Optical semiconductor device and method of fabricating the same

• US 6,383,829 B1
• Filed: 09/22/2000
• Issued: 05/07/2002
• Est. Priority Date: 12/05/1996
• Status: Expired due to Fees

• Current Assignee: NEC Electronics Corporation (Renesas Electronics Corporation)
• Original Assignee: NEC Corporation
• Inventors: Sakata, Yasutaka
• Primary Examiner(s): Fahmy, Wael
• Assistant Examiner(s): TOLEDO, FERNANDO L
• Application Number:
  US09/667,524
• Time in Patent Office: 592 Days
• Field of Search: 438/31, 438/65, 257/9.14, 372/45, 654/06
• US Class Current: 438/31
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 2006/12123 Diode
• CPC Class Codes: G02B 2006/12173 Masking
• CPC Class Codes: G02B 2006/12176 Etching
• CPC Class Codes: G02B 2006/12178 Epitaxial growth
• CPC Class Codes: G02B 2006/12195 Tapering
• CPC Class Codes: G02B 6/1228 Tapered waveguides, e.g. integrated spot-size transformers for coupling with fibres G02B6/305
• CPC Class Codes: H01S 2301/18 Semiconductor lasers with special structural design for influencing the near- or far-field
• CPC Class Codes: H01S 2304/04 MOCVD or MOVPE
• CPC Class Codes: H01S 5/10 Construction or shape of the optical resonator , e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region H01S5/20 takes precedence
• CPC Class Codes: H01S 5/1014 Tapered waveguide, e.g. spotsize converter H01S5/1064 takes precedence
• CPC Class Codes: H01S 5/106 varying thickness along the optical axis
• CPC Class Codes: H01S 5/2077 using lateral bandgap control during growth, e.g. selective growth, mask induced
• CPC Class Codes: H01S 5/227 Buried mesa structure ; Striped active layer
• CPC Class Codes: H01S 5/2272 grown by a mask induced selective growth
• CPC Class Codes: H01S 5/34 comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers H01S5/36 takes precedence
• CPC Class Codes: H01S 5/3409 special GRINSCH structures
• CPC Class Codes: H01S 5/3421 layer structure of quantum wells to influence the near/far field
• CPC Class Codes: H01S 5/34306 emitting light at a wavelength longer than 1000nm, e.g. InP based 1300 and 1500nm lasers
• CPC Class Codes: H01S 5/34313 with a well layer having only As as V-compound, e.g. AlGaAs, InGaAs
• CPC Class Codes: H01S 5/3434 : with a well layer comprising at least both As and P as V-compounds
• CPC Class Codes: H01S 5/50 : Amplifier structures not provided for in groups H01S5/02 - H01S5/30

Abstract

There is provided an optical semiconductor device including an optical waveguide structure having a quantum well layer and an optical confinement layer as a core layer, wherein the core layer has a thickness varying in a lengthwise direction of the optical waveguide to thereby have a function of spot-size conversion, and the quantum well layer is designed to have a band-gap energy which is constant within ±30 meV in the direction. The above-mentioned optical semiconductor device makes it possible to an optical gain to laser oscillation wavelength over all ranges of a resonator, and hence makes it no longer necessary to form a region only for spot-size conversion (SSC). This ensures that a device length can be as small as that of a conventional laser diode. In addition, lower threshold value characteristic and high temperature operation performance could be achieved, and a yield in devices per a wafer can be significantly enhanced.

Claims

1. A method of fabricating an optical semiconductor device including an optical waveguide having a thickness varying in a lengthwise direction thereof, comprising the steps of:

(a) forming a pair of dielectric masks on a compound semiconductor substrate, said masks including a portion where a width thereof varies in said direction;

(b) epitaxially growing a lower optical confinement layer by metal-organic vapor phase epitaxy (MOVPE) selective growth;

(c) forming a quantum well structure by epitaxially growing a quantum well layer or a plurality of quantum well layers with barrier layers sandwiched between said quantum well layers by metal-organic vapor phase epitaxy (MOVPE) selective growth; and

(d) epitaxially growing an upper optical confinement layer by metal-organic vapor phase epitaxy (MOVPE) selective growth,

said quantum well layer or plurality of quantum well layers being grown in said step (c) under a growth pressure lower than that of said lower and upper optical confinement layers in said steps (b) and (d).

2. The method as set forth in claim 1, wherein said barrier layers are grown in said step (c) under a growth pressure equal to or greater than that of said quantum well layers.

3. The method as set forth in claim 1, wherein said barrier layers are grown in said step (c) under a pressure equal to or greater than 100 hPa.

4. The method as set forth in claim 3, wherein said barrier layers are grown under a pressure equal to or greater than 200 hPa.

5. The method as set forth in claim 1, wherein said quantum well layer(s) is(are) grown in said step (c) under a growth pressure equal to or smaller than 40 hPa.

6. The method as set forth in claim 5, wherein said quantum well layer(s) is(are) grown under a growth pressure equal to or smaller than 30 hPa.

7. The method as set forth in claim 1, wherein said lower and upper optical confinement layers are grown in said steps (b) and (d) under a growth pressure equal to or greater than 100 hPa.

8. The method as set forth in claim 7, wherein said lower and upper optical confinement layers are grown under a growth pressure equal to or greater than 200 hPa.

9. A method of fabricating an optical semiconductor device including an optical waveguide having a thickness varying in a lengthwise direction thereof, comprising the steps of:

(a) forming a pair of dielectric masks on a compound semiconductor substrate, said masks including a portion where a width thereof varies in said direction;

(b) epitaxially growing a lower optical confinement layer by metal-organic vapor phase epitaxy (MOVPE) selective growth;

(c) forming a quantum well structure by epitaxially growing a quantum well layer or a plurality of quantum well layers with barrier layers sandwiched between said quantum well layers by metal-organic vapor phase epitaxy (MOVPE) selective growth; and

(d) epitaxially growing an upper optical confinement layer by metal-organic vapor phase epitaxy (MOVPE) selective growth,

said quantum well layer(s) being grown in said step (c) employing tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) having a V/III ratio equal to or greater than 50.

10. The method as set forth in claim 9, wherein said lower and upper optical confinement layers are grown in said steps (b) and (d) employing arsine and phosphine as group V source materials.

11. The method as set forth in claim 9, wherein said lower and upper optical confinement layers are grown in said steps (b) and (d) employing tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) having a V/III ratio equal to or smaller than 5.

12. The method as set forth in claim 9, wherein said barrier layers are grown in said step (c) employing arsine and phosphine as group V source materials.

13. The method as set forth in claim 9, wherein said barrier layers are grown in said step (c) employing tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) having a V/III ratio equal to or smaller than 5.

14. A method of fabricating an optical semiconductor device including an optical waveguide, comprising the steps of:

(a) forming a pair of dielectric masks on a compound semiconductor substrate, said masks including a portion where a width thereof varies in a lengthwise direction of said optical waveguide;

(b) selectively growing a lower confinement layer by metal-organic vapor phase epitaxy (MOVPE);

(c) selectively growing a quantum well layer or a plurality of quantum well layers with barrier layers sandwiched between said quantum well layers, of a quantum well structure on said compound substrate by MOVPE; and

(d) selectively growing an upper confinement layer by MOVPE;

said step of selectively growing a quantum well layer or a plurality of quantum well layers of said quantum well structure providing a band-gap energy which is constant within ±

30 meV in said lengthwise direction, and steps (b), (c) and (d) collectively providing an optical waveguide having a thickness varying in said lengthwise direction to thereby have a function of spot-size conversion.

15. A method of fabricating an optical semiconductor device including an optical waveguide, comprising the steps of:

(a) forming a pair of dielectric masks on a compound semiconductor substrate, said masks including a portion where a width thereof varies in a lengthwise direction of said optical waveguide;

(b) selectively growing a lower confinement layer by metal-organic vapor phase epitaxy (MOVPE);

(c) selectively growing a quantum well layer or a plurality of quantum well layers with barrier layers sandwiched between said quantum well layers, of a quantum well structure on said compound substrate by MOVPE, said quantum well structure having a constant thickness in said lengthwise direction; and

(d) selectively growing an upper confinement layer by MOVPE;

said lower and upper confinement layers selectively growing in steps (b) and (d) to a thickness varying in said lengthwise direction.

16. The method as set forth in claim 15, further comprising the step of growing said lower and upper optical confinement layers to a thickness having a maximum at a center in said lengthwise direction.

17. A method of fabricating an optical semiconductor device including an optical waveguide having a thickness varying in a lengthwise direction thereof, comprising the steps of:

(a) forming a pair of dielectric masks on a compound semiconductor substrate, said masks including a portion where a width thereof varies in said lengthwise direction;

(b) selectively growing a lower confinement layer, forming a lower optical confinement layer having a thickness varying in said lengthwise direction, by metal-organic vapor phase epitaxy (MOVPE);

(c) forming a quantum well structure by epitaxially growing a quantum well layer or a plurality of quantum well layers with barrier layers sandwiched between said quantum well layers by MOVPE, epitaxially growing each quantum well layer with a thickness substantially constant in said lengthwise direction; and

(d) selectively growing an upper confinement layer, forming an upper optical confinement layer having a thickness varying in said lengthwise direction, by MOVPE.

18. The method as set forth in claim 17, further comprising forming said barrier layers with a thickness varying in said lengthwise direction.