The electronic and optical properties of visible InGaN quantum-well (QW) structures grown on In0.03Ga0.97N underlayers have been investigated. A significant improvement of the QW emission is observed as a result of the insertion of the underlayers, which is associated with blueshift in the emission energy, reduced recombination lifetime, increased spatial homogeneity in the QW luminescence, and weaker internal fields inside the QWs. These are explained by partial strain relaxation evidenced by reciprocal space mapping of the X-ray diffraction intensity. Electrostatic potential profiles obtained by electron holography provide evidence for enhanced carrier injection by tunneling from the underlayer into the first QW. © 2013 American Institute of Physics.