Surface emitting laser element, surface emitting laser array, optical scanning device, and image forming apparatus

1. A surface emitting laser element which emits light in a direction perpendicular to a surface of a substrate of the surface emitting laser element, comprising:

a resonator structural body including an active layer; and

first and second semiconductor distributed Bragg reflectors which sandwich the resonator structural body and include a confinement structure which can confine an injection current and a lateral mode of oscillation light at the same time by surrounding a current passing through region with an oxide containing at least an oxide formed by oxidizing a part of a layer to be selectively oxidized containing aluminum; wherein

a thickness of the layer to be selectively oxidized is at least 25 nm; and

a temperature when an oscillation threshold current becomes a minimum value is 25 ° C. or less in a relationship between the temperature and the oscillation threshold current; and

wherein:

when a rectangular current pulse whose pulse period is 1 ms and whose pulse width is 500 μs is supplied to the surface emitting laser element, a relationship of (P1−P2)/P2≧−0.1 is satisfied when a light output after 10 ns of the pulse being supplied is defined as P1 and a light output after 1 μs of the pulse being supplied is defined as P2.

2. The surface emitting laser element as claimed in claim 1 , wherein:

when a width of the current passing through region is defined as “d” μm, and a thickness of the oxide surrounding the current passing through region is defined as “t” nm, a relationship of (−2.54d 2 −0.14t 2 −0.998d·t+53.4d+12.9t−216 ≧0.9) is satisfied.

3. The surface emitting laser element as claimed in claim 1 , wherein:

a part of plural semiconductor layers including the resonator structural body and the first and second semiconductor distributed Bragg reflectors has a mesa shape of a column shape or a quadrangular prism shape extending in a light emitting direction, and

the diameter of the column shape or the length of one side of the quadrangular prism shape in a cross section perpendicular to a light oscillation direction is at least 22 μm.

4. The surface emitting laser element as claimed in claim 1 , wherein:

a doping concentration of an impurity in a region adjacent to the resonator structural body in the first semiconductor distributed Bragg reflector is relatively lower than the doping concentration of the impurity in other regions in the first semiconductor distributed Bragg reflector.

5. The surface emitting laser element as claimed in claim 1 , wherein:

the first semiconductor distributed Bragg reflector includes plural pairs of a low refractive index layer and a high refractive index layer, and

the layer to be selectively oxidized is at a third pair or a fourth pair from the resonator structural body in the first semiconductor distributed Bragg reflector.

6. An optical scanning device which scans a surface to be scanned by light, comprising:

a light source which includes the surface emitting laser element as claimed in claim 1 ;

a deflector which deflects light from the light source; and

a scanning optical system which condenses light deflected by the deflector onto the surface to be scanned.

7. An image forming apparatus, comprising:

at least one image carrier; and

at least one of the optical scanning devices as claimed in claim 6 which scans light including image information onto the image carrier.

8. A surface emitting laser element which emits light in a direction perpendicular to a surface of a substrate of the surface emitting laser element, comprising:

a resonator structural body including an active layer; and

first and second semiconductor distributed Bragg reflectors which sandwich the resonator structural body and include a confinement structure which can confine an injection current and a lateral mode of oscillation light at the same time by surrounding current passing through region with an oxide containing at least an oxide formed by oxidizing a part of a layer to be selectively oxidized containing aluminum; wherein

a thickness of the layer to be selectively oxidized is at least 25 nm; and

a temperature when an oscillation threshold current becomes a minimum value is 25 ° C. or less in a relationship between the temperature and the oscillation threshold current; and ps wherein:

when only a temperature of a current injection region of the resonator structural body is changed from a room temperature to 60 ° C., a changing rate of a light confinement coefficient of a fundamental lateral mode in a lateral direction in the confinement structure is 10% or less.

9. A surface emitting laser element which emits light in a direction perpendicular to a surface of a substrate of the surface emitting laser element, comprising:

a resonator structural body including an active layer; and

first and second semiconductor distributed Bragg reflectors which sandwich the resonator structural body and include a confinement structure which can confine an injection current and a lateral mode of oscillation light at the same time by surrounding a current passing through region with an oxide containing at least an oxide formed by oxidizing a part of a layer to be selectively oxidized containing aluminum; wherein

a thickness of the layer to be selectively oxidized is at least 25 nm;

a maximum thickness of the oxide surrounding the current passing through region is 110 nm or less; and

a temperature when an oscillation threshold current becomes a minimum value is 25 ° C. or less in a relationship between the temperature and the oscillation threshold current; and

wherein:

when a rectangular current pulse whose pulse period is 1 ms and whose pulse width is 500 μs is supplied to the surface emitting laser element, a relationship of (P1 −P2)/P2≧−0.1 is satisfied when a light output after 10 ns of the pulse being supplied is defined as P1 and a light output after 1 μs of the pulse being supplied is defined as P2.

10. The surface emitting laser element as claimed in claim 9 , wherein:

when a width of the current passing through region is defined as “d” μm, and a thickness of the oxide surrounding the current passing through region is defined as “t” nm, a relationship of (−2.54d 2 −0.14t 2 −0.998d·t+53.4d+12.9t−216≧0.9) is satisfied.

11. The surface emitting laser element as claimed in claim 9 , wherein:

the layer to be selectively oxidized is a part of low refractive index layers of the first semiconductor distributed Bragg reflector;

the low refractive index layer including the layer to be selectively oxidized includes a first layer adjacent to the layer to be selectively oxidized and a second layer adjacent to the first layer; and

a content rate of aluminum in the first layer is lower than the content rate of aluminum in the layer to be selectively oxidized, and is higher than the content rate of aluminum in the second layer.

12. The surface emitting laser element as claimed in claim 11 , wherein:

an optical thickness of the low refractive index layer including the layer to be selectively oxidized is (2n+1)λ/4 (n is an integer of 1 or more) when an oscillation wavelength is defined as λ.

13. The surface emitting laser element as claimed in claim 11 , wherein:

a difference between the content rate of aluminum in the layer to be selectively oxidized and the content rate of aluminum in the first layer is 5% or more and 20% or less.

14. The surface emitting laser element as claimed in claim 11 , wherein:

a difference between the content rate of aluminum in the layer to be selectively oxidized and the content rate of aluminum in the second layer is more than 20%.

15. The surface emitting laser element as claimed in claim 9 , wherein:

a gain peak wavelength in the oscillation threshold current at a room temperature is longer than a resonance wavelength in the resonator structural body.

16. An optical scanning device which scans a surface to be scanned by light, comprising:

a light source which includes the surface emitting laser element as claimed in claim 9 ;

a deflector which deflects light from the light source; and

a scanning optical system which condenses light deflected by the deflector onto the surface to be scanned.

17. An image forming apparatus, comprising:

at least one image carrier; and

at least one of the optical scanning devices as claimed in claim 16 which scans light including image information onto the image carrier.