US20110135318A1 - Vertical cavity surface emitting laser, vertical cavity surface emitting laser device, optical transmission device, and information processing apparatus - Google Patents
Vertical cavity surface emitting laser, vertical cavity surface emitting laser device, optical transmission device, and information processing apparatus Download PDFInfo
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- US20110135318A1 US20110135318A1 US12/781,175 US78117510A US2011135318A1 US 20110135318 A1 US20110135318 A1 US 20110135318A1 US 78117510 A US78117510 A US 78117510A US 2011135318 A1 US2011135318 A1 US 2011135318A1
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- multilayer reflector
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—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
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18308—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement
- H01S5/18311—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement using selective oxidation
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—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
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18386—Details of the emission surface for influencing the near- or far-field, e.g. a grating on the surface
- H01S5/18391—Aperiodic structuring to influence the near- or far-field distribution
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S2301/00—Functional characteristics
- H01S2301/16—Semiconductor lasers with special structural design to influence the modes, e.g. specific multimode
- H01S2301/166—Single transverse or lateral mode
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S2301/00—Functional characteristics
- H01S2301/17—Semiconductor lasers comprising special layers
- H01S2301/176—Specific passivation layers on surfaces other than the emission facet
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/02208—Mountings; Housings characterised by the shape of the housings
- H01S5/02212—Can-type, e.g. TO-CAN housings with emission along or parallel to symmetry axis
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
- H01S5/042—Electrical excitation ; Circuits therefor
- H01S5/0425—Electrodes, e.g. characterised by the structure
- H01S5/04254—Electrodes, e.g. characterised by the structure characterised by the shape
Definitions
- the present invention relates to a vertical cavity surface emitting laser, a vertical cavity surface emitting laser device, an optical transmission device, and an information processing apparatus.
- a vertical cavity surface emitting laser (VCSEL) is used as a light source in a communication device and an image forming apparatus.
- VCSEL vertical cavity surface emitting laser
- Single lateral mode, high power and long service life are required for such vertical cavity surface emitting laser used as a light source.
- a single lateral mode is achieved by reducing a radius of the oxidized aperture of a current narrowing layer to about 2 through 3 ⁇ m, but it becomes difficult to obtain an optical output greater than or equal to 3 mW stably.
- a vertical cavity surface emitting laser device including: a substrate; a first semiconductor multilayer reflector of a first conductive type formed on the substrate; an active region formed on the first semiconductor multilayer reflector; a second semiconductor multilayer reflector of a second conductive type formed on the active region; a columnar structure that is formed from the second semiconductor multilayer reflector to the first semiconductor multilayer reflector on the substrate; a current narrowing layer that is formed inside of the columnar structure, and has a conductive region surrounded by an oxidization region selectively oxidized; a first electrode that is annular, is formed at a top of the columnar structure, is electrically connected to the second semiconductor multilayer reflector, and defines a beam window; a first insulating film that is comprised of a material which has a first refractive index capable of transmitting an oscillation wavelength, and formed on the first electrode to cover the beam window; and a second insulating film that is circular, is comprised of a material which has a
- FIG. 1 illustrates a plane view, and a cross-section view taken from line A-A of a vertical cavity surface emitting laser in accordance with a first exemplary embodiment of the present invention
- FIG. 2 is a cross-section view enlarging a top of a mesa of the vertical cavity surface emitting laser illustrated in FIG. 1 ;
- FIG. 3 is a diagram illustrating exemplary combinations of a first insulating film and a second insulating film
- FIG. 4A is a diagram illustrating a simulation result of a reflection ratio of an upper DBR in a region where only a first insulating film exists
- FIG. 4B is a diagram illustrating a simulation result of a reflection ratio of an upper DBR in a region where a first insulating film and a second insulating film are stacked;
- FIG. 5 is a cross-section view enlarging a top of a mesa of a vertical cavity surface emitting laser in accordance with a second exemplary embodiment of the present invention
- FIGS. 6A and 6B are cross-section views for explaining a fabrication process of a vertical cavity surface emitting laser in accordance with a third exemplary embodiment of the present invention.
- FIGS. 7A and 7B are cross-section views for explaining a fabrication process of a vertical cavity surface emitting laser in accordance with the third exemplary embodiment of the present invention.
- FIGS. 8A and 8B are schematic cross-section views illustrating a composition of a vertical cavity surface emitting laser device in which the vertical cavity surface emitting laser of exemplary embodiments and an optical component are packaged;
- FIG. 9 is a diagram illustrating a composition of a light source device using the vertical cavity surface emitting laser of exemplary embodiments.
- FIG. 10 is a schematic cross-section view illustrating a composition of an optical transmission device using the vertical cavity surface emitting laser device illustrated in FIG. 8A .
- FIG. 1 is a schematic cross-section view of a VCSEL in accordance with the first exemplary embodiment of the present invention.
- a VCSEL 10 of the exemplary embodiment is formed by stacking an n-type lower Distributed Bragg Reflector (hereinafter, abbreviated as DBR) 102 , an active region 104 , and a p-type upper DBR 106 on an n-type GaAs substrate 100 .
- the n-type lower DBR 102 is formed by stacking AlGaAs layers with different Al composition alternately.
- the active region 104 includes a quantum well layer sandwiched between upper and lower spacer layers.
- the p-type upper DBR 106 is formed by stacking AlGaAs layers with different Al composition on the active region 104 alternately.
- the n-type lower DBR 102 is a multi-layer stack formed by a pair of an Al0.9Ga0.1As layer and an Al0.3Ga0.7As layer for example.
- the thickness of each layer is ⁇ /4n r ( ⁇ is an oscillation wavelength, and n r is a refractive index of the medium), and the Al 0.9 Ga 0.1 As layer and the Al 0.3 Ga 0.7 As layer are stacked alternately 40 periods.
- a carrier concentration after doping an n-type impurity (silicon) is 3 ⁇ 10 18 cm ⁇ 3 for example.
- a lower spacer layer of the active region 104 is an undoped Al0.6Ga0.4As layer
- quantum well active layers are an undoped Al0.11Ga0.89As quantum well layer and an undoped Al0.3Ga0.7As barrier layer
- an upper spacer layer is an undoped Al0.6Ga0.4As layer.
- the p-type upper DBR 106 is a multi-layer stack formed by a pair of an Al0.9Ga0.1As layer and an Al0.3Ga0.7As layer for example.
- the thickness of each layer is ⁇ /4n r , and the Al 0.9 Ga 0.1 As layer and the Al 0.3 Ga 0.7 As layer are stacked alternately 24 periods.
- a carrier concentration after doping a p-type impurity (carbon) is 3 ⁇ 10 18 cm ⁇ 3 for example.
- a contact layer 106 A comprised of p-type GaAs is formed at a top layer of the upper DBR 106
- a current narrowing layer 108 comprised of p-type AlAs is formed at a bottom layer of the upper DBR 106 or inside of the upper DBR 106 .
- a cylindrical mesa (a columnar structure) M is formed on the substrate 100 by etching a semiconductor layer from the upper DBR 106 to the lower DBR 102 .
- the current narrowing layer 108 is exposed on the side surface of the mesa M, and has an oxidization region 108 A which is selectively oxidized from the side surface, and a conductive region (oxidized aperture) 108 B surrounded by the oxidization region 108 A.
- the oxidation rate of an AlAs layer is faster than that of an AlGaAs layer, and the oxidization proceeds from the side surface of the mesa M to the inside at an almost constant rate.
- the planar shape of the surface which is parallel to the principal surface of the substrate 100 of the conductive region 108 B, becomes a round shape which reflects the outer shape of the mesa M, and the center of the conductive region 108 B corresponds to the axial center of the mesa M which means an optical axis.
- the radius of the conductive region 110 B may have the size at which the high-order lateral mode oscillation occurs.
- the radius of the conductive region 110 B may be equal to or larger than 5 ⁇ m in a wavelength range of 780 nm.
- An annular metallic p-side electrode 110 is formed at the top layer of the mesa M.
- the p-side electrode 110 is comprised of a metal formed by stacking Au or Ti/Au for example, and is ohmic connected to the contact layer 106 A of the upper DBR 106 .
- the outside diameter of the p-side electrode 110 is larger than the radius of the conductive region 108 B.
- the circular opening is formed at the center of the p-side electrode 110 , and this opening defines a beam window 110 A which emits a beam.
- the center of the beam window 110 A corresponds to the optical axis of the mesa M, and the radius of the beam window 110 A is larger than the radius of the conductive region 108 B.
- a circular first insulating film 112 is formed on the p-side electrode 110 to cover the beam window 110 A.
- the first insulating film 112 is comprised of a material that is able to transmit the oscillation wavelength.
- the outside diameter of the first insulating film 112 is smaller than the outside diameter of the p-side electrode, and larger than the radius of the beam window 110 A. Therefore, the beam window 110 A is covered by the first insulating film 112 completely, but a part of the p-side electrode 110 is exposed by the first insulating film 112 .
- An interlayer insulating film 114 covering the edge of the bottom, side, and top of the mesa M is formed.
- the edge of the interlayer insulating film 114 covers the part of the p-side electrode 110 , and a annular contact hole 116 which exposes the p-side electrode 110 is formed between the interlayer insulating film 114 and the first insulating film 112 .
- a circular second insulating film 118 comprised of a material that is able to transmit the oscillation wavelength is formed on the first insulating film 112 .
- the center of the second insulating film 118 corresponds to the optical axis, and the outside diameter of the second insulating film 118 is smaller than the radius of the conductive region 108 B.
- the radius of the conductive region 108 B is about 5 ⁇ m
- the radius of the second insulating film 118 is about 3 ⁇ m.
- the second insulating film 118 can be formed with the same process as that of the interlayer insulating film 114 by using the same material as that of the interlayer insulating film 114 .
- An n-side electrode 120 that is electrically connected to the lower DBR 102 is formed on the back side of the substrate 100 .
- FIG. 2 is an enlarged cross-section views of the top of the mesa of the VCSEL in FIG. 1 .
- the refractive index of the first insulating film 112 is n 1
- the refractive index of the second insulating film 118 is n 2
- the refractive index of the semiconductor layer (the contact layer 106 A) of the upper DBR 106 is n 3 .
- the relation among n 1 , n 2 , and n 3 is n 1 ⁇ n 2 ⁇ n 3 .
- Each film thickness of the first insulating film 112 and the second insulating film 118 is odd multiples of the wavelength of the medium ⁇ /4, which means (2n ⁇ 1) ⁇ /4 (n is positive integer).
- first region Z 1 where the first insulating film 112 is formed and the second insulating film 118 is stacked on the first insulating film 112
- annular second region X 2 where only the first insulating film 112 is formed around the first region Z 1 , on the contact layer 106 A exposed by the beam window 110 A.
- the center of the first region Z 1 corresponds to the center of the conductive region 110 B (the optical axis), but the size of the first region Z 1 is smaller than the radius of the conductive region 110 B.
- the reflection ratio r 1 of the upper DBR 106 including the first region Z 1 is higher than the reflection ratio r 2 of the upper DBR 106 including the second region Z 2 . Therefore, a high-order lateral mode oscillation is suppressed in the upper DBR 106 including the second region Z 2 , and a fundamental transverse mode oscillation is accelerated in the upper DBR 106 including the first region Z 1 . Therefore, it is possible to increase the optical output by making the radius of the conductive region 108 B (the radius of the oxidized aperture) be the size at which a high-order lateral mode oscillates.
- the first insulating film 112 may be comprised of SiON, and the second insulating film 118 may be comprised of SiN.
- the first insulating film 112 and the second insulating film 118 may be comprised of combinations indicated in FIG. 3 .
- the first insulating film 112 when the first insulating film 112 is comprised of SiON, the second insulating film 118 may be comprised of TiO 2 .
- the second insulating film 118 may be comprised of SiN.
- FIG. 4A illustrates a reflection ratio r 2 of the upper DBR including the second region Z 2 when SiON with a film thickness of ⁇ /4 is formed as the first insulating film 112 .
- FIG. 4B illustrates a reflection ratio r 1 of the upper DBR including the first region Z 1 when SiON with a film thickness of ⁇ /4 is formed as the first insulating film 112 , and SiN with a film thickness of ⁇ /4 is formed as the second insulating film 118 .
- the reflection ratio r 2 is about 99.2% in a wavelength range of 780 nm.
- the reflection ratio r 1 is about 99.7% in a wavelength range of 780 nm.
- a reflection ratio needed for a laser oscillation typically is about 99.5%. Therefore, in the first region Z 1 , the fundamental lateral mode generated on the optical axis is easily oscillated, and in the second region Z 2 the high-order lateral mode oscillation away from the optical axis is suppressed.
- the fundamental transverse mode oscillation is selectively accelerated and the high-order lateral mode oscillation is suppressed, by making the difference between reflection ratios r 1 of the first region Z 1 and r 2 of the second region Z 2 .
- Ordinary skilled persons in the art can understand that it is possible to adjust reflection ratios r 1 and r 2 by selecting the periodic number of the upper DBR 106 and materials of first and second insulating films 112 and 118 .
- FIG. 5 is a cross-section view of a main part of a VCSEL in accordance with a second exemplary embodiment of the present invention.
- a taper is formed in the mesa M, and the radius of the mesa gradually narrows along to the top.
- Such taper of the mesa can be formed by selecting proper etching condition.
- the end surface of the first insulating film 112 , the end surface of the interlayer insulating film 114 , and the end surface of the second insulating film 118 are inclined in a tapered shape.
- the mesa M have a taper structure, the step coverage of the adherent interlayer insulating film 114 is improved, and it is possible to prevent the disconnection of the interlayer insulating film 114 .
- the second insulating film 118 is formed with the same process as that of the interlayer insulating film 114 , it is possible to uniformly-control both film thicknesses to be odd multiples of ⁇ /4.
- the third exemplary embodiment relates to a preferable fabrication method of the VCSEL.
- a fabrication method is described with reference to FIGS. 6A through 7B .
- the n-type lower DBR 102 , the active region 104 , and the p-type upper DBR 106 are stacked on the n-type GaAs substrate 100 by the metal organic chemical vapor deposition (MOCVD) method.
- the n-type lower DBR 102 is composed by stacking Al 0.9 Ga 0.1 As and Al 0.3 Ga 0.7 As with a carrier concentration of 2 ⁇ 10 18 cm ⁇ 3 alternately 40 periods so that each film thickness becomes quarter of the wavelength of the medium.
- the active regionl 04 is comprised of an undoped Al 0.6 Ga 0.4 As lower spacer layer, an undoped Al 0.11 Ga 0.89 As quantum well layer, an undoped Al 0.3 Ga 0.7 As barrier layer, and an undoped Al 0.6 Ga 0.4 As upper spacer layer.
- the p-type upper DBR 106 is composed by stacking a p-type Al 0.9 Ga 0.1 As layer and a p-type Al 0.3 Ga 0.7 As layer with a carrier concentration of 3 ⁇ 10 18 cm ⁇ 3 alternately 24 periods so that each film thickness becomes quarter of the wavelength of the medium.
- the p-type GaAs contact layer 106 A with a carrier concentration of 1 ⁇ 10 19 cm ⁇ 3 is formed at the top layer of the upper DBR 106
- a p-type AlAs layer is formed at the bottom of the upper DBR 106 or inside of the upper DBR 106 . It is not illustrated, but a buffer layer may be provided between the substrate 100 and the lower DBR 102 .
- a resist pattern is formed on the contact layer 106 A by the photolithography process conventionally known, and the annular p-side electrode 110 comprised of Au/Ti is formed on the contact layer 106 A by the liftoff process. Then, SiON is deposited on whole surface of the substrate 100 by CVD, and the circular first insulating film 112 covering the beam window 110 A which is the opening of the p-side electrode 110 is formed by patterning SiON. At this time, the inside of the p-side electrode 110 is covered by the first insulating film 112 , and the outside is exposed. The beam window 110 A is protected from an exposure and particles generated in subsequent processes by being covered by the first insulating film 112 .
- a circular mask MK 1 is formed on a region including the p-side electrode 110 and the first insulating film 112 by the photolithography process. Then, a cylindrical mesa M is formed by etching a semiconductor layer from the upper DBR 106 to the lower DBR 102 by the reactive ion etching process using boron trichloride for example. Accordingly, an AlAs layer 108 inside of the upper DBR 106 is exposed on the side surface of the mesa M. Then the oxidization process that exposes the substrate to the water-vapor atmosphere with a temperature of 340° C.
- the oxidation control is performed so that a radius of plane field of the conductive region 108 B surrounded by the oxidization region 108 A becomes larger than the radius needed for a conventional single lateral mode (e.g. 3 ⁇ m), and becomes the size at which the high-order lateral mode occurs (e.g. 5 ⁇ m).
- the mask MK 1 is removed, and the interlayer insulating film 114 comprised of SiN is formed on whole surface of the substrate as illustrated in FIG. 7A .
- the interlayer insulating film 114 is adjusted so that the film thickness of the top of the mesa M becomes quarter of the wavelength of the medium.
- a mask MK 2 is formed by the photolithography process, and the interlayer insulating film 114 exposed by the mask MK 2 is removed by etching.
- the interlayer insulating film 114 is etched under the etching condition that the selectivity between the interlayer insulating film 114 and the first insulating film 112 can be selected.
- the reactive ion etching process using an etchant of SF 6 +O 2 is carried out.
- patterns of the contact hole 116 and the second insulating film 118 to the p-side electrode 110 is formed at the top of the mesa M.
- a metallic wiring that is coupled to the p-side electrode 110 through the contact hole 116 is formed, and the n-side electrode is formed on the back side of the substrate.
- the fabrication method of the present exemplary embodiment it is possible to form the second insulating film 118 with an easy process only changing a mask pattern by forming the second insulating film 118 and the interlayer insulating film 114 simultaneously, and mass production at low cost becomes possible.
- this makes it work for the reliability of the VCSEL.
- the insulating layer is formed inside of the contact layer by etching the contact layer, it is difficult to stop the etching with high accuracy. If the film thickness of the etched layer is not uniform, there is a possibility that a reflection ratio changes, and this makes it difficult to obtain a reproducible composition.
- the radius of the conductive region (the oxidized aperture) of the current narrowing layer can be changed appropriately according to required optical output.
- FIG. 8A is a cross-section view illustrating a composition of a vertical cavity surface emitting laser device in which the VCSEL and an optical component are packaged.
- a vertical cavity surface emitting laser device 300 fixes a chip 310 , on which a long resonator VCSEL is formed, to a disk-shaped metal stem 330 via a conductive bond 320 .
- Conductive leads 340 and 342 are inserted in a through hole (not illustrated) provided to the stem 330 , the lead 340 is electrically connected to the n-side electrode of the VCSEL, and the lead 342 is electrically connected to the p-side electrode.
- a rectangular hollow cap 350 is fixed on the stem 330 including the chip 310 , and a ball lens 360 is fixed in an opening 352 located in the center of the cap 350 .
- the ball lens 360 is laid out so that the optical axis of the ball lens 360 corresponds to the substantial center of the chip 310 .
- a forward current is applied between leads 340 and 342 , a laser beam is emitted from the chip 310 to the vertical direction.
- the distance between the chip 310 and the ball lens 360 is adjusted so that the ball lens 360 is included within the spread angle ⁇ of the laser beam from the chip 310 .
- a light receiving element and a temperature sensor to monitor the emitting condition of the VCSEL can be included in the cap.
- FIG. 8B is a diagram illustrating a composition of another vertical cavity surface emitting laser device.
- a vertical cavity surface emitting laser device 302 illustrated in FIG. 8B fixes a plane glass 362 in the opening 352 located in the center of the cap 350 instead of using the ball lens 360 .
- the plane glass 362 is laid out so that the center of the plane glass 362 corresponds to the substantial center of the chip 310 .
- the distance between the chip 310 and the plane glass 362 is adjusted so that the opening radius of the plane glass 362 becomes equal to or larger than the spread angle ⁇ of the laser beam from the chip 310 .
- FIG. 9 is a diagram illustrating a case where the VCSEL is applied to a light source of an optical information processing apparatus.
- An optical information processing apparatus 370 is provided with a collimator lens 372 which receives the laser beam from the vertical cavity surface emitting laser device 300 or 302 , in which the long resonator VCSEL is packaged, illustrated in FIG.
- a polygon mirror 374 which rotates at constant speed and reflects a beam of light from the collimator lens 372 at constant spread angle
- a f ⁇ lens 376 which receives the laser beam from the polygon mirror 374 and irradiates the laser beam to a reflection mirror 378 , the linear reflection mirror 378 , and a photoreceptor drum (a record medium) 380 which forms latent images based on the reflection beam from the reflection mirror 378 .
- the laser beam from the VCSEL can be used as a light source of the optical information processing apparatus such as a copier and a printer provided with an optical system which focuses the laser beam from the VCSEL onto the photoreceptor drum and a structure which scans the focused laser beam on the photoreceptor drum.
- the optical information processing apparatus such as a copier and a printer provided with an optical system which focuses the laser beam from the VCSEL onto the photoreceptor drum and a structure which scans the focused laser beam on the photoreceptor drum.
- FIG. 10 is a cross-section view illustrating a composition where the vertical cavity surface emitting laser device illustrated in FIG. 8A is applied to an optical transmission device.
- An optical transmission device 400 includes a cylindrical chassis 410 fixed to the stem 330 , a sleeve 420 integrally-formed on the end surface of the chassis 410 , a ferrule 430 held in an opening 422 of the sleeve 420 , and an optical fiber 440 held by the ferrule 430 .
- the end portion of the chassis 410 is fixed to a flange 332 which is circumferentially-formed of the stem 330 .
- the ferrule 430 is laid out in the opening 422 of the sleeve 420 accurately, and the optical axis of the optical fiber 440 is matched to the optical axis of the ball lens 360 .
- the core of the optical fiber 440 is held in a through hole 432 of the ferrule 430 .
- the laser beam emitted from the surface of the chip 310 is focused by the ball lens 360 .
- the focused beam enters to the core of the optical fiber 440 , and is transmitted.
- the ball lens 360 is used, but other lenses such as a biconvex lens and a plane-convex lens can be used besides a ball lens.
- the optical transmission device 400 can include a drive circuit to apply an electrical signal to leads 340 and 342 .
- the optical transmission device 400 can also include a receiving function to receive an optical signal through the optical fiber 440 .
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Abstract
A vertical cavity surface emitting laser that includes: a substrate; a first semiconductor multilayer reflector; an active region; a second semiconductor multilayer reflector; a columnar structure formed from the second semiconductor multilayer reflector to the first semiconductor multilayer reflector; a current narrowing layer formed inside of the columnar structure and having a conductive region surrounded by an oxidization region; a first electrode formed at a top of the columnar structure, electrically connected to the second semiconductor multilayer reflector and defining a beam window; a first insulating film comprised of a material with a first refractive index and formed on the first electrode to cover the beam window; and a second insulating film comprised of a material with a second refractive index and formed on the first insulating film, of which a radius is smaller than a radius of the conductive region.
Description
- This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-279328 filed on Dec. 9, 2009.
- (i) Technical Field
- The present invention relates to a vertical cavity surface emitting laser, a vertical cavity surface emitting laser device, an optical transmission device, and an information processing apparatus.
- (ii) Related Art
- A vertical cavity surface emitting laser (VCSEL) is used as a light source in a communication device and an image forming apparatus. Single lateral mode, high power and long service life are required for such vertical cavity surface emitting laser used as a light source. In an exemplary selective oxidation type vertical cavity surface emitting laser, a single lateral mode is achieved by reducing a radius of the oxidized aperture of a current narrowing layer to about 2 through 3 μm, but it becomes difficult to obtain an optical output greater than or equal to 3 mW stably.
- According to an aspect of the present invention, there is provided a vertical cavity surface emitting laser device including: a substrate; a first semiconductor multilayer reflector of a first conductive type formed on the substrate; an active region formed on the first semiconductor multilayer reflector; a second semiconductor multilayer reflector of a second conductive type formed on the active region; a columnar structure that is formed from the second semiconductor multilayer reflector to the first semiconductor multilayer reflector on the substrate; a current narrowing layer that is formed inside of the columnar structure, and has a conductive region surrounded by an oxidization region selectively oxidized; a first electrode that is annular, is formed at a top of the columnar structure, is electrically connected to the second semiconductor multilayer reflector, and defines a beam window; a first insulating film that is comprised of a material which has a first refractive index capable of transmitting an oscillation wavelength, and formed on the first electrode to cover the beam window; and a second insulating film that is circular, is comprised of a material which has a second refractive index that is able to transmit an oscillation wavelength and greater than the first refractive index, and is formed on the first insulating film, and of which a radius is smaller than a radius of the conductive region.
- Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:
-
FIG. 1 illustrates a plane view, and a cross-section view taken from line A-A of a vertical cavity surface emitting laser in accordance with a first exemplary embodiment of the present invention; -
FIG. 2 is a cross-section view enlarging a top of a mesa of the vertical cavity surface emitting laser illustrated inFIG. 1 ; -
FIG. 3 is a diagram illustrating exemplary combinations of a first insulating film and a second insulating film; -
FIG. 4A is a diagram illustrating a simulation result of a reflection ratio of an upper DBR in a region where only a first insulating film exists, andFIG. 4B is a diagram illustrating a simulation result of a reflection ratio of an upper DBR in a region where a first insulating film and a second insulating film are stacked; -
FIG. 5 is a cross-section view enlarging a top of a mesa of a vertical cavity surface emitting laser in accordance with a second exemplary embodiment of the present invention; -
FIGS. 6A and 6B are cross-section views for explaining a fabrication process of a vertical cavity surface emitting laser in accordance with a third exemplary embodiment of the present invention; -
FIGS. 7A and 7B are cross-section views for explaining a fabrication process of a vertical cavity surface emitting laser in accordance with the third exemplary embodiment of the present invention; -
FIGS. 8A and 8B are schematic cross-section views illustrating a composition of a vertical cavity surface emitting laser device in which the vertical cavity surface emitting laser of exemplary embodiments and an optical component are packaged; -
FIG. 9 is a diagram illustrating a composition of a light source device using the vertical cavity surface emitting laser of exemplary embodiments; and -
FIG. 10 is a schematic cross-section view illustrating a composition of an optical transmission device using the vertical cavity surface emitting laser device illustrated inFIG. 8A . - A description will now be given, with reference to the accompanying drawings, of exemplary embodiments of the present invention. In the following description, a selective oxidation type vertical cavity surface emitting laser will be exemplified, and a vertical cavity surface emitting laser is abbreviated as a VCSEL. The scale in drawings is exaggerated to understand the feature of the present invention, and is not same as the scale of actual devices.
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FIG. 1 is a schematic cross-section view of a VCSEL in accordance with the first exemplary embodiment of the present invention. As illustrated inFIG. 1 , aVCSEL 10 of the exemplary embodiment is formed by stacking an n-type lower Distributed Bragg Reflector (hereinafter, abbreviated as DBR) 102, anactive region 104, and a p-typeupper DBR 106 on an n-type GaAs substrate 100. The n-typelower DBR 102 is formed by stacking AlGaAs layers with different Al composition alternately. Theactive region 104 includes a quantum well layer sandwiched between upper and lower spacer layers. The p-typeupper DBR 106 is formed by stacking AlGaAs layers with different Al composition on theactive region 104 alternately. - The n-type
lower DBR 102 is a multi-layer stack formed by a pair of an Al0.9Ga0.1As layer and an Al0.3Ga0.7As layer for example. The thickness of each layer is λ/4nr (λ is an oscillation wavelength, and nr is a refractive index of the medium), and the Al0.9Ga0.1As layer and the Al0.3Ga0.7As layer are stacked alternately 40 periods. A carrier concentration after doping an n-type impurity (silicon) is 3×1018 cm−3 for example. - A lower spacer layer of the
active region 104 is an undoped Al0.6Ga0.4As layer, quantum well active layers are an undoped Al0.11Ga0.89As quantum well layer and an undoped Al0.3Ga0.7As barrier layer, and an upper spacer layer is an undoped Al0.6Ga0.4As layer. - The p-type
upper DBR 106 is a multi-layer stack formed by a pair of an Al0.9Ga0.1As layer and an Al0.3Ga0.7As layer for example. The thickness of each layer is λ/4nr, and the Al0.9Ga0.1As layer and the Al0.3Ga0.7As layer are stacked alternately 24 periods. A carrier concentration after doping a p-type impurity (carbon) is 3×1018 cm−3 for example. Acontact layer 106A comprised of p-type GaAs is formed at a top layer of theupper DBR 106, and acurrent narrowing layer 108 comprised of p-type AlAs is formed at a bottom layer of theupper DBR 106 or inside of theupper DBR 106. - A cylindrical mesa (a columnar structure) M is formed on the
substrate 100 by etching a semiconductor layer from theupper DBR 106 to thelower DBR 102. Thecurrent narrowing layer 108 is exposed on the side surface of the mesa M, and has anoxidization region 108A which is selectively oxidized from the side surface, and a conductive region (oxidized aperture) 108B surrounded by theoxidization region 108A. In the oxidization process of thecurrent narrowing layer 108, the oxidation rate of an AlAs layer is faster than that of an AlGaAs layer, and the oxidization proceeds from the side surface of the mesa M to the inside at an almost constant rate. Therefore, the planar shape of the surface, which is parallel to the principal surface of thesubstrate 100 of theconductive region 108B, becomes a round shape which reflects the outer shape of the mesa M, and the center of theconductive region 108B corresponds to the axial center of the mesa M which means an optical axis. The radius of the conductive region 110B may have the size at which the high-order lateral mode oscillation occurs. For example, the radius of the conductive region 110B may be equal to or larger than 5 μm in a wavelength range of 780 nm. - An annular metallic p-
side electrode 110 is formed at the top layer of the mesa M. The p-side electrode 110 is comprised of a metal formed by stacking Au or Ti/Au for example, and is ohmic connected to thecontact layer 106A of theupper DBR 106. The outside diameter of the p-side electrode 110 is larger than the radius of theconductive region 108B. The circular opening is formed at the center of the p-side electrode 110, and this opening defines abeam window 110A which emits a beam. The center of thebeam window 110A corresponds to the optical axis of the mesa M, and the radius of thebeam window 110A is larger than the radius of theconductive region 108B. - A circular first
insulating film 112 is formed on the p-side electrode 110 to cover thebeam window 110A. The firstinsulating film 112 is comprised of a material that is able to transmit the oscillation wavelength. The outside diameter of the firstinsulating film 112 is smaller than the outside diameter of the p-side electrode, and larger than the radius of thebeam window 110A. Therefore, thebeam window 110A is covered by the firstinsulating film 112 completely, but a part of the p-side electrode 110 is exposed by the firstinsulating film 112. - An
interlayer insulating film 114 covering the edge of the bottom, side, and top of the mesa M is formed. The edge of the interlayerinsulating film 114 covers the part of the p-side electrode 110, and aannular contact hole 116 which exposes the p-side electrode 110 is formed between theinterlayer insulating film 114 and the firstinsulating film 112. - A circular second
insulating film 118 comprised of a material that is able to transmit the oscillation wavelength is formed on the firstinsulating film 112. The center of the secondinsulating film 118 corresponds to the optical axis, and the outside diameter of the secondinsulating film 118 is smaller than the radius of theconductive region 108B. For example, when the radius of theconductive region 108B is about 5 μm, the radius of the secondinsulating film 118 is about 3 μm. In the preferable exemplary embodiment, the secondinsulating film 118 can be formed with the same process as that of theinterlayer insulating film 114 by using the same material as that of theinterlayer insulating film 114. An n-side electrode 120 that is electrically connected to thelower DBR 102 is formed on the back side of thesubstrate 100. -
FIG. 2 is an enlarged cross-section views of the top of the mesa of the VCSEL inFIG. 1 . In the present exemplary embodiment, the refractive index of the first insulatingfilm 112 is n1, the refractive index of the secondinsulating film 118 is n2, the refractive index of the semiconductor layer (thecontact layer 106A) of theupper DBR 106 is n3. Then, the relation among n1, n2, and n3 is n1<n2<n3. Each film thickness of the first insulatingfilm 112 and the secondinsulating film 118 is odd multiples of the wavelength of the medium λ/4, which means (2n−1)λ/4 (n is positive integer). - As illustrated in
FIG. 2 , there are a circular first region Z1 where the first insulatingfilm 112 is formed and the secondinsulating film 118 is stacked on the first insulatingfilm 112, and an annular second region X2 where only the first insulatingfilm 112 is formed around the first region Z1, on thecontact layer 106A exposed by thebeam window 110A. The center of the first region Z1 corresponds to the center of the conductive region 110B (the optical axis), but the size of the first region Z1 is smaller than the radius of the conductive region 110B. As the secondinsulating film 118 of which the refractive index n2 is greater than the refractive index n1 of the first insulatingfilm 112 is formed in the first region Z1, the reflection ratio r1 of theupper DBR 106 including the first region Z1 is higher than the reflection ratio r2 of theupper DBR 106 including the second region Z2. Therefore, a high-order lateral mode oscillation is suppressed in theupper DBR 106 including the second region Z2, and a fundamental transverse mode oscillation is accelerated in theupper DBR 106 including the first region Z1. Therefore, it is possible to increase the optical output by making the radius of theconductive region 108B (the radius of the oxidized aperture) be the size at which a high-order lateral mode oscillates. - Preferably, it is desirable to select a material that makes the difference between the refractive indexes n1 and n2 large. This makes it possible to make a difference of reflection ratio between the first region Z1 and the first region Z2 (r1−r2) large. For example, the first insulating
film 112 may be comprised of SiON, and the secondinsulating film 118 may be comprised of SiN. In addition to this, the first insulatingfilm 112 and the secondinsulating film 118 may be comprised of combinations indicated inFIG. 3 . For example, when the first insulatingfilm 112 is comprised of SiON, the secondinsulating film 118 may be comprised of TiO2. When the first insulatingfilm 112 is comprised of SiO2, the secondinsulating film 118 may be comprised of SiN. - A description will now be given of a simulation result of a reflection ratio of the upper DBR of the VCSEL of the present exemplary embodiment. Suppose that the
upper DBR 106 is composed by stacking Al0.9Ga0.1As layer and Al0.3Ga0.7As layer 24 periods.FIG. 4A illustrates a reflection ratio r2 of the upper DBR including the second region Z2 when SiON with a film thickness of λ/4 is formed as the first insulatingfilm 112.FIG. 4B illustrates a reflection ratio r1 of the upper DBR including the first region Z1 when SiON with a film thickness of λ/4 is formed as the first insulatingfilm 112, and SiN with a film thickness of λ/4 is formed as the secondinsulating film 118. In the second region Z2 illustrated inFIG. 4A , the reflection ratio r2 is about 99.2% in a wavelength range of 780 nm. In the first region Z1 illustrated inFIG. 4B , the reflection ratio r1 is about 99.7% in a wavelength range of 780 nm. A reflection ratio needed for a laser oscillation typically is about 99.5%. Therefore, in the first region Z1, the fundamental lateral mode generated on the optical axis is easily oscillated, and in the second region Z2 the high-order lateral mode oscillation away from the optical axis is suppressed. The fundamental transverse mode oscillation is selectively accelerated and the high-order lateral mode oscillation is suppressed, by making the difference between reflection ratios r1 of the first region Z1 and r2 of the second region Z2. Ordinary skilled persons in the art can understand that it is possible to adjust reflection ratios r1 and r2 by selecting the periodic number of theupper DBR 106 and materials of first and second insulatingfilms -
FIG. 5 is a cross-section view of a main part of a VCSEL in accordance with a second exemplary embodiment of the present invention. In aVCSEL 10A in accordance with the present exemplary embodiment, a taper is formed in the mesa M, and the radius of the mesa gradually narrows along to the top. Such taper of the mesa can be formed by selecting proper etching condition. In addition to the taper of the mesa M, the end surface of the first insulatingfilm 112, the end surface of theinterlayer insulating film 114, and the end surface of the secondinsulating film 118 are inclined in a tapered shape. By making the mesa M have a taper structure, the step coverage of the adherentinterlayer insulating film 114 is improved, and it is possible to prevent the disconnection of theinterlayer insulating film 114. In addition, it is possible to make the film thickness of theinterlayer insulating film 114 that is formed on the side and top of the mesa M almost uniform. When the secondinsulating film 118 is formed with the same process as that of theinterlayer insulating film 114, it is possible to uniformly-control both film thicknesses to be odd multiples of λ/4. Furthermore, it is possible to prevent the disconnection of metallic wiring that is coupled to the p-side electrode 110 through thecontact hole 116. - A description will now be given of a third exemplary embodiment. The third exemplary embodiment relates to a preferable fabrication method of the VCSEL. A fabrication method is described with reference to
FIGS. 6A through 7B . As illustrated inFIG. 6A , the n-typelower DBR 102, theactive region 104, and the p-typeupper DBR 106 are stacked on the n-type GaAs substrate 100 by the metal organic chemical vapor deposition (MOCVD) method. The n-typelower DBR 102 is composed by stacking Al0.9Ga0.1As and Al0.3Ga0.7As with a carrier concentration of 2×1018 cm−3 alternately 40 periods so that each film thickness becomes quarter of the wavelength of the medium. The active regionl04 is comprised of an undoped Al0.6Ga0.4As lower spacer layer, an undoped Al0.11Ga0.89As quantum well layer, an undoped Al0.3Ga0.7As barrier layer, and an undoped Al0.6Ga0.4As upper spacer layer. The p-typeupper DBR 106 is composed by stacking a p-type Al0.9Ga0.1As layer and a p-type Al0.3Ga0.7As layer with a carrier concentration of 3×1018 cm−3 alternately 24 periods so that each film thickness becomes quarter of the wavelength of the medium. The p-typeGaAs contact layer 106A with a carrier concentration of 1×1019 cm−3 is formed at the top layer of theupper DBR 106, and a p-type AlAs layer is formed at the bottom of theupper DBR 106 or inside of theupper DBR 106. It is not illustrated, but a buffer layer may be provided between thesubstrate 100 and thelower DBR 102. - A resist pattern is formed on the
contact layer 106A by the photolithography process conventionally known, and the annular p-side electrode 110 comprised of Au/Ti is formed on thecontact layer 106A by the liftoff process. Then, SiON is deposited on whole surface of thesubstrate 100 by CVD, and the circular firstinsulating film 112 covering thebeam window 110A which is the opening of the p-side electrode 110 is formed by patterning SiON. At this time, the inside of the p-side electrode 110 is covered by the first insulatingfilm 112, and the outside is exposed. Thebeam window 110A is protected from an exposure and particles generated in subsequent processes by being covered by the first insulatingfilm 112. - As illustrated
FIG. 6B , a circular mask MK1 is formed on a region including the p-side electrode 110 and the first insulatingfilm 112 by the photolithography process. Then, a cylindrical mesa M is formed by etching a semiconductor layer from theupper DBR 106 to thelower DBR 102 by the reactive ion etching process using boron trichloride for example. Accordingly, an AlAslayer 108 inside of theupper DBR 106 is exposed on the side surface of the mesa M. Then the oxidization process that exposes the substrate to the water-vapor atmosphere with a temperature of 340° C. for a given time is carried out, and theoxidization region 108A which is oxidized a certain distance from the side surface of the mesa M is formed inside of the AlAslayer 108. The oxidation control is performed so that a radius of plane field of theconductive region 108B surrounded by theoxidization region 108A becomes larger than the radius needed for a conventional single lateral mode (e.g. 3 μm), and becomes the size at which the high-order lateral mode occurs (e.g. 5 μm). - Then, the mask MK1 is removed, and the
interlayer insulating film 114 comprised of SiN is formed on whole surface of the substrate as illustrated inFIG. 7A . Theinterlayer insulating film 114 is adjusted so that the film thickness of the top of the mesa M becomes quarter of the wavelength of the medium. Then, as illustrated inFIG. 7B , a mask MK2 is formed by the photolithography process, and theinterlayer insulating film 114 exposed by the mask MK2 is removed by etching. Preferably, theinterlayer insulating film 114 is etched under the etching condition that the selectivity between the interlayer insulatingfilm 114 and the first insulatingfilm 112 can be selected. For example, the reactive ion etching process using an etchant of SF6+O2 is carried out. According to this, patterns of thecontact hole 116 and the secondinsulating film 118 to the p-side electrode 110 is formed at the top of the mesa M. Then, a metallic wiring that is coupled to the p-side electrode 110 through thecontact hole 116 is formed, and the n-side electrode is formed on the back side of the substrate. - According to the fabrication method of the present exemplary embodiment, it is possible to form the second
insulating film 118 with an easy process only changing a mask pattern by forming the secondinsulating film 118 and theinterlayer insulating film 114 simultaneously, and mass production at low cost becomes possible. In addition, as the process is processed under the condition that thebeam window 110A is protected by the first insulatingfilm 112, this makes it work for the reliability of the VCSEL. When the insulating layer is formed inside of the contact layer by etching the contact layer, it is difficult to stop the etching with high accuracy. If the film thickness of the etched layer is not uniform, there is a possibility that a reflection ratio changes, and this makes it difficult to obtain a reproducible composition. - In above exemplary embodiments, a description was given of a current narrowing layer comprised of AlAs, but a current narrowing layer may be an AlGaAs layer of which the Al composition is higher than the Al composition of other DBRs. In addition, the radius of the conductive region (the oxidized aperture) of the current narrowing layer can be changed appropriately according to required optical output. Furthermore, in above exemplary embodiments, the description was given of an GaAs-based VCSEL, but the present invention can be applied to other VCSELs using other III-V group compound semiconductors. In above exemplary embodiments, the description was given of a single spot VCSEL, but the VCSEL can be a multi-spot VCSEL where multiple mesas (emission portion) are formed on the substrate, or a VCSEL array.
- A description will be given of a vertical cavity surface emitting laser device, an optical information processing apparatus, and an optical transmission device using the VCSEL of exemplary embodiments with reference to drawings.
FIG. 8A is a cross-section view illustrating a composition of a vertical cavity surface emitting laser device in which the VCSEL and an optical component are packaged. A vertical cavity surface emittinglaser device 300 fixes achip 310, on which a long resonator VCSEL is formed, to a disk-shapedmetal stem 330 via aconductive bond 320. Conductive leads 340 and 342 are inserted in a through hole (not illustrated) provided to thestem 330, thelead 340 is electrically connected to the n-side electrode of the VCSEL, and thelead 342 is electrically connected to the p-side electrode. - A rectangular
hollow cap 350 is fixed on thestem 330 including thechip 310, and aball lens 360 is fixed in anopening 352 located in the center of thecap 350. Theball lens 360 is laid out so that the optical axis of theball lens 360 corresponds to the substantial center of thechip 310. When a forward current is applied betweenleads chip 310 to the vertical direction. The distance between thechip 310 and theball lens 360 is adjusted so that theball lens 360 is included within the spread angle θ of the laser beam from thechip 310. A light receiving element and a temperature sensor to monitor the emitting condition of the VCSEL can be included in the cap. -
FIG. 8B is a diagram illustrating a composition of another vertical cavity surface emitting laser device. A vertical cavity surface emittinglaser device 302 illustrated inFIG. 8B fixes aplane glass 362 in theopening 352 located in the center of thecap 350 instead of using theball lens 360. Theplane glass 362 is laid out so that the center of theplane glass 362 corresponds to the substantial center of thechip 310. The distance between thechip 310 and theplane glass 362 is adjusted so that the opening radius of theplane glass 362 becomes equal to or larger than the spread angle θ of the laser beam from thechip 310. -
FIG. 9 is a diagram illustrating a case where the VCSEL is applied to a light source of an optical information processing apparatus. An opticalinformation processing apparatus 370 is provided with acollimator lens 372 which receives the laser beam from the vertical cavity surface emittinglaser device FIG. 8A or 8B, apolygon mirror 374 which rotates at constant speed and reflects a beam of light from thecollimator lens 372 at constant spread angle, afθ lens 376 which receives the laser beam from thepolygon mirror 374 and irradiates the laser beam to areflection mirror 378, thelinear reflection mirror 378, and a photoreceptor drum (a record medium) 380 which forms latent images based on the reflection beam from thereflection mirror 378. As described above, the laser beam from the VCSEL can be used as a light source of the optical information processing apparatus such as a copier and a printer provided with an optical system which focuses the laser beam from the VCSEL onto the photoreceptor drum and a structure which scans the focused laser beam on the photoreceptor drum. -
FIG. 10 is a cross-section view illustrating a composition where the vertical cavity surface emitting laser device illustrated inFIG. 8A is applied to an optical transmission device. Anoptical transmission device 400 includes acylindrical chassis 410 fixed to thestem 330, asleeve 420 integrally-formed on the end surface of thechassis 410, aferrule 430 held in anopening 422 of thesleeve 420, and anoptical fiber 440 held by theferrule 430. The end portion of thechassis 410 is fixed to aflange 332 which is circumferentially-formed of thestem 330. Theferrule 430 is laid out in theopening 422 of thesleeve 420 accurately, and the optical axis of theoptical fiber 440 is matched to the optical axis of theball lens 360. The core of theoptical fiber 440 is held in a throughhole 432 of theferrule 430. - The laser beam emitted from the surface of the
chip 310 is focused by theball lens 360. The focused beam enters to the core of theoptical fiber 440, and is transmitted. In above exemplary embodiments, theball lens 360 is used, but other lenses such as a biconvex lens and a plane-convex lens can be used besides a ball lens. Furthermore, theoptical transmission device 400 can include a drive circuit to apply an electrical signal to leads 340 and 342. Theoptical transmission device 400 can also include a receiving function to receive an optical signal through theoptical fiber 440. - The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various exemplary embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
Claims (10)
1. A vertical cavity surface emitting laser comprising:
a substrate;
a first semiconductor multilayer reflector of a first conductive type formed on the substrate;
an active region formed on the first semiconductor multilayer reflector;
a second semiconductor multilayer reflector of a second conductive type formed on the active region;
a columnar structure that is formed from the second semiconductor multilayer reflector to the first semiconductor multilayer reflector on the substrate;
a current narrowing layer that is formed inside of the columnar structure, and has a conductive region surrounded by an oxidization region selectively oxidized;
a first electrode that is annular, is formed at a top of the columnar structure, is electrically connected to the second semiconductor multilayer reflector, and defines a beam window;
a first insulating film that is comprised of a material which has a first refractive index capable of transmitting an oscillation wavelength, and formed on the first electrode to cover the beam window; and
a second insulating film that is circular, is comprised of a material which has a second refractive index that is able to transmit an oscillation wavelength and greater than the first refractive index, and is formed on the first insulating film, and of which a radius is smaller than a radius of the conductive region.
2. The vertical cavity surface emitting laser according to claim 1 , wherein a third refractive index to an oscillation wavelength of a semiconductor layer which composes the second semiconductor multilayer reflector is greater than the second refractive index.
3. The vertical cavity surface emitting laser according to claim 1 , further comprising a third insulating layer that covers a sidewall and a part of a top of the columnar structure, wherein an opening to connect to the first electrode is formed between the third insulating film and the first insulating film.
4. The vertical cavity surface emitting laser according to claim 3 , wherein the third insulating film is comprised of a same material as that of the second insulating film.
5. The vertical cavity surface emitting laser according to claim 1 , wherein the radius of the conductive region is at least 5 μm.
6. A fabrication method of a vertical cavity surface emitting laser having a columnar structure on a substrate, the fabrication method comprising:
stacking a semiconductor layer including a first semiconductor multilayer reflector of a first conductive type, an active region, a current narrowing layer which is conductive, a second semiconductor multilayer reflector of a second conductive type on the substrate;
forming a first electrode which is annular and defines a beam window on the second semiconductor multilayer reflector;
forming a first insulating film that is comprised of a material having a first refractive index to an oscillation wavelength on the first electrode to cover a beam window of the first electrode;
forming the columnar structure including the first electrode and the first insulating film at a top on the substrate by etching the semiconductor layer from the second semiconductor multilayer reflector to the first semiconductor multilayer reflector;
forming an oxidization region and a conductive region surrounded by the oxidization region inside of a current narrowing layer by oxidizing the current narrowing layer inside of the columnar structure selectively;
forming a second insulating film that is comprised of a material having a second refractive index that is greater than the first refractive index on whole area of the substrate including the columnar structure; and
forming a pattern of the second insulating film that corresponds to a center of the conductive region and is smaller than a radius of the conductive region, and an opening that exposes the first electrode on the first insulating film by removing the second insulating film at the top of the columnar structure selectively.
7. The fabrication method according to claim 7 wherein a third refractive index to an oscillation wavelength of a semiconductor layer composing the second semiconductor multilayer reflector is greater than the second refractive index.
8. A vertical cavity surface emitting laser device comprising:
a vertical cavity surface emitting laser including:
a substrate;
a first semiconductor multilayer reflector of a first conductive type formed on the substrate;
an active region formed on the first semiconductor multilayer reflector;
a second semiconductor multilayer reflector of a second conductive type formed on the active region;
a columnar structure that is formed from the second semiconductor multilayer reflector to the first semiconductor multilayer reflector on the substrate;
a current narrowing layer that is formed inside of the columnar structure, and has a conductive region surrounded by an oxidization region selectively oxidized;
a first electrode that is annular, is formed at a top of the columnar structure, is electrically connected to the second semiconductor multilayer reflector, and defines a beam window;
a first insulating film that is comprised of a material which has a first refractive index capable of transmitting an oscillation wavelength, and formed on the first electrode to cover the beam window; and
a second insulating film that is circular, is comprised of a material which has a second refractive index that is able to transmit an oscillation wavelength and greater than the first refractive index, and is formed on the first insulating film, and of which a radius is smaller than a radius of the conductive region; and
an optical member that receives a beam from the vertical cavity surface emitting laser.
9. An optical transmission device comprising:
a vertical cavity surface emitting laser device that comprises:
a vertical cavity surface emitting laser that includes:
a substrate;
a first semiconductor multilayer reflector of a first conductive type formed on the substrate;
an active region formed on the first semiconductor multilayer reflector;
a second semiconductor multilayer reflector of a second conductive type formed on the active region;
a columnar structure that is formed from the second semiconductor multilayer reflector to the first semiconductor multilayer reflector on the substrate;
a current narrowing layer that is formed inside of the columnar structure, and has a conductive region surrounded by an oxidization region selectively oxidized;
a first electrode that is annular, is formed at a top of the columnar structure, is electrically connected to the second semiconductor multilayer reflector, and defines a beam window;
a first insulating film that is comprised of a material which has a first refractive index capable of transmitting an oscillation wavelength, and formed on the first electrode to cover the beam window; and
a second insulating film that is circular, is comprised of a material which has a second refractive index that is able to transmit an oscillation wavelength and greater than the first refractive index, and is formed on the first insulating film, and of which a radius is smaller than a radius of the conductive region; and
an optical member that receives a beam from the vertical cavity surface emitting laser; and
a transmission unit that transmits a laser beam emitted from the vertical cavity surface emitting laser device through an optical medium.
10. An information processing apparatus comprising:
a vertical cavity surface emitting laser that includes:
a substrate;
a first semiconductor multilayer reflector of a first conductive type formed on the substrate;
an active region formed on the first semiconductor multilayer reflector;
a second semiconductor multilayer reflector of a second conductive type formed on the active region;
a columnar structure that is formed from the second semiconductor multilayer reflector to the first semiconductor multilayer reflector on the substrate;
a current narrowing layer that is formed inside of the columnar structure, and has a conductive region surrounded by an oxidization region selectively oxidized;
a first electrode that is annular, is formed at a top of the columnar structure, is electrically connected to the second semiconductor multilayer reflector, and defines a beam window;
a first insulating film that is comprised of a material which has a first refractive index capable of transmitting an oscillation wavelength, and formed on the first electrode to cover the beam window; and
a second insulating film that is circular, is comprised of a material which has a second refractive index that is able to transmit an oscillation wavelength and greater than the first refractive index, and is formed on the first insulating film, and of which a radius is smaller than a radius of the conductive region;
a focusing unit that focuses a laser beam emitted from the vertical cavity surface emitting laser onto a record medium; and
a structure which scans the laser beam focused by the focusing unit on the record medium.
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Also Published As
Publication number | Publication date |
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US8465993B2 (en) | 2013-06-18 |
US20130034922A1 (en) | 2013-02-07 |
JP2011124314A (en) | 2011-06-23 |
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