Claims
- 1. A distributed feedback semiconductor laser, comprising:
a lower quantum well structure extending along a resonator direction, said lower quantum well structure having a lamination of alternately stacked lower barrier layer and lower well layer having a band gap narrower than the lower barrier layer; an intermediate layer disposed on said lower quantum well structure, said intermediate layer having a band gap broader than the lower well layer and a thickness thicker than the lower barrier layer; and an upper quantum well structure periodically disposed on said intermediate layer along the resonator direction, said upper quantum well structure having a lamination of alternately stacked upper well layer and upper barrier layer having a band gap broader than the upper well layer.
- 2. The distributed feedback semiconductor laser according to claim 1, further comprising a diffraction-grating-burying layer disposed on said intermediate layer along the resonator direction and covering said upper quantum well structure, said diffraction-grating-burying layer having a band gap broader than the lower and upper well layers.
- 3. The distributed feedback semiconductor laser according to claim 2, wherein said intermediate layer has a surface step of a same repetition period and a same phase in repetition cycle as said upper quantum well structure.
- 4. The distributed feedback semiconductor laser according to claim 2, wherein said diffraction-grating-burying layer has a refractive index not higher than a refractive index of said intermediate layer.
- 5. The distributed feedback semiconductor laser according to claim 4, wherein said diffraction-grating-burying layer has a refractive index lower than a refractive index of said intermediate layer.
- 6. The distributed feedback semiconductor laser according to claim 4, wherein the refractive index of said intermediate layer is lower than a refractive index of the lower barrier layer.
- 7. The distributed feedback semiconductor laser according to claim 4, wherein the refractive index of said intermediate layer is substantially same as a refractive index of the lower barrier layer.
- 8. The distributed feedback semiconductor laser according to claim 4, wherein the refractive index of said intermediate layer has an intermediate value between a refractive index of the upper and lower barrier layers and a refractive index of said diffraction-grating-burying layer.
- 9. The distributed feedback semiconductor laser according to claim 1, wherein said intermediate layer has a thickness of not larger than 300 nm under said upper quantum well structure.
- 10. The distributed feedback semiconductor laser according to claim 4, wherein said intermediate layer an d said diffraction-grating-burying layer have a substantially same refractive index.
- 11. The distributed feedback semiconductor laser according to claim 1, further comprising:
an InP substrate for supporting said lower quantum well structure, wherein the lower and upper well layers are made of InGaAsP having a composition for a 1.5 μm band and the lower and upper barrier layers are made of InGaAsP having a composition for a shorter wavelength than 1.5 μm.
- 12. The distributed feedback semiconductor laser according to claim 11, wherein the lower and upper barrier layers are made of InGaAsP having a composition for a 1.2 μm band to 1.4 μm band.
- 13. The distributed feedback semiconductor laser according to claim 11, wherein said intermediate layer is made of InGaAsP having a composition for a 1.2 μm band to a 1.4 μm band.
- 14. The distributed feedback semiconductor laser according to claim 11, wherein said diffraction-grating-burying layer is made of InGaAsP or InP.
- 15. The distributed feedback semiconductor laser according to claim 8, wherein said diffraction-grating-burying layer is made of InGaAsP and the distributed feedback semiconductor laser further comprises an InP clad layer formed on said diffraction-grating-burying layer.
- 16. The distributed feedback semiconductor laser according to claim 11, wherein said upper quantum well structure, said intermediate layer and said lower quantum well structure are shaped in a stripe form and the distributed feedback semiconductor laser is a mesa or ridge type laser.
- 17. A method of manufacturing a distributed feedback semiconductor laser, comprising the steps of:
(a) growing on a semiconductor substrate a lamination of alternately stacked lower barrier layer and lower well layer having a band gap narrower than the lower barrier layer, to form a lower quantum well structure; (b) growing an intermediate layer on an uppermost lower well layer, the intermediate layer having a band gap broader than the lower well layer and a thickness thicker than the lower barrier layer; (c) growing on the intermediate layer a lamination of alternately stacked upper well layer and upper barrier layer having a band gap broader than the upper well layer and a thickness thinner than the intermediate layer, to form an upper quantum well structure; (d) forming a mask on the upper quantum well structure, the mask having periodical pattern; (e) by using the mask as an etching mask, etching the upper quantum well structure in a periodical shape by using the intermediate layer as an etching margin layer; and (f) removing the mask.
- 18. The method of manufacturing a distributed feedback semiconductor laser according to claim 17, further comprising a step of:
(g) growing a diffraction-grating-burying layer on the intermediate layer after said step (f), the diffraction-grating-burying layer covering the etched upper quantum well structure and having a band gap broader than the upper and lower well layers.
- 19. The method of manufacturing a distributed feedback semiconductor laser according to claim 18, further comprising a step of:
(h) growing a clad layer on the diffraction-grating-burying layer after said step (g).
- 20. The method of manufacturing a distributed feedback semiconductor laser according to claim 18, further comprising the steps of:
(i) forming a stripe-shaped hard mask on the diffraction-grating-burying layer, the stripe-shaped hard mask extending along a direction traversing the periodical patterns; (j) etching the diffraction-grating-burying layer, the upper quantum well structure, the intermediate layer and the lower quantum well structure, using the hard mask as an etching mask, to form a mesa structure; (k) growing a mesa-burying-layer for burying side walls of the etched mesa structure; and (l) removing the hard mask.
- 21. The method of manufacturing a distributed feedback semiconductor laser according to claim 17, wherein the mask having the periodical patterns is formed by performing two-beam interference exposure and development of a photoresist layer.
Priority Claims (2)
Number |
Date |
Country |
Kind |
2000-76908 |
Mar 2000 |
JP |
|
2001-12126 |
Jan 2001 |
JP |
|
Parent Case Info
[0001] This application is based on, and claims priority on Japanese Patent Application 2000-76908 filed on Mar. 17, 2000 and Japanese Patent Application 2001-012126, filed on Jan. 19, 2001, the entire contents of which are incorporated herein by reference.