Reflector, surface-emitting laser, solid-state laser device, optoacoustic system, and image-forming apparatus

• US 9,590,391 B2
• Filed: 08/05/2014
• Issued: 03/07/2017
• Est. Priority Date: 10/10/2013
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Kawashima, Takeshi
• Primary Examiner(s): BRASE, SANDRA L
• Application Number:
  US15/028,320
• Publication Number:
  US 20160268774A1
• Time in Patent Office: 945 Days
• US Class Current: 1/1
• CPC Class Codes: B41J 2/447 using arrays of radiation sources B41J2/475 takes precedence
• CPC Class Codes: B41J 2/473 using multiple light beams, wavelengths or colours
• CPC Class Codes: G03G 15/04036 Details of illuminating systems, e.g. lamps, reflectors lamp housings for copying cameras, reflex exposure lighting G03B27/542
• CPC Class Codes: H01L 21/02458 Nitrides
• CPC Class Codes: H01L 21/02507 Alternating layers, e.g. superlattice
• CPC Class Codes: H01L 21/0254 Nitrides
• CPC Class Codes: H01L 21/0262 Reduction or decomposition of gaseous compounds, e.g. CVD
• CPC Class Codes: H01S 3/0941 of a laser diode
• CPC Class Codes: H01S 5/0212 with a graded composition
• CPC Class Codes: H01S 5/18361 Structure of the reflectors, e.g. hybrid mirrors

Abstract

In a reflector including an AlGaN layer, an InGaN layer, and a GaN layer placed therebetween, high reflectivity and a wide reflection band are achieved. A reflector includes a substrate containing GaN; first layers containing Al_xGa_1-xN; second layers containing In_yGa_1-yN; and a third layer containing GaN, the first, second, and third layers being stacked on the substrate. The first and second layers are alternately stacked, the third layer is placed between one of the first layers and one of the second layers, x and y satisfy a specific formula, the first layers have a thickness less than the thickness of the second layers, and the second layers have an optical thickness of λ/8 to 3λ/8, where λ is the central wavelength of the reflection. band of the reflector.

Claims

1. A reflector comprising:

a substrate containing GaN;

first layers containing Al_xGa_1-xN;

second layers containing In_yGa_1-yN; and

a third layer containing GaN, the first, second, and third layers being stacked on the substrate,

wherein the first and second layers are alternately stacked, the third layer is placed between one of the first layers and one of the second layers,

wherein x in Al_xGa_1-x,N and y in In_yGa_1-yN satisfy the inequality 0.00<

4.66y<

x≦

1.00,

wherein the first layers have a thickness less than the thickness of the second layers, and

wherein the second layers have an optical thickness of λ

/8 to 3λ

/8, where λ

is the central wavelength of the reflection band of the reflector.

2. The reflector according to claim 1, wherein the second layers have an optical thickness of 3λ

/16 to 5λ

/16.

3. The reflector according to claim 1, wherein the third layer is placed between one of the second layers and one of the first layers that is located on a side opposite to a substrate side with respect to the one of the second layers and that is closest to the one of second layers.

4. The reflector according to claim 3, further comprising a fourth layer, wherein the fourth layer is placed between one of the second layers and one of the first layers that is located on a side close to the substrate with respect to the one of the second layers and that is closest to the one of the second layers.

5. The reflector according to claim 4, wherein the fourth layer has a thickness of 5 nm or more.

6. The reflector according to claim 4, wherein the fourth layer has a thickness less than the thickness of the first layers.

7. The reflector according to claim 4, wherein the fourth layer has a thickness less than or equal to half the thickness of the first layers.

8. The reflector according to claim 1, wherein the third layer has a thickness of 5 nm or more.

9. The reflector according to claim 1, wherein the third layer has a thickness less than the thickness of the first layers.

10. The reflector according to claim 1, wherein the third layer has a thickness less than or equal to half the thickness of the first layers.

11. The reflector according to claim 1, wherein y in In_yGa_1-yN is 0.02 to 0.21.

12. The reflector according to claim 1, wherein y in In_yGa_1-yN is 0.02 to 0.11.

13. The reflector according to claim 1, wherein y in In_yGa_1-yN is 0.02 to 0.09.

14. The reflector according to claim 1, wherein x in Al_xGa_1-xN is 0.09 to 0.50.

15. The reflector according to claim 1, wherein x in Al_xGa_1-x,N is 0.09 to 0.40.

16. The reflector according to claim 1, wherein the following inequality is satisfied:

0.80≦

|ε

₂t₂|/|ε

₁t₁|≦

1.20

where ε

₁ is the strain of the first layers, t₁ is the thickness of the first layers, ε

₂ is the strain of the second layers, and t₂ is the thickness of the second layers.

17. A surface-emitting laser comprising:

a pair of reflectors; and

an active layer placed between the reflectors,

wherein at least one of the reflectors is the reflector according to claim 1.

18. A solid-state laser device comprising:

the surface-emitting laser according to claim 17; and

a solid-state laser medium excited by light emitted by the surface-emitting laser.

19. An optoacoustic system comprising:

the solid-state laser device according to claim 18;

a probe which detects an elastic wave generated by irradiating a sample with light emitted by the solid-state laser device and which converts the elastic wave into an electrical signal; and

an acquisition unit which acquires information about optical properties of the sample on the basis of the electrical signal.

20. An image-forming apparatus comprising:

the surface-emitting laser according to claim 17; and

a photosensitive drum exposed to light emitted by the surface-emitting laser.