JP2006332189A - Semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting device which can improve light extraction efficiency. <P>SOLUTION: The light emitting device is provided with a compound semiconductor layer which is comprised of an active layer 12 and first and second clad layers 11 and 13 that have a larger band gap than the active layer 12, and are arranged on both sides of the active layer 12. The compound semiconductor layer has a curved face S which, assuming that an axis vertical to the lamination direction is x and an axis parallel to the lamination direction is y, is obtained by turning a parabola having a focal point on the y axis, by 360° using the y axis as a rotation axis. The active layer 12 has the focal point of the curved face S and a light emitting area 12-1 adjacent thereto, and the light emitting area 12-1 is considered as a point light source provided at the focal point of the curved face S. Thus, a light generating in the light emitting area 12-1 is reflected on the curved face S, and it is emitted nearly vertically from the surface of the compound semiconductor layer. In addition, a light generating in the light emitting area 12-1 does not enter an active layer 12A in almost cases, so that the light is not substantially absorbed by the active layer 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device that emits light in the visible region, and more particularly to a semiconductor light emitting device having an improved shape of a compound semiconductor layer.

  The external quantum efficiency of a semiconductor light emitting device such as a light emitting diode (LED) is composed of two elements, an internal quantum efficiency and a light extraction efficiency. By improving these efficiency, long life and low power consumption are achieved. In addition, a high-power semiconductor light emitting device can be realized. Here, the former internal quantum efficiency is, for example, a layer structure capable of accurately controlling the growth conditions so as to obtain a high-quality crystal with few crystal defects and dislocations and suppressing the occurrence of carrier overflow. It is improved by doing. On the other hand, the latter light extraction efficiency has such a geometry that the light emitted from the active layer is incident on the exit window at an angle less than the escape cone angle before being absorbed by the substrate or the active layer. The shape and the layer structure can be improved.

  As one of elements having such a shape and structure, there is an element in which a thick window layer is provided on the exit window as disclosed in Non-Patent Document 1. In this element, since the thick window layer is provided in the exit window, the ratio of the light emitted from the active layer entering the exit window at an angle less than the escape cone angle increases.

  Patent Document 1 discloses an element in which a plurality of pyramidal projections are provided on the exit window surface. In this element, the ratio of the light emitted from the emission window by the pyramidal projection increases.

  Patent Document 2 discloses an element including an optically transparent substrate. In this element, since the substrate does not absorb light, light is emitted from the substrate to the outside.

  Further, Patent Document 3 discloses an element having an inverted triangular frustum shape and having a thick optically transparent substrate. In this element, the light emitted from the active layer due to the oblique end face of the inverted triangular frustum has a higher ratio of incident on the upper surface of the substrate at an escape cone angle less than that, and the light reflected from the upper surface of the substrate has an inverted triangular frustum shape. The ratio of incidence with respect to the oblique end face is less than the escape cone angle.

  Patent Document 4 discloses an element having a micro-reflector structure in which upper portions of a plurality of concave mesa portions are covered with a cover layer. In this element, by adjusting the end face shape of each mesa portion, the thickness of the cover layer, etc., the ratio of the light emitted from the active layer to the cover layer side entering the cover layer surface with an escape cone angle of less than Become more.

  Patent Document 5 discloses an element including a DBR (Distributed Bragg Reflector) mirror layer. In this element, since light is returned to the semiconductor layer by the DBR mirror layer, absorption at the substrate is suppressed.

  Patent Document 6 discloses an element including an omnidirectional reflection layer. In this element, light is returned to the semiconductor layer by the omnidirectional reflection layer, so that absorption at the substrate is suppressed.

G. B. Stringfall and M.M. G. Graford (ed.): High Brightness Light Emitting Diodes. Semiconductor and Semimetals Vol. 48, Academic Press 1997 Special table 2003-524884 gazette US Pat. No. 5,376,580 Japanese Patent Laid-Open No. 10-341035 Special table 2003-506331 gazette JP-A-9-107123 US Pat. No. 6,784,462

  However, in the techniques described in Non-Patent Document 1, Patent Document 1 to Patent Document 6, light emitted from the light emitting region of the active layer in the direction opposite to the light irradiated surface is emitted to the outside. Since the light enters the active layer before being absorbed, it is absorbed by the active layer. As described above, the above-described techniques have a problem that the light extraction efficiency cannot be increased so much because a factor for greatly reducing the light extraction efficiency is inherent.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a semiconductor light emitting device capable of increasing light extraction efficiency.

  The semiconductor light emitting device of the present invention includes a compound semiconductor layer including an active layer and a pair of clad layers having a band gap larger than that of the active layer and disposed on both sides of the active layer. . This compound semiconductor layer is obtained by rotating a parabola having a focal point on the y-axis by 360 ° about the y-axis, where x is an axis perpendicular to the stacking direction and y is an axis parallel to the stacking direction. The active layer has a curved surface, and has a light emitting region at and near the focal point of the curved surface.

  In the semiconductor light emitting device of the present invention, since the light emitting region of the active layer is provided at the focal point of the curved surface and the vicinity thereof, it can be regarded as a point light source provided at the focal point of the curved surface. Thereby, the light reflected by the curved surface in the light emitting region of the active layer is reflected by the parabolic curved surface, and is emitted almost vertically from the surface of the compound semiconductor layer.

  As a result, the light generated in the light emitting region of the active layer has substantially no possibility of entering the active layer again, so that the light absorption in the active layer does not substantially occur.

  According to the semiconductor light emitting device of the present invention, light absorption in the active layer is substantially prevented, so that the light extraction efficiency can be increased.

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

  FIG. 1 shows a cross-sectional structure of a light emitting diode (LED) according to an embodiment of the present invention. This light emitting diode has a laminated structure in which a first clad 11, an active layer 12, a second clad layer 13 and a contact layer 14 are laminated in this order on one surface side of a substrate 10. A p-side electrode 16 is formed in the center on the surface of the contact layer 16, and an n-side electrode 17 is formed on the back surface of the substrate 10. This light emitting diode is a top emission type light emitting element configured to emit light emitted from the active layer 12 from the opening W of the substrate 10.

  The substrate 10, the first cladding 11, the active layer 12, the second cladding layer 13, and the contact layer 14 are compound semiconductor layers each composed of, for example, an AlGaInP-based semiconductor. Note that an AlGaInP-based semiconductor is a compound semiconductor containing aluminum (Al), gallium (Ga), or indium (In) as a group 3B element and phosphorus (P) as a group 5B element in the long-period periodic table. Say.

  The substrate 10 is made of an optically transparent material that does not absorb light emitted from the active layer 12, such as gallium phosphide (GaP).

The active layer 12 has a multiple quantum well structure in which, for example, quantum well layers (not shown) and barrier layers (not shown) are alternately stacked. For example, the undoped In _a Ga _1-a P ( as 0 <a <1) consisting of a quantum well layer and an undoped _{(Al b Ga 1-b)} 1-c In c P (0 <b ≦ 1,0 < pair and a barrier layer made of c <1), A plurality of such layers are stacked. Here, the In composition values a and c and the Al composition value b of the active layer 12 are determined in consideration of the emission wavelength, carrier density distribution, and the like. The active layer 13 may have a structure other than the multiple quantum well structure, for example, a single quantum well structure or a bulk structure.

The first cladding layer 11 is, for example, n-type (Al _d Ga _1-d ) _1-e In _e P (0 <d ≦ 1, 0 <e <1), and the second cladding layer 13 is, for example, p-type (Al _f Ga _1-f ) _1-g In _g P (0 <f ≦ 1, 0 <g <1). The first cladding layer 11 and the second cladding layer 13 have a larger band gap than the active layer 12. Here, the Al composition and the In composition of the first cladding layer 11 and the second cladding layer 13 are determined in consideration of the carrier confinement property and injection property with respect to the active layer 11.

  The contact layer 14 is made of, for example, p-type GaP.

  The reflective film 15 has a structure in which, for example, a silicon oxide (SiO 2) layer and a silver (Ag) layer are laminated on the surface of the curved surface S in this order, so that the emitted light from the active layer 12 is reflected with high reflectivity. It has become. The reflective film 15 may be composed of an omnidirectional reflective layer.

  The p-side electrode 16 has, for example, a structure in which a titanium (Ti) layer, a platinum (Pt) layer, and a gold (Au) layer are stacked in this order on the surface of the contact layer 14. It is connected. The n-side electrode 17 has a structure in which, for example, an alloy layer of gold (Au) and germanium (Ge), a nickel (Ni) layer, and a gold (Au) layer are stacked in this order. And are electrically connected.

By the way, the semiconductor layer constituted by the first cladding 11, the active layer 12 and the second cladding layer 13 has a curved surface S. The curved surface S is focused on the y-axis, where x is an axis parallel to the surface of the substrate 10 (axis perpendicular to the stacking direction) and y is an axis perpendicular to the surface of the substrate 10 (axis parallel to the stacking direction). And a parabola having a vertex on the y-axis opposite to the substrate 10 with respect to the focal point thereof, is obtained by rotating 360 ° about the y-axis as a rotation axis. Here, if the distance between the focal point and the vertex of the curved surface S is p, the curved surface S is expressed by a function of y = x ² / (4p), for example.

  Further, the active layer 12 and the light emitting region 12-1 of the active layer 12 are disposed at the focal point of the curved surface S and in the vicinity thereof. That is, the light emitting region 12-1 is arranged as a point light source at the focal point of the curved surface S and in the vicinity thereof. Further, the contact layer 14 is disposed at the apex of the curved surface S and in the vicinity thereof, and surrounds the region corresponding to the opening W of the curved surface S (the region surrounded by the end portions P1 and P2 of the curved surface S) of the substrate 10. In this manner, the n-side electrode 17 is arranged.

  The opening angle θ1 obtained by doubling the angle (<90 °) at which the symmetry axis of the curved surface S intersects the focal point of the curved surface S and the generatrix of the surface passing through the end portions P1 and P2 of the curved surface S is an escape. The cone angle θ0 or less. Here, the escape cone angle θ0 is a value obtained by doubling the maximum incident angle at which light incident from the active layer 12 side can be emitted to the outside without being totally reflected on the outer surface of the substrate 10. It is.

  The light emitting diode having such a configuration can be manufactured, for example, as follows.

In order to manufacture this light emitting diode, an AlGaInP-based semiconductor layer is formed on a substrate 100 made of, for example, GaAs, for example, by MOCVD (Metal Organic Chemical Vapor Deposition). At this time, for example, trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMIn), and phosphine (PH ₃ ) are used as the raw material for the AlGaInP-based semiconductor. (H ₂ Se) is used, and dimethyl zinc (DMZn), for example, is used as the acceptor impurity raw material.

  Specifically, as shown in FIG. 2A, first, the precursor first cladding 11A and the precursor active layer 12A are laminated in this order on the surface of the substrate 100, and then the light emitting region 12-1 is formed. A resist layer T1 is formed on the region to be formed. Subsequently, as shown in FIG. 2B, the precursor active layer 12A is etched to form the active layer 12, and then the resist layer T1 is removed. Next, as illustrated in FIG. 2C, the precursor second cladding layer 13 </ b> A and the precursor contact layer 14 </ b> A are stacked in this order on the precursor first cladding 11 </ b> A and the active layer 12.

  Next, as shown in FIG. 3A, the substrate 100 is removed by, for example, etching, and the substrate 10 is bonded using a wafer bonding technique. Thereafter, a resist layer T <b> 2 is formed on a part of the surface of the contact layer 14.

  Next, as shown in FIG. 3B, the precursor contact layer 14A, the precursor second clad layer 13A, the active layer 12 and the precursor first clad 11A are etched by using, for example, a resist reflow technique. Form. Thereafter, the resist layer T2 is removed.

  Next, as shown in FIG. 4A, after forming a resist layer T3 on the precursor contact layer 14A, as shown in FIG. 4B, the precursor contact layer 14A is etched to contact the contact layer 14A. Form. Thereafter, the resist layer T3 is removed.

  Next, as shown in FIG. 1, the reflective film 15 is formed on the surface of the curved surface S, the p-side electrode 16 is formed on the surface of the contact layer 14, and the ring shape is formed on the back surface of the substrate 10 by, for example, vacuum deposition. N-side electrodes 17 are formed respectively.

  Next, the operation and effect of the light emitting diode of the present embodiment will be described.

  In the light emitting diode of the present embodiment, when a predetermined voltage is applied between the p-side electrode 16 and the n-side electrode 17, electrons from the n-side electrode 17 and holes from the p-side electrode 16 are active layers. 12 is injected. Then, the electrons and holes injected into the active layer 12 are recombined to generate photons from the light emitting region 12-1, and as a result, the emitted light is emitted from the back surface of the substrate 10 to the outside.

  Here, as described above, the opening angle θ1 is equal to or smaller than the escape cone angle θ0. Thereby, the light reflected by the curved surface S among the emitted light rays emitted from the light emitting region 12-1 is reflected by the curved surface S and is emitted almost vertically from the back surface of the substrate 10. On the other hand, the light directly incident on the substrate 10 without being reflected by the curved surface S among the emitted light rays emitted from the light emitting region 12-1 is an angle of 1/2 or less of the escape cone angle θ 0 on the outer surface of the substrate 10. Therefore, the light is emitted to the outside at an angle of 1/2 or less of the escape cone angle θ0 without being totally reflected.

  As a result, in the light emitting diode of the present embodiment, the light reflected from the curved surface S among the emitted light rays emitted from the light emitting region 12-1 and the curved surface S among the emitted light rays emitted from the light emitting region 12-1. Light that is directly incident on the substrate 10 without being reflected is emitted to the outside by only one or one reflection, and is reflected to the outside after being reflected a plurality of times as in a conventional light emitting diode. There is no. Further, the emitted light beam emitted from the light emitting region 12-1 is not substantially incident on the active layer 12 again. Therefore, absorption of light in the first cladding 11, the active layer 12, and the second cladding layer 13 can be suppressed.

  Thus, in the light emitting diode according to the present embodiment, light absorption in the first cladding 11, the active layer 12, and the second cladding layer 13 can be suppressed, so that the light extraction efficiency can be increased.

  By the way, a general light emitting diode does not have directivity like a semiconductor laser. Therefore, for example, in applications where light needs to be collected on the surface to be illuminated, it is necessary to arrange components for redirecting the light of the light emitting diodes, such as arranging the light emitting diodes inside the reflector. Become.

  However, since the light emitting diode of the present embodiment has the curved surface S, it has the directivity equivalent to the case where a part for redirecting the light of the light emitting diode is newly provided. Therefore, in this embodiment, it is not necessary to newly provide a part for redirecting the light of the light emitting diode, so that the size can be reduced.

  In addition, when the curved surface S is configured such that the opening angle θ1 is sufficiently smaller than the escape cone angle θ0, the curved surface S is not reflected by the curved surface S among the emitted light rays emitted from the light emitting region 12-1. The spread angle of the light that is directly incident on the substrate 10 and is emitted to the outside is very small as compared with the case where the opening angle θ1 is equal to the escape cone angle θ0. Therefore, by making the opening angle θ1 sufficiently smaller than the escape cone angle θ0, the spread angle of the light emitted to the outside can be made very small. As described above, the light-emitting diode of this embodiment can emit light having an arbitrary spread angle.

  On the other hand, when the curved surface S is configured such that the opening angle θ1 is smaller than the escape cone angle θ0 and the difference between the opening angle θ1 and the escape cone angle θ0 is small, the curved surface S is slightly more than the above case. Although the light spread angle increases, the thickness of the first cladding layer 11, that is, the thickness of the light emitting diode can be reduced. Further, since the thickness of the first cladding layer 11 is reduced, light absorption in the first cladding layer 11 is suppressed as compared with the above case. Therefore, by making the opening angle θ1 smaller than the escape cone angle θ0 and reducing the difference between the opening angle θ1 and the escape cone angle θ0, the light emitting diode can be further reduced in size, and the light extraction efficiency can be further increased. Can be high.

  Note that as shown in FIGS. 5 and 6A and 6B, the light-emitting diodes of this embodiment may be arranged in parallel in a lattice shape or a staggered pattern to form an optical integrated light-emitting diode. Here, when the curved surface S of the light emitting diode constituting the optical integrated light emitting diode is configured such that the opening angle θ1 is sufficiently smaller than the escape cone angle θ0, the opening area of the curved surface S is reduced. Therefore, the light emitting diodes can be arranged with high density. Thereby, an optical integrated light emitting diode can be reduced in size.

  Similarly, in this optical integrated light emitting diode, there is no need to newly provide a component for redirecting the light of the light emitting diode, so that even in an application where it is necessary to collect the light on the light irradiated surface, It can be downsized.

[Modification]
Hereinafter, modifications of the light emitting diode of the above embodiment will be described. As shown in FIG. 7, the light-emitting diode is configured such that the curved surface S has an opening angle θ1 larger than the escape cone angle θ0 compared to the light-emitting diode of the above-described embodiment, and further, diffused light reflection It is different in that the unit 18 is provided.

  The diffused light reflection portion 18 is a line segment formed by intersecting the outer surface of the substrate 10 with the generatrix of the surface passing through the focal point of the curved surface S and the terminal portions P1 and P2 of the curved surface S. And a region R sandwiched between the generatrix of the surface formed by extending from the focal point of the curved surface S in the direction of the escape cone angle θ0 and the outer surface of the substrate 10. Is provided. This light irregular reflection part 18 is comprised by the micro unevenness | corrugation provided in the ring-shaped area | region R among the outer surfaces of the board | substrate 10, and this area | region R among the emitted light rays emitted from the light emission area | region 12-1 is comprised. The incident light is irregularly reflected. Thereby, the light incident on the region R is emitted to the outside without being multiple-reflected in the substrate 10.

  Further, since the curved surface S is configured such that the opening angle θ1 is larger than the escape cone angle θ0, the thickness of the entire element can be made thinner than in the above embodiment. Thereby, in the light emitting diode which concerns on this modification, it can reduce in size further.

  In addition, since the light emitting diode is provided with the curved surface S, the light reflected from the curved surface S among the emitted light emitted from the light emitting region 12-1 and the emitted light emitted from the light emitting region 12-1. Of these, light that is directly incident on the substrate 10 without being reflected by the curved surface S is incident on the outer surface of the substrate 10 with only one or one reflection, and is reflected a plurality of times as in a conventional light emitting diode. After that, it does not enter the outer surface of the substrate 10. In addition, the emitted light emitted from the light emitting region 12-1 hardly enters the active layer 12 again. Therefore, absorption of light in the first cladding 11, the active layer 12, and the second cladding layer 13 can be suppressed. The light incident on the region R is irregularly reflected by the light irregular reflection portion 18 and emitted to the outside, so that the light extraction efficiency due to the light irregular reflection portion 18 is hardly lowered.

  As described above, in this modification, the light absorption in the first cladding 11, the active layer 12, and the second cladding layer 13 can be suppressed, and the light extraction efficiency caused by the light irregular reflection portion 18 is hardly reduced. Therefore, the light extraction efficiency can be increased. Moreover, since the curved surface S is provided, it has directivity equivalent to that of the above embodiment. Therefore, it is not necessary to newly provide a part for redirecting the light of the light emitting diode in an application where it is necessary to collect the light on the surface to be irradiated with light. Since it can be made thinner than that, the size can be further reduced.

  The present invention has been described with reference to the embodiment. However, the present invention is not limited to the above embodiment, and various modifications can be made.

  For example, in the above-described embodiment and modification, the precursor active layer 12A is etched to form the light emitting region 12-1 as a micro light source at and near the focal point of the curved surface S. FIG. In FIG. 8, by diffusing impurities such as zinc (Zn) into the region other than the focal point of the curved surface S and the vicinity thereof in the precursor active layer 12A, the focal point of the curved surface S as shown in FIG. You may make it form the light emission area | region 22-1 as a micro light source. Note that no light is emitted from a region (inactive region 22-2) in which impurities are diffused in the precursor active layer 12A.

It is a section lineblock diagram of a light emitting diode concerning one embodiment of the present invention. FIG. 2 is a cross-sectional configuration diagram for explaining a manufacturing process of the light emitting diode of FIG. 1. FIG. 3 is a cross-sectional configuration diagram for explaining a manufacturing process continued from FIG. 2. FIG. 4 is a cross-sectional configuration diagram for explaining a manufacturing process continued from FIG. 3. FIG. 2 is a cross-sectional configuration diagram of an optical integrated light emitting diode in which the light emitting diodes of FIG. 1 are arranged in parallel in an array. FIG. 6 is a top view of the optical integrated light emitting diode of FIG. 5. It is a cross-sectional block diagram of the light emitting diode which concerns on one modification. It is a cross-sectional block diagram of the light emitting diode which concerns on another modification.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,100 ... Substrate, 11 ... First clad layer, 12 ... Active layer, 12-1 ... Light emitting region, 13 ... Second clad layer, 14 ... Contact layer, 15 ... Reflective film, 16 ... P-side electrode, 17 ... n-side electrode, 18 ... light diffuse reflection part, 19 ... light absorption part, θ0 ... opening angle, θ1 ... escape cone angle, R ... region, S ... surface, P1, P2 ... end, W ... opening.

Claims (5)

A semiconductor light emitting device comprising a compound semiconductor layer comprising an active layer and a pair of cladding layers having a band gap larger than that of the active layer and disposed on both sides of the active layer,
The compound semiconductor layer is obtained by rotating a parabola having a focal point on the y-axis by 360 ° about the y-axis, where x is an axis perpendicular to the stacking direction and y is an axis parallel to the stacking direction. Has a curved surface,
The active layer has a light emitting region at and near the focal point of the curved surface. The opening angle obtained by doubling the angle (<90 °) at which the symmetry axis of the curved surface intersects with the focal point of the curved surface and the generatrix of the surface passing through the end of the curved surface is equal to or less than the escape cone angle. The semiconductor light emitting device according to claim 1. The opening angle obtained by doubling the angle (<90 °) at which the symmetry axis of the curved surface intersects the focal point of the curved surface and the line segment passing through the end of the curved surface is larger than the escape cone angle,
Of the outer surface of the compound semiconductor layer, a line segment formed by intersecting the outer surface of the compound semiconductor layer with a generatrix of the surface passing through the focal point of the curved surface and the terminal portion of the curved surface, and the focal point of the curved surface A diffused light reflection portion in a region sandwiched between a generatrix formed by intersecting a generatrix of the surface formed extending in the direction of the escape cone angle with the outer surface of the compound semiconductor layer The semiconductor light emitting element according to claim 1, wherein the semiconductor light emitting element is provided. The semiconductor light emitting element according to claim 1, further comprising a reflective film on the curved surface. The compound semiconductor layer has a plurality of the curved surfaces arranged in parallel in the x-axis direction,
The semiconductor light emitting element according to claim 1, wherein the active layer has a light emitting region at and near the focal point of each curved surface.

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