We have proposed a strain-relaxed quadruple-layer buffer on the basis of our previously proposed thin double- and triple-layer formation mechanisms. With the quadruple-layer buffer, we have demonstrated that misfit dislocations are mainly generated and distributed in the two lower interfaces and the third and fourth layers drive the dislocation generation and prevent the dislocations from propagating to the surface. A resonant tunneling diode fabricated with the quadruple-layer buffer exhibits both a high current density and a high peak-to-valley current ratio.