In a luminescent diode and a method for manufacturing the same, a planar buried heterostructure (PBH) and a ridge waveguide structure are combined, so that the luminescent diode can be operated to generate a high output of 100 mW or more at low current. Further, it is possible to reduce electro-optic loss. In addition, the luminescent diode is applied to a wavelength tunable external cavity laser, so that it is possible to provide an external cavity laser having excellent output characteristics.