JP5494936B2 - Surface emitting semiconductor laser - Google Patents

Description

  The present invention relates to a surface emitting semiconductor laser.

  In recent years, it has been desired to increase the output while reducing the number of oscillation modes of the surface emitting semiconductor laser by expanding the application of the surface emitting semiconductor laser. For example, in a surface emitting semiconductor laser having an oxidized constricting layer, the number of modes can be reduced by reducing the opening diameter of the oxidized constricting layer.

  On the other hand, the output of the semiconductor laser increases with the injected current value, and reaches a maximum value (roll-off point) at a certain current value. This is because in a semiconductor laser, the device temperature rises due to current injection, the gain spectrum shifts, and the gain reaches its maximum value at a certain temperature. For example, when the opening diameter of the oxide confinement layer of the surface emitting semiconductor laser is small, the device temperature is likely to rise, and the roll-off point is reached at a low current value, so that a sufficient output may not be obtained. Therefore, in order to prevent an increase in device temperature, for example, in Patent Document 1 below, a groove reaching the current confinement portion is dug in the peripheral portion of the light emitting portion, and an electrode is formed directly on this groove, so that the electrode from the heat generating portion is formed. A technique for improving the heat dissipation performance by shortening the distance is disclosed.

JP 2003-86895 A

  An object of the present invention is to provide a surface emitting semiconductor laser capable of reducing the number of oscillation modes of laser light and capable of achieving higher output than when the diameter of the current confinement layer is simply reduced. is there.

The surface emitting semiconductor laser according to the present invention is:
The lower mirror,
An active layer formed above the lower mirror;
An upper mirror formed above the active layer,
The lower mirror and the upper mirror are multilayer mirrors in which a plurality of unit multilayer films are laminated,
The unit multilayer film has a pair of a low refractive index layer and a high refractive index layer laminated in the vertical direction,
The unit multilayer film satisfies the following formula (1):
The active layer satisfies the following formula (2).
d _D <λ / 2n _D (1)
d _A > mλ / 2n _A (2)
However,
λ is the design wavelength of the surface emitting semiconductor laser,
m is a positive integer;
d _D is the thickness of the unit multilayer film;
n _D is an average refractive index of the unit multilayer film,
d _A is the thickness of the active layer;
n _A is the average refractive index of the active layer.

In the surface emitting semiconductor laser according to the present invention, the above formulas (1) and (2) are satisfied. Thereby, for example, the energy increase rate of the low-order resonance mode component of the light resonating in the active layer (hereinafter referred to as “resonant light”) is hardly reduced regardless of the thickness or diameter of the current confinement layer. In addition, the energy increase rate of the higher-order resonance mode component can be reduced. This has also been confirmed in numerical calculation examples described later. As a result, it is possible to prevent the resonance light of a higher-order resonance mode component from lasing without reducing the output of the surface emitting semiconductor laser as compared with the case of simply reducing the opening diameter of the current confinement layer. it can. Therefore, according to the present invention, there is provided a surface emitting semiconductor laser capable of reducing the number of oscillation modes of laser light and capable of achieving higher output than when the diameter of the current confinement layer is simply reduced. be able to.

  In the present invention, the design wavelength refers to the wavelength of light having the maximum intensity among the light generated in the surface emitting semiconductor laser.

  Further, in the description according to the present invention, the word “upper” refers to, for example, “another specific thing (hereinafter referred to as“ B ”) formed“ above ”a specific thing (hereinafter referred to as“ A ”)”. Etc. In the description of the present invention, in the case of this example, there are a case where B is directly formed on A and a case where B is formed on A via another. The word “above” is used as included.

  In the present invention, when “a pair of a low refractive index layer and a high refractive index layer laminated in the vertical direction” is referred to, another layer is laminated between the low refractive index layer and the high refractive index layer. It is assumed that such cases are included.

In the description of the present invention, for example, λ / 2n _D represents λ / (2n _D ).

In the surface emitting semiconductor laser according to the present invention,
Formula (1) may be satisfied for at least one of the plurality of unit multilayer films.

In the surface emitting semiconductor laser according to the present invention,
Formula (1) may be satisfied for all of the plurality of unit multilayer films.

In the surface emitting semiconductor laser according to the present invention,
The unit multilayer film that does not satisfy the formula (1) can satisfy the following formula (3).
d _D = λ / 2n _D (3)

In the surface emitting semiconductor laser according to the present invention,
The following formula (4) can be satisfied.
d _H + d _L <λ / 4n _L + λ / 4n _H (4)
However,
d _H is the thickness of the low refractive index layer;
d _L is the thickness of the high refractive index layer;
n _L is the refractive index of the low refractive index layer;
n _H is the refractive index of the high refractive index layer.

In the surface emitting semiconductor laser according to the present invention,
The lower mirror and the upper mirror may be distributed Bragg reflection (DBR) mirrors.

In the surface emitting semiconductor laser according to the present invention,
Of the light resonating in the active layer,
Low-order resonance mode components lead to laser oscillation,
Higher order resonance mode components can not lead to laser oscillation.

In the surface emitting semiconductor laser according to the present invention,
Of the light resonating in the active layer,
The energy amplification factor of the low-order resonance mode component is positive,
The energy amplification factor of higher order resonance mode components can be negative.

In the surface emitting semiconductor laser according to the present invention,
The low-order resonance mode component is a zero-order resonance mode component,
The higher-order resonance mode component may be a first-order or higher-order resonance mode component.

1 is a cross-sectional view schematically showing a surface emitting semiconductor laser according to an embodiment. 1 is a cross-sectional view schematically showing a part of a surface emitting semiconductor laser according to an embodiment. Sectional drawing which shows roughly one manufacturing process of the surface emitting semiconductor laser of this embodiment. Sectional drawing which shows roughly one manufacturing process of the surface emitting semiconductor laser of this embodiment. The figure which shows the calculation result of the energy increase rate of the resonant light of each mode of the numerical calculation example. The figure which shows the calculation result of the energy increase rate of the resonant light of each mode of the numerical calculation example. The figure which shows the relationship between the mode number in an experiment example, and the total number of samples. The figure which shows the relationship between the mode number in an experiment example, and the total number of samples. The figure which shows the relationship between the mode number in an experiment example, and the total number of samples. The figure which shows the relationship between the mode number in an experiment example, and the total number of samples. The figure which shows the relationship between the mode number in an experiment example, and the total number of samples. The figure which shows the relationship between the mode number in an experiment example, and the total number of samples. The figure which shows the radiation angle in two orthogonal axes | shafts concerning an experiment example. The figure which shows the radiation angle in two orthogonal axes | shafts concerning an experiment example. Sectional drawing which shows schematically the modification of the surface emitting semiconductor laser of this embodiment.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

  1. First, the surface emitting semiconductor laser 100 according to this embodiment will be described.

  FIG. 1 is a cross-sectional view schematically showing a surface-emitting type semiconductor laser 100, and FIG. 2 is an enlarged schematic view showing a region V in FIG.

  As shown in FIG. 1, the surface emitting semiconductor laser 100 includes a substrate 101, a lower mirror 10, an active layer 103, an upper mirror 20, an insulating layer 110, a first electrode 107, a second electrode 109, , Can be included.

  As the substrate 101, for example, a first conductivity type (for example, n-type) GaAs substrate or the like can be used.

On the substrate 101, for example, a first conductivity type lower mirror 10 is formed. The lower mirror 10 is a multilayer mirror in which a plurality of unit multilayer films 10p are stacked. As shown in FIG. 2, the unit multilayer film 10p can be composed of, for example, a low refractive index layer 10L and a high refractive index layer 10H formed under the low refractive index layer 10L. That is, the lower mirror 10 can be, for example, a distributed Bragg reflection (DBR) mirror in which low refractive index layers 10L and high refractive index layers 10H are alternately stacked. The low refractive index layer 10L can be composed of, for example, an n-type Al _0.9 Ga _0.1 As layer (refractive index 3.049). The high refractive index layer 10H can be composed of, for example, an n-type Al _0.15 Ga _0.85 As layer (refractive index 3.525). The number of stacked units (number of pairs) of the unit multilayer film 10p can be, for example, 35.5 pairs to 43.5 pairs. The unit multilayer film 10p of the lower mirror 10 may be any unit as long as the lower mirror 10 is configured by repeating the layer configuration of the unit multilayer film 10p. For example, the unit multilayer film 10p can include a low refractive index layer 10L and a high refractive index layer 10H formed on the low refractive index layer 10L.

An active layer 103 is formed on the lower mirror 10. The active layer 103 has, for example, a multiple quantum well (MQW) structure in which three quantum well structures each composed of a GaAs well layer and an Al _0.2 Ga _0.8 As barrier layer are stacked.

On the active layer 103, for example, a second conductivity type (for example, p-type) upper mirror 20 is formed. The upper mirror 20 is a multilayer film mirror in which a plurality of unit multilayer films 20p are stacked. As shown in FIG. 2, the unit multilayer film 20p can include, for example, a low refractive index layer 20L and a high refractive index layer 20H formed under the low refractive index layer 20L. That is, the upper mirror 20 can be, for example, a DBR mirror in which low refractive index layers 20L and high refractive index layers 20H are alternately stacked. The low refractive index layer 20L can be composed of, for example, a p-type Al _0.9 Ga _0.1 As layer (refractive index 3.049). The high refractive index layer 20H can be composed of, for example, a p-type Al _0.15 Ga _0.85 As layer (refractive index 3.525). The number of stacked unit multilayer films 20p (number of pairs) can be, for example, 19 to 31 pairs. The unit multilayer film 20p of the upper mirror 20 may be any unit as long as the upper mirror 20 is configured by repeating the layer configuration of the unit multilayer film 20p. For example, the unit multilayer film 20p can include a low refractive index layer 20L and a high refractive index layer 20H formed on the low refractive index layer 20L.

In the present embodiment, for example, the following equation (1) can be satisfied for all of the plurality of unit multilayer films 10p and 20p described above. In the present embodiment, the active layer 103 satisfies the following formula (2).
d _D <λ / 2n _D (1)
d _A > mλ / 2n _A (2)
However,
λ is a design wavelength of the surface emitting semiconductor laser 100,
m is a positive integer;
d _D is the thickness of the unit multilayer films 10p and 20p,
n _D is an average refractive index of the unit multilayer films 10p and 20p,
d _A is the thickness of the active layer 103;
n _A is the average refractive index of the active layer 103.

The lower limit value of d _D and the upper limit value of d _A can be determined by whether or not λ falls within the reflection band of the multilayer mirror (lower mirror 10 and upper mirror 20). For example, in the multilayer mirror made of Al _x Ga _1-x As (x = 0.15, 0.90) with λ = 850 nm, the lower limit value of d _D is, for example, about 5% smaller than λ / 2n _D. Value. The upper limit value of d _A is appropriately determined according to the design wavelength λ, and can be set to a value increased by about 20% with respect to mλ / 2n _A , for example.

Also, the above-described equations (1) and (2) can be rewritten as the following equation (A).
2n _D · d _D <λ <(2n _A · d _A ) / m (A)

Further, from the above formulas (1) and (2), the ratio (d _A / d _D ) between the thickness d _A of the active layer 103 and the thickness d _D of the unit multilayer films 10p and 20p is expressed by the following formula (B ) Can be satisfied.
d _A / d _D > mn _D / n _A (B)

  The design wavelength λ is, for example, 780 nm, 850 nm, 1300 nm, etc., but is not particularly limited. When m is 2, for example, a 1λ resonator is configured, but m is not particularly limited.

In the present embodiment, for example, as shown in FIG. 2, the thickness of each of the plurality of unit multilayer films 10p in the lower mirror 10 is the same as the thickness of each of the plurality of unit multilayer films 20p in the upper mirror 20. Can be _D. In this embodiment, for example, the average refractive index of each of the plurality of unit multilayer films 10p in the lower mirror 10 and the average refractive index of each of the plurality of unit multilayer films 20p in the upper mirror 20 are the same n _D. Can be.

Further, for example, among the plurality of unit multilayer films 10p in the lower mirror 10, the thickness of at least two unit multilayer films 10p may be different from each other. Further, for example, the average refractive index of at least two unit multilayer films 10p among the plurality of unit multilayer films 10p in the lower mirror 10 may be different from each other. Similarly, for example, among the plurality of unit multilayer films 20p in the upper mirror 20, the thickness and average refractive index of at least two unit multilayer films 20p may be different from each other. The above-described equation (1) only needs to be satisfied for at least one of the plurality of unit multilayer films 10p and 20p in the lower mirror 10 and the upper mirror 20. For example, the following formula (3) can be satisfied for the unit multilayer films 10p and 20p that do not satisfy the above-described formula (1).
d _D = λ / 2n _D (3)

For example, as shown in FIG. 2, the unit multilayer film 10p of the lower mirror 10 includes a low refractive index layer 10L and a high refractive index layer 10H, and the unit multilayer film 20p of the upper mirror 20 has a low refractive index layer 20L and a high refractive index. In the case of the rate layer 20H, the above-described formula (1) can be rewritten as the following formula (4).
d _H + d _L <λ / 4n _L + λ / 4n _H (4)
However,
d _H is the thickness of the low refractive index layer;
d _L is the thickness of the high refractive index layer;
n _L is the refractive index of the low refractive index layer;
n _H is the refractive index of the high refractive index layer.

  Further, the threshold value of the surface emitting semiconductor laser 100 is adjusted by appropriately adjusting the number of unit multilayer films 10p in the lower mirror 10 and the number of unit multilayer films 20p in the upper mirror 20 described above. Can do.

  The lower mirror 10, the active layer 103, and the upper mirror 20 can constitute a vertical resonator. The composition and the number of layers constituting the lower mirror 10, the active layer 103, and the upper mirror 20 can be appropriately adjusted as necessary. The p-type upper mirror 20, the active layer 103 not doped with impurities, and the n-type lower mirror 10 constitute a pin diode. A part of the upper mirror 20, the active layer 103, and the lower mirror 10 can constitute a columnar semiconductor deposited body (hereinafter referred to as “columnar portion”) 30. The planar shape of the columnar portion 30 is, for example, a circle.

  As shown in FIG. 1, for example, at least one of the layers constituting the upper mirror 20 can be a current confinement layer 105. The current confinement layer 105 is formed in a region close to the active layer 103. As the current confinement layer 105, for example, an oxidized AlGaAs layer or a proton implanted layer can be used. The current confinement layer 105 is an insulating layer having an opening. The current confinement layer 105 is formed in a ring shape.

  A first electrode 107 is formed on the back surface of the substrate 101 (the surface opposite to the lower mirror 10 side). The first electrode 107 is electrically connected to the lower mirror 10 through the substrate 101. For example, the first electrode 107 can be formed on the upper surface of the lower mirror 10.

  A second electrode 109 is formed on the upper mirror 20 and the insulating layer 110. The second electrode 109 is electrically connected to the upper mirror 20. The second electrode 109 has an opening on the columnar part 30. Due to the opening, a region where the second electrode 109 is not provided is formed on the upper surface of the upper mirror 20. This region is the laser light emission surface 108. The planar shape of the emission surface 108 is, for example, a circle.

  The insulating layer 110 is formed on the lower mirror 10. The insulating layer 110 is formed so as to surround the columnar portion 30. The insulating layer 110 can electrically separate the second electrode 109 and the lower mirror 10.

  2. Next, an example of a method for manufacturing the surface emitting semiconductor laser 100 according to the present embodiment will be described with reference to the drawings.

  3 and 4 are cross-sectional views schematically showing one manufacturing process of the surface-emitting type semiconductor laser 100 of the present embodiment shown in FIG.

  (1) First, as shown in FIG. 3, for example, an n-type GaAs substrate is prepared as the substrate 101. Next, the semiconductor multilayer film 150 is formed on the substrate 101 by epitaxial growth while modulating the composition. The semiconductor multilayer film 150 is formed by sequentially laminating the lower mirror 10, the active layer 103, and the semiconductor layers constituting the upper mirror 20. When the upper mirror 20 is grown, at least one layer in the vicinity of the active layer 103 can be a layer that is oxidized later to become the current confinement layer 105. As the layer that becomes the current confinement layer 105, for example, an AlGaAs layer having an Al composition of 0.95 or more can be used.

  (2) Next, as shown in FIG. 4, the semiconductor multilayer film 150 is patterned to form the lower mirror 10, the active layer 103, and the upper mirror 20 having desired shapes. Thereby, the columnar part 30 is formed. The patterning of the semiconductor multilayer film 150 can be performed using, for example, a lithography technique and an etching technique.

  Next, for example, by introducing the substrate 101 on which the columnar portion 30 is formed by the above process in a steam atmosphere at about 400 ° C., the layer that becomes the current confinement layer 105 is oxidized from the side surface, and the current confinement layer 105 is formed.

  (3) Next, as shown in FIG. 1, an insulating layer 110 is formed on the lower mirror 10 so as to surround the columnar portion 30. First, an insulating layer made of polyimide resin or the like is formed on the entire surface by using, for example, a spin coating method. Next, the upper surface of the columnar portion 30 is exposed using, for example, a CMP method. Next, the insulating layer is patterned using, for example, a lithography technique and an etching technique. In this manner, the insulating layer 110 having a desired shape can be formed.

  Next, the first electrode 107 and the second electrode 109 are formed. These electrodes can be formed in a desired shape by, for example, a combination of a vacuum deposition method and a lift-off method. In addition, the order which forms each electrode is not specifically limited.

  (4) Through the above steps, the surface emitting semiconductor laser 100 of the present embodiment is obtained as shown in FIG.

  3. Next, a numerical calculation example will be described.

In this numerical calculation example, an optical simulation was performed on the surface-emitting type semiconductor laser 100 according to the present embodiment using a time domain difference method (FDTD method). The simulation was performed on six samples (Nos. 1 to 6). The structure of the sample to which numerical calculation is applied is as follows.
Substrate 101: n-type GaAs substrate (refractive index 3.62)
The unit multilayer film 10p of the lower mirror 10 comprises an n-type Al _0.9 Ga _0.1 As layer (refractive index 3.049) and an n-type Al _0.15 Ga _0.85 As layer (refractive index 3.525). Two-layer structure Average refractive index n _D of unit multilayer film 10p of lower mirror 10: 2n _H n _L / (n _H + n _L ) =
3.2697
Active layer 103: 3QW structure in which three quantum well structures each composed of a GaAs layer (refractive index 3.6201) and an Al _0.2 Ga _0.8 As layer (refractive index 3.4297) are stacked. Average refraction of the active layer 103 Rate n _A : 3.3838
The unit multilayer film 20p of the upper mirror 20 is composed of a p-type Al _0.9 Ga _0.1 As layer (refractive index 3.049) and a p-type Al _0.15 Ga _0.85 As layer (refractive index 3.525). Two-layer structure Average refractive index n _D of unit multilayer film 20p of upper mirror 20: 2n _H n _L / (n _H + n _L ) = 3.2697
Insulating layer 110: polyimide resin (refractive index 1.78)
External space 40 of surface emitting semiconductor laser 100: air (refractive index 1.00)
Inclination angle (post inclination angle) θ of the columnar part 30: 80 degrees Outer diameter (post diameter) of the columnar part 30 in a plan view: about 50 μm
Number of pairs of the lower mirror 10 in the columnar part 30: 4 pairs Current confinement layer 105: oxidized first AlGaAs layer on the active layer 103 (refractive index 1.6)
Opening diameter of current confinement layer 105: 13 μm
Current confinement layer 105 thickness: 12 nm, 30 nm
Design wavelength λ: 850 nm
M in formula (2) described above: 2

In each sample of this numerical calculation example, the thickness of each layer constituting the plurality of unit multilayer films 10p in the lower mirror 10 and the thickness of each layer constituting the plurality of unit multilayer films 20p in the upper mirror 20 are as follows: The ratio was determined to be the same. Specifically, it was determined to be inversely proportional to n _H and n _L. Further, each of the average refractive index of the plurality of unit multilayer films 10p in the lower mirror 10, and the respective average refractive index of the plurality of unit multilayer films 20p in the upper mirror 20 were the same n _D.

The ratio d _A / d _D between the thickness d _A of the active layer 103 and the thickness d _D of the unit multilayer films 10p and 20p in each numerical calculation sample is No. 1 and No. 4 is 1.15 times 2n _D / n _A (= 1.9325), No. 4 2 and No. No. 5, 1.10 times, No. 3 and no. 6 was 1.05 times. As a comparative example, d _A / d _D is equal to 2n _D / n _A , that is, d _D = λ / 4n _H + λ / 4n _L = λ / 2n _D (= 0.129998 μm), and d _A = _A simulation was also performed for mλ / 2n _A (= 0.25119 μm).

Each of the numerical calculation samples (No. 1 to 6) and the unit multilayer films 10p and 20p in the comparative example have a thickness d _D , a thickness d _A of the active layer 103, a ratio d _A / d _D thereof, a pair of the lower mirror 10 Tables 1 and 2 show the numbers and the number of pairs of the upper mirror 20. Table 1 shows a case where the thickness of the current confinement layer 105 is 12 nm, and Table 2 shows a case where the thickness is 30 nm. Although it is an effective digit exceeding the lattice period of AlGaAs, it is a value used for calculation to the last, and there is no particular problem if a value according to reality is used. Each thickness d _D and d _A is adjusted such that the design wavelength λ is 850 nm. The thickness _{d D} and _{d A} in each of the numerical calculation samples (Nanba1～6) satisfies the above formula (1) and (2).
d _D <λ / 2n _D (1)
d _A > mλ / 2n _A (2)
However, in this numerical calculation example, m = 2.

In addition, for each number of pairs, the photon lifetime is calculated using the one-dimensional FDTD method so that the mirror loss when the thickness d _D of the unit multilayer films 10p and 20p is changed is equal in each sample. Calculated. For comparison, this is performed only to maintain the photon lifetime of the zeroth-order resonance mode component, which will be described later, at the same level, and it does not depart from the present invention even when the number of pairs is different from this case.

For each numerical calculation sample (Nos. 1 to 6) and the comparative example, using a two-dimensional FDTD method, a zero-order resonance mode component (hereinafter referred to as “0-order mode component”) and a first-order resonance mode component ( FIG. 5 and FIG. 6 show the results of calculating the increase rate of the active layer energy of the resonant light (hereinafter referred to as “first-order mode component”). The active layer 103 is calculated by giving a gain corresponding to the current injection. FIG. 5 shows the case where the thickness of the current confinement layer 105 is 12 nm, and FIG. 6 shows the case where it is 30 nm. The horizontal axis represents the thickness d _D of the unit multilayer films 10p and 20p, and the vertical axis represents the increase rate of the active layer energy. As shown in FIGS. 5 and 6, when d _D is reduced (d _A / d _D is increased), the energy increase rate of the resonance light of the zero-order mode component hardly changes, whereas the first-order mode component It can be seen that the energy increase rate of the resonant light decreases. When d _D is decreased (d _A / d _D is increased), the energy increase rate of the resonance light of the first-order mode component turns negative, and laser oscillation may not be achieved. I understand. That is, in the resonance light, the first-order or higher-order resonance mode component does not oscillate (thus, it is not emitted from the surface emitting semiconductor laser 100), and only the zero-order mode component resonance light oscillates (therefore, It is emitted from the surface emitting semiconductor laser 100). Therefore, the laser light emitted from the surface emitting semiconductor laser 100 can be converted into a single mode. In addition, it can be seen that the higher-order resonance mode component (for example, the first-order mode component) in the resonance light can be reduced regardless of the thickness of the current confinement layer 105 as shown in FIGS. .

  In the numerical calculation example described above, the zero-order mode component is used as the low-order resonance mode component (hereinafter referred to as “low-order mode component”) of the resonance light, and the high-order resonance mode component (hereinafter referred to as “high-order mode”). Although the simulation was performed using the first-order mode component as the “component”), the present embodiment is not limited to this. The low-order mode component only needs to have a lower order than the high-order mode component. Therefore, for example, it is possible to use a third or lower order resonance mode component as the lower order mode component and a fourth or higher order resonance mode component as the higher order mode component.

  4). Next, experimental examples will be described.

In this experimental example, first, using a one-dimensional time domain difference method (FDTD method), an optical simulation is performed on the surface-emitting semiconductor laser 100 according to the present embodiment, and a Q value (because it is a one-dimensional calculation, (Corresponding to the light confinement effect in the direction) was designed to be comparable. By aligning the Q values to the same extent, the threshold currents, that is, the current values at which the lowest order mode oscillates can be made to the same extent. In this simulation, the surface-emitting type semiconductor laser under three conditions A to C was used. The structure of the sample to which numerical calculation is applied is as follows. Unless otherwise specified, the sample structure is the same as that of the numerical calculation example described above.
The unit multilayer film 10p of the lower mirror 10 comprises an n-type Al _0.9 Ga _0.1 As layer (refractive index 3.049) and an n-type Al _0.12 Ga _0.88 As layer (refractive index 3.544). Two-layer structure Average refractive index n _D of unit multilayer film 10p of lower mirror 10: 2n _H n _L / (n _H + n _L ) = 3.278
Active layer 103: A 3QW structure in which three quantum well structures each composed of a GaAs layer (refractive index 3.6201) and an Al _0.2 Ga _0.8 As layer (refractive index 3.4297) are stacked. GRIN-SCH (graded-index separate-confinement heterostructure) structure sandwiched between graded index layers as follows: Average refractive index n _A of active layer 103: 3.3838
The unit multilayer film 20p of the upper mirror 20 is composed of a p-type Al _0.9 Ga _0.1 As layer (refractive index 3.049) and a p-type Al _0.12 Ga _0.88 As layer (refractive index 3.544). Two-layer structure Average refractive index n _D of unit multilayer film 20p of upper mirror 20: 2n _H n _L / (n _H + n _L ) = 3.278
Opening diameter (opening diameter) of current confinement layer 105: 4.5 μm, 6.0 μm
The thickness of the current confinement layer 105: 12 nm

Further, the ratio d _A / d _D between the thickness d _A of the active layer 103 and the thickness d _D of the unit multilayer films 10p and 20p of each sample is 2n _D / n _A (= r ₀ = 1. 96), 1.05 times under condition B, and 1.15 times under condition C. As a comparative example, d _A / d _D is equal to 2n _D / n _A , that is, d _D = λ / 4n _H + λ / 4n _L = λ / 2n _D (= 129.66 nm), and d _A = _A simulation was also performed for the case of mλ / 2n _A (= 253.77 nm).

The total thickness d _D of the unit multilayer films 10p and 20p in each sample (conditions A to C) and the comparative example, and the breakdown of the d _D (that is, the thickness of the high refractive index layers 10H and 20H and the low refractive index layer 10L) , the thickness of 20L), the thickness _{d a} of the active layer 103, and the ratio _d a / _{d D} for _{d D} of _{d a} shown in Table 3. Although it is an effective digit exceeding the lattice period of AlGaAs, it is a value used for calculation to the last, and there is no particular problem if a value according to reality is used. Table 4 shows the design wavelength, the number of pairs of the lower mirror 10, the number of pairs of the upper mirror 20, and the Q value in each sample (conditions A to C) and the comparative example. The thickness _{d D} and _{d A} in each sample (conditions A through C) satisfies the above formula (1) and (2).
d _D <λ / 2n _D (1)
d _A > mλ / 2n _A (2)
However, in this numerical calculation example, m = 2.

  From Tables 3 and 4, it can be seen that the Q values can be designed to be the same under all conditions.

  Next, each sample (conditions A to C) was actually manufactured by the above-described design. The number produced is 144. Table 5 shows an average value of oscillation wavelengths (peak wavelengths) of the manufactured surface emitting semiconductor lasers.

  As shown in Table 5, it can be understood that the manufactured surface-emitting type semiconductor laser oscillates at the same wavelength under any condition.

  Table 6 below shows average values of threshold currents of the surface emitting semiconductor lasers.

  As shown in Table 6, it can be seen that the threshold currents are equal to each other both when the opening diameter of the current confinement layer 105 is 4.5 μm and when it is 6.0 μm. Thus, it can be seen that the currents that cause the lowest-order resonance mode component to oscillate can be made equal.

  Next, current (3.0 mA, 4.0 mA, 5.0 mA) is injected into each sample (conditions A to C), and the number of oscillated resonance mode components (hereinafter also referred to as “mode number”) is measured. did. 7 to 12 show the total number of samples in which the number of modes is 1, 2, 3, 4, and 5 or more. 7 to 9 show a case where the opening diameter of the current confinement layer 105 is 4.5 μm, and FIGS. 10 to 12 show a case where the opening diameter is 6.0 μm. 7 and 10 are for the condition A, FIGS. 8 and 11 are for the condition B, and FIGS. 9 and 12 are for the condition C.

As shown in FIGS. 7 to 12, when d _D is reduced (d _A / d _D is reduced at the same current value in both cases where the opening diameter of the current confinement layer 105 is 4.5 μm and 6.0 μm. It can be seen that the total number of samples with 3 or more modes decreases. Therefore, it can be seen that by increasing d _A / d _D , oscillation of higher order resonance mode components (for example, second or higher order resonance mode components) can be suppressed while maintaining the threshold current at the same level. That is, it can be seen that the oscillation of the higher-order resonance mode component can be suppressed while maintaining the ease of oscillation of the lowest-order resonance mode component at the same level.

Further, as shown in FIGS. 7 to 12, Table 4, and Table 6, the structure having the smallest number of samples having three or more modes is the condition B (d _A / d _D = 1.10r ₀₎ structure and not the, it is understood that the structure of large Q value (i.e. small threshold current) condition _{C (d a / d D =} 1.15r 0). Therefore, the suppression of higher-order resonance mode component oscillation in this experimental result is not due to the fact that all resonance mode components are less likely to oscillate due to the increase in the threshold current. It can be seen that this is because the oscillation of the resonance mode component is suppressed.

Next, each sample (conditions A to C) was laser-oscillated, and the radiation angle of the laser light in FFP (Far Field Pattern) was measured. Here, as the definition of the radiation angle, on both sides of the angle at which the intensity becomes maximum, the angle at which the intensity becomes 1 / e ² of the maximum intensity (e is the base of the natural logarithm and the Napier number e = 2.71828...). The difference (full width) was used. For example, when 1 / e ² is obtained at +14 degrees and −13 degrees, the radiation angle is 14 − (− 13) = 27 degrees. FIG. 13 and FIG. 14 show radiation angles (FFP _x and FFP _y ) on the orthogonal x-axis and y-axis, respectively. FIG. 13 shows the case where the opening diameter of the current confinement layer 105 is 4.5 μm, and FIG. 14 shows the case where it is 6.0 μm.

As shown in FIGS. 13 and 14, when d _D is decreased (d _A / d _D is increased) in both cases where the opening diameter of the current confinement layer 105 is 4.5 μm and 6.0 μm, radiation is increased. It can be seen that the corners are reduced. This is because according to the surface emitting semiconductor laser 100 of the present embodiment, k _// (described later) having a large value cannot be solved.

  5. Next, a modification of this embodiment will be described. In addition, a different point from the Example mentioned above is demonstrated, and description is abbreviate | omitted about the same point.

  FIG. 15 is a cross-sectional view schematically showing a part of a surface emitting semiconductor laser according to this modification. The unit multilayer film 10p of the lower mirror 10 includes, for example, a low refractive index layer 10L and a first graded index layer (hereinafter referred to as “first GI layer”) 12 formed below the low refractive index layer 10L. And a high refractive index layer 10H formed under the first GI layer 12, and a second graded index layer (hereinafter referred to as “second GI layer”) 14 formed under the high refractive index layer 10H. be able to. As the first GI layer 12, for example, a layer in which the Al composition of the AlGaAs layer is continuously increased downward from 0.12 to 0.9 can be used. Further, as the second GI layer 14, for example, a layer in which the Al composition of the AlGaAs layer is continuously decreased downward from 0.9 to 0.12 can be used. Similarly, the unit multilayer film 20p of the upper mirror 20 is formed, for example, under the low refractive index layer 20L, the first GI layer 22 formed under the low refractive index layer 20L, and the first GI layer 22. The high refractive index layer 20H and the second GI layer 24 formed under the high refractive index layer 20H.

  In addition, the modification mentioned above is an example, Comprising: It is not necessarily limited to this.

6). In the surface-emitting type semiconductor laser 100 according to the present embodiment, the following formulas (1) and (2) are satisfied.
d _D <λ / 2n _D (1)
d _A > mλ / 2n _A (2)

  Thereby, the energy increase rate of the resonance light of the low-order mode component is not reduced so much regardless of the thickness of the current confinement layer 105, the opening diameter, the inclination angle θ of the post (columnar section 30), the outer diameter, and the like. The energy increase rate of the resonance light of the higher-order mode component can be reduced. This is also confirmed in the numerical calculation examples described above. As a result, high-order mode resonant light can be prevented from lasing without reducing the output of the surface emitting semiconductor laser 100. Furthermore, even if the output is increased, it is possible to prevent the high-order mode resonance light from being laser-oscillated. Therefore, according to the present embodiment, there is provided a surface emitting semiconductor laser capable of reducing the number of oscillation modes of laser light and capable of achieving higher output than when the diameter of the current confinement layer is simply reduced. can do. The reason why the effects of the surface emitting semiconductor laser 100 according to the present embodiment are achieved by satisfying the above expressions (1) and (2) is as follows.

The wave vector magnitude | k | in the resonator is an effective refractive index n _eff times the wave vector magnitude k ₀ in vacuum. This can be expressed as follows.

Here, k _z is a component in the vertical direction of the wave vector in the resonator, and k _// is a component in the plane direction.

k _z and k _// satisfy the continuity of the electromagnetic field within the range satisfying the total reflection condition at the boundary between the clad region including the current confinement layer 105 and the core region not including the current confinement layer 105. To be determined. In the surface emitting semiconductor laser, k _z and n _eff k ₀ are close to each other, so that k _// is a small value as can be seen from the above-described equation. Therefore, the solution of k _// that satisfies the above-described continuity of the electromagnetic field, that is, the number of transverse modes allowed in the equation is limited. In the surface emitting semiconductor laser, only those that satisfy the total reflection condition oscillate. In the present invention, by further increasing k _z , the solution of k _// is further limited than the total reflection condition. The k _z can be increased by reducing the thickness d _D of the unit multilayer films 10p and 20p of the lower mirror 10 and the upper mirror 20. Thus, by limiting the solution of k _//, the number of laser light oscillation modes can be reduced. Further, shortening the wavelength can be prevented by increasing the thickness d _A of the active layer 103.

Therefore, by reducing d _D and increasing d _A, that is, increasing the thickness ratio d _A / d _D (specifically, greater than mn _D / n _A ), the current confinement layer 105 Regardless of the thickness or the like, the number of oscillation modes of laser light can be reduced, and laser oscillation can be performed at a desired design wavelength.

  7). Although the embodiments of the present invention have been described in detail as described above, those skilled in the art will readily understand that many modifications are possible without substantially departing from the novel matters and effects of the present invention. Accordingly, all such modifications are intended to be included in the scope of the present invention.

For example, the surface-emitting type semiconductor laser according to the above-described embodiment of the present invention includes, for example, an element having an exhaust heat structure, an element having a flip chip structure, an element having an electrostatic discharge (ESD) countermeasure structure, a monitor photodiode ( It is applied to elements having MPD), elements having inkjet microlenses, elements having dielectric mirrors, optical modules such as OSA (Optical Sub-Assembly) using CAN and ceramic packages, and optical transmission devices incorporating them. Can.

  Further, for example, when the epitaxial lift-off (ELO) method or the like is used, the substrate 101 of the surface emitting semiconductor laser 100 can be separated. That is, the surface emitting semiconductor laser 100 may not have the substrate 101.

10 Lower mirror, 10p Unit multilayer film, 10L Low refractive index layer, 10H High refractive index layer, 12 First GI layer, 14 Second GI layer, 20 Upper mirror, 20p Unit multilayer film, 20L Low refractive index layer, 20H High refractive index Layer, 22 1st GI layer, 24 2nd GI layer, 30 columnar part, 40 external space, 100 surface emitting semiconductor laser, 101 substrate, 103 active layer, 105 current confinement layer, 107 1st electrode, 108 emission surface, 109 1st 2 electrodes, 110 insulating layer, 150 semiconductor multilayer film

Claims (6)

A plurality of first layers having a first refractive index, a plurality of second layers having a second refractive index different from the first refractive index, the first layer and the second layer; A first mirror that is a distributed Bragg reflection type (DBR) mirror,
A plurality of third layers having a third refractive index, a plurality of fourth layers having a fourth refractive index different from the third refractive index, the third layer and the fourth layer; A second mirror that is a distributed Bragg reflection (DBR) mirror,
An active layer located between the first mirror and the second mirror,
Of the light resonating in the active layer,
Low-order resonance mode components lead to laser oscillation,
Higher order resonance mode components do not lead to laser oscillation,
In the first layer and the second layer , at least one of a plurality of two layers in contact with each other , and in the third layer and the fourth layer, at least of a plurality of two layers in contact with each other One satisfies the following formula (1),
The active layer satisfies the following formula (2):
The surface emitting semiconductor laser in which the two layers in contact with each other not satisfying the formula (1) satisfy the following formula (3).
d _D <λ / 2n _D (1)
d _A > mλ / 2n _A (2)
d _D = λ / 2n _D (3)
However,
λ is the design wavelength of the surface emitting semiconductor laser,
m is a positive integer;
d _D is the total thickness of the two layers in contact with each other in the first layer, the second layer, the third layer, and the fourth layer ;
n _D is an average refractive index of the two layers in contact with each other in the first layer, the second layer, the third layer, and the fourth layer ;
d _A is the thickness of the active layer;
n _A is the average refractive index of the active layer. In claim 1,
The first refractive index and the third refractive index are the same refractive index,
The surface emitting semiconductor laser, wherein the second refractive index and the fourth refractive index are the same. In claim 1 or 2,
Including a substrate supporting the first mirror;
A surface emitting semiconductor laser in which the substrate, the first mirror, the active layer, and the second mirror are stacked in this order. In any one of Claims 1 thru | or 3,
A surface emitting semiconductor laser that satisfies the following formula (4).
d _H + d _L <λ / 4n _L + λ / 4n _H (4)
However,
d _H is a thickness of a layer having a large refractive index among the two layers in contact with each other;
d _L is the thickness of a layer having a small refractive index among the two layers in contact with each other;
n _H is a refractive index of a layer having a large refractive index among the two layers in contact with each other,
n _L is a refractive index of a layer having a small refractive index among the two layers in contact with each other. In any one of Claims 1 thru | or 4 ,
Of the light resonating in the active layer,
Energy amplification factor of the low-order resonance mode component is positive,
A surface emitting semiconductor laser in which an energy amplification factor of the higher-order resonance mode component is negative. In any one of Claims 1 thru | or 5 ,
The low-order resonance mode component is a zero-order resonance mode component,
The surface emitting semiconductor laser, wherein the higher-order resonance mode component is a first-order or higher-order resonance mode component.

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