a micron as suggested by y sasai et al cited hereinabove the thin low doped layer serves as a buffer layer and prevents the active layer from becoming highly zinc doped the second layer represents the bulk of the p type inp layer the 1 to 2 microns thickness preserves the good optical characteristic of the device because of the presence of the thin p buffer layer the thick layer can be made highly doped the series resistance can be reduced to the lowest possible value and the voltage drop across the combined p inp layers can be made as small as possible referring to fig1 there is shown a cross section of a semiconductor laser constructed in accordance with the teachings of this invention the semiconductor laser includes an n doped inp substrate 11 which can have a concentration of about 2 u00d7 10 18 cm 3 the n dopant can be sulfur or tin for example a buffer layer 12 is applied thereto the buffer layer 12 being an n doped layer having a concentration of about 2 u00d7 10 18 atoms cm 3 an active layer 13 is deposited upon the buffer layer 12 the active layer 13 is not intentionally doped in the embodiment depicted in fig1 there is further shown an inp regrown layer 14 which.