Effects of InxGa1-xAs strain relaxation layers on the optical and structural properties of InAs quantum dots (QDs) were studied systemically. 300 K-photoluminescence (PL) shows that PL peak energy of the QDs is blue-shifted in GaAs/InAs QDs/5 nm-thick In0.1Ga0.9As structure compared to GaAs/InAs QDs/GaAs structure. This is attributed to the intermixing of materials between the QDs and the InGaAs layer below the QDs, whereas capping of a 5 nm-thick In0.1Ga0.9As layer leads to red shift due to strain relaxation effect. As thickness of InxGa1-xAs capping layer (TI) increases, 300 K-PL peaks experience red shift below TI < ~7 nm. Unlikely, TI above 7 nm results in blue shift. Considering average height of the QDs is ~ 7 nm, this is attributed to intermixing of material between the QDs and InGaAs capping layers. The blue shift in x = 0.2 over TI > ~7 nm is relatively smaller compared to that in x = 0.1. It is noteworthy that strain difference between the InAs QDs and the InxGa1-xAs is smaller in x = 0.2 rather than in x = 0.1. Finally, InAs QDs are sandwiched by asymmetric thickness (7.5 nm-thick capping InGaAs, 0, 1.2, and 2.5 nm-thick bottom InGaAs) of In0.2Ga0.8As layers. 300 K-PL spectrum shows that 1.2 nm-thick bottom InGaAs leads to the longest wavelength (1306 nm) among this sample set. This is attributed to reduced barrier height and ignorable accumulated strain effect in thin bottom InGaAs layers. In this report, we justify merit of dots in an asymmetric well structure over conventional dots in a symmetric well structure and strain relaxation structure for the control of PL peak energy.