Semiconductor laser and fabricating method thereof

1. A semiconductor laser comprising

a lower clad layer,

a multiple quantum well (MQW) configuration,

guide layers adjacent to said MQW configuration, and

an upper clad layer formed above a semiconductor substrate,

said semiconductor laser having a window region including a portion in which said MQW configuration and said guide layers are intermixed in the vicinity of a light emitting end face perpendicular to the surface of said semiconductor substrate, wherein

said lower clad layer has a refractive index higher than that of said upper clad layer, and

said MQW configuration and said guide layers are intermixed so that the light intensity distribution in said window region spreads more widely in the direction perpendicular to the surface of said semiconductor substrate than the light intensity distribution in a gain region of said semiconductor laser.

2. A semiconductor laser comprising

a lower clad layer,

a multiple quantum well (MQW) configuration,

guide layers adjacent to said MQW configuration, and

an upper clad layer formed above a semiconductor substrate,

said semiconductor laser having a window region including a portion in which said MQW configuration and said guide layers are intermixed in the vicinity of a light emitting end face perpendicular to the surface of said semiconductor substrate, wherein

said lower clad layer includes a layer having a refractive index higher than that of said upper clad layer, and

said MQW configuration and said guide layers are intermixed so that the light intensity distribution in said window region spreads more widely in the direction perpendicular to the surface of said semiconductor substrate than the light intensity distribution in a gain region of said semiconductor laser.

3. The semiconductor laser according to claim 2 , wherein

said window region, a transition region where the spread of the light intensity distribution varies and said gain region are arranged in this order from said light emiffing end face, and

the photoluminescence wavelength in said MQW configuration and said guide layers within said window region is shorter than the photoluminescence wavelength in said MQW configuration and said guide layers within said gain region by 15 nm or more.

4. The semiconductor laser according to claim 2 , wherein

said window region, a transition region where the spread of the light intensity distribution varies and said gain region are arranged in this order from said light emitting end face, and

the photoluminescence wavelength in said MQW configuration and said guide layers within said window region is shorter than the photoluminescence wavelength in said MQW configuration and said guide layers within said gain region by 40 nm or more.

5. The semiconductor laser according to claim 2 , wherein

said window region, a transition region where the spread of the light intensity distribution varies and said gain region are arranged in this order from said light emitting end face, and

said transition region has a width of 16 μm or more in the direction perpendicular to said light emitting end face.

6. The semiconductor laser according to claim 2 , further comprising:

a cap layer having a valence band energy higher than that of said upper clad layer, above said upper clad layer, wherein

said layer intermixing is achieved by injecting impurity from a portion above said cap layer and causing the impurity to diffuse.

7. The semiconductor laser according to claim 2 , wherein

said lower clad layer, said MQW configuration, said guide layers, and said upper clad layer are formed from semiconductor layers represented by the general formula: (Al x Ga 1-x ) y In 1-y P (where 0≦x≦1 and 0≦y≦1) or Ga z In 1-z P (where 0≦z≦1).

8. The semiconductor laser according to claim 2 , wherein

said lower clad layer, said MQW configuration, said guide layers, and said upper clad layer are formed from semiconductor layers represented by the general formula: Al r Ga 1-r As (where 0≦r≦1) or GaAs.

9. A semiconductor laser comprising

a lower clad layer,

an active layer including at least one quantum well layer, and

an upper clad layer formed in this order above a semiconductor substrate,

said semiconductor laser having a window region including a portion in which the quantum well layer in said active layer and layers adjacent to said active layer are intermixed in the vicinity of a light emitting end face perpendicular to the surface of said semiconductor substrate, wherein

said lower clad layer includes a layer haying a refractive index higher than that of said upper clad layer, and

the light intensity distribution in said window region spreads more widely in the direction perpendicular to the surface of said semiconductor substrate than the light intensity distribution in a gain region of said semiconductor laser,

said lower clad layer includes a first lower clad layer closer to said semiconductor substrate and a second lower clad layer closer to said active layer, and

said first lower clad layer has a refractive index higher than that of said second lower clad layer.

10. The semiconductor laser according to claim 9 , wherein

said first lower clad layer has a refractive index higher than that of said second lower clad layer by 0.003 or more to 0.02 or less.

11. The semiconductor laser according to claim 9 , wherein

said second lower clad layer has a thickness of 0.05 μm or more to 0.9 μm or less.