In recent years, accompanied with popularization of an optical disk device which has compatibility between a DVD and a CD, a monolithic semiconductor laser is used as a light source, which emits laser light having two wavelengths from places apart from each other with a determined interval by forming an InGaAlP based semiconductor laser element for red light and an AlGaAs based semiconductor laser element for infrared light on the same semiconductor substrate (cf. for example PATENT DOCUMENT 1).
As shown in FIG. 3, the AlGaAs based semiconductor laser element 50a is provided, on a semiconductor substrate 51 made of, for example, n-type GaAs, with, for example, an infrared light emitting layer forming portion 59a, which is composed of an n-type cladding layer 52a made of n-type AlGaAs based semiconductor, an active layer 53a made of AlGaAs based semiconductor and a p-type cladding layer 54a made of p-type AlGaAs based semiconductor and having a ridge shape, and a current constriction layer 55a for an infrared element made of n-type GaAs, which is formed on sides of the ridge portion, and a contact layer 56a made of, for example, p-type GaAs is provided thereon. On the other hand, the InGaAlP based semiconductor laser element 50b is provided, on the same semiconductor substrate 51 where the AlGaAs based semiconductor laser element 50a is formed, with, for example, an red light emitting layer forming portion 59b, which is composed of an n-type cladding layer 52b made of n-type InGaAlP based semiconductor, an active layer 53b made of InGaAlP based semiconductor and a p-type cladding layer 54b made of p-type InGaAlP based semiconductor, and a current constriction layer 55b for the red element made of n-type GaAs which is the same material as that of the current constriction layer 55a, which is formed on sides of the ridge portion, and a contact layer 56b made of, for example, p-type GaAs is provided thereon. Further, p-side electrodes 57a and 57b are formed on the contact layers 56a and 56b, and a common n-side electrode 58 is formed at a back surface side of the semiconductor substrate 51, thereby a monolithic semiconductor laser is formed in which both elements are electrically separated. PATENT DOCUMENT 1: Japanese Patent Application Laid-Open No. 2000-11417 (FIG. 9)