Light emitting device and projector

Abstract

To provide a light emitting device that can reduce the current flowing through the side surface of a columnar section.SOLUTION: A light emitting device has a laminate having a plurality of columnar sections, each of the plurality of columnar sections has a first semiconductor layer, a second semiconductor layer having a different conductivity type from the first semiconductor layer, and a light emitting layer provided between the first semiconductor layer and the second semiconductor layer, the second semiconductor layer has a first portion and a second portion, which surrounds the first portion and has a larger band gap than the first portion in plan view from the stacking direction of the first semiconductor layer and the light-emitting layer, and the second portion constitutes a side surface of the columnar section.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a light emitting device and a projector. [Background technology]

[0002] Semiconductor lasers are expected to become the next generation of high-brightness light sources. In particular, semiconductor lasers that incorporate nanocolumns are expected to be able to achieve high-output light emission with a narrow radiation angle due to the photonic crystal effect of the nanocolumns.

[0003] For example, Patent Document 1 describes a compound semiconductor light-emitting device having a plurality of GaN nanocolumns formed by sequentially laminating an n-type GaN layer, a light-emitting layer, and a p-type GaN layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-152474 A Summary of the Invention [Problem to be solved by the invention]

[0005] Since dangling bonds exist on the side surfaces of the nanocolumns as described above, there is a high possibility that carrier recombination in the vicinity of the side surfaces of the nanocolumns will be non-radiative recombination. [Means for solving the problem]

[0006] One aspect of the light emitting device according to the present invention is A laminate having a plurality of columnar portions, Each of the plurality of columnar portions is A first semiconductor layer; A second semiconductor layer having a conductivity type different from that of the first semiconductor layer; a light emitting layer provided between the first semiconductor layer and the second semiconductor layer; having The second semiconductor layer is A first part; a second portion that surrounds the first portion and has a band gap larger than that of the first portion when viewed in a plan view from a stacking direction of the first semiconductor layer and the light emitting layer; having The second portion constitutes a side surface of the columnar portion.

[0007] One aspect of the projector according to the present invention is The present invention has one aspect of the light emitting device. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view illustrating a light emitting device according to an embodiment of the present invention. [Diagram 2] FIG. 3 is a cross-sectional view showing a schematic view of a columnar portion of the light emitting device according to the embodiment. [Diagram 3] FIG. 2 is a plan view showing a columnar portion of the light emitting device according to the embodiment. [Figure 4] 5A to 5C are cross-sectional views each showing a schematic process for manufacturing the light emitting device according to the embodiment. [Diagram 5] FIG. 4 is a cross-sectional view illustrating a columnar portion of a light emitting device according to a first modified example of the embodiment. [Figure 6] FIG. 11 is a cross-sectional view illustrating a columnar portion of a light emitting device according to a second modified example of the embodiment. [Figure 7] FIG. 11 is a cross-sectional view illustrating a columnar portion of a light emitting device according to a third modified example of the embodiment. [Figure 8] FIG. 1 is a diagram illustrating a projector according to an embodiment of the present invention. [Figure 9] STEM image of an example experiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Note that the embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, not all of the configurations described below are necessarily essential components of the present invention.

[0010] 1. Light-emitting device 1.1. Overall structure First, the light emitting device according to the present embodiment will be described with reference to the drawings. Fig. 1 is a cross-sectional view that shows a schematic diagram of a light emitting device 100 according to the present embodiment.

[0011] 1, the light emitting device 100 includes, for example, a substrate 10, a laminate 20, a first electrode 40, and a second electrode 42. The light emitting device 100 is, for example, a semiconductor laser.

[0012] The substrate 10 is, for example, a Si substrate, a GaN substrate, a sapphire substrate, a SiC substrate, or the like.

[0013] The laminate 20 is provided on the substrate 10. In the illustrated example, the laminate 20 is provided on the substrate 10. The laminate 20 has, for example, a buffer layer 22 and a columnar portion 30.

[0014] In this specification, in the stacking direction of the laminate 20 (hereinafter also simply referred to as the "stacking direction"), when the light emitting layer 34 is used as a reference, the direction from the light emitting layer 34 toward the second electrode 42 is described as "upper", and the direction from the light emitting layer 34 toward the substrate 10 is described as "lower". A direction perpendicular to the stacking direction is also referred to as an "in-plane direction". Moreover, the "stacking direction of the laminate 20" refers to the stacking direction of the first semiconductor layer 32 and the light emitting layer 34 of the columnar section 30.

[0015] The buffer layer 22 is provided on the substrate 10. The buffer layer 22 is, for example, a Si-doped n-type GaN layer. A mask layer 50 for forming the columnar section 30 is provided on the buffer layer 22. The mask layer 50 is, for example, a silicon oxide layer, a titanium layer, a titanium oxide layer, an aluminum oxide layer, or the like.

[0016] The columnar section 30 is provided on the buffer layer 22. The columnar section 30 has a columnar shape protruding upward from the buffer layer 22. In other words, the columnar section 30 protrudes upward from the substrate 10 via the buffer layer 22. The columnar section 30 is also called, for example, a nanocolumn, a nanowire, a nanorod, or a nanopillar. The planar shape of the columnar section 30 is, for example, a polygon such as a regular hexagon, or a circle.

[0017] The diameter of the columnar section 30 is, for example, 50 nm or more and 500 nm or less. By making the diameter of the columnar section 30 500 nm or less, it is possible to obtain a light-emitting layer 34 of high quality crystals and reduce distortion inherent in the light-emitting layer 34. This allows the light generated in the light-emitting layer 34 to be amplified with high efficiency.

[0018] The "diameter of the columnar portion" refers to the diameter when the planar shape of the columnar portion 30 is a circle, and refers to the diameter of the smallest inclusive circle when the planar shape of the columnar portion 30 is not a circle. For example, when the planar shape of the columnar portion 30 is a polygon, the diameter of the columnar portion 30 refers to the diameter of the smallest circle that includes the polygon, and when the planar shape of the columnar portion 30 is an ellipse, the diameter of the smallest circle that includes the ellipse. .

[0019] A plurality of columnar sections 30 are provided. The interval between adjacent columnar sections 30 is, for example, 1 nm or more and 500 nm or less. The plurality of columnar sections 30 are arranged in a predetermined direction at a predetermined pitch when viewed from the stacking direction. The plurality of columnar sections 30 are arranged in, for example, a triangular lattice pattern. The arrangement of the plurality of columnar sections 30 is not particularly limited, and may be arranged in a square lattice pattern. The plurality of columnar sections 30 can exhibit the effect of a photonic crystal.

[0020] The "pitch of the columnar portion" is the distance between the centers of adjacent columnar portions 30 along a predetermined direction. When the planar shape of the columnar portion 30 is a circle, the "center of the columnar portion" is the center of the circle, and when the planar shape of the columnar portion 30 is a shape other than a circle, the center of the smallest inclusive circle. For example, when the planar shape of the columnar portion 30 is a polygon, the center of the columnar portion 30 is the center of the smallest circle that includes the polygon inside, and when the planar shape of the columnar portion 30 is an ellipse, the center of the smallest circle that includes the ellipse inside.

[0021] The columnar section 30 includes a first semiconductor layer 32, a light emitting layer , and a second semiconductor layer .

[0022] The first semiconductor layer 32 is provided on the buffer layer 22. The first semiconductor layer 32 is provided between the substrate 10 and the light emitting layer 34. The first semiconductor layer 32 is, for example, an n-type semiconductor layer doped with Si.

[0023] The light emitting layer 34 is provided on the first semiconductor layer 32. The light emitting layer 34 is provided between the first semiconductor layer 32 and the second semiconductor layer 36. The light emitting layer 34 generates light when a current is injected into it. The light emitting layer 34 has, for example, a well layer 33 and a barrier layer 35. The well layer 33 and the barrier layer 35 are i-type semiconductor layers that are not intentionally doped with impurities. The light emitting layer 34 has an MQW (Multiple Quantum Well) structure composed of the well layer 33 and the barrier layer 35. In the illustrated example, three well layers 33 are provided. Four barrier layers 35 are provided.

[0024] The number of well layers 33 and barrier layers 35 constituting the light-emitting layer 34 is not particularly limited. For example, only one well layer 33 may be provided, in which case the light-emitting layer 34 has a SQW (Single Quantum Well) structure.

[0025] The second semiconductor layer 36 is provided on the light emitting layer 34. The second semiconductor layer 36 is a layer of a conductivity type different from that of the first semiconductor layer 32. The second semiconductor layer 36 is, for example, a p-type semiconductor layer doped with Mg. The first semiconductor layer 32 and the second semiconductor layer 36 are cladding layers having a function of confining light in the light emitting layer 34.

[0026] Although not shown, an OCL (Optical Confinement Layer) may be provided between the first semiconductor layer 32 and the light emitting layer 34. In addition, an EBL (Electron Blocking Layer) may be provided between the light emitting layer 34 and the second semiconductor layer 36.

[0027] In the light emitting device 100, a pin diode is formed by the p-type second semiconductor layer 36, the i-type light emitting layer 34 that is not doped with impurities, and the n-type first semiconductor layer 32. In the light emitting device 100, when a forward bias voltage of the pin diode is applied between the first electrode 40 and the second electrode 42, a current is injected into the light emitting layer 34, causing recombination of electrons and holes in the light emitting layer 34. This recombination produces light. The light generated in the light emitting layer 34 propagates in the in-plane direction, forms a standing wave due to the effect of the photonic crystal of the multiple columnar sections 30, receives gain in the light emitting layer 34, and oscillates as a laser. The light emitting device 100 then emits +1st order diffracted light and The -1st order diffracted light is emitted as laser light in the stacking direction.

[0028] Although not shown, a reflective layer may be provided between the substrate 10 and the buffer layer 22 or under the substrate 10. The reflective layer is, for example, a DBR (Distributed Bragg Reflector) layer. The reflective layer can reflect light generated in the light-emitting layer 34, and the light-emitting device 100 can emit light only from the second electrode 42 side.

[0029] The first electrode 40 is provided on the buffer layer 22. The buffer layer 22 may be in ohmic contact with the first electrode 40. The first electrode 40 is electrically connected to the first semiconductor layer 32. In the illustrated example, the first electrode 40 is electrically connected to the first semiconductor layer 32 via the buffer layer 22. The first electrode 40 is one of the electrodes for injecting a current into the light-emitting layer 34. As the first electrode 40, for example, a layer formed by laminating a Cr layer, a Ni layer, and an Au layer in this order from the buffer layer 22 side is used.

[0030] The second electrode 42 is provided on the second semiconductor layer 36. The second electrode 42 is electrically connected to the second semiconductor layer 36. The second semiconductor layer 36 may be in ohmic contact with the second electrode 42. The second electrode 42 is the other electrode for injecting a current into the light-emitting layer 34. The second electrode 42 is made of, for example, ITO (indium tin oxide) or the like.

[0031] 1.2. Detailed structure of the column Fig. 2 is a cross-sectional view that typically shows the columnar section 30. Fig. 3 is a plan view that typically shows the columnar section 30. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 3.

[0032] 2, the first semiconductor layer 32 has a low band gap portion 32a and a high band gap portion 32b. The first semiconductor layer 32 is an AlGaN layer containing Al (aluminum), Ga (gallium), and N (nitrogen).

[0033] The band gap of the high band gap portion 32b is larger than the band gap of the low band gap portion 32a. In a plan view from the stacking direction (hereinafter, simply referred to as "in a plan view"), the high band gap portion 32b surrounds the low band gap portion 32a. The high band gap portion 32b constitutes a side surface 31 of the columnar portion 30. The side surface 31 connects the upper surface of the buffer layer 22 and the lower surface of the second electrode 42. The angle of the side surface 31 with respect to the upper surface of the substrate 10 is 60° or more and 90° or less, and is 90° in the illustrated example. The atomic concentration (at%) of Al in the high band gap portion 32b is higher than the atomic concentration of Al in the low band gap portion 32a.

[0034] The barrier layer 35 of the light emitting layer 34 has a low band gap portion 35a and a high band gap portion 35b. The barrier layer 35 is an AlGaN layer. The well layer 33 is, for example, an InGaN layer.

[0035] The band gap of the high band gap portion 35b is larger than the band gap of the low band gap portion 35a. The high band gap portion 35b surrounds the low band gap portion 35a in a plan view. The high band gap portion 35b constitutes the side surface 31 of the columnar portion 30. The atomic concentration of Al in the high band gap portion 35b is higher than the atomic concentration of Al in the low band gap portion 35a.

[0036] The second semiconductor layer 36 has a low band gap portion 36a and a high band gap portion 36b. The second semiconductor layer 36 is an AlGaN layer.

[0037] The band gap of the high band gap portion 36b is equal to the band gap of the low band gap portion 36a. The high band gap portion 36b is larger than the low band gap portion 36a in plan view, as shown in FIG. 3. In the illustrated example, the planar shape of the columnar portion 30 is a regular hexagon. The high band gap portion 36b constitutes the side surface 31 of the columnar portion 30, as shown in FIGS. 2 and 3. The atomic concentration of Al in the high band gap portion 36b is higher than the atomic concentration of Al in the low band gap portion 36a. In the columnar portion 30, Al is unevenly distributed on the side surface 31.

[0038] The high band gap portions 32b, 35b, and 36b are portions in which the atomic concentration of Al is higher than the atomic concentration of Ga. In the high band gap portions 32b, 35b, and 36b, the ratio of the atomic concentration of Al to the sum of the atomic concentrations of Al and Ga (hereinafter also referred to as the "Al ratio") may be greater than 0.5 and may be equal to or greater than 0.8. Furthermore, in the high band gap portions 32b, 35b, and 36b, the Al ratio may be 1.0, in which case the material of the high band gap portions 32b, 35b, and 36b is AlN.

[0039] The low band gap portions 32a, 35a, and 36a are portions in which the atomic concentration of Al is equal to or lower than the atomic concentration of Ga. The low band gap portions 32a, 35a, and 36a have an Al ratio of 0.5 or less, and may be 0.4 or less.

[0040] The Al atomic concentration and the Ga atomic concentration can be measured by STEM-EDS (Scanning Transmission Electron Microscope - Energy Dispersive X-ray Spectroscopy).

[0041] 1.3. Effects In the light emitting device 100, the second semiconductor layer 36 has a low band gap portion 36a as a first portion, and a high band gap portion 36b as a second portion that surrounds the low band gap portion 36a in a plan view and has a larger band gap than the low band gap portion 36a, and the high band gap portion 36b constitutes the side surface 31 of the columnar portion 30. Therefore, in the light emitting device 100, the current flowing through the side surface 31 of the columnar portion 30 can be reduced compared to when the band gaps of the first portion and the second portion are equal. This reduces the current that undergoes non-radiative recombination. As a result, the current injection efficiency can be improved.

[0042] In the light emitting device 100, the second semiconductor layer 36 is an AlGaN layer, and the atomic concentration of Al in the high band gap portion 36b is higher than the atomic concentration of Al in the low band gap portion 36a. Therefore, in the light emitting device 100, by growing the second semiconductor layer 36 under conditions in which Al is unevenly distributed on the side surface 31 of the columnar portion 30, the band gap of the high band gap portion 36b can be easily made higher than the band gap of the low band gap portion 36a.

[0043] In the light emitting device 100, the first semiconductor layer 32 has a low band gap portion 32a as a third portion, and a high band gap portion 32b as a fourth portion that surrounds the low band gap portion 32a in a plan view and has a larger band gap than the low band gap portion 32a, and the high band gap portion 32b forms the side surface 31 of the columnar portion 30. Therefore, in the light emitting device 100, the current flowing through the side surface 31 of the columnar portion 30 can be made smaller.

[0044] In the light emitting device 100, the first semiconductor layer 32 is an AlGaN layer, and the atomic concentration of Al in the high band gap portion 32b is higher than the atomic concentration of Al in the low band gap portion 32a. Therefore, in the light emitting device 100, by growing the first semiconductor layer 32 under conditions in which Al is unevenly distributed on the side surface 31 of the columnar portion 30, the band gap of the high band gap portion 32b can be easily made higher than the band gap of the low band gap portion 32a.

[0045] In the light-emitting device 100, the light-emitting layer 34 includes a well layer 33 and a barrier layer 35. The layer 35 has a low band gap portion 35a as a fifth portion, and a high band gap portion 35b as a sixth portion that surrounds the low band gap portion 35a in a plan view and has a larger band gap than the low band gap portion 35a, and the high band gap portion 35b forms the side surface 31 of the columnar portion 30. Therefore, in the light emitting device 100, the current flowing through the side surface 31 of the columnar portion 30 can be made smaller.

[0046] In the light emitting device 100, the barrier layer 35 is an AlGaN layer, and the atomic concentration of Al in the high band gap portion 35b is higher than the atomic concentration of Al in the low band gap portion 35a. Therefore, in the light emitting device 100, by growing the barrier layer 35 under conditions in which Al is unevenly distributed on the side surface 31 of the columnar portion 30, the band gap of the high band gap portion 35b can be easily made higher than the band gap of the low band gap portion 35a.

[0047] The light emitting device 100 is not limited to a laser, and may be an LED (Light Emitting Diode).

[0048] 2. Manufacturing method of light-emitting device Next, a method for manufacturing the light emitting device 100 according to this embodiment will be described with reference to the drawings. Fig. 4 is a cross-sectional view that typically shows the manufacturing process of the light emitting device 100 according to this embodiment.

[0049] 4, the buffer layer 22 is epitaxially grown on the substrate 10. Examples of the epitaxial growth method include a metal organic chemical vapor deposition (MOCVD) method and a molecular beam epitaxy (MBE) method.

[0050] Next, a mask layer 50 is formed on the buffer layer 22. The mask layer 50 is formed by, for example, deposition using an electron beam deposition method or a sputtering method, and patterning. The patterning is performed by photolithography and etching. The thickness of the mask layer 50 is, for example, about 5 nm.

[0051] 1, the first semiconductor layer 32, the light emitting layer 34, and the second semiconductor layer 36 are epitaxially grown in this order on the buffer layer 22 using the mask layer 50 as a mask. Examples of the epitaxial growth method include the MOCVD method and the MBE method. By this process, a plurality of columnar sections 30 can be formed.

[0052] The epitaxial growth of the first semiconductor layer 32, the barrier layer 35, and the second semiconductor layer 36 is performed under conditions that cause Al to be unevenly distributed on the side surface 31 of the columnar section 30. Specifically, the first semiconductor layer 32, the barrier layer 35, and the second semiconductor layer 36 are epitaxially grown at a growth temperature of 830° C. or higher and 870° C. or lower, preferably 850° C. This allows Al to be unevenly distributed on the side surface 31 of the columnar section 30.

[0053] Next, a first electrode 40 is formed on the buffer layer 22, and a second electrode 42 is formed on the second semiconductor layer 36. The first electrode 40 and the second electrode 42 are formed by, for example, a vacuum deposition method. The order in which the first electrode 40 and the second electrode 42 are formed is not particularly limited.

[0054] Through the above steps, the light emitting device 100 can be manufactured.

[0055] 3. Modifications of the Light Emitting Device 3.1. First variant Next, a light emitting device according to a first modified example of this embodiment will be described with reference to the drawings. Fig. 5 is a cross-sectional view showing a columnar section 30 of a light emitting device 200 according to a first modified example of this embodiment. FIG.

[0056] Hereinafter, in the light emitting device 200 according to the first modified example of this embodiment, the components having the same functions as the components of the light emitting device 100 according to this embodiment described above are denoted by the same reference numerals, and detailed description thereof will be omitted. This also applies to the light emitting devices according to the second to fourth modified examples of this embodiment described below.

[0057] In the above-described light emitting device 100, the barrier layer 35 has the low band gap portion 35a and the high band gap portion 35b as shown in Fig. 2. The barrier layer 35 is an AlGaN layer.

[0058] In contrast, in the light emitting device 200, the barrier layer 35 does not have the low band gap portion 35a and the high band gap portion 35b, as shown in Fig. 5. The barrier layer 35 is, for example, a GaN layer.

[0059] In the light emitting device 200, similarly to the light emitting device 100 described above, the current flowing through the side surface 31 of the columnar section 30 can be reduced.

[0060] Furthermore, in the light emitting device 200, the low band gap portion 35a and the high band gap portion 35b are not formed in the barrier layer 35 constituting the light emitting layer 34, which has a complex structure, so that the columnar portion 30 can be formed easily.

[0061] 3.2. Second variant Next, a light emitting device according to a second modified example of this embodiment will be described with reference to the drawings. Fig. 6 is a cross-sectional view that shows a schematic view of a columnar section 30 of a light emitting device 300 according to a second modified example of this embodiment.

[0062] In the light emitting device 100 described above, as shown in Fig. 2, the first semiconductor layer 32 had a low band gap portion 32a and a high band gap portion 32b. Furthermore, the barrier layer 35 had a low band gap portion 35a and a high band gap portion 35b. The first semiconductor layer 32 and the barrier layer 35 were AlGaN layers.

[0063] 6, the first semiconductor layer 32 does not have a low band gap portion 32a or a high band gap portion 32b. Furthermore, the barrier layer 35 does not have a low band gap portion 35a or a high band gap portion 35b. The first semiconductor layer 32 and the barrier layer 35 are, for example, GaN layers.

[0064] In the light emitting device 300, similarly to the light emitting device 100 described above, the current flowing through the side surface 31 of the columnar section 30 can be reduced.

[0065] 3.3. Third variant Next, a light emitting device according to a third modified example of this embodiment will be described with reference to the drawings. Fig. 7 is a cross-sectional view that shows a schematic view of a columnar section 30 of a light emitting device 400 according to a third modified example of this embodiment.

[0066] In the light emitting device 100 described above, as shown in FIG. 2, the first semiconductor layer 32 had a low band gap portion 32a and a high band gap portion 32b. Furthermore, the barrier layer 35 had a low band gap portion 35a and a high band gap portion 35b. The first semiconductor layer 32 and the barrier layer 35 were AlGaN layers. Furthermore, the first semiconductor layer 32 was provided under the light emitting layer 34 and was an n-type semiconductor layer. Furthermore, the second semiconductor layer 36 was an n-type semiconductor layer. It was provided on the optical layer 34 and was a p-type semiconductor layer.

[0067] 7, the first semiconductor layer 32 does not have a low band gap portion 32a or a high band gap portion 32b. Furthermore, the barrier layer 35 does not have a low band gap portion 35a or a high band gap portion 35b. The first semiconductor layer 32 and the barrier layer 35 are, for example, GaN layers.

[0068] The first semiconductor layer 32 is provided on the light emitting layer 34. The first semiconductor layer 32 is provided between the light emitting layer 34 and the second electrode 42. The first semiconductor layer 32 is a p-type semiconductor layer.

[0069] The second semiconductor layer 36 is provided below the light emitting layer 34. The second semiconductor layer 36 is provided on the buffer layer 22. The second semiconductor layer 36 is provided between the substrate 10 and the light emitting layer 34. The second semiconductor layer 36 is an n-type semiconductor layer.

[0070] In the light emitting device 400, similarly to the light emitting device 100 described above, the current flowing through the side surface 31 of the columnar section 30 can be reduced.

[0071] In the light emitting devices 300 and 400 described above, the barrier layer 35 may be an AlGaN layer, and may have a low band gap portion 35a and a high band gap portion 35b.

[0072] 3.4. Fourth variant Next, a light emitting device according to a fourth modified example of this embodiment will be described.

[0073] In the light emitting device 100 described above, the first semiconductor layer 32, the barrier layer 35, and the second semiconductor layer 36 are AlGaN layers.

[0074] In contrast, in the light emitting device according to the fourth modification of this embodiment, the first semiconductor layer 32, the barrier layer 35, and the second semiconductor layer 36 are BGaN layers containing B (boron), Ga, and N.

[0075] The atomic concentration of B in the high band gap portion 32b of the first semiconductor layer 32 is higher than the atomic concentration of B in the low band gap portion 32a. The atomic concentration of B in the high band gap portion 35b of the barrier layer 35 is higher than the atomic concentration of B in the low band gap portion 35a. The atomic concentration of B in the high band gap portion 36b of the second semiconductor layer 36 is higher than the atomic concentration of B in the low band gap portion 36a. In the columnar portion 30, B is unevenly distributed on the side surface 31.

[0076] The high band gap portions 32b, 35b, and 36b are portions in which the atomic concentration of B is higher than the atomic concentration of Ga. In the high band gap portions 32b, 35b, and 36b, the ratio of the atomic concentration of B to the sum of the atomic concentrations of B and Ga (hereinafter also referred to as the "B ratio") may be, for example, greater than 0.5 and equal to or greater than 0.8. Furthermore, the B ratio may be 1.0, in which case the material of the high band gap portions 32b, 35b, and 36b is BN.

[0077] The low band gap portions 32a, 35a, and 36a are portions in which the atomic concentration of B is equal to or lower than the atomic concentration of Ga. The low band gap portions 32a, 35a, and 36a have a B ratio of 0.5 or less, and may be 0.4 or less. The atomic concentration of B can be measured by STEM-EDS.

[0078] The epitaxial growth of the first semiconductor layer 32, the barrier layer 35, and the second semiconductor layer 36 is The condition is such that B is unevenly distributed on the side surface 31 of the columnar portion 30 .

[0079] In the light emitting device according to the fourth modification of this embodiment, similarly to the light emitting device 100 described above, the current flowing through the side surface 31 of the columnar section 30 can be reduced.

[0080] 4. Projector Next, a projector according to this embodiment will be described with reference to the drawings. Fig. 8 is a diagram showing a schematic diagram of a projector 900 according to this embodiment.

[0081] The projector 900 includes, for example, a light emitting device 100 as a light source.

[0082] Projector 900 has a housing (not shown) and red light source 100R, green light source 100G, and blue light source 100B that are provided in the housing and emit red light, green light, and blue light, respectively. For convenience, red light source 100R, green light source 100G, and blue light source 100B are simplified in FIG. 8.

[0083] The projector 900 further includes a first optical element 902R, a second optical element 902G, a third optical element 902B, a first light modulation device 904R, a second light modulation device 904G, a third light modulation device 904B, and a projection device 908, which are provided in the housing. The first light modulation device 904R, the second light modulation device 904G, and the third light modulation device 904B are, for example, transmissive liquid crystal light valves. The projection device 908 is, for example, a projection lens.

[0084] The light emitted from red light source 100R is incident on first optical element 902R. The light emitted from red light source 100R is collected by first optical element 902R. Note that first optical element 902R may have a function other than collecting light. The same applies to second optical element 902G and third optical element 902B described later.

[0085] The light collected by the first optical element 902R is incident on the first light modulation device 904R. The first light modulation device 904R modulates the incident light in accordance with image information. The projection device 908 then enlarges the image formed by the first light modulation device 904R and projects it onto the screen 910.

[0086] The light emitted from green light source 100G is incident on second optical element 902G. The light emitted from green light source 100G is collected by second optical element 902G.

[0087] The light collected by the second optical element 902G is incident on the second light modulation device 904G. The second light modulation device 904G modulates the incident light in accordance with image information. The projection device 908 then enlarges the image formed by the second light modulation device 904G and projects it onto the screen 910.

[0088] The light emitted from blue light source 100B is incident on third optical element 902B. The light emitted from blue light source 100B is collected by third optical element 902B.

[0089] The light collected by the third optical element 902B enters the third light modulation device 904B. The third light modulation device 904B modulates the incident light in accordance with image information. The projection device 908 then enlarges the image formed by the third light modulation device 904B and projects it onto the screen 910.

[0090] The projector 900 also includes a first light modulation device 904R, a second light modulation device 904G, and a cross dichroic prism 906 that combines the light emitted from the third light modulation device 904B and directs the combined light to a projection device 908.

[0091] The three color lights modulated by the first light modulation device 904R, the second light modulation device 904G, and the third light modulation device 904B enter a cross dichroic prism 906. The cross dichroic prism 906 is formed by bonding four right-angle prisms together, and a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are disposed on its inner surface. The three color lights are synthesized by these dielectric multilayer films to form light that represents a color image. The synthesized light is then projected by a projection device 908 onto a screen 910, and an enlarged image is displayed.

[0092] Note that red light source 100R, green light source 100G, and blue light source 100B may directly form an image without using first light modulation device 904R, second light modulation device 904G, and third light modulation device 904B, by controlling light emitting device 100 as pixels of an image according to image information. Then, projection device 908 may enlarge and project the image formed by red light source 100R, green light source 100G, and blue light source 100B onto screen 910.

[0093] In the above example, a transmissive liquid crystal light valve is used as the light modulation device, but a light valve other than liquid crystal may be used, or a reflective light valve may be used. Examples of such light valves include a reflective liquid crystal light valve and a digital micro mirror device. The configuration of the projection device is changed as appropriate depending on the type of light valve used.

[0094] The light source can also be applied to a light source device of a scanning type image display device having a scanning means, which is an image forming device that displays an image of a desired size on a display surface by scanning light from the light source on a screen.

[0095] The light emitting device according to the above embodiment can be used for purposes other than projectors. Examples of uses other than projectors include indoor and outdoor lighting, display backlights, laser printers, scanners, car lights, sensing devices that use light, and light sources for communication devices. The light emitting device according to the above embodiment can also be applied to the light emitting elements of LED displays that display images by arranging minute light emitting elements in an array.

[0096] 5. Experimental Example The columnar section was fabricated by epitaxially growing an n-type GaN layer, an n-type AlGaN layer, and an n-type GaN layer in that order. The MBE method was used for the epitaxial growth. The growth temperature of the AlGaN layer was 850°C.

[0097] The columnar section fabricated as described above was observed by STEM, and the distribution of Al was investigated by EDS. Figure 9 is a STEM image showing the distribution of Al in the columnar section. In Figure 9, areas with less Al are shown in darker colors, and areas with more Al are shown in lighter colors.

[0098] As shown in FIG. 9, it was found that by epitaxially growing the AlGaN layer at a growth temperature of 850° C., Al can be unevenly distributed on the side surface of the columnar portion.

[0099] The above-described embodiment and modifications are merely examples, and the present invention is not limited to these. For example, the embodiments and modifications can be appropriately combined.

[0100] The present invention has substantially the same configuration, e.g., function, method, and This includes configurations that achieve the same results or have the same purpose and effect. The present invention also includes configurations that replace non-essential parts of the configurations described in the embodiments. The present invention also includes configurations that achieve the same effects as the configurations described in the embodiments or that can achieve the same purpose. The present invention also includes configurations that add publicly known technology to the configurations described in the embodiments.

[0101] The following can be derived from the above-described embodiment and modifications.

[0102] One aspect of the light emitting device is A laminate having a plurality of columnar portions, Each of the plurality of columnar portions is A first semiconductor layer; A second semiconductor layer having a conductivity type different from that of the first semiconductor layer; a light emitting layer provided between the first semiconductor layer and the second semiconductor layer; having The second semiconductor layer is A first part; a second portion that surrounds the first portion and has a band gap larger than that of the first portion when viewed in a plan view from a stacking direction of the first semiconductor layer and the light emitting layer; having The second portion constitutes a side surface of the columnar portion.

[0103] In this light emitting device, the current flowing through the side surface of the columnar portion can be reduced, thereby reducing the current that undergoes non-radiative recombination, thereby improving the current injection efficiency.

[0104] In one embodiment of the light emitting device, the second semiconductor layer is an AlGaN layer; The second portion may have a higher atomic concentration of Al than the first portion.

[0105] In this light emitting device, the band gap of the second portion can easily be made higher than the band gap of the first portion.

[0106] In one embodiment of the light emitting device, The first semiconductor layer is A third part; a fourth portion that surrounds the third portion and has a band gap larger than that of the third portion when viewed in a plan view from the stacking direction; having The fourth portion may form a side surface of the columnar portion.

[0107] According to this light emitting device, the current flowing through the side surface of the columnar portion can be reduced.

[0108] In one embodiment of the light emitting device, the first semiconductor layer is an AlGaN layer; The atomic concentration of Al in the fourth portion may be higher than the atomic concentration of Al in the third portion.

[0109] According to this light emitting device, the band gap of the fourth portion can be easily adjusted to the band gap of the third portion. It can be made higher than the top.

[0110] In one embodiment of the light emitting device, the light emitting layer has a well layer and a barrier layer, The barrier layer is A fifth part; a sixth portion that surrounds the fifth portion and has a band gap larger than that of the fifth portion when viewed in a plan view from the stacking direction; having The sixth portion may form a side surface of the columnar portion.

[0111] According to this light emitting device, the current flowing through the side surface of the columnar portion can be reduced.

[0112] In one embodiment of the light emitting device, the barrier layer is an AlGaN layer; The sixth portion may have a higher atomic concentration of Al than the fifth portion.

[0113] According to this light emitting device, the band gap of the sixth portion can easily be made higher than the band gap of the fifth portion.

[0114] One aspect of the projector is The present invention has one aspect of the light emitting device. [Explanation of symbols]

[0115] 10...substrate, 20...laminated body, 22...buffer layer, 30...columnar portion, 31...side surface, 32...first semiconductor layer, 32a...low band gap portion, 32b...high band gap portion, 33...well layer, 34...light emitting layer, 35...barrier layer, 35a...low band gap portion, 35b...high band gap portion, 36...second semiconductor layer, 36a...low band gap portion, 36b...high band gap portion, 40...first electrode, 42...second electrode, Reference Signs List 100...light emitting device, 100R...red light source, 100G...green light source, 100B...blue light source, 200, 300, 400...light emitting device, 900...projector, 902R...first optical element, 902G...second optical element, 902B...third optical element, 904R...first light modulation device, 904G...second light modulation device, 904B...third light modulation device, 906...cross dichroic prism, 908...projection device, 910...screen

Claims

1. A laminate having a plurality of columnar portions, Each of the plurality of columnar portions is A first semiconductor layer; A second semiconductor layer having a conductivity type different from that of the first semiconductor layer; a light emitting layer provided between the first semiconductor layer and the second semiconductor layer; having The second semiconductor layer is A first part; and a second portion that surrounds the first portion and has a band gap larger than that of the first portion when viewed in a plan view from a stacking direction of the first semiconductor layer and the light emitting layer; having the second portion constitutes a side surface of the columnar portion, the first semiconductor layer is a GaN layer and forms a side surface of the columnar portion; The first portion and the second portion have the same conductivity type.

2. In claim 1, the second semiconductor layer is an AlGaN layer; The atomic concentration of Al in the second portion is higher than the atomic concentration of Al in the first portion.

3. In claim 1 or 2, the light emitting layer has a well layer and a barrier layer, The barrier layer is A fifth part; and In a plan view from the stacking direction, the fifth portion is surrounded by the fifth portion. The sixth part has a large gap, having The sixth portion constitutes a side surface of the columnar portion.

4. In claim 3, the barrier layer is an AlGaN layer; the sixth portion has a higher atomic concentration of Al than the fifth portion.

5. A projector comprising the light emitting device according to claim 1 .

Images