JP2009164466A - Surface emitting semiconductor laser, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-emitting semiconductor laser that is manufactured in a simplified way and also inexpensively stabilizing the direction of polarization of the laser light to direct in one direction while providing a high power. <P>SOLUTION: The surface-emitting semiconductor laser includes, on a substrate 10, a lamination structure 20 provided with: a lower first DBR layer 12; a lower second DBR layer 13; a lower cladding layer 14; an active layer 15; an upper cladding layer 16; a current constriction layer 17; an upper DBR layer 18; and a contact layer 19, which are stacked in the above-described order. The lower first DBR layer 12 has an oxidized portion 30 in one region out of opposite regions to a current injection region 17B, and anisotropic stress corresponding to an non-uniform distribution of the oxidized portion 30 is generated in an active layer 15, and further an optical field intensity distribution of a basic lateral mode gravitates in a direction of the oxidized portion 30. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface-emitting type semiconductor laser that emits laser light from the upper surface and a method for manufacturing the same, and more particularly to a surface-emitting type semiconductor laser that can be suitably applied to applications that require a stable optical output in the polarization direction and the method. It relates to a manufacturing method.

  A surface emitting semiconductor laser emits light in a direction orthogonal to a substrate, unlike a conventional edge emitting type laser, and a large number of elements are arranged in a two-dimensional array on the same substrate. In recent years, it has attracted attention as a light source for digital copiers and printers.

  Conventionally, this type of surface-emitting type semiconductor laser has a pair of multilayer reflectors formed on a semiconductor substrate, and has an active layer serving as a light emitting region between the pair of multilayer reflectors. One multilayer reflector is provided with a current confinement layer having a structure in which the current injection region is narrowed in order to increase the current injection efficiency into the active layer and reduce the threshold current. Further, an n-side electrode is provided on the lower surface side, and a p-side electrode is provided on the upper surface side, and a light emission port is provided on the p-side electrode for emitting laser light. In this surface-emitting type semiconductor laser, a current is confined by a current confinement layer and then injected into an active layer, where it emits light, which is reflected by a pair of multilayer reflectors as a laser beam and emitted from the p-side electrode. It is injected from the exit.

  By the way, the surface emitting semiconductor laser described above generally has non-uniformity in which the polarization direction varies due to variations in elements, and instability in which the polarization direction changes depending on output and environmental temperature. Therefore, when such a surface-emitting type semiconductor laser is applied to a polarization-dependent optical element such as a mirror or a beam splitter, for example, when used as a light source for a digital copying machine or a printer, There is a problem that the variation causes a difference in image formation position and output, and blurring and color unevenness occur.

  In view of this problem, several techniques have been reported for providing a polarization control function inside a surface emitting semiconductor laser and stabilizing the polarization direction in one direction.

  For example, as one of such techniques, there is a technique using a special inclined substrate made of gallium arsenide (GaAs) with the (311) plane as a normal. When a surface emitting semiconductor laser is configured using a special inclined substrate in this way, gain characteristics with respect to the [−233] direction are enhanced, and the polarization direction of the laser light can be controlled in this direction. Further, the polarization ratio of the laser light is very high, and this is an effective technique for stabilizing the polarization direction of the surface emitting semiconductor laser in one direction.

  Patent Document 1 discloses a technique for controlling polarization by making the size of the post cross section smaller than the mode size of light.

  Further, in Patent Document 2, a discontinuous portion is formed in a part of the metal contact layer that does not affect the characteristics of the laser light emitted from the light emission port, and is parallel to the boundary of the discontinuous portion. A technique for obtaining polarized light forming the following is disclosed.

Japanese Patent No. 2891133 JP-T-2001-525995

  However, since the above-described inclined substrate is a special substrate having the (311) plane as a normal line, it is very expensive compared to a (001) plane substrate which is a standard substrate. Further, when such a special inclined substrate is used, the epitaxial growth conditions such as the growth temperature, doping conditions, and gas flow rate are completely different from those of the (001) plane substrate, so that it is difficult to manufacture easily.

  In Patent Document 1, since the post cross-sectional size is made smaller than the light mode size, the light output becomes as low as about 1 mW, which is a high output such as a light source for a digital copier or printer. It is not suitable for the required applications.

  Moreover, in the said patent document 2, what formed the groove | channel (discontinuous part) of the depth of 4.0-4.5 micrometers in the position 7 micrometers away from the edge part of the light emission port is described as an Example. In this way, polarized light that is parallel to the groove is obtained. However, since the polarization direction cannot be stabilized in one direction unless the distance on the short side of the resonance region is reduced to such an extent that the diffraction loss effect occurs, the range in which the diffraction loss effect cannot be obtained (the short side) It seems that the discontinuity formed at a distance of 7 μm) cannot be stabilized.

  As described above, in the conventional technique, it has been difficult to easily and inexpensively manufacture a high-output surface-emitting semiconductor laser capable of stabilizing the polarization direction of laser light in one direction.

  The present invention has been made in view of such problems, and its object is to produce a surface emitting light that can be easily and inexpensively manufactured and can stabilize the polarization direction of laser light in one direction and increase the output. TYPE SEMICONDUCTOR LASER AND METHOD FOR MANUFACTURING THE SAME

  The surface-emitting type semiconductor laser of the present invention has a laminated structure including a first multilayer reflector, an active layer, and a second multilayer reflector in this order from the substrate side on a substrate. At least one of the first multilayer film reflecting mirror and the second multilayer film reflecting mirror has a current confinement layer including a current injection region and an annular current confinement region surrounding the current injection region from the in-plane direction of the laminated surface. Further, at least one of the first multilayer film reflecting mirror and the second multilayer film reflecting mirror has an oxidized portion in one of the regions facing the current confinement region.

  In the surface-emitting type semiconductor laser of the present invention, at least one of the first multilayer-film reflective mirror and the second multilayer-film reflective mirror is provided with an oxidized portion in one of the regions facing the current confinement region. As a result, anisotropic stress due to the oxidized portion is generated in the active layer, so that the polarization component in the direction orthogonal to the direction of the stress is strengthened, while the polarization component in the direction parallel to the direction of the stress is suppressed. Thereby, the polarization component of the laser beam is fixed in one direction. Furthermore, the light field intensity distribution of the fundamental transverse mode is attracted in the direction of the oxidized portion, and the peak position of the light field intensity distribution of the fundamental transverse mode approaches the edge position of the current injection region, and consequently the peak position of the carrier density distribution. The gain of the basic transverse mode can be increased.

The manufacturing method of the surface emitting semiconductor laser of the present invention includes the following steps (A) to (D).
(A) A step of forming a laminated structure including the first multilayer film reflecting mirror, the active layer, and the second multilayer film reflecting mirror in this order from the substrate side on the substrate. (B) A width of only one place on the upper surface of the laminated structure. A step of forming a covering layer having a wide annular opening (C) A step of forming a groove having a non-uniform depth according to the width of the opening in the laminated structure by dry etching using the covering layer as a mask ( D) A step of forming an oxidized portion that is unevenly distributed corresponding to the depth of the groove portion in at least one of the first multilayer film reflecting mirror and the second multilayer film reflecting mirror by oxidizing the side surface of the groove portion.

  In the method for manufacturing a surface emitting semiconductor laser according to the present invention, a groove having a non-uniform depth corresponding to the width of the opening is formed by dry etching, and non-uniformly distributed corresponding to the depth of the groove by subsequent oxidation. An oxidized portion is formed. As a result, anisotropic stress due to the oxidized portion is generated in the active layer, so that the polarization component in the direction orthogonal to the direction of the stress is strengthened, while the polarization component in the direction parallel to the direction of the stress is suppressed. Thereby, the polarization component of the laser beam is fixed in one direction. Furthermore, the light field intensity distribution of the fundamental transverse mode is attracted in the direction of the oxidation part, and the peak position of the light field intensity distribution of the fundamental transverse mode approaches the peak position of the carrier density distribution, so that the gain of the fundamental transverse mode is increased. Can do.

  According to the surface-emitting type semiconductor laser of the present invention, at least one of the first multilayer-film reflective mirror and the second multilayer-film reflective mirror is provided with the oxidized portion in one of the regions opposed to the current confinement region. Therefore, it is possible to stabilize the polarization direction of the laser light in one direction and increase the output. Further, the substrate need not be a special substrate such as an (n11) plane substrate (n is an integer), and may be a (100) plane substrate, and can be manufactured easily and inexpensively.

  According to the method for manufacturing a surface emitting semiconductor laser of the present invention, a groove having a non-uniform depth corresponding to the width of the opening is formed by dry etching, and then non-uniform corresponding to the depth of the groove by oxidation. As a result, the polarization direction of the laser beam can be stabilized in one direction and the output can be increased. Further, the substrate need not be a special substrate such as an (n11) plane substrate (n is an integer), and may be a (100) plane substrate, and can be manufactured easily and inexpensively.

  Thus, according to the surface emitting semiconductor laser and the manufacturing method thereof of the present invention, it can be manufactured easily and inexpensively, and the polarization direction of the laser light can be stabilized in one direction and the output can be increased.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a top view of a surface emitting semiconductor laser 1 according to an embodiment of the present invention. 2 shows a cross-sectional configuration of the semiconductor laser 1 in FIG. 1 in the direction of arrow AA, and FIG. 3 shows a cross-sectional configuration of the semiconductor laser 1 in FIG. 1 in the direction of arrow BB. FIG. 4 shows an example of a cross-sectional configuration of the lower DBR layer 11 (described later). FIG. 5 shows a planar configuration of the current confinement layer 17 and the oxidized portion 30 (described later) when the semiconductor laser 1 of FIG. 1 is viewed through the top surface. 1 to 4 are schematic representations, and are different from actual dimensions and shapes.

  In the semiconductor laser 1 of the present embodiment, a lower DBR layer 11, a lower spacer layer 14, an active layer 15, an upper spacer layer 16, a current confinement layer 17, an upper DBR layer 18 and a contact layer 19 are formed on one surface side of a substrate 10. A laminated structure 20 (vertical resonator) is provided that is laminated in this order. In the upper part of the stacked structure 20, specifically, a part of the lower DBR layer 11, the lower spacer layer 14, the active layer 15, the upper spacer layer 16, the current confinement layer 17, the upper DBR layer 18 and the contact layer 19, For example, a columnar mesa portion 21 having a width of about 20 μm and a groove portion 22 surrounding the mesa portion 21 are formed.

  In the present embodiment, the lower DBR layer 11 corresponds to a specific example of the “first multilayer reflector” of the present invention, and the current confinement layer 17 and the upper DBR layer 18 are the “second multilayer film” of the present invention. This corresponds to a specific example of “reflecting mirror”.

  The groove portion 22 is an annular groove having a non-uniform width, and has a non-uniform depth corresponding to (proportional to) the width of the groove. Specifically, as shown in FIG. 1, the groove 22 has a groove 22A having a radial width Ly and a circumferential width Lx and a groove 22A communicating with the groove 22A and having a radial width ΔR. And a groove 22B. That is, the groove part 22 has a wide part only by one place.

  The groove 22 </ b> A has a depth D <b> 1 (see FIG. 2) that reaches the lower first DBR layer 12 (described later) of the lower DBR layer 11. On the other hand, the groove 22B has a depth D2 (see FIG. 3) that does not reach the inside of the lower first DBR layer 12. That is, the depth D2 of the groove 22B is shallower than the depth D1 of the groove 22A. As a result, the height of the mesa portion 21 is not uniform corresponding to the depth of the groove portion 22, and the mesa portion The layer structure exposed on the side surface of 21 differs depending on the depth of the groove 22. FIG. 3 illustrates the case where the groove 22 </ b> B reaches the lower second DBR layer 13 (described later) of the lower DBR layer 11.

  Here, Lx and Ly are preferably large enough not to slow the etching rate described later, and preferably 5 μm or more. Further, ΔR is smaller than Lx and Ly, and is preferably such that the etching rate of the groove 22B is slower than that of the groove 22A due to the loading effect described later, preferably 1 μm or more and 3 μm or less. It is more preferable that

  The substrate 10 is, for example, an n-type GaAs substrate, and this GaAs substrate is preferably a (100) plane substrate, for example, but may be a special substrate such as an (n11) plane substrate (n is an integer). .

  The lower DBR layer 11 has a structure in which a lower first DBR layer 12 and a lower second DBR layer 13 are stacked in this order from the substrate 10 side. In the present embodiment, the lower first DBR layer 12 corresponds to a specific example of the “third multilayer reflector” of the present invention, and the lower second DBR layer 13 is the “fourth multilayer reflector” of the present invention. It corresponds to one specific example.

For example, as shown in FIG. 4, the lower first DBR layer 12 is formed by laminating a plurality of sets of a low refractive index layer 12A and a high refractive index layer 12B. Low refractive index layer 12A is, for example, a thickness of λ / 4n _a (λ is the oscillation wavelength, _{n a} is the refractive index), an n-type _Al x1 _{Ga 1-x1} As, and the high refractive index layer 12B is, for example, a thickness of lambda / _4n b _{(n b} is the refractive index) of n-type _Al x2 _{Ga 1-x2} As the. The lower second DBR layer 13 is configured, for example, by stacking a plurality of sets of the low refractive index layer 13A and the high refractive index layer 13B as one set. Low refractive index layer 13A is made of n-type _Al x3 _{Ga 1-x3} As, for example, a thickness of λ _/ 4n _{c (n} c is the refractive index), the high refractive index layer 12B is, for example, a thickness of lambda / _4n d (n _d is a refractive index) n-type Al _x4 Ga _1-x4 As. Examples of n-type impurities include silicon (Si) and selenium (Se).

  Here, the Al composition values x1 to x4 in the lower DBR layer 11 satisfy the following expressions. As a result, the low refractive index layer 12A of the lower first DBR layer 12 is more easily oxidized than the low refractive index layer 13A of the lower second DBR layer 13, and has the property of being equal to or less oxidized than the current confinement layer 17. Yes.

1 ≧ x9 ≧ x1> (x3, x10)> 0.8> (x2, x4) ≧ 0 (1)

  (X3, x10) in the formula (1) means x3 or x10, and (x2, x4) means x2 or x4. X9 is the value of the Al composition contained in the material constituting the current confinement layer 17, and x10 is the value of the Al composition contained in the material constituting the low refractive index layer of the upper DBR layer 18. 0.8 corresponds to the boundary between the refractive index of the low refractive index layer and the refractive index of the high refractive index layer.

  By the way, in the present embodiment, the oxidized portion 30 is formed in one region of the low refractive index layer 12A of the lower first DBR layer 12 that is opposed to the current confinement region 17A (described later). As shown in FIGS. 2 and 4, the oxidized portion 30 has a stacked structure of a plurality of oxidized layers 30 </ b> A, and faces the edge of the current injection region 17 </ b> B (described later) from the side surface of the mesa portion 21. It is formed within a range that does not reach the region, and is formed corresponding to the deeper groove 22 </ b> A of the groove 22. That is, the oxidized portion 30 is unevenly distributed in one place in the region facing the current confinement region 17A, and non-uniform stress corresponding to the distribution is generated in the active layer 15.

The oxide layer 30A includes Al ₂ O ₃ (aluminum oxide). As described later, the high concentration Al contained in the low refractive index layer 12A is formed from the side surface side of the mesa portion 21 (groove portion 22). It is obtained by oxidation. Accordingly, each oxide layer 30 </ b> A constitutes a multilayer film that is laminated in the lower DBR layer 11 via the high refractive index layer 12 </ b> B. Since the lower first DBR layer 12 is not exposed at the portion of the side surface of the mesa portion 21 that faces the groove 22B, the oxide layer 30A is distributed in the portion other than the portion adjacent to the groove 22A. Not done.

By the way, the low refractive index layer 12A of the lower first DBR layer 12 is not limited to the above configuration. For example, as shown in FIG. 6B, the optical thickness is kept at λ / 4. It is also possible to take a configuration. As shown in FIG. 6B, the first refractive index layer 12C made of Al _x5 Ga _1-x5 As and the second refractive index layer 12D made of Al _x6 Ga _1-x6 As are stacked in this order from the substrate 10 side. When configured, the Al composition values x2 to x6 are set to values satisfying the following expression (2). Further, in this case, the oxide layer 30 </ b> A is a second refractive index layer located at or near the portion corresponding to the antinode P <b> 1 of the standing wave generated in the stacked structure 20 (see FIG. 6A). It will be formed in 12D.

1 ≧ x6 = x9> (x5, x3, x10)> 0.8> (x2, x4) ≧ 0 (2)

  In the formula (2), (x6, x3, x10) means x6, x3 or x10.

The lower spacer layer 14 is made of, for example, Al _x7 Ga _1-x7 As (0 <x7 <1). The active layer 15 is made of, for example, a GaAs material. In the active layer 15, a region facing a current injection region 17B, which will be described later, is a light emitting region 15A, and the edge of the light emitting region 15A (current injection region 17B) or the vicinity thereof corresponds to the peak of the carrier density distribution. The upper spacer layer 16 is made of, for example, Al _x8 Ga _1-x8 As (0 <x8 <1). These lower spacer layer 14, active layer 15 and upper spacer layer 16 are preferably free of impurities, but may contain p-type or n-type impurities. Examples of the p-type impurity include zinc (Zn), magnesium (Mg), and beryllium (Be).

The current confinement layer 17 has a current confinement region 17A in a region from the side surface of the mesa portion 21 to a predetermined depth, and the other region (the central region of the mesa portion 21) is a current injection region 17B. The current injection region 17B is made of, for example, p-type Al _x9 Ga _1-x9 As (0 <x9 ≦ 1). The current confinement region 17A includes, for example, Al ₂ O ₃ (aluminum oxide), and is formed by oxidizing high concentration Al contained in the oxidized layer 17D from the side surface, as will be described later. is there. Therefore, the current confinement layer 17 has a function of confining current.

The current injection region 17A has, for example, a quadrilateral (for example, rhombus) shape having diagonal lines in the [011] direction and the [01-1] direction, and has in-plane anisotropy. The reason why the current injection region 15B becomes a quadrilateral having diagonal lines in the [011] direction and the [01-1] direction is that, for example, the oxidation rate of Al _x7 Ga _1-x7 As is in the [011] direction and the [011] direction. This is because the [01-1] direction differs from the [001] direction and the [010] direction that form an angle of 45 degrees with these directions. Here, the width (diagonal length) Dox of the current injection region 17A is preferably 3 μm or more and 8 μm or less in order to suppress high-order transverse mode oscillation. Furthermore, when it is desired to further suppress higher-order transverse mode oscillation, the thickness is preferably 3 μm or more and 5 μm or less. The current injection region 17B may be circular. The current confinement layer 17 is preferably formed at or near a portion corresponding to the node P2 (see FIG. 6) of the standing wave generated in the stacked structure 20.

The upper DBR layer 18 is formed by laminating a plurality of sets of low refractive index layers and high refractive index layers. A p-type _Al x10 _Ga 1-x10 As the low refractive index layer is, for example, a thickness of λ _/ 4n _{e (n} e is the refractive index) (0 <x10 <1) , the high refractive index layer is, for example, a thickness of lambda / 4n _f (n _f is the refractive index) p-type Al _x11 Ga _1-x11 As (0 <x11 <1). The contact layer 19 is made of, for example, p-type GaAs.

  An annular upper electrode 24 having an opening (light emission port 24A) in a region facing the current injection region 17B is formed on the upper surface of the mesa unit 21 (upper surface of the contact layer 19). A protective film 23 is formed on the peripheral surface. An upper electrode pad 25 for bonding a wire (not shown) and a connection portion 26 are provided on the surface of the protective film 23, and the upper electrode pad 25 and the upper electrode 24 are formed in the groove 22B. They are electrically connected to each other through a connecting portion 26 formed inside. A lower electrode 27 is provided on the back surface of the substrate 10.

  Here, the protective film 23 is made of an insulating material such as oxide or nitride. The upper electrode 24 and the upper electrode pad 25 are formed by, for example, laminating titanium (Ti), platinum (Pt), and gold (Au) in this order, and are electrically connected to the contact layer 19 above the mesa portion 21. It is connected to the. The connection part 26 is formed by plating, for example. The lower electrode 27 has, for example, a structure in which an alloy of gold (Au) and germanium (Ge), nickel (Ni), and gold (Au) are sequentially stacked from the substrate 10 side. It is connected to the.

  Further, in the present embodiment, the transverse mode adjustment unit 50 is provided in the opening of the upper electrode 24, that is, in the light emission port 24A. The transverse mode adjustment unit 50 is provided in contact with the upper surface of the stacked structure 20 (the upper surface of the contact layer 19), and includes a first adjustment layer 51, a second adjustment layer 52, and a third adjustment layer 53. It consists of

Here, the first adjustment layer 51 has a film thickness of (2a-1) λ / 4n ₁ (a is an integer equal to or greater than ₁ , n ₁ is a refractive index), and the refractive index n ₁ is the uppermost layer ( For example, the contact layer 19) is made of a material having a lower refractive index, for example, a dielectric such as SiO ₂ (silicon oxide). Specifically, the second adjustment layer 52 has a film thickness of (2b-1) λ / 4n ₂ (b is an integer of 1 or more, n ₂ is a refractive index), and the refractive index n ₂ is the first adjustment layer 51. high material than the refractive index n ₁ of, for example, a dielectric such as SiN (silicon nitride). Therefore, the laminated structure composed of the first adjustment layer 51 and the second adjustment layer 52 has a function of reflecting light from the active layer 15 with high reflectivity, and in the high reflectivity region in the transverse mode adjustment unit 50. It corresponds.

The third adjustment layer 53 has a film thickness of (2c-1) λ / 4n ₃ (c is an integer of 1 or more, n ₃ is a refractive index), and the refractive index n ₃ is the refractive index n of the first adjustment layer 51. _It is made of a material higher than ₁ , for example, a dielectric such as SiN (silicon nitride). Accordingly, the third adjustment layer 53 has a function of reflecting the light from the active layer 15 with a lower reflectance than the laminated structure including the first adjustment layer 51 and the second adjustment layer 52, thereby adjusting the transverse mode. This corresponds to the low reflectance region in the portion 50.

  In addition, it is preferable that the 2nd adjustment layer 52 and the 3rd adjustment layer 53 are comprised by the same film thickness and material. This is because these layers can be collectively formed as described later, and the manufacturing process can be simplified.

  By the way, in this Embodiment, the laminated structure which consists of the 1st adjustment layer 51 and the 2nd adjustment layer 52 becomes circular shape, for example, as shown with the broken line of FIG. 1, and it starts from the center of the current injection area | region 17B. It is provided shifted to the oxidation unit 30 side. Here, in the case where the current injection region 17B has a quadrilateral shape, it is preferable that the oxidation portion 30 be provided on a line extending one diagonal line of the current injection region 17B. The width (diameter) Hr of the laminated structure composed of the first adjustment layer 51 and the second adjustment layer 52 is expressed by the following formulas (3) and (4), where Dox is the width (or diagonal length) of the current injection region 17B. It is preferable that it is in a range satisfying. Moreover, it is preferable that the difference (shift amount) between the center of the laminated structure including the first adjustment layer 51 and the second adjustment layer 52 and the center of the current injection region 17B is about 1 μm.

3 μm ≦ Hr ≦ 5 μm (3)
0.4 ≦ Hr / Dox ≦ 0.7 (4)

  The semiconductor laser 1 according to the present embodiment can be manufactured as follows, for example.

  7A and 7B to FIG. 9A and FIG. 9B show the manufacturing method in the order of steps. 7A, FIG. 8A, and FIG. 9A are cross-sectional configurations obtained by cutting the element in the manufacturing process in the same direction as the direction of arrows AA in FIG. ) Represents the top configuration of FIG. 7A, FIG. 8B represents the top configuration of FIG. 8A, and FIG. 9B represents the top configuration of FIG. 9A.

Here, the compound semiconductor layer on the substrate 10 made of GaAs is formed by, for example, MOCVD (Metal Organic Chemical Vapor Deposition). At this time, for example, trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMIn), and arsine (AsH3) are used as the source of the III-V group compound semiconductor. For example, dimethyl zinc (DMZ) is used as a material for acceptor impurities using H ₂ Se.

  First, the lower first DBR layer 12, the lower second DBR layer 13, the lower spacer layer 14, the active layer 15, the upper spacer layer 16, the oxidized layer 17D, the upper DBR layer 18 and the contact layer 19 are stacked on the substrate 10 in this order. After that, a resist layer R having an annular opening W having a non-uniform width is formed on the surface of the contact layer 19 (FIGS. 7A and 7B). Specifically, the opening W includes an opening W1 having a radial width Ly and a circumferential width Lx, and an arcuate opening W2 having a radial width ΔR that communicates with the opening W1.

  Next, etching is performed from the contact layer 19 side by, for example, reactive ion etching (RIE). Then, a loading effect occurs due to the non-uniform width of the opening W, and the etching rate in the narrow opening W2 becomes slower than that in the wide opening W1. As a result, a groove 22A having a depth D1 is formed corresponding to the opening W1, and a groove 22B having a depth D2 is formed corresponding to the opening W2 (FIGS. 8A and 8B). Thus, by forming the groove 22A and the groove 22B, the mesa portion 21 is formed in a portion surrounded by the groove 22A and the groove 22B.

  Next, an oxidation treatment is performed at a high temperature in a water vapor atmosphere to selectively oxidize Al in the low refractive index layer 12A and the layer to be oxidized 17D from the inside of the groove 22. As a result, the outer edge regions of the oxidized layer 17D and the low refractive index layer 12A become insulating layers (aluminum oxide), and the current confinement layer 17 and the oxidized portion 30 are formed (FIGS. 9A and 9B).

  As described above, by using the resist layer R having the annular opening W having a non-uniform width to generate the loading effect, the groove 22 having a non-uniform depth can be formed by a single etching process. . Further, the current confinement layer 17 and the oxidized portion 30 can be formed simultaneously and easily by performing an oxidation process using the groove portion 22 having the uneven depth.

  Next, after depositing the above-mentioned dielectric on the entire surface including the surface of the mesa portion 21 by, for example, the CVD (Chemical Vapor Deposition) method, it corresponds to a region of the upper surface of the mesa portion 21 where the first adjustment layer 51 is formed. The deposited dielectric is selectively removed by etching so that a portion to be left remains. Thereby, the first adjustment layer 51 is formed.

  Next, after the second adjustment layer 52 is formed on the first adjustment layer 51 using the same method as described above, the third adjustment layer 53 is formed in a region other than the first adjustment layer 51 on the upper surface of the mesa portion 21. Further, a protective film 23 is formed on the side surface of the mesa unit 21 and the surface around the mesa unit 21. The dielectric has an excellent selectivity with respect to the uppermost semiconductor layer of the stacked structure 20 and does not need to have a more complicated shape. Therefore, the first adjustment layer 51 can be easily formed by etching. can do.

  In addition, when the 2nd adjustment layer 52, the 3rd adjustment layer 53, and the protective film 23 are comprised by the same film thickness and material, it is preferable to form these layers collectively from the point of simplification of a manufacturing process. .

  Next, after laminating the above-mentioned metal material on the entire surface by, for example, vacuum deposition, the upper electrode 24 having an opening in the central region of the upper surface of the mesa unit 21 is formed by, for example, selective etching, and the periphery of the mesa unit 21 is formed. Upper electrode pads 25 and connecting portions 26 are formed on the surface.

  Next, after the back surface of the substrate 10 is appropriately polished and the thickness thereof is adjusted, the lower electrode 24 is formed on the back surface of the substrate 10. In this way, the semiconductor laser 1 of the present embodiment is manufactured.

  By the way, in the above manufacturing process, when the etching time is changed to change the depth D1 of the groove 22A, the number of the low refractive index layers 12A exposed on the inner surface of the groove 22A changes. Therefore, if the etching time is lengthened and the depth D1 of the groove 22A is increased, the number of exposed low refractive index layers 12A increases. Conversely, if the etching time is shortened and the depth D1 of the groove 22A is decreased, The number of exposed low refractive index layers 12A is reduced. At this time, the depth D2 of the groove 22B also changes in accordance with the etching time. However, when changing within the above-described range, the low refractive index layer 12A is not exposed on the inner surface of the groove 22B. The portion of the low refractive index layer 12A facing the groove 22B is hardly oxidized, and there is no possibility that stress in the direction in which the grooves 22B face each other is generated in the active layer 15. Therefore, even if the depth D1 of the groove 22A is shallow, it is possible to generate a stress in the active layer 15 in the direction in which the grooves 22A face each other, and according to the depth D1 of the groove 22A (in proportion) ), The stress in the direction in which the grooves 22A face each other can be increased. That is, it is possible to freely set the magnitude of the anisotropic stress generated in the active layer 15.

  Further, as illustrated in FIG. 6B, when the low refractive index layer 12A has a stacked structure of a layer having a high Al composition and a layer having a low Al composition, these layers are kept in a state where the Al composition of these layers is kept constant. By changing the thickness of this layer, the oxidation rate of the low refractive index layer 12A can be freely controlled. And, for example, since it is possible to make the oxidation rate equivalent to the case where the low refractive index layer 12A is a single layer, when the low refractive index layer 12A is a single layer, the lower DBR layer As in the case of satisfying the formula (1), the low refractive index layer 12A is more easily oxidized than the low refractive index layer 13A, and is equal to or equal to the current confinement layer 17 It is possible to make it less susceptible to oxidation.

  Further, for example, the Al composition value of the high refractive index layer of the low refractive index layer 12A is made the same as the Al composition value of the current confinement layer 17, and the low refractive index layer 12A of the low Al composition layer Al. It is also possible to make the composition value the same as the Al composition value of the low refractive index layer of the upper DBR layer 18. In such a case, when forming the low refractive index layer 12A, it is possible to use the epitaxial growth conditions such as the doping conditions and the gas flow rate used when the current confinement layer 17 and the upper DBR layer 18 are manufactured. Therefore, the low refractive index layer 12A can be easily manufactured.

  Next, the operation and effect of the semiconductor laser 1 of the present embodiment will be described.

  In the semiconductor laser 1 of the present embodiment, when a predetermined voltage is applied between the lower electrode 27 and the upper electrode 24, current is injected into the active layer 15 through the current injection region 17B in the current confinement layer 17, As a result, light is emitted by recombination of electrons and holes. This light is reflected by the pair of lower DBR layer 11 and upper DBR layer 18, causes laser oscillation at a predetermined wavelength, and is emitted to the outside as a laser beam.

  By the way, in the present embodiment, the oxidized portion 30 is provided in one region (one location) of the lower first DBR layer 12 of the lower DBR layer 11 in the region facing the current confinement region 17A. As a result, stress due to the oxidized portion 30 is generated non-uniformly in the active layer 15, so that the polarization component in the direction orthogonal to the direction of the stress is strengthened, while the polarization component in the direction parallel to the direction of the stress is suppressed. As a result, the polarization component of the laser light is fixed in one direction. Further, as shown in FIGS. 10A to 10E, the light field intensity distribution of the fundamental transverse mode is attracted toward the oxidation portion 30, and the peak position of the light field intensity distribution of the fundamental transverse mode is the current injection region. Since it approaches the position of the edge of 17B, and eventually the peak position of the carrier density distribution, the gain of the fundamental transverse mode can be increased. 10A to 10E schematically show the relationship between the transverse mode adjustment layer 50, the current confinement layer 17, and the oxidized portion 30, and the carrier density distribution and the light field intensity distribution. Accordingly, it is possible to stabilize the polarization direction of the laser light in one direction and increase the output.

  In addition, as illustrated in FIG. 6B, the low refractive index layer 12A is composed of two layers, and a layer having a high Al composition is a portion corresponding to the antinode P1 of the standing wave generated in the stacked structure 20 or its When provided in the vicinity, the asymmetry of the refractive index becomes stronger, and the peak position of the light field intensity distribution of the fundamental transverse mode is closer to the peak position of the carrier density distribution, so that the gain of the fundamental transverse mode is further increased. be able to. Thereby, the oscillation intensity of the fundamental transverse mode can be further increased.

  By the way, in this embodiment, as described above, the substrate does not have to be a special substrate such as an (n11) plane substrate (n is an integer), and may be a general (100) plane substrate. Typical (100) plane substrate doping conditions and epitaxial growth conditions such as gas flow rates can be used. Thereby, it can manufacture simply and cheaply.

  In the present embodiment, the anisotropic stress can be increased as the number of oxide layers 30A is increased. Therefore, the region corresponding to the light emitting region 15A in order to apply a greater stress to the active layer 15. It is not necessary to provide the oxidation part 30. Thereby, there is almost no possibility that the light output is lowered by the oxidation unit 30, and a high-power laser beam can be emitted.

  Therefore, in this embodiment, the semiconductor laser 1 can be manufactured easily and inexpensively, and the polarization direction of the laser light can be stabilized in one direction and the output can be increased.

  While the present invention has been described with reference to the embodiment and its modifications, the present invention is not limited to the above-described embodiment and the like, and various modifications can be made.

  For example, in the above-described embodiment and the like, the connection portion 26 that connects the upper electrode 24 and the upper electrode pad 25 is formed in the groove 22B. However, as shown in FIGS. 11 and 12, for example, It may be formed. At this time, for example, as shown in FIGS. 11 and 12, the contact layer 19 and the upper electrode 24 are one region (for example, an edge on the groove 22 </ b> A side) of the upper surface of the multilayer structure 20 facing the oxidized portion 30. ). In this case, as shown in FIGS. 13A to 13E, the current can be efficiently injected at the peak position of the light field intensity distribution of the fundamental transverse mode, so that the fundamental transverse mode is The oscillation intensity can be made extremely large.

  Further, in the above-described embodiment and the like, the shape of the groove 22A viewed from the upper surface side is substantially a quadrilateral shape. However, for example, a fan shape as shown in FIG. 14 or a nail as shown in FIG. It is also possible to have a shape like that of the cross section.

  Moreover, although the said embodiment etc. demonstrated the case where only one mesa part 21 was provided on the board | substrate 10, you may arrange | position the several mesa part 21 in an array form. For example, as shown in the semiconductor laser 2 of FIG. 16A, a plurality of mesa portions 21 are arranged in a line, and the mesa portions 21 at the center with respect to the mesa portions 21 at the both ends (the mesa portions other than the center). A groove 22A is provided on the side, the oxide layer 30 is unevenly distributed on the center mesa portion 21 side, and a lateral mode adjustment layer 50 is provided in which the first adjustment layer 51 and the second adjustment layer 52 are unevenly distributed on the center mesa portion 21 side. Further, the transverse mode in which the entire periphery of the central mesa portion 21 is surrounded by the groove 22B, and the first adjustment layer 51 and the second adjustment layer 52 are disposed at the center of the mesa portion 21 with respect to the central mesa portion 21. An adjustment layer 50 can be provided. In this case, as illustrated in FIG. 16B, the light field intensity distribution of the fundamental transverse mode of the light emitted from the mesa portions 21 at the both ends (the mesa portions other than the center) is the center mesa. It becomes unevenly distributed on the part 21 side. As a result, for example, a lens is disposed on the light emission side of the semiconductor laser 2, and when this lens receives light emitted from each mesa portion 21 of the semiconductor laser 2, an oxide layer is formed on all the mesa portions 21. Coupling efficiency can be improved as compared with the case where 30 and the transverse mode adjustment layer 50 are provided symmetrically without being unevenly distributed.

  In the above-described embodiment and the like, the contact layer 19 is the uppermost layer of the stacked structure 20. However, an opening is provided in the central region of the contact layer 19, and the uppermost layer of the upper DBR layer 18 is the uppermost layer of the stacked structure 20. Good.

  In the above-described embodiments and the like, the present invention has been described by taking an AlGaAs compound semiconductor laser as an example. However, other compound semiconductor lasers, for example, GaInP, AlGaInP, InGaAs, GaInP, InP, and GaN It is also applicable to compound semiconductor lasers such as GaInN and GaInNAs.

1 is a top view of a semiconductor laser according to an embodiment of the present invention. It is sectional drawing of the AA arrow direction of the semiconductor laser of FIG. It is sectional drawing of the BB arrow direction of the semiconductor laser of FIG. FIG. 3 is an enlarged view of an example of a cross-sectional configuration of a lower DBR layer in FIG. 2. It is a top view of the oxidation part and current confinement layer of FIG. FIG. 4 is an enlarged view of another example of the cross-sectional configuration of the lower DBR layer in FIG. 2. FIGS. 2A and 2B are a cross-sectional view and a top view for explaining a manufacturing process of the semiconductor laser of FIG. FIG. 8 is a cross-sectional view and a top view for explaining the process following FIG. 7. FIG. 9 is a cross-sectional view and a top view for explaining the process following FIG. 8. It is a schematic diagram for demonstrating carrier density distribution and light field intensity distribution. It is a top view of the semiconductor laser concerning one modification. It is sectional drawing of the AA arrow direction of the semiconductor laser of FIG. FIG. 12 is a schematic diagram for explaining a carrier density distribution and an optical field intensity distribution in the semiconductor laser of FIG. 11. It is a top view of the semiconductor laser which concerns on another modification. It is a top view of the semiconductor laser concerning other modifications. It is a top view of the semiconductor laser concerning other modifications.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 10 ... Substrate, 11 ... Lower DBR layer, 12 ... Lower first DBR layer, 12A, 13A ... Low refractive index layer, 12B, 13B ... High refractive index layer, 13 ... Lower second DBR layer, 14 ... Lower Cladding layer, 15 ... active layer, 15A ... light emitting region, 16 ... upper cladding layer, 17 ... current confinement layer, 17A ... current confinement region, 17B ... current injection region, 17D ... oxidized layer, 18 ... upper DBR layer, 19 DESCRIPTION OF SYMBOLS ... Contact layer, 20 ... Laminated structure, 21 ... Mesa part, 22 ... Groove part, 22A, 22B ... Groove, 23 ... Protective film, 24 ... Upper electrode, 24A ... Light emission port, 25 ... Upper electrode pad, 26 ... Connection part 27 ... lower electrode, 30 ... oxidation part, 30A ... oxidation layer, 50 ... transverse mode adjustment layer, 51 ... first adjustment layer, 52 ... second adjustment layer, 53 ... third adjustment layer, Lx, Ly, ΔR ... Width, D1, D2 ... Depth, Dox ... Width of the flow injection region, W, W1, W2 ... opening.

Claims (18)

On the substrate, a multilayer structure including a first multilayer film reflector, an active layer and a second multilayer film reflector in this order from the substrate side,
At least one of the first multilayer reflector and the second multilayer reflector has a current confinement layer including a current injection region and an annular current confinement region surrounding the current injection region from the in-plane direction of the stack. ,
At least one of the first multilayer-film reflective mirror and the second multilayer-film reflective mirror has an oxidized portion in one of the regions opposed to the current confinement region. The surface emitting semiconductor laser according to claim 1, wherein the oxidation portion is formed of a multilayer film. The stacked structure has a groove portion surrounding the current confinement layer and the oxidized portion,
The surface emitting semiconductor laser according to claim 1, wherein the groove has a non-uniform depth corresponding to the distribution of the oxidized portion. The oxidation part is composed of a multilayer film,
The surface emitting semiconductor laser according to claim 3, wherein the multilayer film is formed corresponding to a deep portion of the groove. The surface emitting semiconductor laser according to claim 3, wherein the groove has a non-uniform width corresponding to the distribution of the oxidized portion. The oxidation part is composed of a multilayer film,
The surface emitting semiconductor laser according to claim 5, wherein the multilayer film is formed corresponding to a wide portion of the groove. 4. The surface-emitting type semiconductor laser according to claim 3, wherein a width of a portion of the groove corresponding to a deep portion is not less than 1 μm and not more than 3 μm. Of the first multilayer reflector and the second multilayer reflector, the reflector having the oxidized portion is a third multilayer reflector that is relatively easily oxidized and a fourth multilayer reflector that is relatively less likely to be oxidized. It has a structure in which mirrors are stacked in this order from the substrate side,
The surface emitting semiconductor laser according to claim 1, wherein the oxidation portion is formed in the third multilayer-film reflective mirror. The third multilayer-film reflective mirror is formed by laminating a plurality of sets of low refractive index layers made of Al _x1 Ga _1-x1 As and high refractive index layers made of Al _x2 Ga _1-x2 As. And
The fourth multilayer-film reflective mirror is formed by laminating a plurality of low-refractive index layers made of Al _x3 Ga _1-x3 As and high-refractive index layers made of Al _x4 Ga _1-x4 As. And
The surface-emitting type semiconductor laser according to claim 8, wherein the x1 to x4 satisfy the following expression.
1 ≧ x1>x3>0.8> (x2, x4) ≧ 0 (1) The third multilayer-film reflective mirror includes a low refractive index layer having a first refractive index layer made of Al _x5 Ga _1-x5 As and a second refractive index layer made of Al _x6 Ga _1-x6 As, and Al _x2 Ga _{1- A} high refractive index layer made of _x2 As is set as one set, and a plurality of sets are stacked.
The fourth multilayer-film reflective mirror is formed by laminating a plurality of low-refractive index layers made of Al _x3 Ga _1-x3 As and high-refractive index layers made of Al _x4 Ga _1-x4 As. And
The surface-emitting type semiconductor laser according to claim 8, wherein the x2 to x6 satisfy the following expression.
1 ≧ x6> (x5, x3)>0.8> (x2, x4) ≧ 0 (2) The second refractive index layer is formed at or near a portion corresponding to an antinode of a standing wave generated in the stacked structure,
The surface emitting semiconductor laser according to claim 10, wherein the oxidation portion is formed in the second refractive index layer. The surface emitting semiconductor laser according to claim 10, wherein the current confinement layer is formed at or near a portion corresponding to a node of a standing wave generated in the stacked structure. A contact layer and an electrode electrically connected to the upper surface of the multilayer structure are provided in this order from the multilayer structure side in one region of the upper surface of the multilayer structure opposite to the oxidized portion. The surface emitting semiconductor laser according to claim 1. A lateral mode adjustment layer including a high reflectivity region and a low reflectivity region in the laminate surface in a region facing the current injection region in the upper surface of the laminate structure,
The surface emitting semiconductor laser according to claim 1, wherein the high reflectance region is provided so as to be shifted from a center of the current injection region toward the oxidation portion. The high reflectivity region has a film thickness of (2a-1) λ / 4n ₁ (a is an integer of 1 or more, λ is an emission wavelength, and n ₁ is a refractive index), and a refractive index n ₁ is the reflection of the first multilayer film. A first adjustment layer having a value lower than that of the surface of the mirror, a film thickness of (2b-1) λ / 4n ₂ (b is an integer of 1 or more, n ₂ is a refractive index), and the refractive index n ₂ is Having a structure in which a second adjustment layer having a value higher than that of the first adjustment layer is laminated in this order;
In the transverse mode adjusting portion, the low reflectance region has a film thickness of (2c-1) λ / 4n ₃ (c is an integer of 1 or more, n ₃ is a refractive index), and a refractive index n ₃ is the first adjustment. The surface emitting semiconductor laser according to claim 14, further comprising a third adjustment layer having a value higher than that of the layer. The surface emitting semiconductor laser according to claim 15, wherein the first adjustment layer and the second adjustment layer are made of different types of dielectrics. The first adjustment layer is made of an oxide,
The surface emitting semiconductor laser according to claim 15, wherein the second adjustment layer and the third adjustment layer are made of nitride. Forming a laminated structure including a first multilayer mirror, an active layer, and a second multilayer mirror in this order from the substrate side on the substrate;
Forming a covering layer having an annular opening having a wide width at one place on the upper surface of the laminated structure;
Forming a groove with a non-uniform depth according to the width of the opening in the stacked structure by dry etching using the coating layer as a mask;
Oxidizing a side surface of the groove to form an oxidized portion that is unevenly distributed corresponding to the depth of the groove on at least one of the first multilayer mirror and the second multilayer mirror. A method of manufacturing a surface-emitting type semiconductor laser comprising:

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