Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-05-18
2001-04-24
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S026000, C372S045013, C372S046012, C372S096000
Reexamination Certificate
active
06222867
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical semiconductor device and a method of producing the same and, more particularly, to an integrated semiconductor device feasible for high temperature or high optical output operation because of a minimum amount of current leak to occur from its current blocking layer, and a method of producing the same.
Today, the applicable range of optical communication is extending from trunk lines to branch lines or even to access lines. Semiconductor lasers for optical communication are therefore required to have advanced performance and new functions. For a trunk line, for example, a semiconductor laser whose drive spectrum involves a minimum of jitter at the time of modulation is essential in order to implement high speed, long distance transmission. A distributed feedback (DFB) laser having an electro absorption type optical modulator integrated therewith is one type of semiconductor laser meeting the above requirement. As for an access line, there is an increasing demand for a semiconductor laser to be easy to mount and capable of being efficiently coupled to an optical fiber. This kind of laser may be typified by a so-called spot size conversion type laser including a portion for converting the size of a beam.
Japanese Patent Laid-Open Publication No. 62-102583, for example, teaches a semiconductor laser desirable in high temperature or high optical output characteristic. However, the problem with the laser taught in this document is that the characteristic and yield are limited for the following reasons. To form layers different in band gap and thickness on a single substrate, crystal growth and crystal etching must be repeated, increasing the number of steps. Moreover, it is difficult to connect waveguides different in band gap and thickness accurately. As a result, a light loss occurs at the connecting portion and deteriorates the optical output characteristic.
To implement an integrated semiconductor laser, selective metalorganic vapor phase epitaxial growth (MOVPE) procedure capable of forming waveguide layers different in band gap and thickness collectively is attracting increasing attention. A semiconductor laser produce by selective MOVPE is disclosed in, e.g., the Papers of 56th Japanese Science Lecture Meeting, 1995, 27p-ZA-7, p. 930. This kind of scheme, however, brings about a problem that a current blocking layer included in the laser cannot function sufficiently in a high temperature environment or on the injection of a great current. Specifically, while a laser portion usually has the smallest band gap, it is necessary with selective MOVPE to increase the width of an anti-growth mask in the waveguide portion where the band gap should be reduced, i.e., the laser portion. It follows that in the laser portion the current blocking layer implemented only by InP and having a p-n-p-n thyristor structure has a broad area at both sides of an active layer. As a result, current leakage from the current blocking layer and ascribable to the storage of electrons is aggravated.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an integrated semiconductor laser feasible for high temperature or high output operation, and a method of producing the same.
In accordance with the present invention, in an optical semiconductor device having an electro absorption type modulator and a DFB laser in an integrated structure, the modulator and laser are formed on an InP substrate formed with an InGaAsP layer, and waveguide layers respectively functioning as the modulator and laser are buried in an InP current blocking layer.
Also, in accordance with the present invention, in an optical semiconductor device including a laser having a spot size converting portion integrally therewith, the laser is formed on an InP substrate formed with an InGaAsP layer, and waveguide layers respectively functioning as the laser and spot size converting portion are buried in an InP current blocking layer.
Further, in accordance with the present invention, a method of producing a semiconductor device has the steps .of forming two SiO
2
stripes on an InP substrate formed with a n InGasP layer, and forming a waveguide including a multiple quantum well active layer by selective MOVPE between the two stripes, and burying the waveguide in an InP current blocking layer.
REFERENCES:
patent: 5539763 (1996-07-01), Takemi et al.
patent: 5548607 (1996-08-01), Tsang
patent: 5717710 (1998-02-01), Miyazaki et al.
patent: 62-102583 (1987-05-01), None
patent: 8-330665 (1996-12-01), None
Moerman et al, “Monolithic Integration of a Spot Transformer with a Planar Buried Heterostructure InGaAsP/InP Laser Using the Shadow Masked Growth Technique”, IEEE Photonics Technolgy Letters, vol. 6, No. 8, pp. 888-890, Aug. 1994.*
Kobayashi et al, “Tapered Thickness MQW Waveguide BH MQW Lasers”, IEEE Photonics Tech. Letters, vol. 6, No. 9, pp. 1080-1081, Sep. 1994.*
Tohmori et al, “Spot-size Converted 1.3 &mgr;m Laser with Butt-Jointed Selectively Growth Vertically Tapered Waveguide”, Electronics Letters, vol. 31, No. 13, pp. 1069-1070, Jun. 1995.*
Proceedings of the 1997 IEICE General Conference; Mar. 24-27, 1997, Kansai University, Suita, p. 420.
Electronics Letter, an International Publication; The Institution of Electrical Engineers; Jan. 16, 1992; vol. 28, No. 2; pp. 153 and 154.
Sakata, et al. “Novel MQW-DCPBH-LDS fabricated by all selective MOVPE laser diodes (ASM-DCPBH-LDs),” Papers of 56th Japanese Science Lecture Meeting, 1995, 27p-ZA-7, p. 930 (No Month Available).
Inomoto Yasumasa
Sakata Yasutaka
Arroyo Teresa M.
Foley & Lardner
Leung Quyen Phan
NEC Corporation
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