As a strain-relief relaxed Si1-xGex buffer that is used for type II band offset formation, we have proposed a quadruple-Si1-xGex-layer (QL) buffer where misfit dislocations are evenly distributed in the lower two interfaces and a buffer surface with good crystallinity was obtained. The crystallinity of the buffer surface does not degrade by high P doping with a P concentration of similar to 10(19) cm(-3) during the buffer growth. A vertical-type electron-tunneling Si/Si1-xGex resonant tunneling diode (RTD) formed with the highly P-doped QL buffer exhibits a high current density and a high peak-to-valley current ratio (PVCR) value. A planer-type electron-tunneling Si/Si1-xGex RTD formed with the same buffer using tetramethyl ammonium hydroxide (TMAH) etching and polyimide insulator, which is better suited for device integration, also exhibits a high current density and a high PVCR value and good initial static performance reproducibility. (c) 2007 Elsevier B.V. All rights reserved.