Surface-emitting laser array, optical scanning device, and image forming device

Abstract

A surface-emitting laser array includes a plurality of surface-emitting laser elements. Each surface-emitting laser element includes a first reflection layer formed on a substrate, a resonator formed in contact with the first reflection layer and containing an active layer, and a second reflection layer formed over the first reflection layer and in contact with the resonator. The second reflection layer contains a selective oxidation layer. The first reflection layer contains on the active layer side at least a low refractive index layer having an oxidation rate equivalent to or larger than an oxidation rate of a selective oxidation layer contained in the second reflection layer. The resonator is made of an AlGaInPAs base material containing at least In. A bottom of a mesa structure is located under the selective oxidation layer and over the first reflection layer.

1 . A surface-emitting laser array including a plurality of surface-emitting laser elements, each of the plurality of surface-emitting laser elements comprising:
 a first reflection layer formed on a substrate to constitute a semiconductor Bragg reflector;   a resonator formed in contact with the first reflection layer and containing an active layer; and   a second reflection layer formed over the first reflection layer and in contact with the resonator to constitute the semiconductor Bragg reflector, the second reflection layer containing a selective oxidation layer therein,   wherein the first reflection layer contains on the active layer side at least a low refractive index layer having an oxidation rate equivalent to or larger than an oxidation rate of a selective oxidation layer contained in the second reflection layer, the resonator is made of an AlGaInPAs base material containing at least In, and a bottom of a mesa structure in each surface-emitting laser element is located under the selective oxidation layer and over the first reflection layer.   
     
     
         2 . The surface-emitting laser array of  claim 1 , wherein the resonator has an etching rate smaller than an etching rate of the second reflection layer. 
     
     
         3 . The surface-emitting laser array of  claim 1 , wherein the second reflection layer containing on the active layer side a layer made of the AlGaInPAs base material containing at least In. 
     
     
         4 . The surface-emitting laser array of  claim 1 , wherein the bottom of the mesa structure is located inside the resonator or at an interface between the second reflection layer and the resonator. 
     
     
         5 . The surface-emitting laser array of  claim 1 , wherein the first reflection layer contains the low refractive index layer, which is made of AlAs, over an entire area of the surface-emitting laser element. 
     
     
         6 . The surface-emitting laser array of  claim 1 , wherein the selective oxidation layer contained in the second reflection layer constitutes a selective oxidation type current narrowing portion. 
     
     
         7 . The surface-emitting laser array of  claim 1 , wherein a difference between an etching depth in an inter-element gap of the plurality of surface-emitting laser elements and an etching depth of a peripheral portion of the plurality of surface-emitting laser elements is equal to or smaller than ½ of a beam-emission wavelength of each surface-emitting laser element. 
     
     
         8 . The surface-emitting laser array of  claim 7 , wherein the inter-element gap between two adjacent ones of the plurality of surface-emitting laser elements is set to a smaller one of a gap between top surface positions of two mesa structures in the plurality of surface-emitting laser elements and a gap between bottom surface positions of the two mesa structures, and is equal to or smaller than 20 micrometers. 
     
     
         9 . The surface-emitting laser array of  claim 1 , wherein a side of the first reflection layer is covered by a protection film. 
     
     
         10 . The surface-emitting laser array of  claim 9 , wherein the protection film is made of any of SiO 2 , SiN and SiON. 
     
     
         11 . The surface-emitting laser array of  claim 1 , wherein a content of aluminum of the low refractive index layer arranged on the resonator side of the first reflection layer is larger than a content of aluminum of the selective oxidation layer. 
     
     
         12 . The surface-emitting laser array of  claim 1 , wherein a content of aluminum of a low refractive index layer arranged on the resonator side of the first reflection layer is the same as a content of aluminum of the selective oxidation layer, and a thickness of the low refractive index layer arranged on the resonator side of the first reflection layer is larger than a thickness of the selective oxidation layer. 
     
     
         13 . An optical scanning device comprising:
 the surface-emitting laser array according to  claim 1 ;   a deflection unit deflecting a plurality of laser beams emitted by the surface-emitting laser array, and   a scanning optical element drawing the laser beams from the deflection unit on a scanned surface of a photoconductor.   
     
     
         14 . An image forming device in which the optical scanning device according to  claim 13  is provided. 
     
     
         15 . An image forming device in which the surface-emitting laser array according to  claim 1  is provided as a light source emitting a plurality of laser beams. 
     
     
         16 . A surface-emitting laser element having a mesa structure which emits a laser beam, comprising:
 a substrate;   a first reflection layer formed on the substrate to constitute a semiconductor Bragg reflector;   a resonator formed in contact with the first reflection layer and containing an active layer;   a second reflection layer formed in contact with the resonator to constitute the semiconductor Bragg reflector; and   an absorption layer arranged to absorb a difference of an etching depth in an in-surface direction of the substrate when forming the mesa structure,   wherein a bottom of the mesa structure is located in the absorption layer in a direction perpendicular to the substrate, and the absorption layer is formed in at least a part of the resonator in a thickness direction of the resonator.   
     
     
         17 . The surface-emitting laser element of  claim 16 , wherein the absorption layer is formed in an entire area of the resonator in a thickness direction of the resonator. 
     
     
         18 . The surface-emitting laser element of  claim 16 , wherein the absorption layer is formed in an entire area of the resonator in a thickness direction of the resonator and formed partially in a thickness direction of the second reflection layer. 
     
     
         19 . The surface-emitting laser element of  claim 16 , wherein the absorption layer contains at least In. 
     
     
         20 . A method of manufacturing a surface-emitting laser array, the surface-emitting laser array including: an element-arrangement portion provided on a substrate and having a plurality of surface-emitting laser elements arranged; and a flat part provided on the substrate and arranged in a circumference of the element-arrangement portion in an in-surface direction of the substrate, each of the plurality of surface-emitting laser elements including a mesa structure which emits a laser beam, and the flat part and the element-arrangement portion including an absorption layer arranged to absorb a difference of an etching depth in the in-surface direction when forming the mesa structure, the method comprising the steps of:
 forming a multilayer semiconductor film on the substrate; and   etching the multilayer semiconductor film to cause a bottom of the mesa structure to be located in the absorption layer, so that the element-arrangement portion and the flat part are formed.