WO2005093918A1 - Laser à émission par la surface - Google Patents

Laser à émission par la surface Download PDF

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Publication number
WO2005093918A1
WO2005093918A1 PCT/JP2005/001458 JP2005001458W WO2005093918A1 WO 2005093918 A1 WO2005093918 A1 WO 2005093918A1 JP 2005001458 W JP2005001458 W JP 2005001458W WO 2005093918 A1 WO2005093918 A1 WO 2005093918A1
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Prior art keywords
layer
surface emitting
emitting laser
laser
type
Prior art date
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PCT/JP2005/001458
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English (en)
Japanese (ja)
Inventor
Takahiro Nakamura
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Nec Corporation
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Priority to JP2006511397A priority Critical patent/JPWO2005093918A1/ja
Publication of WO2005093918A1 publication Critical patent/WO2005093918A1/fr

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Classifications

    • 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]
    • H01S5/18302—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] comprising an integrated optical modulator
    • 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
    • H01S5/04256—Electrodes, e.g. characterised by the structure characterised by the configuration
    • 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
    • H01S5/04256—Electrodes, e.g. characterised by the structure characterised by the configuration
    • H01S5/04257—Electrodes, e.g. characterised by the structure characterised by the configuration having positive and negative electrodes on the same side of the substrate
    • 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
    • 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]
    • H01S5/18341—Intra-cavity contacts
    • 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
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/2004—Confining in the direction perpendicular to the layer structure
    • H01S5/2018—Optical confinement, e.g. absorbing-, reflecting- or waveguide-layers
    • H01S5/2022—Absorbing region or layer parallel to the active layer, e.g. to influence transverse modes
    • 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
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/305—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure
    • H01S5/3095—Tunnel junction

Definitions

  • the present invention relates to a surface emitting laser used as a light source for optical communication and an optical transmission module using the same.
  • a surface emitting laser has advantages such as low power consumption and low cost as compared with an edge emitting laser. By using this surface emitting laser, a low power consumption and low cost optical transmission module is expected to be realized. . In optical interconnection between boards or between chips, it is necessary to mount optical transmission modules densely in a limited area. It is considered that an optical transmission module using a surface emitting laser is essential.
  • Fig. 1 shows the structure of a conventional 0.85 m band surface emitting laser widely used in general.
  • an n-type Bragg reflection mirror 82, an n-type cladding layer 83, an active layer 84, a p-type cladding layer 85, a p-type AlGaAs layer 86, and a p-type Bragg reflection mirror 87 are sequentially formed.
  • a p-electrode 91 is formed in contact with the p-type Bragg reflection mirror 87
  • an n-electrode 92 is formed in contact with the n-type cladding layer 83.
  • An opening 90 for extracting a laser beam is formed in the p-electrode 91.
  • an insulating layer 88 having a current opening is formed in the p-type layer region. It is desirable that the size of the current aperture of the insulating layer 88 be small in order to shape the transverse mode of the laser beam. The smaller this size is, the more stable the fundamental transverse mode oscillation can be obtained.
  • the outer edges of the p-type layer, the insulating layer, and the active layer are etched into a post shape 89.
  • a laser resonator is formed by the two Bragg reflection mirrors 82 and 87. By setting the reflectance of these reflection mirrors to a high reflectance of about 99%, the resonator is formed. Mirror loss is reduced to several cm 1 and the current aperture of the insulating layer 88 is set to 5-10 m By confining the current in a small region as ⁇ , a low oscillation threshold can be obtained. According to the surface emitting laser having such a structure, a low oscillation threshold current is about 1 mA, an optical output is about several mW, and a modulation band of about 10 GHz can be obtained with an average optical output of about 2 mW.
  • FIG. 2 shows a drive circuit for the surface emitting laser shown in FIG.
  • This drive circuit includes a laser driver IC95 for driving a surface emitting laser chip 94 composed of the surface emitting laser shown in FIG. 1, and a digital LSI 96 for supplying a voltage signal V to the laser driver IC95.
  • Digital m Digital m
  • the voltage signal V is input to the laser driver IC95 from the IZO port of the LSI96.
  • the laser driver IC 95 is an analog IC, and converts a voltage signal V input from the digital LSI 96 into a laser modulation current I.
  • the laser modulation current I is 91
  • the laser driver IC 95 has a function of superimposing the DC bias current I on the laser modulation current I and supplying it to the diode 93.
  • the diode 93 corresponds to a pn junction region around the active layer in the surface emitting laser chip 94.
  • the digital LSI 96 and laser driver IC95 are designed with a 50 ⁇ input and output.
  • the surface emitting laser In order for the surface emitting laser to flow through the surface emitting laser, the
  • the laser driver IC 95 is a low power consumption Si—CMOS—IC.
  • the power supply is a 3.3 V power supply
  • the operating voltage of the surface emitting laser needs to be 2.3 V or less. This is because a single stage of Si-CMOS transistor requires a voltage drop of about IV.
  • the above-described surface emitting lasers are widely used.
  • the surface emitting laser has a structure in which the laser light intensity is modulated by direct current modulation, the active layer current changes with time, and thus the laser wavelength changes with time. Therefore, when used for long-distance optical communication, the optical waveform after passing through the optical fiber is deteriorated due to wavelength fluctuation, and the transmission band of the optical signal is limited. Therefore, a surface emitting laser with an integrated optical modulator (hereinafter referred to as an optical modulator integrated type surface emitting laser) capable of suppressing wavelength fluctuation and increasing the transmission band has been proposed.
  • an optical modulator integrated type surface emitting laser capable of suppressing wavelength fluctuation and increasing the transmission band.
  • Fig. 3 shows a structural example of an optical modulator integrated type surface emitting laser (Japanese Patent Publication No. 7-93473). reference).
  • an n-type Bragg reflection mirror 122, an n-type cladding layer 123, an active layer 124, a p-type cladding layer 125, a p-type Bragg reflection mirror 126, a p-type contact layer 127, a high resistance layer 128, n A type cladding layer 129, a multiple quantum well layer 130, and a p-type cladding layer 131 are sequentially stacked.
  • the p-electrode 132 contacts the p-type contact layer 127
  • the n-electrode 133 contacts the n-type cladding layer 129
  • the p-electrode 134 contacts the p-type cladding layer 131
  • the n-electrode 135 contacts the n-type substrate 121.
  • the p-electrode 134 has an opening (not shown) for extracting a laser beam.
  • a laser resonator is formed by the two Bragg reflection mirrors 122 and 126. Outside the resonator, a multiple quantum well layer 130 whose absorption coefficient changes with voltage is formed by an n-type cladding layer 129 and a p-type cladding layer 129. An optical modulator sandwiched by 131 is formed.
  • the active layer 124 emits light by applying a forward bias voltage V between the p electrode 132 and the n electrode 135. At this time, p electrode 134 and n electrode
  • the laser light from the laser resonator passes through the multiple quantum well layer 130 as it is, and the active layer current due to the forward bias voltage V oscillates.
  • the surface emitting laser oscillates at a value current or more.
  • a reverse bias voltage V is applied between the p-electrode 134 and the n-electrode 133, the light absorption coefficient of the multiple quantum well layer 130 increases and the laser output becomes m
  • the laser light is modulated by changing the reverse bias voltage V of the optical modulator.
  • an optical modulator integrated type surface emitting laser as shown in FIG. 4 has also been proposed (see Japanese Patent Application Laid-Open No. 5-152674).
  • an n-type Bragg reflection mirror 142, an n-type cladding layer 143, an active layer 144, a p-type cladding layer 145, a p-type Bragg reflection mirror 146, a p-type contact layer 147, a p-type cladding layer 148, multiple A quantum well layer 149, an n-type cladding layer 150, and an n-type Bragg reflection mirror 151 are sequentially formed.
  • the p-electrodes 152 and 153 are formed in contact with the p-type contact layer 147, the n-electrode 154 is formed in contact with the n-type Bragg reflection mirror 151, and the n-electrode 155 is formed in contact with the n-type clad layer 143.
  • the n-electrode 154 has an opening (not shown) for extracting a laser beam.
  • a laser resonator is formed by the two Bragg reflection mirrors 142 and 146, and a multi-quantum well layer 149 whose optical absorption coefficient changes with voltage is formed outside the resonator by a p-type cladding layer 1
  • An optical modulator sandwiched between 48 and the n-type cladding layer 150 is formed. This optical modulator is disposed inside a resonator consisting of two Bragg reflection mirrors 146 and 151, which is separate from the laser resonator.
  • the active layer 144 emits light by applying a forward bias voltage V between the p-electrode 152 and the n-electrode 155. At this time, p electrode 153 and n electrode
  • the laser light from the laser resonator passes through the multiple quantum well layer 149 as it is, and the active layer current due to the forward bias voltage V oscillates.
  • the surface emitting laser oscillates at a value current or more.
  • a reverse bias voltage V is applied between the p-electrode 153 and the n-electrode 154, the light absorption coefficient of the multiple quantum well layer 149 increases and the laser output becomes m
  • the laser light is modulated by changing the reverse bias voltage V of the optical modulator.
  • the effective optical absorption change of the optical modulator is It is larger than.
  • the laser driver IC95 that modulates the current of a surface emitting laser is often designed so that the input and output characteristic impedances are matched at 50 ⁇ .
  • the force required to set the series resistance of the surface emitting laser to 50 ⁇ under DC bias is not always easy.
  • the surface emitting laser is configured so that the current flow region in the P-type layer is limited to a small value.
  • the series resistance easily exceeds 50 ⁇ as soon as it is affected by the interface resistance at the mirror 87. It is.
  • the problem of an increase in the series resistance is a force that can be alleviated by high-concentration doping of the p-type layer.
  • an increase in p concentration causes an increase in valence band absorption, which results in an increase in the lasing threshold and a decrease in slope efficiency.
  • the allowable limit value of the p concentration is low, it is difficult to decrease the resistance value by increasing the p concentration.
  • the resistance value varies due to the variation in the current opening size of the insulating layer 88.
  • the yield of an element with an operating frequency of 10 GHz is poor.
  • the power consumption of the surface emitting laser itself is as low as about 10 mW, whereas the laser driver IC95 requires several stages of transistors to convert a low-voltage digital signal from the digital LSI 96 into a current modulation signal. Its power consumption is as large as several hundred mW.
  • the power consumption of the laser driver IC95 is It will increase further. For this reason, in order to reduce the power of a surface emitting laser, it is necessary to reduce the power of a laser driver IC, which is one of the important issues in reducing the power of an optical transmission module. Has become. In particular, in the field of optical interconnection between chips, the necessity of reducing the power of laser driver ICs is increasing.
  • optical modulator integrated type surface emitting lasers have a structure in which a DC bias current is applied to an active layer, and a modulation voltage is applied to the optical modulator to modulate laser light. Only the modulation voltage is applied to the optical modulator, and the DC bias can be supplied by another circuit. In this case, if the modulation voltage can be applied with a 50 ⁇ impedance and a low amplitude voltage, the power consumption of the laser driver IC can be reduced without deteriorating the modulation waveform.
  • both optical modulator integrated surface emitting lasers have a structure in which an absorption layer is inserted between the p-type and n-type Bragg reflecting mirrors by the quantum confinement quantum effect (QCSE) using multiple quantum wells.
  • QCSE quantum confinement quantum effect
  • An object of the present invention is to solve the above-mentioned problems and to provide a surface-emitting laser capable of reducing power consumption while maintaining an optical output.
  • a further object of the present invention is to provide a high-bandwidth operation that can reliably achieve impedance matching with a laser driver IC, can be manufactured with high yield,
  • An object of the present invention is to provide a stable surface emitting laser in a transverse mode.
  • the surface emitting laser of the present invention oscillates in the thickness direction of the active layer in a laser resonator having two Bragg reflection mirrors stacked so as to sandwich the active layer. And a light modulation layer having a resonance tunnel structure for modulating light to be emitted.
  • the supply of a small voltage causes the band edge of the n-type clad layer to bend, and absorption by the Franz-Keldysh effect occurs largely. Therefore, the voltage required for the modulation operation is greatly reduced as compared with the conventional one.
  • the change in the light absorption coefficient required for performing light modulation is smaller than when the light modulation layer is provided outside the laser resonator. It can be small. Further, the light absorption modulation amount required for laser beam modulation also mirror loss of the laser resonator (e.g., in the case the reflectivity of the Bragg reflection mirror is about 99%, about several cm 1) and requires the same extent. The smaller the change in light absorption coefficient and the amount of light absorption modulation, the lower the voltage required for the modulation operation.
  • the active layer and the light modulation layer may be galvanically separated.
  • the light modulation layer has a structure in which a double barrier layer is sandwiched between two cladding layers of the same conductivity type, and the cladding layer in contact with the active layer of the two cladding layers has the active layer.
  • a ground electrode for supplying a DC bias voltage to the layer may be formed.
  • a high resistance layer or an insulating layer may be provided between the active layer and the light modulation layer.
  • the element resistance value of the modulation circuit is determined by the value of the terminating resistor provided outside the surface emitting laser resonator, and thus can be determined independently of the DC bias series resistance. The value can also be determined accurately. Therefore, the P concentration of the P-type layer and the size of the aperture of the current confinement can be optimized in a direction to optimize the oscillation threshold, the slope efficiency, and the beam shape.
  • the current with respect to the peak voltage and the valley voltage of the resonance tunnel is higher than the threshold current of the active layer by V and the deviation is also higher.
  • the laser light can be modulated stably.
  • the current with respect to the peak voltage of the resonance tunnel lower than the saturation current of the active layer, it is possible to obtain a sufficient extinction ratio.
  • the absorption by the Franz-Keldysh effect of the n-type cladding layer using the resonance tunnel structure is used, the light output without light absorption by the p layer is improved. Is effective.
  • the voltage required for the modulation operation is greatly reduced.
  • a surface emitting laser with low power consumption can be provided, and the power of the laser driver IC can be reduced.
  • the value of the impedance matching and the terminating resistance can be set accurately, so that high-speed modulation is possible.
  • a surface emitting laser having a stable transverse mode can be obtained with a high yield.
  • the modulation voltage can be applied with a 50 ⁇ impedance and a low amplitude voltage, the power consumption of the laser driver IC can be reduced without deteriorating the modulation waveform. There is an effect that can be.
  • the laser driver IC does not require a transistor for converting an input modulation voltage into a modulation current, and thus has an effect that power consumption of the laser driver IC can be significantly reduced.
  • the extinction ratio of the laser light may be low, for example, when the modulation voltage is set to 0.5 V or less, the surface emitting laser is directly driven only by the digital LSI without the laser driver IC. There is an effect that can be.
  • FIG. 1 is a cross-sectional view of a conventional 0.85 ⁇ m band surface emitting laser.
  • FIG. 2 is a drive circuit diagram of the surface emitting laser shown in FIG. 1.
  • FIG. 3 is a sectional view of a conventional light modulator integrated type surface emitting laser.
  • FIG. 4 is a cross-sectional view of another conventional light modulator integrated type surface emitting laser.
  • FIG. 5 is a cross-sectional view of the surface emitting laser according to the first embodiment of the present invention.
  • FIG. 6 is an equivalent circuit diagram for driving the surface emitting laser shown in FIG. 5.
  • FIG. 7 is a schematic diagram showing a relationship between a light intensity distribution in a layer thickness direction in the laser resonator shown in FIG. 5 and an arrangement of each layer.
  • FIG. 8 is a view for explaining a resonance tunnel structure.
  • FIG. 9 is a sectional view of a surface emitting laser according to a second embodiment of the present invention.
  • FIG. 10 is an equivalent circuit diagram for driving the surface emitting laser shown in FIG. 9.
  • FIG. 11 is a sectional view of a surface emitting laser according to a third embodiment of the present invention.
  • FIG. 12 shows an equivalent circuit when the surface emitting laser shown in FIG. 11 is driven.
  • FIG. 5 is a cross-sectional view of the surface emitting laser according to the first embodiment of the present invention.
  • This surface-emitting laser consists of an n-type GaAs substrate (or high-resistance substrate) 1, an n-type Bragg reflection mirror 2, an n-type cladding layer 3, a double barrier structure 4, an n-type cladding layer 5, and a multiple quantum well.
  • An active layer 8, a p-type cladding layer 9, a p-type AlGaAs layer 10, and a p-type Bragg reflection mirror 11 are sequentially laminated.
  • a p-electrode 15 is formed so as to be in contact with the surface of the p-type Bragg reflection mirror 11, and an n-electrode 16 is formed so as to be in contact with the n-type cladding layer 3.
  • the p-electrode 15 has a ring-shaped opening 14 through which laser light is emitted.
  • the active layer 8, the p-type cladding layer 9, the p-type AlGaAs layer 10, and the p-type Bragg reflection mirror 11 are formed into a post shape 13 by etching.
  • a high-resistance layer 12 having a current aperture is formed between the p-type cladding layer 9 and the p-type Bragg reflection mirror 11 and outside the p-type AlGaAs layer 10 for current confinement.
  • the size of the current aperture is desirably small in order to shape the transverse mode of the laser beam, and the smaller the size, the more stable fundamental transverse mode oscillation can be obtained.
  • the double barrier layer 4 is composed of, for example, two potential barrier structures composed of AlAs barrier layers and a GaAs quantum well layer surrounded by the two potential barrier structures.
  • the thickness of the AlAs barrier layer is, for example, 2 nm
  • the thickness of the GaAs quantum well layer is, for example, 5 nm.
  • the double barrier structure 4 can be configured by various combinations. Examples of combinations include a combination using AlAs or InAlAs for the barrier layer and using InAs or InGaAs for the quantum well layer, and a combination using AlSb for the barrier layer and InAs for the quantum well layer.
  • a laser resonator including two Bragg reflection mirrors 2 and 11 has a double barrier structure 4 sandwiched between n-type cladding layers 3 and 5. It has a tunnel structure light modulation layer. In this light modulation layer, the light absorption coefficient changes when a voltage is applied to the resonance tunnel structure (voltage is applied between the P electrode 15 and the n electrode 16).
  • FIG. 6 shows an equivalent circuit for driving the surface emitting laser shown in FIG.
  • Diode 40 is composed of n-type black reflective mirror 2, n-type cladding layer 3, double barrier structure 4, n-type cladding layer 5, multiple quantum well active layer 8, p-type cladding layer 9, p-type AlGaAs layer 10, p-type This is a portion including the black reflection mirror 11.
  • the diode 40 is biased in the forward direction through the p-electrode 15 and the n-electrode 16, the multiple quantum well 8 emits light.
  • a DC noise voltage V is applied between the p electrode 15 and the n electrode 16, and in this state, the resonance tunnel structure (the n-type cladding layer 3,
  • the light modulation layer utilizes the light absorption by the Franz-Keldysh effect of the n-type cladding layer using the resonance tunnel structure, and has the same structure as the conventional structure. Since the light output does not decrease due to the valence band absorption of the p-type cladding layer, the light output can be improved.
  • oscillation light from the laser resonator passes through the modulation layer only once.
  • the oscillated light passes through the optical modulation layer each time it reciprocates in the laser resonator. Therefore, even if the change in light absorption of the modulation layer is small, the modulation is strong while the oscillation light is reciprocating within the laser resonator.
  • the reflectance of the two Bragg reflector mirror 2, 11 constituting the laser resonator is a degree about 99%, the mirror loss of the surface emitting laser is about several cm 1.
  • the amount of light absorption modulation required for light modulation is about several cm 1 , which is about the same as the mirror loss.
  • the light modulation layer is arranged at a place where the light intensity is high inside the laser resonator so that light modulation can be performed efficiently.
  • FIG. 7 schematically shows the relationship between the light intensity distribution in the layer thickness direction in the laser resonator and the arrangement of each layer.
  • the light intensity distribution in the laser cavity is a sine wave as shown in Fig. 7, and the multiple quantum well 8 and the double barrier structure 4 are at the peak of the sine wave (the high light intensity portion). It is arranged to be located. According to this arrangement, it is possible to efficiently modulate the oscillation light.
  • FIG. 8 is a diagram for explaining the resonance tunnel structure, in which (a) is a characteristic diagram showing a current-voltage relationship, and (b)-(d) are current-voltage characteristics of (a).
  • FIG. 2 is a band structure diagram at points A, B, and C. These (a)-(d) constitute one figure.
  • FIG. 8A shows current-voltage characteristics in a resonance tunnel structure composed of GaAs and AlAs.
  • the resonant tunneling structure in this example consists of a double barrier layer consisting of two potential barrier structures with an AlAs barrier layer and a GaAs quantum well layer surrounded by them, with a thickness of 2 nm and 5 nm, respectively.
  • electrons can only penetrate the double barrier layer when they have an energy that matches the quantum level in the quantum well. Therefore, a negative resistance characteristic characteristic of the current-voltage characteristic (IV) occurs as shown in FIG. According to this current-voltage characteristic, the current flows up to the peak current, but then becomes a valley current where no current flows.
  • Figures 8 (b)-(d) show the respective band structures at point A (starting point), point B (peak current), and point C (valley current) of this current-voltage characteristic.
  • point A starting point
  • point B peak current
  • point C valley current
  • the depletion layer Depletion Layer
  • the band edge bends greatly, and the absorption of short-wave light is larger than in the band. Since the voltage required to transition from peak current to valley current is small, large absorption can be obtained at low voltage. As a result, the voltage required for the modulation operation can be greatly reduced.
  • the surface emitting laser of the present embodiment does not have an extra Bragg reflection mirror for forming a modulator, stable laser oscillation that does not cause the composite resonator effect can be obtained.
  • the surface emitting laser of the present embodiment can reduce power consumption while maintaining a stable light output.
  • the surface emitting laser of the present embodiment can be easily manufactured by applying a well-known semiconductor manufacturing process. Hereinafter, the manufacturing procedure will be briefly described.
  • an n-type black reflective mirror 2 made of GaAsZAlAs and an n-type cladding layer 3 made of GaAs are formed on an n-type GaAs substrate (or high-resistance substrate) 1 by metal organic chemical vapor deposition or molecular beam epitaxy.
  • a p-type cladding layer 10 made of GaAs, a p-type AlGaAs layer 10 are sequentially formed.
  • the laminated portion from the active layer (multiple quantum well) 8 to the p-type black reflection mirror 11 is processed into a circular post shape having a diameter of 20 ⁇ m by dry etching, and the p-type AlGaAs layer 10 is formed to a diameter of 5 ⁇ m by steam oxidation.
  • the current confinement structure is produced by oxidation while leaving only the area of m.
  • the n-type cladding layer 5 and a part of the double barrier structure 4 are etched until the n-type cladding layer 3 is exposed, and an n-electrode 16 is formed there.
  • the p-electrode 15 is formed concentrically except for the central light emitting portion of the post shape 13.
  • a surface emitting laser having the structure shown in FIG. 5 is obtained.
  • the light modulation layer and the active layer (multiple quantum well) 8 serving as the DC bias layer can be separated from the dc electric current by the pn junction. It is also possible to adopt a configuration in which the modulation layer and the active layer 8 are driven by independent circuits. Here, an embodiment having such a configuration will be described.
  • FIG. 9 is a sectional view of a surface emitting laser according to a second embodiment of the present invention.
  • This surface emitting laser has the same structure as that shown in FIG. 5 except that a ground electrode 30 is provided so as to be in contact with the n-type cladding layer 5.
  • the same parts are denoted by the same reference numerals. To avoid repetition, the description of the same parts will be omitted, and only different parts will be described.
  • FIG. 10 shows an equivalent circuit for driving the surface emitting laser shown in FIG.
  • the surface emitting laser chip 20 includes two diodes 21a and 21b whose one ends are commonly connected to the ground (ground electrode 30).
  • the diode 21a corresponds to the n-type cladding layer 5, the active layer 8, the p-type cladding layer 9, the p-type AlGaAs layer 10, and the p-type black reflection mirror 11.
  • the active layer 8 emits light by forward-biasing the diode 21a through the p-electrode 15 and the n-electrode 16. At this time, DC bias voltage V is applied to p electrode 15 and ground electrode 30,
  • the one resonator oscillates at an oscillation threshold current or higher.
  • the diode 21b includes an n-type black reflection mirror 2, an n-type cladding layer 3, a double barrier layer 4, Corresponds to the part of the mold clad layer 5.
  • a voltage is applied to the diode 21b via the ground electrode 30 and the n-electrode 16
  • a "depletion layer depletion layer” is generated in the n-type cladding layer 5, the band edge is bent, and the light absorption coefficient changes.
  • the modulation voltage V is applied to the ground electrode 30 and the n-electrode 16.
  • This modulation voltage V is mm by a laser driver IC with 50 ⁇ impedance.
  • a 50 ⁇ termination resistor 19 is inserted in parallel with the diode 21b. In this way, impedance matching is achieved.
  • the terminating resistor 19 is a chip resistor mounted outside the surface emitting laser chip 20.
  • the first advantage is that the fluctuation of the DC bias current flowing in the active layer when a modulation voltage is applied to the light modulation layer can be suppressed. As a result, fluctuations in the average output of the laser beam can be suppressed.
  • the second advantage is that the resistance of the laser driver IC that performs modulation driving, which is related to the series resistance for DC bias, is also determined by the terminating resistance 19. Therefore, what value is the series resistance for DC bias? However, the impedance matching of the modulation circuit can be accurately achieved. For example, if the resistance value of the terminating resistor is set to 50 ⁇ , the termination can always be 50 ⁇ even if the characteristics of the surface emitting laser vary. Therefore, the p concentration of the p-type layer and the size of the current confinement aperture can be optimized in the direction of optimizing the oscillation threshold, slope efficiency, and beam shape.
  • the second advantage is particularly remarkable. It becomes. Note that even if the series resistance of the DC bias varies due to manufacturing variations in the current aperture size due to current constriction, the impedance matching of the modulation circuit does not change.
  • the first and second advantages described above are also effective when a resistor is integrated inside a surface emitting laser chip. In this case, manufacturing variability can be easily suppressed simply by controlling the size of the resistor and the carrier concentration.
  • the surface emitting laser of the present embodiment As described above, according to the surface emitting laser of the present embodiment, a high band operation is possible. In addition, it is possible to obtain a surface emitting laser having a stable transverse mode and a high yield.
  • the surface emitting laser of the present embodiment can be easily manufactured by applying a well-known semiconductor manufacturing process. Hereinafter, the manufacturing procedure will be briefly described.
  • an n-type black reflection mirror 2 made of GaAsZAlAs and an n-type cladding layer 3 made of GaAs are formed on an n-type GaAs substrate (or high-resistance substrate) 1 by metal organic chemical vapor deposition or molecular beam epitaxy.
  • Double barrier structure consisting of AlAs barrier layer and GaAs quantum well layer 4.
  • N-type cladding layer consisting of Ga As
  • three-layer GalnNAs quantum well and active layer consisting of GaAs barrier layer (multiple quantum well) 8
  • a p-type cladding layer 9 made of GaAs, a p-type AlGaAs layer 10, and a p-type black reflection mirror 11 made of GaAs / AlAs are sequentially formed.
  • the laminated portion from the active layer (multiple quantum well) 8 to the p-type black reflection mirror 11 is formed into a circular post having a diameter of 20 / zm by dry etching, and the p-type AlGaAs layer 10 is formed by steam oxidation.
  • the current confinement structure is fabricated by oxidizing leaving only the area of 5 m in diameter.
  • the n-type cladding layer 5 and a part of the double barrier structure 4 are etched until the n-type cladding layer 3 is exposed, and an n-electrode 16 is formed there.
  • the p-electrode 15 is formed concentrically except for the light emission portion at the center of the post shape 13.
  • a ground electrode 30 is formed so as to be in contact with the n-type cladding layer 5.
  • the light modulating layer and the active layer have a structure in which the light modulating layer and the active layer are DC-electrically separated by a pn junction.
  • the problem of high-frequency coupling due to the pn junction capacitance can be solved by electrically isolating the pn junction.
  • an embodiment having such a structure will be described.
  • FIG. 11 is a sectional view of a surface emitting laser according to a third embodiment of the present invention.
  • This surface emitting laser has a structure shown in FIG. 9, in which a high-resistance layer 6 made of, for example, AIGaAs and an n-type cladding layer 7 are provided between an n-type cladding layer 5 and an active layer 8, and a ground electrode 30 is formed. Instead, a p-electrode 17 and an n-electrode 18 are provided.
  • the same portions are denoted by the same reference numerals. In order to avoid duplication of description, the description of the same parts will be omitted here, and only different parts will be described.
  • n-type cladding layer 5 On the n-type cladding layer 5, a high resistance layer 6 and an n-type cladding layer 7 are sequentially laminated.
  • a stacked structure (active layer 8, p-type cladding layer 9, p-type AlGaAs layer 10, and p-type black reflection mirror 11) having a post shape 13 is formed on the pad layer 7.
  • a p-electrode 17 is provided so as to be in contact with the n-type clad layer 5, and an n-electrode 18 is provided so as to be in contact with the n-type clad layer 7.
  • FIG. 12 shows an equivalent circuit for driving the surface emitting laser shown in FIG.
  • the surface emitting laser chip 20 includes two diodes 22a and 22b separated by direct current by a high resistance layer.
  • the diode 22a corresponds to the n-type cladding layer 7, the active layer 8, the p-type cladding layer 9, the p-type AlGaAs layer 10, and the p-type black reflection mirror 11.
  • the active layer 8 emits light by forward-biasing the diode 22a through the p-electrode 15 and the n-electrode 18. At this time, a DC bias voltage V is applied to the p-electrode 15 and the n-electrode 18, and the laser resonator is
  • the diode 22b corresponds to the n-type black reflection mirror 2, the n-type cladding layer 3, the double barrier layer 4, and the n-type cladding layer 5.
  • a voltage is applied to the diode 22a via the p-electrode 17 and the n-electrode 16
  • a "depletion layer depletion layer” is generated in the n-type cladding layer 5, and the band edge is bent and the light absorption coefficient changes.
  • modulation voltage V is applied to p electrode 17 and n electrode 16.
  • This modulation voltage V is applied by a laser driver IC with 50 ⁇ impedance.
  • a termination resistor 19 of 50 ⁇ is inserted in parallel with the diode 22.
  • impedance matching is achieved.
  • the terminating resistor 19 is a chip resistor mounted outside the surface emitting laser chip 20.
  • the circuit that oscillates the surface emitting laser by applying a DC bias and the circuit that modulates the laser light are DC-electrically separated by the high-resistance layer 6. Even if the resistance for DC biasing the light emitting laser is high, the element resistance seen from the laser driver IC for modulation drive is determined by the terminating resistor 19. For this reason, if the resistance value of the terminating resistor is set to 50 ⁇ , even if the characteristics of the surface emitting laser vary, the termination can always be terminated at 50 ⁇ .
  • the design of the surface emitting laser it is possible to determine the P concentration of the P-type layer and the current aperture size of the high-resistance layer 12 without considering the resistance of the high-frequency circuit, thereby reducing the oscillation threshold and increasing the slope efficiency. And a good beam shape can be designed. Wear.
  • the surface emitting laser of the present embodiment can be easily manufactured by applying a well-known semiconductor manufacturing process. Hereinafter, the manufacturing procedure will be briefly described.
  • an n-type black reflective mirror 2 made of GaAsZAlAs 2 and an n-type cladding layer 3 made of GaAs are formed on an n-type GaAs substrate (or high-resistance substrate) 1 by metal organic chemical vapor deposition or molecular beam epitaxy.
  • AlAs barrier layer and GaAs quantum well layer double barrier structure 4 n-type cladding layer made of Ga As 5, high resistance layer made of AlGaAs 6, n-type cladding layer made of GaAs 7, three-layer GalnNAs
  • An active layer (multiple quantum well) having a quantum well and a GaAs barrier layer 8, a p-type cladding layer 9 of GaAs, a p-type AlGaAs layer 10, and a p-type black reflecting mirror 11 of GaAsZAlAs are formed in this order.
  • the laminated portion from the active layer (multiple quantum well) 8 to the p-type black reflecting mirror 11 is added to a circular post shape having a diameter of 20 ⁇ m by dry etching, and the p-type AlGaAs layer 10 is formed by steam oxidation.
  • a current constriction structure is manufactured by oxidizing while leaving only a region with a diameter of 5 m.
  • a part of the laminated portion up to the n-type cladding layer 7 with the double barrier structure 4 is etched until the n-type cladding layer 3 is exposed, and the n-electrode 16 is formed there.
  • a part of the high-resistance layer 6 and the n-type cladding layer 7 are etched until the n-type cladding layer 5 is exposed, and a p-electrode 17 is formed there.
  • the p-electrode 15 is formed concentrically except for the central light-emitting portion of the post shape 13, and the n-electrode 18 is formed so as to be in contact with the n-type cladding layer 7.
  • a surface emitting laser having the structure shown in FIG. 11 is obtained.
  • a force using a high-resistance or n-type GaAs substrate as a semiconductor substrate can be replaced with a p-type substrate.
  • a conductive substrate can be used, and electrodes can be formed on the back surface of the substrate according to the design.
  • the current with respect to the peak voltage and the valley voltage of the resonance tunnel is not increased.
  • each force to be higher than the threshold current of the active layer 8
  • stable optical modulation can be obtained.
  • a sufficient extinction ratio can be obtained by setting the current force to be lower than the saturation current of the active layer 8 with respect to the peak voltage of the resonance tunnel.
  • an optical transmission module with low power consumption and low cost can be obtained.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Semiconductor Lasers (AREA)

Abstract

Un laser à émission par la surface qui consomme une faible électricité tout en maintenant un flux lumineux. Un résonateur laser est constitué de deux miroirs de réflexion de Bragg (2) et (11) qui sont empilés de façon à entourer une couche d’activation (8). Dans le résonateur laser, une couche de modulation lumineuse ayant une structure de type tunnel de résonance (double structure barrière (4)) est disposée pour moduler une lumière oscillée dans un sens d’épaisseur de couche de la couche d’activation (8).
PCT/JP2005/001458 2004-03-26 2005-02-02 Laser à émission par la surface WO2005093918A1 (fr)

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JP2009302078A (ja) * 2008-06-10 2009-12-24 Ricoh Co Ltd 光源装置、光走査装置及び画像形成装置

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JPS63129685A (ja) * 1986-11-20 1988-06-02 Sanyo Electric Co Ltd 半導体レ−ザ
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JPH05232522A (ja) * 1992-02-18 1993-09-10 Nippon Telegr & Teleph Corp <Ntt> 光素子の駆動方法
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JPS62128585A (ja) * 1985-11-29 1987-06-10 Matsushita Electric Ind Co Ltd 半導体レ−ザ装置
JPS63129685A (ja) * 1986-11-20 1988-06-02 Sanyo Electric Co Ltd 半導体レ−ザ
JPH0194689A (ja) * 1987-10-06 1989-04-13 Furukawa Electric Co Ltd:The 光半導体素子
JPH05152674A (ja) * 1991-11-25 1993-06-18 Nec Corp 外部変調器付き面発光半導体レーザ
JPH05232522A (ja) * 1992-02-18 1993-09-10 Nippon Telegr & Teleph Corp <Ntt> 光素子の駆動方法
JPH10335758A (ja) * 1997-03-29 1998-12-18 Shojiro Kawakami ３次元周期構造体及びその作製方法並びに膜の製造方法

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Publication number Priority date Publication date Assignee Title
JP2008177430A (ja) * 2007-01-19 2008-07-31 Sony Corp 発光素子及びその製造方法、並びに、発光素子集合体及びその製造方法
US8183074B2 (en) 2007-01-19 2012-05-22 Sony Corporation Light emitting element, method for manufacturing light emitting element, light emitting element assembly, and method for manufacturing light emitting element assembly
JP2009302078A (ja) * 2008-06-10 2009-12-24 Ricoh Co Ltd 光源装置、光走査装置及び画像形成装置
US8207996B2 (en) 2008-06-10 2012-06-26 Ricoh Company, Ltd. Light source device, optical scanning device, and image forming apparatus

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