JP2007299896A - Surface-emitting laser element, surface-emitting laser array having same, and image forming apparatus having same laser array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-emitting laser element having its life time not shorter than a reference value. <P>SOLUTION: The surface-emitting laser element 10 has a substrate 1, reflecting layers 2, 6, cavity spacer layers 3, 5, an active layer 4, a selectively oxidized layer 7, a contact layer 8, a passivation film 9, a wiring electrode 11, and an n-side electrode 12. The element 10 is produced by laminating successively on the substrate 1 the reflecting layer 2, the cavity spacer layer 3, the active layer 4, the cavity spacer layer 5, the reflecting layer 6, the selectively oxidized layer 7, and the contact layer 8. Further, the element constitutes a mesa structure 20 by using the active layer 4, the cavity spacer layer 5, the reflecting layer 6, the selectively oxidized layer 7, and the contact layer 8. The passivation film 9 is so formed as to be contacted with the mesa structure 20, the wiring electrode 11 is formed on a portion of the contact layer 8 and on the passivation film 9. and further, the n-side electrode 12 is formed on the rear surface of the substrate 1. The passivation film 9 has the total stress of -6×10<SP>4</SP>dyn/cm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface emitting laser element, a surface emitting laser array including the same, and an image forming apparatus including the surface emitting laser array.

  Surface emitting laser elements have many advantages such as lower manufacturing costs and easier integration by two-dimensional arrays compared to edge emitting laser elements, so optical communication, optical interconnection, and optical recording It is expected to be used in many fields.

  The surface emitting laser element has, for example, a laminated structure in which an n-type multilayer reflector, a lower spacer layer, a multiple quantum well active layer, an upper spacer layer, and a p-type multilayer reflector are sequentially laminated on a substrate made of n-type GaAs. The upper part of the laminated structure is a mesa structure having a columnar structure. The surface-emitting laser element includes an insulating film that covers the side wall of the mesa structure, a semiconductor around the mesa structure, an upper electrode connected to a contact layer disposed on the uppermost surface of the mesa structure, And a lower electrode formed on the back surface of the substrate. The surface emitting laser element emits laser light from an opening provided on the uppermost surface of the mesa structure.

  The surface emitting laser array has a structure in which the surface emitting laser elements having the above-described configuration are two-dimensionally integrated.

  Among the surface emitting laser elements, a selective oxidation type surface emitting laser element is the most promising from the viewpoint of laser characteristics such as threshold current and power consumption. In this selective oxidation type surface emitting laser element, an AlAs layer (or an AlGaAs layer whose Al composition is extremely close to “1”) is formed as a part of a p-type multilayer mirror when the above-described stacked structure is formed by crystal growth. This is a surface emitting laser element in which a current confinement structure that limits the current injected into the active layer is formed in the mesa structure by selectively oxidizing the AlAs layer.

Any of silicon oxide, silicon nitride, silicon oxynitride, or the like is used as an insulating film that covers the mesa structure and the semiconductor layer around the mesa structure, and the internal stress of the insulating film is 1.5 × 10 ⁹ dyn / cm. by ² or less, deterioration of the mesa structure, prevent deformation and damage or the like, to stabilize long-term output of the laser light emitted is known from the mesa structures (Patent Document 1).

In Patent Document 1, four types of internal stress (= 3 × 10 ⁸ dyn / cm ² , 1.5 × 10 ⁹ dyn / cm ² , 3 × 10 ⁹ dyn / cm ² , 4 × 10 ⁹ dyn / cm ^{2 are used.} ), An acceleration experiment was conducted in which a current of 9 mA was passed at a temperature of 100 ° C. And in patent document 1, the internal stress was made into 1.5 * 10 < ⁹ > dyn / cm < ² > or less (preferably 3 * 10 < ⁸ > dyn / cm < ² > or less), and the result that a laser output hardly decreased was obtained. Yes.

A surface-emitting laser element having a structure in which polyimide is further formed on an insulating film covering the mesa structure and the mesa structure and its peripheral portion are planarized is also known (Patent Document 2).
JP 2004-200211 A JP 2002-270959 A

  However, as described in Patent Document 1, there is a problem that it is difficult to extend the lifetime of the surface emitting laser element only by reducing the internal stress.

  The surface emitting laser element includes a mesa structure and an insulating film formed in contact with the mesa structure, and the force applied to the mesa structure is determined by the total stress of the insulating film. The total stress of the insulating film is determined by (internal stress) × (film thickness).

  Therefore, even if the internal stress is small, if the thickness of the insulating film is large, the total stress of the insulating film increases, and a large force is applied to the mesa structure. As a result, the lifetime of the surface emitting laser element is shortened.

  On the other hand, even if the internal stress is large, if the film thickness of the insulating film is thin, the total stress of the insulating film is small and the force applied to the mesa structure is small. As a result, the lifetime of the surface emitting laser element is extended.

  Thus, it is difficult to extend the lifetime of the surface emitting laser element only by reducing the internal stress.

  Accordingly, the present invention has been made to solve such a problem, and an object thereof is to provide a surface emitting laser element having a lifetime equal to or greater than a reference value.

  Another object of the present invention is to provide a surface emitting laser array including a surface emitting laser element having a lifetime equal to or greater than a reference value.

  Furthermore, another object of the present invention is to provide an image forming apparatus provided with a surface emitting laser array having a lifetime equal to or greater than a reference value.

  According to this invention, the surface emitting laser element includes the substrate, the mesa structure, and the insulating film. The mesa structure is formed on the substrate and has a columnar structure. The insulating film covers the periphery of the mesa structure in the in-plane direction of the substrate. The insulating film has a total stress that sets the lifetime of the surface emitting laser element to a reference value or more.

Preferably, the absolute value of the total stress is 6 × 10 ⁴ dyn / cm or less.

  Preferably, the surface emitting laser element further includes a wiring. The wiring is connected to a semiconductor layer included in the mesa structure. The insulating film includes first and second insulating films. The first insulating film is formed in contact with the mesa structure and the semiconductor layer around the mesa structure in the in-plane direction. The second insulating film is formed in contact with the first insulating film and the wiring and substantially flattens the wiring in the in-plane direction.

  Preferably, one of the first and second insulating films has an internal stress composed of one of a compressive stress and a tensile stress. The other of the first and second insulating films has an internal stress consisting of either the compressive stress or the tensile stress.

  According to the present invention, the surface emitting laser array includes a plurality of surface emitting laser elements. Each of the plurality of surface emitting laser elements includes the surface emitting laser element according to any one of claims 1 to 4.

  Preferably, the plurality of surface emitting laser elements are write light sources for optical writing.

  Further, according to the present invention, an image forming apparatus includes a writing light source comprising the surface emitting laser array according to claim 6.

  The surface emitting laser element according to the present invention includes an insulating film formed in contact with the mesa structure and having a total stress that sets the lifetime of the surface emitting laser element to a reference value or more.

  Therefore, according to the present invention, the lifetime of the surface emitting laser element can be made longer than the reference value.

  The surface emitting laser array and the image forming apparatus according to the present invention include the surface emitting laser element according to the present invention.

  Therefore, according to the present invention, the lifetime of the surface emitting laser array and the image forming apparatus can be extended.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  FIG. 1 is a schematic sectional view of a surface emitting laser element according to an embodiment of the present invention. Referring to FIG. 1, a surface emitting laser element 10 according to an embodiment of the present invention includes a substrate 1, reflection layers 2 and 6, resonator spacer layers 3 and 5, an active layer 4, and a selective oxidation layer 7. A contact layer 8, a passivation film 9, a wiring electrode 11, and an n-side electrode 12. The surface emitting laser element 10 oscillates laser light having a wavelength of 780 nm.

The substrate 1 is made of n-type gallium arsenide (n-GaAs). The reflective layer 2 has [n-Al _0.9 Ga ₀ .4 of 40.5 periods when a pair of n-Al _0.9 Ga _0.1 As / Al _0.3 Ga _0.7 As is taken as one period _{. 1} As / Al _0.3 Ga _0.7 As] and formed on one main surface of the substrate 1. Although not shown in FIG. 1, the reflective layer 2 is changed from one composition of n-Al _0.9 Ga _0.1 As and n-Al _0.3 Ga _0.7 As to the other composition. The composition gradient layer which consists of n-AlGaAs which changed the composition toward this is included.

The resonator spacer layer 3 is made of non-doped Al _0.6 Ga _0.4 As and is formed on the reflective layer 2. The active layer 4 has a quantum well structure in which three layers of GaInPAs and four layers of Ga _0.6 In _0.4 P are alternately stacked. GaInPAs has a compressive strain composition, and Ga _0.6 In _0.4 P lattice-matches with GaInPAs and has tensile strain.

The resonator spacer layer 5 is made of non-doped Al _0.6 Ga _0.4 As and is formed on the active layer 4. The reflective layer 6 has [p-Al _0.9 Ga _0.1 As of 24 periods when a pair of p-Al _0.9 Ga _0.1 As / Al _0.3 Ga _0.7 As is taken as one period. / Al _0.3 Ga _0.7 As] and is formed on the resonator spacer layer 5. Although not shown in FIG. 1, the reflective layer 6 has a composition from one composition of p-Al _0.9 Ga _0.1 As and p-Al _0.3 Ga _0.7 As to the other composition. It includes a composition gradient layer made of p-AlGaAs whose composition is changed toward the front.

  The selective oxidation layer 7 is made of p-AlAs and is provided in the reflection layer 6. The selective oxidation layer 7 includes a non-oxidized region 7a and an oxidized region 7b.

The contact layer 8 is made of p-GaAs and is formed on the reflective layer 6. The passivation film 9 is made of, for example, SiO ₂ , one main surface of a part of the resonator spacer layer 3, and end surfaces of the active layer 4, the resonator spacer layer 5, the reflective layer 6, the selective oxidation layer 7, and the contact layer 8. And so as to cover.

  The wiring electrode 11 is formed on a part of the contact layer 8 and on the passivation film 9. The wiring electrode 11 is made of Cr / AuZn / Au or Ti / Au. The n-side electrode 12 is formed on the back surface of the substrate 1. The n-side electrode 12 is made of AuGe / Ni / Au.

Each of the reflection layers 2 and 6 constitutes a semiconductor distributed Bragg reflector that reflects the oscillation light oscillated in the active layer 4 by Bragg multiple reflection and confines it in the active layer 4. In this case, the film thicknesses of n-Al _0.9 Ga _0.1 As and n-Al _0.3 Ga _0.7 As constituting the reflective layer 2 are set so that the Bragg multiple reflection phase condition is satisfied. Λ / 4n (n is the refractive index of each semiconductor layer) with respect to the laser oscillation wavelength (λ = 780 nm). Further, the film thicknesses of p-Al _0.9 Ga _0.1 As and p-Al _0.3 Ga _0.7 As constituting the reflective layer 6 are also set so as to satisfy the Bragg multiple reflection phase condition. It is set to λ / 4n (n is the refractive index of each semiconductor layer) with respect to the laser oscillation wavelength (λ = 780 nm).

  In the surface emitting laser element 10, the resonator spacer layers 3 and 5 and the active layer 4 constitute a resonance region. The resonance region composed of the resonator spacer layers 3 and 5 and the active layer 4 is set so that the phase change amount of the oscillation light in these semiconductor layers is 2π to form a one-wavelength resonator structure. .

  Further, in the surface emitting laser element 10, the active layer 4, the resonator spacer layer 5, the reflective layer 6 and the selective oxidation layer 7 constitute a mesa structure 20.

  Further, in the surface emitting laser element 10, the selective oxidation layer 7 is disposed in the reflection layer 6 that is separated from the resonator spacer layer 5 by λ / 4. The film thickness of λ / 4n is such that the phase change amount of the oscillation light in each semiconductor layer is π / 2.

Further, in the surface emitting laser element 10, the passivation film 9 has a film thickness of 150 nm and an internal stress of −4 × 10 ⁹ dyn / cm ² . As a result, the passivation film 9 has a total stress S of −6 × 10 ⁴ dyn / cm.

  2 and 3 are first and second process diagrams showing a method of manufacturing the surface-emitting laser element 10 shown in FIG. 1, respectively. Referring to FIG. 2, when a series of operations is started, a reflective layer 2, a resonator spacer layer 3, an active layer 4, a resonance layer are formed using metal organic chemical vapor deposition (MOCVD). A container spacer layer 5, a reflective layer 6, a selective oxidation layer 7, and a contact layer 8 are sequentially stacked on the substrate 1 (see step (a) in FIG. 2).

In this case, n-Al _0.9 Ga _0.1 As and n-Al _0.3 Ga _0.7 As of the reflective layer 2 are changed from trimethylaluminum (TMA), trimethylgallium (TMG), arsine (AsH ₃ ), and selenium. Hydrogen fluoride (H ₂ Se) is formed as a raw material.

Further, non-doped Al _0.6 Ga _0.4 As for the resonator spacer layer 3 is formed using trimethylaluminum (TMA), trimethylgallium (TMG) and arsine (AsH ₃ ) as raw materials, and GaInPAs / Ga _{0 of the} active layer 4 is formed. _.6 In _0.4 P is formed using trimethylgallium (TMG), trimethylindium (TMI), phosphine (PH ₃ ) and arsine (AsH ₃ ) as raw materials.

Further, non-doped Al _0.6 Ga _0.4 As for the resonator spacer layer 5 is formed using trimethylaluminum (TMA), trimethylgallium (TMG), and arsine (AsH ₃ ) as raw materials, and p-Al _{0 of the} reflective layer 6 is formed. _.9 Ga _0.1 As / Al _0.3 Ga _0.7 As is formed using trimethylaluminum (TMA), trimethylgallium (TMG), arsine (AsH ₃ ) and carbon tetrabromide (CBr ₄ ) as raw materials.

Further, p-AlAs of the selective oxidation layer 7 is formed using trimethylaluminum (TMA), arsine (AsH ₃ ) and carbon tetrabromide (CBr ₄ ) as raw materials, and p-GaAs of the contact layer 8 is formed of trimethylgallium (TMG). , Arsine (AsH ₃ ) and carbon tetrabromide (CBr ₄ ).

  Thereafter, a resist is applied on the contact layer 8, and a resist pattern 30 is formed on the contact layer 8 using a photoengraving technique (see step (b) in FIG. 2). In this case, the resist pattern 30 has a square shape whose one side is 20 μm, for example.

  When the resist pattern 30 is formed, the periphery of the active layer 4, the resonator spacer layer 5, the reflective layer 6, the selective oxide layer 7 and the contact layer 8 is removed by dry etching using the formed resist pattern 30 as a mask. Further, the resist pattern 30 is removed (see step (c) in FIG. 2). Thereby, a mesa structure 20 having a columnar shape is formed on the substrate 1.

  Next, referring to FIG. 3, after the step (c) shown in FIG. 2, the sample is heated to 425 ° C. in an atmosphere in which water heated to 85 ° C. is bubbled with nitrogen gas, thereby selectively oxidizing layer 7. Is oxidized from the outer peripheral portion toward the central portion to form a non-oxidized region 7a and an oxidized region 7b in the selective oxidation layer 7 (see step (d) in FIG. 3). In this case, the non-oxidized region 7a is made of a square having a side of 4 μm, for example.

Thereafter, a passivation film 9 made of SiO ₂ is formed on the entire surface of the sample by using a chemical vapor deposition (CVD) method. More specifically, the passivation film 9 made of SiO ₂ is formed by a plasma CVD method using silane (SiH 4) and nitrous oxide (N ₂ O) as source gases and helium (He) as a carrier gas. The conditions for forming the passivation film 9 made of SiO ₂ are as shown in Table 1.

  Then, after the passivation film 9 is formed, the passivation film 9 in the region serving as the light emitting portion and its peripheral region is removed using photolithography (see step (e) in FIG. 3).

  Thereafter, a resist pattern having a side of 8 μm is formed on the region to be the light emitting portion, a p-side electrode material is formed on the entire surface of the sample by vapor deposition, and the p-side electrode material on the resist pattern is removed by lift-off. A wiring electrode 11 is formed on the passivation film 9. Then, the back surface of the substrate 1 is polished, the n-side electrode 12 is formed on the back surface of the substrate 1, and further annealed to obtain ohmic conduction between the wiring electrode 11 and the n-side electrode 12 (see step (f) in FIG. 3). ). Thus, the surface emitting laser element 10 is manufactured.

Stress of the SiO ₂ formed under the conditions shown in Table 1 in advance, the SiO ₂ is formed under the conditions shown in the Si substrate 4-inch in Table 1, using a stress measuring device (KLA Tencor Corporation, Model FLX-2320) And evaluated. The evaluation method is as follows. The initial warpage amount SP ₀ of the Si substrate is measured, and then the warpage amount SP _{Si /} SiO ₂ of the Si substrate after the formation of SiO ₂ is measured. Then, by subtracting the amount of warp SP ₀ from warpage _{SP Si / SiO2} calculated warpage _{SP SiO2} of SiO ₂ per se, based on the amount of warpage _{SP SiO2} was the measurement to determine the internal stress of the SiO ₂ sigma. Then, determine the total stress S of SiO ₂ by multiplying the film thickness of the SiO ₂ to the internal stress sigma.

As a result of evaluating the total stress of SiO ₂ by such a method, as described above, the internal stress σ of SiO ₂ is −4 × 10 ⁹ dyn / cm ² , and the total stress S of SiO ₂ is 150 nm. The film thickness was −6 × 10 ⁴ dyn / cm.

  FIG. 4 is a diagram showing the results of a life test of the surface emitting laser element 10 shown in FIG. 4A and 4B, the vertical axis represents the optical output P / P0 of the surface emitting laser element 10 normalized by the initial optical output in CW driving, and the horizontal axis represents time. In FIG. 4C, the vertical axis represents the optical output P / P0 of the surface emitting laser element including the active layer whose well layer is made of AlGaAs, and the horizontal axis represents time.

Curve k1~k5, respectively, 29.9Myuemu ² is the area of the non-oxidized region 7a of the selective oxidation layer 7 respectively, 27.7μm ^2, 26.9μm ^2, when a 25.5 ² and 8.7 .mu.m ² The curves k6 and k7 show the time dependency of the light output P / P0 when the area of the non-oxidized region 7a of the selective oxidation layer 7 is 7.9 μm ^2. Curves k8 to k10 show the time dependence of the light output P / P0 when the area of the non-oxidized region 7a of the selective oxidation layer 7 is 15.5 μm ² . The life test was conducted in an environment of 60 ° C.

  When a surface emitting laser element is used in an optical writing device or the like, the standard determines that the light output when the surface emitting laser element is continuously operated for 1000 hours is 80% or more of the initial light output. Yes.

  From the results shown in FIG. 4, even if the area of the non-oxidized region 7a of the surface emitting laser element 10 is set to any of the above-described areas, a light output P / P0 of 80% or more is obtained in 1000 hours of continuous operation. Therefore, the standard for using the surface emitting laser element in an optical writing device or the like is satisfied.

Further, as the area of the non-oxidized region 7a increases, the amount of current injected into the active layer 4 increases and the amount of heat generated in the surface emitting laser element 10 increases, which is disadvantageous for deterioration, but the total stress is increased. by using a passivation film 9 made of SiO ₂ is -6 × ¹⁰ 4 dyn / cm, can be realized a surface emitting laser element 10 having 1000 hours of life.

  Further, even when the well layer of the active layer 4 is made of AlGaAs, a light output P / P0 of 80% or more is obtained by continuous operation for 1000 hours, and the surface emitting laser element is used for an optical writing device or the like. Meet the standards. Therefore, regardless of whether the well layer of the active layer 4 is made of GaInP or AlGaAs, an optical output P / P0 of 80% or more can be obtained in 1000 hours of continuous operation, and the surface emitting laser element is used for an optical writing device or the like. A surface emitting laser element satisfying the standard of the case can be manufactured.

In the above description, it has been described that the active layer 4 of the surface emitting laser element 10 is made of GaInPAs / Ga _0.6 In _0.4 P. However, in the present invention, the active layer 4 is not limited to this. _It may _{consist of 0.12} Ga _0.88 As / Al _0.3 Ga _0.7 As.

In the above description, the resonator spacer layers 3 and 5 are made of non-doped Al _0.6 Ga _0.4 As. However, in the present invention, the resonator spacer layers 3 and 5 are not limited to this. It may consist of (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P. By forming the resonator spacer layers 3 and 5 with (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, the resonator spacer layers 3 and 5 are made of an AlGaAs-based material. The effect of confining carriers in the active layer 4 is increased, and the light output of the surface emitting laser element 10 can be improved.

Further, in the above description, the selective oxidation layer 7 is made of p-AlAs. However, the present invention is not limited to this, and the selective oxidation layer 7 is made of Al _x Ga _1-x As (0.9 ≦ x <1). Generally, the selective oxidation layer 7 only needs to be made of Al _x Ga _1-x As (0.9 ≦ x ≦ 1).

In the above description, the passivation film 9 is made of SiO _2. However, the present invention is not limited to this, and the passivation film 9 is made of any one of a SiN film, a SiON film, a SiOH film, and a polyimide film. It may be. When the passivation film 9 is composed of an SiON film having an internal stress of −8 × 10 ⁸ dyn / cm ² , the total stress S of the passivation film 9 is set to −6 by setting the thickness of the SiON film to 750 nm or less. It can set to x10 < ⁴ > dyn / cm or less.

  The surface emitting laser element according to the embodiment of the present invention may be a surface emitting laser element 10A shown in FIG. FIG. 5 is another schematic cross-sectional view of a surface emitting laser element according to an embodiment of the present invention. Referring to FIG. 5, surface emitting laser element 10 </ b> A is obtained by adding polyimide film 13 to surface emitting laser element 10 shown in FIG. 1, and is otherwise the same as surface emitting laser element 10.

  The polyimide film 13 is formed between the passivation film 9 and the wiring electrode 11 in contact with the passivation film 9 and the wiring electrode 11. The polyimide film 13 has substantially the same thickness as the mesa structure 20 (= the active layer 4, the resonator spacer layer 5, the reflective layer 6 and the selective oxidation layer 7). As a result, the wiring electrode 11 can be flattened, and disconnection at the step portion of the wiring electrode 11 can be prevented.

  The surface emitting laser element 10A is manufactured according to the steps (a) to (f) shown in FIGS. 2 and 3, and in the step (f), before the wiring electrode 11 is formed on the passivation film 9. A polyimide film 13 is formed, and a wiring electrode 11 is formed on the formed polyimide film 13.

  The polyimide film 13 is formed on the passivation film 9 by spin coating. More specifically, the polyimide film 13 is formed by applying photosensitive polyimide (trade name: PIMEL G-7640E) to a thickness of 4 μm by spin coating at 2200 rpm. Then, exposure and development are performed so that the contact layer 8 on the upper portion of the mesa structure 20 is exposed, and post-baking and curing are performed, so that a film can be formed in the recess adjacent to the mesa structure 20.

  Using the polyimide film 13 thus formed as a mask, the upper insulator of the mesa structure 20 is etched with buffered hydrofluoric acid (BHF) to open a window for forming the wiring electrode 11. Thereafter, the above-described wiring electrode 11 is formed.

Since the solvent is removed by curing the polyimide, the film thickness of the polyimide film 13 is half (= 2 μm) of the applied film thickness (= 4 μm). As a result of measuring the internal stress of this polyimide film 13, it was a tensile stress of 3.7 × 10 ⁸ dyn / cm ² . As a result, the total stress S of the polyimide film 13 is 7.4 × 10 ⁴ dyn / cm (= 3.7 × 10 ⁸ dyn / cm ² × 2 × 10 ⁻⁴ cm).

The polyimide film 13 is formed in contact with the passivation film 9, and the passivation film 9 has a total stress of −6 × 10 ⁴ dyn / cm as described above. Therefore, the entire synthesis of the passivation film 9 and the polyimide film 13 is performed. The stress is 1.4 × 10 ⁴ dyn / cm (= 7.4 × 10 ⁴ dyn / cm + (− 6 × 10 ⁴ dyn / cm)), which is smaller than the total stress of the passivation film 9 alone.

  As a result of conducting a life test of the surface emitting laser element 10A, no deterioration of the emitted light was observed even when operated at a temperature of 60 ° C. for 1000 hours.

Thus, by combining the polyimide film 13 having the total stress opposite to that of the passivation film 9 with the passivation film 9, strain compensation can be performed, and the total stress can be reduced to 1.4 × 10 ⁴ dyn / cm. It was. As a result, the surface emitting laser element 10A can be used as a semiconductor laser for writing.

In the above, the surface emitting laser element 10 comprises a passivation film 9 having a total stress of -6 × ¹⁰ 4 dyn / cm, the passivation film 9 and the polyimide film 13 having a total stress of 1.4 × ¹⁰ 4 dyn / cm The surface emitting laser element 10A provided with the above has been described, but the surface emitting laser element according to the present invention only needs to include an insulating film having an absolute value of the total stress of 6 × 10 ⁴ dyn / cm or less, and is more general. Includes an insulating film having a total stress for setting the lifetime of the surface emitting laser element to a reference value (= 80% of the deterioration rate of light output when continuously operated at an operating temperature of 60 ° C. for 1000 hours) or more. It only has to be.

  FIG. 6 is a plan view of a surface emitting laser array including the surface emitting laser element according to the present invention. Referring to FIG. 6, the surface emitting laser array 100 includes 16 surface emitting laser elements 10. In FIG. 6, the mesa structure 20 of the surface emitting laser element 10 is shown as having a circular shape with a diameter of 20 μm.

  In the surface emitting laser array 100, the surface emitting laser elements 10 are arranged in 4 × 4, and the interval between the four surface emitting laser elements 10 arranged in the sub-scanning direction is 40 μm, and is in the main scanning direction. The interval between the four surface-emitting laser elements 10 arranged in (1) is also 40 μm. The centers of the four surface emitting laser elements arranged in the main scanning direction are shifted by 10 μm in the sub scanning direction. The intervals d between the four perpendicular lines 111 to 114 dropped from the four surface emitting laser elements 10 arranged in the main scanning direction to the line 110 arranged in the sub-scanning direction are equal intervals.

  As a result, 2400 DPI (dot / inch) can be realized by writing using the surface emitting laser array 100.

  FIG. 7 is another plan view of a surface emitting laser array including the surface emitting laser element according to the present invention. Referring to FIG. 7, surface emitting laser array 100 </ b> A includes 40 surface emitting laser elements 10, 40 wirings 120, and 40 pads 130.

  The 40 surface emitting laser elements 10 are 4 × 10 surface emitting lasers in which four surface emitting laser elements 10 are arranged in the sub-scanning direction and ten surface emitting laser elements 10 are arranged in the main scanning direction. It consists of the element 10. Each of the 40 wirings 120 connects one surface emitting laser element 10 to one pad 130. In this case, of the 40 surface emitting laser elements 10, the 16 wirings 120 that connect the 16 surface emitting laser elements 10 arranged on the inner periphery to the 16 pads 130 are arranged in the main scanning direction. The ten surface-emitting laser elements 10 are arranged. More specifically, the 16 wires 120 are arranged so that one wire 120 passes between two adjacent surface emitting laser elements 10 arranged in the main scanning direction.

  In the surface emitting laser array 100A, no wiring 120 is arranged between two adjacent surface emitting laser elements 10 arranged in the sub-scanning direction. Thereby, the dimension of a subscanning direction can be shortened and the surface emitting laser array 100A whole size can be made small.

  As a result of conducting a life test of the surface emitting laser array 100A at 60 ° C., the degradation rate of the light output is within 20% in 1000 hours of continuous operation, and the surface emitting laser array 100A is used as a light source for optical writing. Meets the standard.

  In the surface emitting laser arrays 100 and 100A, the surface emitting laser element 10A may be used instead of the surface emitting laser element 10.

  In the above description, 4 × 4 surface emitting laser elements 10 and 4 × 10 surface emitting laser elements 10 are shown as a plurality of surface emitting laser elements constituting the surface emitting laser array. The laser array may include other numbers of surface emitting laser elements, and the arrangement thereof is also free.

  FIG. 8 is a schematic view showing the configuration of a laser printer provided with a surface emitting laser array according to the present invention. Referring to FIG. 8, the laser printer 200 includes a surface emitting laser array 100 </ b> A, lenses 101 and 103, a polygon mirror 102, and a photoreceptor 104. Laser printer 200 constitutes an “image forming apparatus” according to the present invention.

  The surface emitting laser array 100A emits 40 beams. The lens 101 guides 40 beams emitted from the surface emitting laser array 100 </ b> A to the polygon mirror 102.

  The polygon mirror 102 rotates clockwise at a predetermined speed, scans 40 beams received from the lens 101 in the main scanning direction and the sub-scanning direction, and guides them to the lens 103. The lens 103 guides the 40 beams scanned by the polygon mirror 102 to the photosensitive member 104.

  As described above, the laser printer 200 uses the same optical system including the lenses 101 and 103 and the polygon mirror 102 for the 40 beams from the surface emitting laser array 100A, rotates the polygon mirror 102 at a high speed, and sets the dot position. The light timing is adjusted and the light is condensed on the photoconductor 104 as the surface to be scanned as 40 light spots separated in the sub-scanning direction.

  In the laser printer 200, writing is possible at an interval of about 10 μm in the sub-scanning direction (rotating direction of the photoconductor 104), and 2400 DPI can be realized. The writing interval in the main scanning direction can be easily controlled by adjusting the lighting timing of the 40 surface emitting laser elements 10 in the surface emitting laser array 100A as a light source.

  Thus, in the laser printer 200, 40 dots can be written simultaneously, high-speed printing can be performed, and higher-speed printing can be performed by increasing the number of surface-emitting laser elements 10 in the surface-emitting laser array 100A. Further, by adjusting the interval between the surface emitting laser elements 10, the interval in the sub-scanning direction can be adjusted, and writing can be performed at a higher density than 2400 DPI.

  In the laser printer 200, the surface emitting laser array 100 may be used instead of the surface emitting laser array 100A.

  In the above description, the surface emitting laser arrays 100 and 100A are applied to the laser printer. However, the surface emitting laser arrays 100 and 100A may be applied to other image forming apparatuses.

  According to the embodiment of the present invention, a surface emitting laser element according to the present invention includes an insulating film formed in contact with a mesa structure and having a total stress that sets a lifetime of the surface emitting laser element to a reference value or more. Prepare.

  Therefore, according to the present invention, the lifetime of the surface emitting laser element can be made longer than the reference value.

  The surface emitting laser array and the image forming apparatus according to the present invention include the surface emitting laser element according to the present invention.

  Therefore, according to the present invention, the lifetime of the surface emitting laser array and the image forming apparatus can be extended.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  The present invention is applied to a surface emitting laser element having a lifetime equal to or greater than a reference value. Further, the present invention is applied to a surface emitting laser array provided with a surface emitting laser element having a lifetime equal to or greater than a reference value. Furthermore, the present invention is applied to an image forming apparatus including a surface emitting laser array having a lifetime equal to or greater than a reference value.

It is a schematic sectional drawing of the surface emitting laser element by embodiment of this invention. FIG. 3 is a first process diagram showing a method for manufacturing the surface emitting laser element shown in FIG. 1. FIG. 6 is a second process diagram illustrating a method for manufacturing the surface emitting laser element illustrated in FIG. 1. It is a figure which shows the result of the lifetime test of the surface emitting laser element shown in FIG. It is another schematic sectional drawing of the surface emitting laser element by embodiment of this invention. It is a top view of the surface emitting laser array provided with the surface emitting laser element by this invention. It is another top view of the surface emitting laser array provided with the surface emitting laser element by this invention. It is the schematic which shows the structure of the laser printer provided with the surface emitting laser array by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Substrate, 2, 6 Reflective layer, 3, 5 Cavity spacer layer, 4 Active layer, 7 Selective oxidation layer, 7a Non-oxidation region, 7b Oxidation region, 8 Contact layer, 9 Passivation film, 10, 10A Surface emitting laser element 11 wiring electrode, 12 n side electrode, 13 polyimide film, 20 mesa structure, 30 resist pattern, 100, 100A surface emitting laser array, 110 line, 111-114 perpendicular, 120 wiring, 130 pad, 200 laser printer, 101 , 103 lens, 102 polygon mirror, 104 photoconductor.

Claims (7)

A surface emitting laser element,
A substrate,
A mesa structure formed on the substrate and having a columnar structure;
An insulating film covering the periphery of the mesa structure in the in-plane direction of the substrate;
The surface-emitting laser element, wherein the insulating film has a total stress that sets a lifetime of the surface-emitting laser element to a reference value or more. The surface emitting laser element according to claim 1, wherein an absolute value of the total stress is 6 × 10 ⁴ dyn / cm or less. A wiring connected to a semiconductor layer included in the mesa structure;
The insulating film is
A first insulating film formed in contact with the mesa structure and a semiconductor layer around the mesa structure in the in-plane direction;
3. The surface-emitting laser element according to claim 1, further comprising: a second insulating film formed in contact with the first insulating film and the wiring and substantially planarizing the wiring in the in-plane direction. . One of the first and second insulating films has an internal stress composed of either a compressive stress or a tensile stress,
4. The surface emitting laser element according to claim 3, wherein the other of the first and second insulating films has an internal stress composed of one of the compressive stress and the tensile stress. Comprising a plurality of surface emitting laser elements,
Each of these surface emitting laser elements is a surface emitting laser array which consists of a surface emitting laser element of any one of Claims 1-4.   6. The surface emitting laser array according to claim 5, wherein the plurality of surface emitting laser elements are write light sources for optical writing. With a writing light source,
The image forming apparatus, wherein the writing light source includes the surface emitting laser array according to claim 6.

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