Source: http://www.google.com/patents/US6107112?dq=6246862
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Patent US6107112 - Periodically forming grooves at a surface of an indium phosphide substrate ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsIn a distributed feedback semiconductor laser includes an InP substrate and a multiple layer structure formed on a main surface of the InP substrate, the multiple layer structure includes at least an active layer for emitting laser light and a periodical structure for distributed feedback of the laser...http://www.google.com/patents/US6107112?utm_source=gb-gplus-sharePatent US6107112 - Periodically forming grooves at a surface of an indium phosphide substrate, heating the substrate with a mixture of phosphine and arsine to grow indium-arsenic-phsophide layer in each groove, and forming multilayer; crystalllizationAdvanced Patent SearchPublication numberUS6107112 APublication typeGrantApplication numberUS 09/414,756Publication dateAug 22, 2000Filing dateOct 7, 1999Priority dateSep 28, 1994Fee statusLapsedAlso published asEP0706243A2, EP0706243A3, EP1130715A2, EP1130716A2, US6151351Publication number09414756, 414756, US 6107112 A, US 6107112A, US-A-6107112, US6107112 A, US6107112AInventorsMasahiro Kito, Masato Ishino, Nobuyuki Otsuka, Yasushi Matsui, Shinji NakamuraOriginal AssigneeMatsushita Electric Industrial Co., Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (20), Non-Patent Citations (24), Referenced by (2), Classifications (43), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetPeriodically forming grooves at a surface of an indium phosphide substrate, heating the substrate with a mixture of phosphine and arsine to grow indium-arsenic-phsophide layer in each groove, and forming multilayer; crystalllizationUS 6107112 AAbstract In a distributed feedback semiconductor laser includes an InP substrate and a multiple layer structure formed on a main surface of the InP substrate, the multiple layer structure includes at least an active layer for emitting laser light and a periodical structure for distributed feedback of the laser light, and the periodical structure includes a plurality of semiconductor regions each having a triangular cross section in a direction perpendicular to the main surface of the InP substrate and parallel to a cavity length of the distributed feedback semiconductor laser, the triangular cross section projecting toward the InP substrate.
What is claimed is: 1. A method for producing a distributed feedback semiconductor laser, comprising the steps of:periodically forming a plurality of grooves at a surface of an InP substrate; heating the InP substrate in an atmosphere containing at least a mixture of phosphine and arsine to grow an InAsP layer in each of the grooves; and forming a multiple layer structure comprising an active layer on the InP substrate, covering the InAsP layers. 2. A method for producing a distributed feedback semiconductor laser, comprising the steps of:forming a multiple layer structure on an InP substrate, the multiple layer comprising an active layer and an InP top layer; periodically forming a plurality of grooves at a surface of the InP top layer; and heating the multiple layer structure in an atmosphere containing at least a mixture of phosphine and arsine to grow an InAsP layer in each of the grooves. 3. A method according to claim 1, further comprising the step of growing an InGaP layer on the InAsP layers before the formation of the multiple layer structure.
4. A method according to claim 2, further comprising the step of growing an InGaP layer on the InAsP layers.
5. A crystal growth method, comprising the steps of:corrugating a surface of a layer formed of InP crystals by etching; and heating the InP crystals in an atmosphere comprising at least a mixture of phosphine and arsine to grow an InAsP layer in grooves of the corrugated surface. Description
This application is a division of U.S. patent application Ser. No. 08/534,959 filed Sep. 28, 1995 (allowed).
SUMMARY OF THE INVENTION In one aspect of the present invention, in a distributed feedback semiconductor laser including an InP substrate and a multiple layer structure formed on a main surface of the InP substrate, the multiple layer structure includes at least an active layer for emitting laser light and a periodical structure for distributed feedback of the laser light, and the periodical structure includes a plurality of semiconductor regions each having a triangular cross section in a direction perpendicular to the main surface of the InP substrate and parallel to a cavity length of the distributed feedback semiconductor laser, the triangular cross section projecting toward the InP substrate.
In still another aspect of the present invention, a distributed feedback semiconductor laser includes a semiconductor substrate having a first cladding layer of a first conductivity type having a bandgap λg1; and a striped multiple layer structure including a first part and a second part which are optically coupled to each other due to continuity of the striped multiple layer structure along an identical optical axis. The first part includes a cavity structure including a multiple quantum well active layer having a bandgap wavelength λg2, a first optical waveguide layer of the first conductivity type having a bandgap wavelength λg3, a second cladding layer of a second conductivity type having a bandgap wavelength λg1, and a quantum well light absorption layer which has a bandgap wavelength λg4 and is buried between the first optical waveguide layer and the semiconductor substrate to form an absorption type diffraction grating periodical in a direction of the optical axis. The second part includes a buried quantum well layer having a bandgap wavelength λg6, a second optical waveguide layer having a bandgap wavelength λg2, a multiple quantum well light modulation layer having a bandgap wavelength λg5, and a third cladding layer of the second conductivity type having a bandgap wavelength λg1. The quantum well light absorption layer in the first part and the buried quantum well layer in the second part are formed in the same growth step simultaneously, the first optical waveguide layer in the first part and the second optical waveguide layer in the second part are formed in the same growth step simultaneously, the multiple quantum well active layer in the first part and the multiple quantum well light modulation layer in the second part are formed in the same growth step simultaneously, and the second cladding layer in the first part and the third cladding layer in the second part are formed in the same growth step simultaneously. The bandgap wavelengths have the relationship of λg4>λg2>λg3≧λg1, λg6<λg4, and λg5<λg2. A Bragg wavelength λB determined by an effective refractive index of the cavity in the first part and the periodicity of the absorption type diffraction grating is set in a range including λg2.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cut isometric view of a DFB laser in a first example according to the present invention;
FIGS. 3A through 3C are cross sectional views illustrating a specific part of the method for producing the DFB laser shown in FIG. 1;
FIGS. 19A through 19C are cross sectional views illustrating a method for producing the conventional DFB laser shown in FIG. 18;
EXAMPLE 1 FIG. 1 is a partially cut isometric view of a DFB laser 100 in a first example according to the present invention.
Thereafter, as is shown in FIG. 2D, the mesa stripe is formed by etching. Then, the p-type InP current blocking layer 8, the n-type InP current blocking layer 9, the p-type InP burying layer 10, and the p-type InGaAsP contact layer 11 are sequentially grown by liquid phase epitaxy. The insulation layer 12 formed of SiO2 is deposited on the p-type InGaAsP contact layer 11 and a stripe-shaped window is formed. Then, the p-type electrode 13 is formed by evaporation. On the bottom surface of the n-type InP substrate 1, the n-type electrode 14 is formed by evaporation. The resultant body is cleaved to obtain the DFB laser 100 of FIG. 1 as is shown in FIG. 2E.
FIG. 3A is a cross sectional view of the n-type InP substrate 1 having the corrugations 2 formed by etching. By heating the n-type InP substrate 1 with the corrugations 2 in a hydrogen atmosphere mixed with phosphine (PH3) and arsine (AsH3), the InAsP absorption layers 3 are formed in the grooves of the corrugations 2 by mass-transport during heating, as is shown in FIG. 3B. By growing the n-type InP cladding layer 4, the InAsP absorption layers 3 having an inverted triangular cross section and arranged periodically are obtained. From the point of light absorbance, the thickness of each InAsP absorption layer 3 is preferably 10 nm or more.
EXAMPLE 2 FIG. 9 is a partially cut isometric view of a DFB laser 200 in a second example according to the present invention. Identical elements as those in the first example will bear identical reference numerals therewith and a description thereof will be omitted.
Thereafter, as is shown in FIG. 10E, the mesa stripe is formed by etching. Then, the p-type InP current blocking layer 8, the n-type InP current blocking layer 9, the p-type InP burying layer 10, and the p-type InGaAsP contact layer 11 are sequentially grown by liquid phase epitaxy. The insulation layer 12 formed of SiO2 is deposited on the p-type InGaAsP contact layer 11 and a stripe-shaped window is formed. Then, the p-type electrode 13 is formed by evaporation. On the bottom surface of the n-type InP substrate 1, the n-type electrode 14 is formed by evaporation. The resultant body is cleaved to obtain the DFB laser 200 of FIG. 9 as is shown in FIG. 10F.
EXAMPLE 3 FIG. 11 is a partially cut isometric view of a DFB laser 300 in a third example according to the present invention. Identical elements as those in the first example will bear identical reference numerals therewith and a description thereof will be omitted.
Then, as is shown in FIG. 12E, the mesa stripe is formed by etching. The p-type InP current blocking layer 8, the n-type InP current blocking layer 9, the p-type InP burying layer 10, and the p-type InGaAsP contact layer 11 (λg=1.3 μm) are sequentially grown by liquid phase epitaxy. The insulation layer 12 formed of SiO2 is deposited on the p-type InGaAsP contact layer 11 and a stripe-shaped window is formed. Then, the p-type electrode 13 is formed by evaporation. On the bottom surface of the n-type InP substrate 1, the n-type electrode 14 is formed by evaporation. The resultant body is cleaved to obtain the DFB laser 300 of FIG. 11 as is shown in FIG. 12F.
EXAMPLE 4 FIG. 13 is a partially cut isometric view of a DFB laser 400 in a fourth example according to the present invention. Identical elements as those in the first example will bear identical reference numerals therewith and a description thereof will be omitted.
Thereafter, as is shown in FIG. 14E, the mesa stripe is formed by etching. Then, the p-type InP current blocking layer 8, the n-type InP current blocking layer 9, the p-type InP burying layer 10, and the p-type InGaAsP contact layer 11 (λg=1.3 μm) are sequentially grown by liquid phase epitaxy. The insulation layer 12 formed of SiO2 is deposited on the p-type InGaAsP contact layer 11 and a stripe-shaped window is formed. Then, the p-type electrode 13 is formed by evaporation. On the bottom surface of the n-type InP substrate 1, the n-type electrode 14 is formed by evaporation. The resultant body is cleaved to obtain the DFB laser 400 of FIG. 13 as is shown in FIG. 14F.
EXAMPLE 5 FIG. 15 is a partially cut isometric view of a DFB laser 500 in a third example according to the present invention. Identical elements as those in the first example will bear identical reference numerals therewith and a description thereof will be omitted.
Then, as is shown in FIG. 16E, the mesa stripe is formed by etching. The p-type InP current blocking layer 8, the n-type InP current blocking layer 9, the p-type InP burying layer 10, and the p-type InGaAsP contact layer 11 (λg=1.3 μm) are sequentially grown by liquid phase epitaxy. The insulation layer 12 formed of SiO2 is deposited on the p-type InGaAsP contact layer 11 and a stripe-shaped window is formed. Then, the p-type electrode 13 is formed by evaporation. On the bottom surface of the n-type InP substrate 1, the n-type electrode 14 is formed by evaporation. The resultant body is cleaved to obtain the DFB laser 500 of FIG. 15 as is shown in FIG. 16F.
EXAMPLE 6 A DFB laser having an integrated modulator is expected as a light source generating an excessively low level of wavelength chirp. With the conventional structure, the production yield is not sufficiently high. In the case of gain coupled type DFB lasers, the production yield in terms of laser oscillation having a single wavelength is satisfactory, but the level of wavelength chirp cannot be sufficiently low.
Next, the n-type InGaAsP optical waveguide layer 55, the undoped InGaAsP MQW active layer 56, the p-type InP cladding layer 58A, and the p-type InGaAsP contact layer 59 are grown on the entire top surface of the n-type InP substrate 51, covering the n-type InGaAs absorption type diffraction grating. In the area corresponding to the modulation part 72, the semiconductor layers thus grown are removed. In detail, an area of a top surface of the p-type InGaAsP contact layer 59 corresponding to the emission part 71 is masked by SiO2, and the resultant lamination is etched by a mixture solution of H2 SO4 :H2 O2 :H2 O=5:1:1 to remove a part of the p-type InGaAsP contact layer 59 corresponding to the modulation part 72. Then, the p-type InP cladding layer 58A is etched by a mixture of HCl:H3 PO4 =1:2, the undoped InGaAsP MQW active layer 56 and the n-type InGaAsP optical waveguide layer 55 are etched by H2 SO4 :H2 O2 :H2 O=5:1:1, to remove a part of the respective layers corresponding to the modulation part 72.
On the area of the n-type InP substrate 51 exposed by such etching, the undoped InGaAsP light modulation layer 57 and the p-type InP cladding layer 58B are grown by a third step of MOVPE. Thus, the modulation part 72 is formed.
Even in the case when the reflectivity of the front end is 0.2%, such a yield of the DFB laser 600 is approximately the same as the yield of the conventional DFB laser obtained when the reflectivity is only 0.1%. This indicates that less strictness is allowed for controlling the thickness of the reflection film in the production of the DFB laser, which facilitates the production. Such freedom in the production makes possible to form a window structure in the vicinity of the front end, and also to provide a semi-insulation layer between the emission part 71 and the modulation part 72 for increasing th e resistance between the emission part 71 and the modulation part 72. Needless to say, these extra steps improve the characteristics of the DFB laser 600.
EXAMPLE 7 FIG. 21 is a cross sectional view along the cavity length direction of a DFB laser 700 in a seventh example according to the present invention. Identical elements as those in the sixth example will bear identical reference numerals therewith and a description thereof will be omitted.
EXAMPLE 8 FIG. 22 is a cross sectional view along the cavity length direction of a DFB laser 800 in an eighth example according to the present invention. Identical elements as those in the sixth example will bear identical reference numerals therewith and a description thereof will be omitted.
EXAMPLE 9 FIG. 23 is a cross sectional view along the cavity length direction of a DFB laser 900 in a ninth example according to the present invention. Identical elements as those in the sixth example will bear identical reference numerals therewith and a description thereof will be omitted.
After an area of a top surface of the p-type InP cladding layer 58 corresponding to the emission part 71 is covered with a SiO2 mask, the n-InGaAs contact layer in the area corresponding to the modulation part 72 is selectively etched away by a mixture solution of H2 SO4 :H2 O2 :H2 O=5:1:1. Then, the p-type InP cladding layer is etched by a mixture of HCl:H3 PO4 =1:2, the undoped InGaAsP MQW active layer 56 and the n-type InGaAsP a optical waveguide layer 55 are etched by H2 SO4 :H2 O2 :H2 O=5:1:1, to remove a part of the respective layers corresponding to the modulation part 72.
EXAMPLE 10 FIG. 24 is a cross sectional view along the cavity length direction of a DFB laser 1000 in a tenth example according to the present invention. Identical elements as those in the sixth example will bear identical reference numerals therewith and a description thereof will be omitted.
In more detail, the emission part 71 includes a plurality of n-type InAsP light absorption layers 52 formed on corrugations formed at a surface of the n-type InP substrate 51 to form a diffraction grating periodically arranged at a pitch of 201 nm (λg=1.4 μm), an n-type InGaAsP optical waveguide layer 55 (cladding layer) (λg=1.05 μm; thickness: 150 nm), an undoped InGaAsP MQW active layer 56, a p-type InP cladding layer 58, a p-type InGaAsP contact layer 59, and a p-type electrode 60 which are laminated on the n-type J-P substrate 51 in this order. The n-type InAsP light absorption layers 52 absorb the light from the MQW active layer 56.
The modulation part 72 includes an n-type InGaAsP optical waveguide layer 55 (λg=1.05 μm; thickness: 70 nm), an undoped InGaAsP light modulation layer 57, a p-type InP cladding layer 58, and a p-type electrode 61 which are laminated on the n-type InP substrate 51 in this order. The n-type InP substrate 51 has an n-type electrode 62 on a bottom surface thereof.
The DFB laser 1000 has the same structure with the DFB laser 800 shown in FIG. 22 except for the n-type InGaAs light absorption layers 52 forming the diffraction grating.
The n-type InGaAs light absorption layers 52 are formed in stripes in accordance with corrugations formed at a top surface of the n-type InP substrate 51. Each stripe of the n-type InGaAs light absorption layers 52 are extended in a direction perpendicular to the cavity length direction and selectively formed in an area corresponding to the emission part 71. The n-type InGaAs light absorption layers 52 each have a maximum thickness of 20 nm (effective λg=1.6 μm) in the groove of the corrugations but have a thickness of only several nanometers or less (PL wavelength>1.3 μm) on the ridge of the corrugations. The thickness of the n-type InGaAs light absorption layers 52 changes periodically in accordance with the corrugations of the n-type InP substrate 51. Thus, the thickness of the n-type InGaAs light absorption layers 52 changes periodically in accordance with the positional change in the bandgap. In this example, the n-type InGaAs light absorption layers 52 need not be separated from each other, but it is sufficient as long as the thickness thereof changes periodically in the cavity length direction. The n-type InGaAs light absorption layers 52 can be separated from each other, in which case no layer is existent on the ridges of the corrugations. In the modulation part 72, the thickness of the n-type InGaAs light absorption layers 52 is 4 nm.
EXAMPLE 11 Next, referring to FIG. 26, a distributed Bragg reflective laser (DBR) laser in the eleventh example according to the present invention will be described. FIG. 26 is a cross sectional view along the cavity length direction of a DBR laser in the eleventh example according to the present invention.
EXAMPLE 12 Next, referring to FIG. 27, a DBR laser in a twelfth example according to the present invention will be described. FIG. 27 is a cross sectional view along the cavity length direction of a DBR laser in the twelfth example according to the present invention.
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Lett., vol. 56, No. 17, pp. 1620 1622, 1990.* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS6426515 *Mar 30, 2001Jul 30, 2002Fujitsu LimitedSemiconductor light-emitting deviceUS7816160Aug 29, 2008Oct 19, 2010Mitsubishi Electric CorporationManufacturing method for semiconductor device* Cited by examinerClassifications U.S. Classification438/44, 438/42, 117/953, 438/46International ClassificationH01S5/227, H01S5/0625, H01L21/205, H01S5/323, H01S5/026, H01S5/125, H01S5/20, H01S5/343, H01S5/12Cooperative ClassificationH01S5/1231, H01L21/02392, H01L21/02463, H01S5/1228, H01S5/34373, H01S5/2275, H01S5/2077, H01L21/02546, H01S5/12, H01S5/34306, H01L21/02461, B82Y20/00, H01L21/0262, H01S5/32391, H01L21/02505, H01S5/3434, H01S5/0265, H01S5/06256, H01S5/2272, H01S5/125, H01L21/02543, H01L21/0243, H01L21/02513, H01S5/2081European ClassificationB82Y20/00, H01S5/125, H01L21/205C, H01S5/026F, H01S5/12G, H01S5/12Legal EventsDateCodeEventDescriptionOct 14, 2008FPExpired due to failure to pay maintenance feeEffective date: 20080822Aug 22, 2008LAPSLapse for failure to pay maintenance feesMar 3, 2008REMIMaintenance fee reminder mailedJan 21, 2004FPAYFee paymentYear of fee payment: 4RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google