Semiconductor laser diode

1. A semiconductor laser diode comprising:

an active layer, wherein the active layer is composed of a compound semiconductor of GaInP series;

an upper clad layer formed above the active layer, wherein the upper clad layer is composed of p-(Al 0.7 Ga 0.3 ) 0.5 In 0.5 P;

a first lower clad layer formed below the active layer;

a second lower clad layer formed under the first lower clad layer; and

a substrate formed beneath the second lower clad layer,

wherein a refractive index of the first lower clad layer is identical with a refractive index of the upper clad layer and is lower than a refractive index of the second lower clad layer and wherein the first and second lower clad layers are composed of compound semiconductors of n-AlGaInP series and wherein the second lower clad layer is composed of n-(Al 0.68 Ga 0.32 ) 0.5 In 0.5 P.

2. The semiconductor laser diode of claim 1 , wherein an etch stop layer is formed in the upper clad layer.

3. The semiconductor laser diode of claim 1 , wherein first and second electrode layers are provided on the top surface of the upper clad layer and the bottom surface of the substrate, respectively.

4. The semiconductor laser diode of claim 1 , wherein the active layer has one of multiple quantum well structures and a single quantum well structure.

5. The semiconductor laser diode of claim 1 , wherein an upper waveguide layer and a lower waveguide layer are further formed between the active layer and the upper clad layer and between the active layer and the first lower clad layer, respectively.

6. The semiconductor laser diode of claim 1 , wherein the upper waveguide layer and the lower waveguide layer are composed of compound semiconductors of p-AlGaInP series and n-AlGaInP series, respectively.