Surface Emitting Laser and Method for Manufacturing the Same

Abstract

A columnar portion is formed by etching parts of an active layer and a first reflective layer. In this etching process, the columnar portion is formed by etching the first reflective layer to a position of a semiconductor layer. For example, it is etched to a thickness of approximately 3 μm.

Claims

1-6. (canceled)

7. A method for producing a surface emitting laser, the method comprising: forming, on a substrate, a first reflective layer having a distributed Bragg reflector structure in which a plurality of compound semiconductor materials each having a different refractive index are alternately laminated; forming, on the first reflective layer, an active layer formed of a compound semiconductor; forming a columnar portion by etching the active layer and a part of the first reflective layer; embedding the columnar portion by forming an embedded layer on the first reflective layer around the columnar portion; and forming, on the columnar portion and the embedded layer, a second reflective layer having a distributed Bragg reflector structure in which the plurality of compound semiconductor materials each having a different refractive index are alternately layered, wherein the first reflective layer has a semiconductor layer having a thickness which is an odd multiple of 1/(4nλ), wherein λ is a wavelength of target light, wherein n is a positive integer, and wherein in forming of the columnar portion, the columnar portion is formed by etching the first reflective layer to a position of the semiconductor layer.

8. The method for producing a surface emitting laser according to claim 7, the method further comprising: forming, on the active layer, a tunnel junction layer as a pn junction; wherein in forming of the columnar portion, the columnar portion is formed by etching the tunnel junction layer, the active layer, and the first reflective layer.

9. The method for producing a surface emitting laser according to claim 7, wherein, in forming of the columnar portion, a plurality of the columnar portions are formed and a layer formed of a same semiconductor is exposed on a surface of the first reflective layer around the columnar portion.

10. A surface emitting laser comprising: a first reflective layer having a distributed Bragg reflector structure in which a plurality of compound semiconductor materials each having a different refractive index are alternately disposed, the first reflective layer being disposed on a substrate; a columnar portion on the first reflective layer; an active layer comprising a compound semiconductor, the active layer being disposed on the first reflective layer of the columnar portion; an embedded layer on the first reflective layer around the columnar portion, the embedded layer embedding the active layer and the first reflective layer of the columnar portion; and a second reflective layer having a distributed Bragg reflector structure in which compound semiconductor layers each having a different refractive index are alternately disposed, the second reflective layer being disposed on the columnar portion and the embedded layer, wherein the first reflective layer near a lowermost portion of the columnar portion has a semiconductor layer having a thickness which is an odd multiple of 1/(4nλ), wherein λ is a wavelength of target light, and wherein n is a positive integer.

11. The surface emitting laser according to claim 10, further comprising a tunnel junction layer comprising a pn junction on the active layer, wherein the embedded layer embeds the tunnel junction layer, the active layer, and the first reflective layer of the columnar portion, and wherein the second reflective layer is disposed on the tunnel junction layer.

12. The surface emitting laser according to claim 10 further comprising a plurality of columnar portions, the plurality of columnar portions comprising the columnar portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1A is a cross-sectional view illustrating a state of each of layers in an intermediate process for explaining a method for producing a surface emitting laser according to an embodiment of the present invention.

[0020] FIG. 1B is a cross-sectional view illustrating the state of each of layers in the intermediate process for explaining the method for producing a surface emitting laser according to the embodiment of the present invention.

[0021] FIG. 1C is a cross-sectional view illustrating the state of each of layers in the intermediate process for explaining the method for producing a surface emitting laser according to the embodiment of the present invention.

[0022] FIG. 1D is a cross-sectional view illustrating the state of each of layers in the intermediate process for explaining the method for producing a surface emitting laser according to the embodiment of the present invention.

[0023] FIG. 1E is a cross-sectional view illustrating the state of each of layers in the intermediate process for explaining the method for producing a surface emitting laser according to the embodiment of the present invention.

[0024] FIG. 1F is a cross-sectional view illustrating the state of each of layers in the intermediate process for explaining the method for producing a surface emitting laser according to the embodiment of the present invention.

[0025] FIG. 2 is a characteristics diagram illustrating characteristics of the surface emitting laser actually produced.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0026] Hereinafter, a method for producing a surface emitting laser according to an embodiment of the present invention will be described with reference to FIGS. 1A to 1F.

[0027] First, as illustrated in FIG. 1A, a first reflective layer 102 having a distributed Bragg reflector (DBR) structure in which compound semiconductor layers having different refractive indices are alternately laminated is formed on a substrate 101 (a first step). The first reflective layer 102 has a semiconductor layer 121a having a thickness which is an odd multiple of 1/(4nλ). λ is a wavelength (an oscillation wavelength) of target light. The substrate 101 is composed of, for example, an n type InP. In addition, the first reflective layer 102 has a superlattice structure in which, for example, 54 sets of n-InP layers 121 formed of an n type InP and n-InAlGaAs layers 122 formed of an n type InAlGaAs are alternately laminated. In this example, one of the n-InP layers 121 is the semiconductor layer 121a. The first reflective layer 102 having the above-described configuration serves as a semi-reflective layer.

[0028] Next, as illustrated in FIG. 1B, an active layer 104 formed of a compound semiconductor is formed the first reflective layer 102 (a second step). For example, an active layer 104 is formed on the first reflective layer 102 via a spacer layer 103 formed of the n type InP. Further, a spacer layer 105 formed of a p type InP is formed on the active layer 104. Also, in the present embodiment, a tunnel junction layer 106 is formed on the spacer layer 105 (a sixth step). The tunnel junction layer 106 is composed of a pn junction of a p.sup.++-InP layer 161 formed of InP into which p-type impurities are introduced in a high concentration, and an n.sup.++-InP layer 162 formed of InP into which n-type impurities are introduced in a high concentration.

[0029] Further, in the present embodiment, a laminated structure 107 in which five sets of an n-InP layer 171 formed of an n type InP and an n-InAlGaAs layer 172 formed of an n type InAlGaAs are laminated on the tunnel junction layer 106 is provided. The laminated structure 107 is a distributed Bragg reflector layer having a superlattice structure.

[0030] Each of the above-described semiconductor layers is formed by crystal growth (epitaxial growth) using a well-known metalorganic vapor phase growth method, molecular beam epitaxy method, or the like.

[0031] Next, parts of the active layer 104 and the first reflective layer 102 are etched to form a columnar portion 108 (a third step), as illustrated in FIG. 1C. In the present embodiment, the columnar portion 108 is formed by patterning due to an etching process using a SiO.sub.2 pattern (not illustrated) formed of SiO.sub.2 as a mask. First, SiO.sub.2 is deposited on the laminated structure 107 by a known chemical vapor deposition (CVD) method, for example, to form a SiO.sub.2 layer. Then, the SiO.sub.2 pattern can be formed by patterning the SiO.sub.2 layer due to the etching process using a known lithographic and RIE device.

[0032] Next, the columnar portion 108 is formed by etching the laminated structure 107, the tunnel junction layer 106, the spacer layer 105, the active layer 104, the spacer layer 103, and a part of the first reflective layer 102 due to ICP dry etching using a mixed gas of hydrogen iodide (HI) and argon (Ar) with the formed SiO.sub.2 pattern as a mask. Although one columnar portion 108 is illustrated in the drawing, a plurality of columnar portions 108 are formed on a substrate 101 in another region not illustrated in the drawings in a state in which each of them is separated in a surface direction of the substrate 101.

[0033] In the etching process, the first reflective layer 102 is etched to a position of the semiconductor layer 121a to form the columnar portion 108. In the present embodiment, for example, the etching is performed to a thickness of about 3 μm. For example, in a typical etching treatment device which performs the above-described etching, due to a variation in etching in a surface of the substrate 101, an etching amount is the smallest in the center of the substrate 101, and the etching amount tends to increase toward the outer periphery, and for example, a variation in an etching depth is within about 7%.

[0034] In this case, the fifth set of the n-InP layer 121 from an upper end of the first reflective layer 102 can be set as the semiconductor layer 121a, and a thickness thereof can be set to 3/(4nλ). In this example, 3/(4nλ) corresponds to approximately 0.3 μm. A thickness of the semiconductor layer 121a having a thickness which is an odd multiple of 1/(4nλ) is set appropriately according to characteristics (the variation in the etching amount) of an environment (device) in which the etching process for forming the columnar portion 108 is performed. Because the thickness of the semiconductor layer 121a is an odd multiple of 1/(4nλ), the characteristics (reflection characteristics) of the first reflective layer 102 are not affected.

[0035] When the etching process is performed by an etching device having the above-described variation, and the etching is stopped at a location on the center portion of the substrate 101 at which the uppermost portion of the semiconductor layer ma appears (is exposed), the semiconductor layer 121a is removed at the outer peripheral portion of the substrate 101, and the n-InAlGaAs layer 122 which is located therebelow is exposed.

[0036] As described above, in order to eliminate a condition in which a different layer is exposed on the substrate 101, first, the etching process under conditions in which InP is selectively etched with respect to InAlGaAs is performed, and the semiconductor layer 121a exposed in a region forming an embedded layer other than the columnar portion 108 is removed. For example, the semiconductor layer ma formed of InP can be selectively removed by the etching process using an aqueous solution obtained by mixing HCl, H.sub.3PO.sub.4, and CH.sub.3COOH as an etching solution. In this etching process, the etching is automatically stopped at the n-InAlGaAs layer 122 below the semiconductor layer 121a, and the n-InAlGaAs layer 122 below the semiconductor layer 121a is exposed in the entire region of the substrate 101. In this way, in each of the plurality of formed columnar portions 108, a layer formed of the same semiconductor is exposed at the surface of the surrounding first reflective layer 102.

[0037] In the present embodiment, in order to use InP as a surface on which the embedded layer is re-grown, following the above-described process, an etching process under a condition in which InAlGaAs is selectively etched with respect to InP is performed, and the n-InAlGaAs layer 122 exposed in the region forming the embedded layer other than the columnar portion 108 is selectively removed. For example, the n-InAlGaAs layer 122 can be selectively removed by an etching process using an aqueous solution in which H.sub.2SO.sub.4 and H.sub.2O.sub.2 are mixed as an etching solution. In this etching process, the etching is automatically stopped at the n-InP layer 121, and the n-InP layer 121 is exposed in the entire region of the substrate 101. In a state in which the n-InP layer 121 is exposed, this can be visually confirmed due to a change in a color, or the like.

[0038] Next, as illustrated in FIG. 1E, an embedded layer 109 is formed on the first reflective layer 102 around the columnar portion 108 to embed the columnar portion 108 (a fourth step). For example, the embedded layer 109 can be formed by re-growing InP from the n-InP layer 121 of the first reflective layer 102 around the columnar portion 108 which is exposed as described above using the above-described SiO.sub.2 pattern as a selective growth mask. The embedded layer 109 can be a pn embedded structure. In addition, the embedded layer 109 is formed to form a current path.

[0039] Next, as illustrated in FIG. 1F, a second reflective layer no having a distributed Bragg reflector structure in which compound semiconductor layers having different refractive indices are alternately laminated is formed on the columnar portion 108 and the embedded layer 109 (a fifth step). After the above-described SiO.sub.2 pattern is removed, for example, a GaAs layer 111 formed of GaAs and a AlGaAs layer 112 formed of AlGaAs are alternately grown by metamorphic growth to form the second reflective layer no. The second reflective layer no having the above-described configuration is a total reflective layer. Thus, in the present embodiment, the first reflective layer 102 and the second reflective layer no constitute a resonator, and laser is emitted from the side of the first reflective layer 102.

[0040] Further, after the second reflective layer no is formed, an upper electrode (not illustrated) and a lower electrode (not illustrated) are formed, and separation between elements is performed. The separation between elements is performed by an etching process using, for example, hydrogen bromide (HBr) as an etching solution. Furthermore, an anti-reflective layer 201 is formed on the back surface of the substrate 101.

[0041] As described above, a surface emitting laser is obtained, the surface emitting laser including a first reflective layer 102, a columnar portion 108, an active layer 104, an embedded layer 109, and a second reflective layer no. The first reflective layer 102 is formed on a substrate 101 and has a distributed Bragg reflector structure in which compound semiconductor layers each having a different refractive index are alternately laminated. The columnar portion 108 is formed on the first reflective layer 102. The active layer 104 is formed on the first reflective layer 102 of the columnar portion 108 and formed of a compound semiconductor. The embedded layer 109 is formed on the first reflective layer 102 around the columnar portion 108 and configured to embed the active layer 104 and the first reflective layer 102 of the columnar portion 108. The second reflective layer no is formed on the columnar portion 108 and the embedded layer 109 and has a distributed Bragg reflector structure in which compound semiconductor layers each having a different refractive index are alternately laminated. The first reflective layer 102 near a lowermost portion of the columnar portion 108 has a semiconductor layer 121a having a thickness which is an odd multiple of 1/(4nλ).

[0042] The surface emitting laser further includes a tunnel junction layer 106 formed by a pn junction formed on the active layer 104, the embedded layer 109 embeds the tunnel junction layer 106, the active layer 104, and the first reflective layer 102 of the columnar portion 108, and the second reflective layer no is formed on the tunnel junction layer 106. Additionally, a plurality of the columnar portions 108 are formed.

[0043] Next, evaluation results of characteristics of an actually produced surface emitting laser according to the present embodiment will be described. In the evaluation of the characteristics, the produced surface emitting laser is mounted with the second reflective layer no side down and is cooled from the second reflective layer no side, and laser light emitted from the substrate 101 side via the anti-reflective layer 201 is measured. In addition, the surface emitting laser actually produced includes 10 columnar portions (elements) on the same substrate. FIG. 2 illustrates s a relationship between a current and a voltage of the surface emitting laser, and a relationship between the current and the light characteristics. As illustrated in FIG. 2, according to the present embodiment, laser oscillation in a single lateral mode having a large emission diameter of 12 μm square is observed with characteristics that oscillation threshold variation is small between the elements and maximum light outputs are approximately the same.

[0044] As described above, according to embodiments of the present invention, because a semiconductor layer having a thickness which is an odd multiple of 1/(4nλ) is provided on the first reflective layer, and the first reflective layer is etched to the position of the semiconductor layer to form the columnar portion, variations between elements and the like can be curbed, and a plurality of surface emitting laser elements can be produced on the same substrate.

[0045] Meanwhile, the present invention is not limited to the embodiment described above, and it will be obvious to those skilled in the art that various modifications and combinations can be implemented within the technical idea of the present invention. For example, in the above description, although the surface emitting laser produced using the InP substrate has been described as an example, the present invention is not limited thereto, and the same applies to a surface emitting laser having a DBR reflective layer formed of GaAs/AlGaAs having an oscillation wavelength of 0.98 μm, which is produced using a GaAs substrate.

REFERENCE SIGNS LIST

[0046] 101 Substrate

[0047] 102 First reflective layer

[0048] 103 Spacer layer

[0049] 104 Active layer

[0050] 105 Spacer layer

[0051] 106 Tunnel junction layer

[0052] 107 Laminated structure

[0053] 108 Columnar portion

[0054] 109 Embedded layer

[0055] 110 Second reflective layer

[0056] 111 GaAs Layer

[0057] 112 AlGaAs Layer

[0058] 121 n-InP layer

[0059] 121a Semiconductor layer

[0060] 122 n-InAlGaAs Layer

[0061] 161 p.sup.++-InP layer

[0062] 162 n.sup.++-InP layer

[0063] 171 n-InP layer

[0064] 172 n-InAlGaAs Layer

[0065] 201 Anti-reflective layer.