degraded with increase in strain. For the +1.25/ −1.25% cases, PL intensity decreased when the number of periods increased from 5 to 15, and defects were observed in a 15-period sample. Moreover, crystal quality was degraded by using the +1.25/ −1.25% strain-compensated MQW instead of the +1.25/0% compressively strained MQW.