Light-emitting device and projector

Abstract

The present invention provides a light-emitting device and a projector that can reduce the current flowing on the side surface of a columnar portion. The light-emitting device includes a laminate having a plurality of columnar portions, and each of the plurality of columnar portions has: a first semiconductor layer; a second semiconductor layer having a conductivity type different from that of the first semiconductor layer; and a light-emitting layer disposed between the first semiconductor layer and the second semiconductor layer. The second semiconductor layer has: a first portion; and a second portion that surrounds the first portion when viewed from above in the stacking direction of the first semiconductor layer and the light-emitting layer and has a larger bandgap than the first portion, and the second portion constitutes the side surface of the columnar portion.

Description

Technical Field

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

[0002] Semiconductor lasers are expected to be the next-generation light sources with high brightness. Among them, semiconductor lasers using nanocolumns are expected to achieve high-output light emission with a narrow radiation angle through the effect of photonic crystals based on the nanocolumns.

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

[0004] [Prior Art Documents]

[0005] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-152474

[0007] [Problems to be Solved by the Invention]

[0008] There are dangling bonds on the side surfaces of the nanocolumns as described above. Therefore, the recombination of carriers near the side surfaces of the nanocolumns is likely to be non-radiative recombination. Summary of the Invention

[0009] [Means for Solving the Problems]

[0010] One aspect of the light-emitting device of the present invention includes a laminate having a plurality of columnar portions.

[0011] Each of the plurality of columnar portions has:

[0012] a first semiconductor layer;

[0013] a second semiconductor layer having a conductivity type different from that of the first semiconductor layer; and

[0014] a light-emitting layer disposed between the first semiconductor layer and the second semiconductor layer.

[0015] The second semiconductor layer has:

[0016] a first portion; and

[0017] a second portion that surrounds the first portion and has a larger bandgap than the first portion when viewed from above in the lamination direction of the first semiconductor layer and the light-emitting layer.

[0018] The second portion constitutes the side surface of the columnar portion.

[0019] One form of the projector of the present invention includes one form of the light-emitting device. Description of the Drawings

[0020] Figure 1 It is a cross-sectional view schematically showing the light-emitting device of the present embodiment.

[0021] Figure 2 It is a cross-sectional view schematically showing the columnar portion of the light-emitting device of the present embodiment.

[0022] Figure 3 It is a plan view schematically showing the columnar portion of the light-emitting device of the present embodiment.

[0023] Figure 4 It is a cross-sectional view schematically showing the manufacturing process of the light-emitting device of the present embodiment.

[0024] Figure 5 It is a cross-sectional view schematically showing the columnar portion of the light-emitting device of the first modification of the present embodiment.

[0025] Figure 6 It is a cross-sectional view schematically showing the columnar portion of the light-emitting device of the second modification of the present embodiment.

[0026] Figure 7 It is a cross-sectional view schematically showing the columnar portion of the light-emitting device of the third modification of the present embodiment.

[0027] Figure 8 It is a view schematically showing the projector of the present embodiment.

[0028] Figure 9 It is a Scanning Transmission Electron Microscopy (STEM) image of an experimental example.

[0029] [Description of Reference Signs]

[0030] 10: Substrate

[0031] 20: Laminate

[0032] 22: Buffer layer

[0033] 30: Columnar portion

[0034] 31: Side surface

[0035] 32: First semiconductor layer

[0036] 32a: Low bandgap portion

[0037] 32b: High bandgap portion

[0038] 33: Well layer

[0039] 34: Light-emitting layer

[0040] 35: Blocking layer

[0041] 35a: Low bandgap portion

[0042] 35b: High bandgap portion

[0043] 36: Second semiconductor layer

[0044] 36a: Low bandgap portion

[0045] 36b: High bandgap portion

[0046] 40: First electrode

[0047] 42: Second electrode

[0048] 100: Light-emitting device

[0049] 100R: Red light source

[0050] 100G: Green light source

[0051] 100B: Blue light source

[0052] 200, 300, 400: Light-emitting devices

[0053] 900: Projector

[0054] 902R: First optical element

[0055] 902G: Second optical element

[0056] 902B: Third optical element

[0057] 904R: First light modulation device

[0058] 904G: Second light modulation device

[0059] 904B: Third light modulation device

[0060] 906: Cross dichroic prism

[0061] 908: Projection device

[0062] 910: Screen Detailed implementation manners

[0063] Hereinafter, suitable implementation manners of the present invention will be described in detail with reference to the accompanying drawings. In addition, the implementation manners described below do not unduly limit the content of the present invention recited in the claims. Also, the structures described below are not all essential components of the present invention.

[0064] 1. Light-emitting device

[0065] 1.1 Overall structure

[0066] First, the light-emitting device of the present embodiment will be described with reference to the accompanying drawings. Figure 1 It is a cross-sectional view schematically showing the light-emitting device 100 of the present embodiment.

[0067] As Figure 1 shown, 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.

[0068] The substrate 10 is, for example, a Si substrate, a GaN substrate, a sapphire substrate, a SiC substrate, etc.

[0069] 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.

[0070] In this specification, in the stacking direction of the laminate 20 (hereinafter, also simply referred to as the "stacking direction"), when taking the light-emitting layer 34 as a reference, the direction from the light-emitting layer 34 toward the second electrode 42 is set as "up", and the direction from the light-emitting layer 34 toward the substrate 10 is set as "down" for explanation. In addition, the direction orthogonal to the stacking direction is also referred to as the "in-plane direction". In addition, the so-called "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 portion 30.

[0071] The buffer layer 22 is provided on the substrate 10. The buffer layer 22 is, for example, an n-type GaN layer doped with Si. A mask layer 50 for forming the columnar portion 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, etc.

[0072] The columnar portion 30 is provided on the buffer layer 22. The columnar portion 30 has a columnar shape protruding upward from the buffer layer 22. In other words, the columnar portion 30 protrudes upward from the substrate 10 with the buffer layer 22 interposed therebetween. The columnar portion 30 is also referred to as a nanocolumn, a nanowire, a nanorod, a nano-columnar object, for example. The planar shape of the columnar portion 30 is, for example, a polygon such as a regular hexagon, a circle.

[0073] The diameter of the columnar portion 30 is, for example, 50 nm or more and 500 nm or less. By setting the diameter of the columnar portion 30 to 500 nm or less, a high-quality crystalline light-emitting layer 34 can be obtained, and the inherent strain in the light-emitting layer 34 can be reduced. Thereby, the light generated in the light-emitting layer 34 can be amplified with high efficiency.

[0074] In addition, the so-called "diameter of the columnar portion" is the diameter when the planar shape of the columnar portion 30 is a circle, and is the diameter of the smallest enclosing circle when the planar shape of the columnar portion 30 is not a circular shape. For example, when the planar shape of the columnar portion 30 is a polygon, the diameter of the columnar portion 30 is the diameter of the smallest circle that encloses the polygon inside, and when the planar shape of the columnar portion 30 is an ellipse, the diameter of the columnar portion 30 is the diameter of the smallest circle that encloses the ellipse inside.

[0075] A plurality of columnar portions 30 are provided. The interval between adjacent columnar portions 30 is, for example, 1 nm or more and 500 nm or less. When viewed from the stacking direction, the plurality of columnar portions 30 are arranged at a prescribed pitch in a prescribed direction. The plurality of columnar portions 30 are, for example, arranged in a triangular lattice. In addition, the arrangement of the plurality of columnar portions 30 is not particularly limited, and they may also be arranged in a square lattice. The plurality of columnar portions 30 can exhibit the effect of a photonic crystal.

[0076] In addition, the so-called "pitch of the columnar portions" refers to the distance between the centers of adjacent columnar portions 30 along the prescribed direction. The so-called "center of the columnar portion" is the center of the circle when the planar shape of the columnar portion 30 is a circle, and is the center of the smallest enclosing circle when the planar shape of the columnar portion 30 is not a circular shape. For example, the center of the columnar portion 30 is the center of the smallest circle that encloses the polygon inside when the planar shape of the columnar portion 30 is a polygon, and is the center of the smallest circle that encloses the ellipse inside when the planar shape of the columnar portion 30 is an ellipse.

[0077] The columnar portion 30 has a first semiconductor layer 32, a light-emitting layer 34, and a second semiconductor layer 36.

[0078] 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.

[0079] 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 by injecting current. The light-emitting layer 34, for example, has 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 a multiple quantum well (MQW) structure including 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.

[0080] In addition, 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 this case, the light-emitting layer 34 has a single quantum well (SQW) structure.

[0081] The second semiconductor layer 36 is provided on the light-emitting layer 34. The second semiconductor layer 36 is a layer having 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.

[0082] In addition, although not shown, an optical confinement layer (OCL) may be provided between the first semiconductor layer 32 and the light-emitting layer 34. Further, an electron blocking layer (EBL) may be provided between the light-emitting layer 34 and the second semiconductor layer 36.

[0083] In the light-emitting device 100, a pin diode is formed by the p-type second semiconductor layer 36, the undoped i-type light-emitting layer 34, 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, current is injected into the light-emitting layer 34, and recombination of electrons and holes occurs in the light-emitting layer 34. Light emission is generated by the recombination. The light generated in the light-emitting layer 34 propagates in the in-plane direction, a standing wave is formed by the effect of the photonic crystal based on the plurality of columnar portions 30, gain is received by the light-emitting layer 34, and laser oscillation occurs. Then, the light-emitting device 100 emits the +1st order diffracted light and the -1st order diffracted light as laser light in the stacking direction.

[0084] In addition, although not shown, a reflective layer may be provided between the substrate 10 and the buffer layer 22 or below the substrate 10. The reflective layer is, for example, a distributed Bragg reflector (DBR) layer. By the reflective layer, the light generated in the light-emitting layer 34 can be reflected, so that the light-emitting device 100 can emit light only from the second electrode 42 side.

[0085] The first electrode 40 is disposed on the buffer layer 22. The buffer layer 22 can 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 current into the light-emitting layer 34. As the first electrode 40, for example, an electrode formed by laminating a Cr layer, a Ni layer, and an Au layer in this order from the buffer layer 22 side is used.

[0086] The second electrode 42 is disposed on the second semiconductor layer 36. The second electrode 42 is electrically connected to the second semiconductor layer 36. The second semiconductor layer 36 can be in ohmic contact with the second electrode 42. The second electrode 42 is the other electrode for injecting current into the light-emitting layer 34. As the second electrode 42, for example, indium tin oxide (ITO) or the like is used.

[0087] 1.2. Detailed structure of the columnar portion

[0088] Figure 2 is a cross-sectional view schematically showing the columnar portion 30. Figure 3 is a plan view schematically showing the columnar portion 30. In addition, Figure 2 is Figure 3 a cross-sectional view taken along line II-II of

[0089] As Figure 2 shown, the first semiconductor layer 32 has a low bandgap portion 32a and a high bandgap portion 32b. The first semiconductor layer 32 is an AlGaN layer containing Al (aluminum), Ga (gallium), and N (nitrogen).

[0090] The bandgap of the high bandgap portion 32b is larger than that of the low bandgap portion 32a. When viewed from the stacking direction (hereinafter, also simply referred to as "when viewed from above"), the high bandgap portion 32b surrounds the low bandgap portion 32a. The high bandgap portion 32b constitutes the side surface 31 of the columnar portion 30. The side surface 31 connects the upper surface of the buffer layer 22 to 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 bandgap portion 32b is higher than that of Al in the low bandgap portion 32a.

[0091] The blocking layer 35 of the light-emitting layer 34 has a low bandgap portion 35a and a high bandgap portion 35b. The blocking layer 35 is an AlGaN layer. The well layer 33 is, for example, an InGaN layer.

[0092] The bandgap of the high bandgap portion 35b is larger than that of the low bandgap portion 35a. When viewed from above, the high bandgap portion 35b surrounds the low bandgap portion 35a. The high bandgap portion 35b constitutes the side surface 31 of the columnar portion 30. The atomic concentration of Al in the high bandgap portion 35b is higher than the atomic concentration of Al in the low bandgap portion 35a.

[0093] The second semiconductor layer 36 has a low bandgap portion 36a and a high bandgap portion 36b. The second semiconductor layer 36 is an AlGaN layer.

[0094] The bandgap of the high bandgap portion 36b is larger than that of the low bandgap portion 36a. As Figure 3 shown, when viewed from above, the high bandgap portion 36b surrounds the low bandgap portion 36a. In the illustrated example, the planar shape of the columnar portion 30 is a regular hexagon. As Figure 2 and Figure 3 shown, the high bandgap portion 36b constitutes the side surface 31 of the columnar portion 30. The atomic concentration of Al in the high bandgap portion 36b is higher than the atomic concentration of Al in the low bandgap portion 36a. In the columnar portion 30, Al tends to be present in the side surface 31.

[0095] The high bandgap portions 32b, 35b, and 36b are portions where the atomic concentration of Al is higher than the atomic concentration of Ga. In the high bandgap portions 32b, 35b, and 36b, the ratio of the atomic concentration of Al to the total of the atomic concentrations of Al and Ga (hereinafter, also referred to as "Al ratio") is greater than 0.5, and may also be 0.8 or more. Further, in the high bandgap portions 32b, 35b, and 36b, the Al ratio may also be 1.0. In this case, the materials of the high bandgap portions 32b, 35b, and 36b are AlN.

[0096] The low bandgap portions 32a, 35a, and 36a are portions where the atomic concentration of Al is equal to or less than the atomic concentration of Ga. The Al ratios of the low bandgap portions 32a, 35a, and 36a are 0.5 or less, and may also be 0.4 or less.

[0097] In addition, the atomic concentrations of Al and Ga can be measured by Scanning Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy (STEM-EDS).

[0098] 1.3. Effects

[0099] In the light-emitting device 100, the second semiconductor layer 36 has a low bandgap portion 36a as a first part and a high bandgap portion 36b as a second part that surrounds the low bandgap portion 36a in a plan view and has a larger bandgap than the low bandgap portion 36a. The high bandgap portion 36b constitutes the side surface 31 of the columnar portion 30. Therefore, in the light-emitting device 100, compared with, for example, the case where the bandgaps of the first part and the second part are equal, the current flowing through the side surface 31 of the columnar portion 30 can be reduced. As a result, the current of non-light-emitting recombination can be reduced. As a result, the current injection efficiency can be improved.

[0100] In the light-emitting device 100, the second semiconductor layer 36 is an AlGaN layer, and the atomic concentration of Al in the high bandgap portion 36b is higher than the atomic concentration of Al in the low bandgap portion 36a. Therefore, in the light-emitting device 100, by growing the second semiconductor layer 36 under the condition that the Al bias exists on the side surface 31 of the columnar portion 30, the bandgap of the high bandgap portion 36b can be easily made higher than the bandgap of the low bandgap portion 36a.

[0101] In the light-emitting device 100, the first semiconductor layer 32 has a low bandgap portion 32a as a third part and a high bandgap portion 32b as a fourth part that surrounds the low bandgap portion 32a in a plan view and has a larger bandgap than the low bandgap portion 32a. The high bandgap portion 32b 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 further reduced.

[0102] In the light-emitting device 100, the first semiconductor layer 32 is an AlGaN layer, and the atomic concentration of Al in the high bandgap portion 32b is higher than the atomic concentration of Al in the low bandgap portion 32a. Therefore, in the light-emitting device 100, by growing the first semiconductor layer 32 under the condition that the Al bias exists on the side surface 31 of the columnar portion 30, the bandgap of the high bandgap portion 32b can be easily made higher than the bandgap of the low bandgap portion 32a.

[0103] In the light-emitting device 100, the light-emitting layer 34 has a well layer 33 and a blocking layer 35. The blocking layer 35 has a low bandgap portion 35a as a fifth part and a high bandgap portion 35b as a sixth part that surrounds the low bandgap portion 35a in a plan view and has a larger bandgap than the low bandgap portion 35a. The high bandgap portion 35b 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 further reduced.

[0104] In the light-emitting device 100, the blocking layer 35 is an AlGaN layer, and the atomic concentration of Al in the high bandgap portion 35b is higher than the atomic concentration of Al in the low bandgap portion 35a. Therefore, in the light-emitting device 100, by growing the blocking layer 35 under the condition that the Al bias exists on the side surface 31 of the columnar portion 30, the bandgap of the high bandgap portion 35b can be easily made higher than the bandgap of the low bandgap portion 35a.

[0105] In addition, the light-emitting device 100 is not limited to a laser, and may also be a light-emitting diode (LED).

[0106] 2. Manufacturing method of the light-emitting device

[0107] Next, a manufacturing method of the light-emitting device 100 according to the present embodiment will be described with reference to the accompanying drawings. Figure 4 It is a cross-sectional view schematically showing the manufacturing process of the light-emitting device 100 according to the present embodiment.

[0108] As Figure 4 shown, a buffer layer 22 is epitaxially grown on the substrate 10. As a method of epitaxial growth, for example, a metal organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy (MBE) method, etc. can be cited.

[0109] Next, a mask layer 50 is formed on the buffer layer 22. The mask layer 50 is formed, for example, by film formation and patterning using an electron beam evaporation method or a sputtering method, etc. Patterning is performed by photolithography and etching. The thickness of the mask layer 50 is, for example, about 5 nm.

[0110] As Figure 1 shown, using the mask layer 50 as a mask, a first semiconductor layer 32, a light-emitting layer 34, and a second semiconductor layer 36 are sequentially epitaxially grown on the buffer layer 22. As a method of epitaxial growth, for example, a MOCVD method, a MBE method, etc. can be cited. By this process, a plurality of columnar portions 30 can be formed.

[0111] The epitaxial growth of the first semiconductor layer 32, the blocking layer 35, and the second semiconductor layer 36 is performed under the condition that an Al bias exists on the side surface 31 of the columnar portion 30. Specifically, the growth temperature of the first semiconductor layer 32, the blocking layer 35, and the second semiconductor layer 36 is set to 830 °C or higher and 870 °C or lower, preferably set to 850 °C for epitaxial growth. Thereby, an Al bias can be made to exist on the side surface 31 of the columnar portion 30.

[0112] 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, for example, by a vacuum evaporation method, etc. In addition, the formation order of the first electrode 40 and the second electrode 42 is not particularly limited.

[0113] Through the above process, the light-emitting device 100 can be manufactured.

[0114] 3. Modification example of the light-emitting device

[0115] 3.1. First modified example

[0116] Next, the light-emitting device according to the first modified example of the present embodiment will be described with reference to the accompanying drawings. Figure 5 It is a cross-sectional view schematically showing the columnar portion 30 of the light-emitting device 200 according to the first modified example of the present embodiment.

[0117] Hereinafter, in the light-emitting device 200 according to the first modified example of the present embodiment, members having the same functions as the constituent members of the light-emitting device 100 described above are denoted by the same reference numerals, and their detailed descriptions are omitted. The same applies to the light-emitting devices according to the second to fourth modified examples of the present embodiment shown below.

[0118] In the light-emitting device 100 described above, as Figure 2 shown, the blocking layer 35 has a low bandgap portion 35a and a high bandgap portion 35b. The blocking layer 35 is an AlGaN layer.

[0119] In contrast, in the light-emitting device 200, as Figure 5 shown, the blocking layer 35 does not have a low bandgap portion 35a and a high bandgap portion 35b. The blocking layer 35 is, for example, a GaN layer.

[0120] In the light-emitting device 200, similarly to the light-emitting device 100 described above, the current flowing on the side surface 31 of the columnar portion 30 can be reduced.

[0121] Furthermore, in the light-emitting device 200, in the blocking layer 35 constituting the complex light-emitting layer 34, the low bandgap portion 35a and the high bandgap portion 35b are not formed, so that the columnar portion 30 can be easily formed.

[0122] 3.2. Second modified example

[0123] Next, the light-emitting device according to the second modified example of the present embodiment will be described with reference to the accompanying drawings. Figure 6 It is a cross-sectional view schematically showing the columnar portion 30 of the light-emitting device 300 according to the second modified example of the present embodiment.

[0124] In the light-emitting device 100 described above, as Figure 2 shown, the first semiconductor layer 32 has a low bandgap portion 32a and a high bandgap portion 32b. Furthermore, the blocking layer 35 has a low bandgap portion 35a and a high bandgap portion 35b. The first semiconductor layer 32 and the blocking layer 35 are AlGaN layers.

[0125] In contrast, in the light-emitting device 300, as Figure 6As shown, the first semiconductor layer 32 does not have a low bandgap portion 32a and a high bandgap portion 32b. Further, the blocking layer 35 does not have a low bandgap portion 35a and a high bandgap portion 35b. The first semiconductor layer 32 and the blocking layer 35 are, for example, GaN layers.

[0126] In the light-emitting device 300, similar to the light-emitting device 100 described above, the current flowing through the side surface 31 of the columnar portion 30 can be reduced.

[0127] 3.3. Third modification

[0128] Next, a light-emitting device according to a third modification of the present embodiment will be described with reference to the accompanying drawings. Figure 7 FIG. is a cross-sectional view schematically showing the columnar portion 30 of the light-emitting device 400 according to the third modification of the present embodiment.

[0129] In the light-emitting device 100 described above, as Figure 2 shown, the first semiconductor layer 32 has a low bandgap portion 32a and a high bandgap portion 32b. Further, the blocking layer 35 has a low bandgap portion 35a and a high bandgap portion 35b. The first semiconductor layer 32 and the blocking layer 35 are AlGaN layers. Further, the first semiconductor layer 32 is provided below the light-emitting layer 34 and is an n-type semiconductor layer. Further, the second semiconductor layer 36 is provided on the light-emitting layer 34 and is a p-type semiconductor layer.

[0130] In contrast, in the light-emitting device 400, as Figure 7 shown, the first semiconductor layer 32 does not have a low bandgap portion 32a and a high bandgap portion 32b. Further, the blocking layer 35 does not have a low bandgap portion 35a and a high bandgap portion 35b. The first semiconductor layer 32 and the blocking layer 35 are, for example, GaN layers.

[0131] 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.

[0132] 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.

[0133] In the light-emitting device 400, similar to the light-emitting device 100 described above, the current flowing through the side surface 31 of the columnar portion 30 can be reduced.

[0134] In addition, in the light-emitting devices 300 and 400 described above, the blocking layer 35 may also be an AlGaN layer and may have a low bandgap portion 35a and a high bandgap portion 35b.

[0135] 3.4. Fourth Modified Example

[0136] Next, a light-emitting device according to a fourth modified example of the present embodiment will be described.

[0137] In the light-emitting device 100 described above, the first semiconductor layer 32, the blocking layer 35, and the second semiconductor layer 36 are AlGaN layers.

[0138] In contrast, in the light-emitting device according to the fourth modified example of the present embodiment, the first semiconductor layer 32, the blocking layer 35, and the second semiconductor layer 36 are BGaN layers containing B (boron), Ga, and N.

[0139] The atomic concentration of B in the high bandgap portion 32b of the first semiconductor layer 32 is higher than the atomic concentration of B in the low bandgap portion 32a. The atomic concentration of B in the high bandgap portion 35b of the blocking layer 35 is higher than the atomic concentration of B in the low bandgap portion 35a. The atomic concentration of B in the high bandgap portion 36b of the second semiconductor layer 36 is higher than the atomic concentration of B in the low bandgap portion 36a. In the columnar portion 30, B tends to be present on the side surface 31.

[0140] The high bandgap portions 32b, 35b, and 36b are portions where the atomic concentration of B is higher than the atomic concentration of Ga. In the high bandgap 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 "B ratio") is, for example, greater than 0.5, and may be 0.8 or more. Further, the B ratio may be 1.0. In this case, the materials of the high bandgap portions 32b, 35b, and 36b are BN.

[0141] The low bandgap portions 32a, 35a, and 36a are portions where the atomic concentration of B is equal to or less than the atomic concentration of Ga. The B ratios of the low bandgap portions 32a, 35a, and 36a are 0.5 or less, and may be 0.4 or less. In addition, the atomic concentration of B can be measured by STEM-EDS.

[0142] The epitaxial growth of the first semiconductor layer 32, the blocking layer 35, and the second semiconductor layer 36 is performed under conditions such that B tends to be present on the side surface 31 of the columnar portion 30.

[0143] In the light-emitting device according to the fourth modified example of the present embodiment, similar to the light-emitting device 100 described above, the current flowing on the side surface 31 of the columnar portion 30 can be reduced.

[0144] 4. Projector

[0145] Next, a projector according to the present embodiment will be described with reference to the drawings. Figure 8It is a diagram schematically showing the projector 900 of the present embodiment.

[0146] The projector 900 has, for example, a light-emitting device 100 as a light source.

[0147] The projector 900 has a housing (not shown) and a red light source 100R, a green light source 100G, and a blue light source 100B that are provided in the housing and emit red light, green light, and blue light, respectively. In addition, for convenience, in Figure 8 the red light source 100R, the green light source 100G, and the blue light source 100B are simplified.

[0148] 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 that 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.

[0149] The light emitted from the red light source 100R is incident on the first optical element 902R. The light emitted from the red light source 100R is focused by the first optical element 902R. In addition, the first optical element 902R may have functions other than focusing. The same applies to the second optical element 902G and the third optical element 902B described later.

[0150] The light focused 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 according to the image information. Then, the projection device 908 magnifies and projects the image formed by the first light modulation device 904R onto the screen 910.

[0151] The light emitted from the green light source 100G is incident on the second optical element 902G. The light emitted from the green light source 100G is focused by the second optical element 902G.

[0152] The light focused 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 according to the image information. Then, the projection device 908 magnifies and projects the image formed by the second light modulation device 904G onto the screen 910.

[0153] The light emitted from the blue light source 100B is incident on the third optical element 902B. The light emitted from the blue light source 100B is focused by the third optical element 902B.

[0154] The light focused by the third optical element 902B is incident on the third light modulation device 904B. The third light modulation device 904B modulates the incident light according to the image information. Then, the projection device 908 magnifies and projects the image formed by the third light modulation device 904B onto the screen 910.

[0155] In addition, the projector 900 may include a cross dichroic prism 906 that combines the light emitted from the first light modulation device 904R, the second light modulation device 904G, and the third light modulation device 904B and guides it to the projection device 908.

[0156] The three colors of light modulated by the first light modulation device 904R, the second light modulation device 904G, and the third light modulation device 904B are incident on the cross dichroic prism 906. The cross dichroic prism 906 is formed by fitting four right-angled prisms, 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 colors of light are combined by these multilayer dielectric films to form light for displaying a color image. Then, the combined light is projected onto the screen 910 by the projection device 908, and an enlarged image is displayed.

[0157] In addition, the red light source 100R, the green light source 100G, and the blue light source 100B may also directly form an image without using the first light modulation device 904R, the second light modulation device 904G, and the third light modulation device 904B by controlling the light-emitting device 100 according to the image information of the pixels of the video. Moreover, the projection device 908 may also magnify and project the image formed by the red light source 100R, the green light source 100G, and the blue light source 100B onto the screen 910.

[0158] In addition, 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 also be used, and a reflective light valve may also be used. Examples of such a light valve include a reflective liquid crystal light valve or a Digital Micro Mirror Device. In addition, the structure of the projection device is appropriately changed according to the type of light valve used.

[0159] In addition, the light source can also be applied to a light source device of a scanning type image display device having a scanning component, 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.

[0160] The light-emitting device of the above-described embodiment can also be used for applications other than projectors. In applications other than projectors, for example, there are light sources for indoor and outdoor lighting, backlights for displays, laser printers, scanners, vehicle-mounted lights, light-sensing devices using light, communication devices, and the like. In addition, the light-emitting device of the above-described embodiment can also be applied to the light-emitting elements of an LED display in which minute light-emitting elements are arranged in an array for image display.

[0161] 5. Experimental Example

[0162] A columnar portion was fabricated by epitaxially growing an n-type GaN layer, an n-type AlGaN layer, and an n-type GaN layer in this order. As the epitaxial growth method, the MBE method was used. The growth temperature of the AlGaN layer was set to 850 °C.

[0163] The columnar portion fabricated in the above manner was observed by STEM, and the distribution of Al was investigated by EDS. Figure 9 This is a STEM image showing the distribution of Al in the columnar portion. In Figure 9 it, portions with less Al are shown in darker colors, and portions with more Al are shown in lighter colors.

[0164] As Figure 9 shown, it was found that by epitaxially growing the AlGaN layer at a growth temperature of 850 °C, Al can be biased to exist on the side surfaces of the columnar portion.

[0165] The above-described embodiments and modification examples are merely examples and are not limited to these. For example, the respective embodiments and modification examples can also be appropriately combined.

[0166] The present invention includes structures that are substantially the same as the structures described in the embodiments, such as structures having the same functions, methods, and results, or structures having the same objectives and effects. In addition, the present invention includes structures in which non-essential parts of the structures described in the embodiments are replaced. In addition, the present invention includes structures that can exhibit the same operational effects as the structures described in the embodiments, or structures that can achieve the same objectives. In addition, the present invention includes structures in which the structures described in the embodiments are combined with known technologies.

[0167] The following is derived from the above-described embodiments and modification examples.

[0168] One form of the light-emitting device includes a laminate having a plurality of columnar portions,

[0169] Each of the plurality of columnar portions has:

[0170] a first semiconductor layer;

[0171] a second semiconductor layer having a conductivity type different from that of the first semiconductor layer; and

[0172] A light-emitting layer, disposed between the first semiconductor layer and the second semiconductor layer,

[0173] The second semiconductor layer has:

[0174] A first portion; and

[0175] A second portion that surrounds the first portion when viewed from above in the stacking direction of the first semiconductor layer and the light-emitting layer, and has a larger bandgap than the first portion,

[0176] The second portion constitutes the side surface of the columnar portion.

[0177] In the light-emitting device, the current flowing through the side surface of the columnar portion can be reduced. As a result, the current of non-light-emitting recombination can be reduced. Consequently, the current injection efficiency can be improved.

[0178] In one form of the light-emitting device, it may also be:

[0179] The second semiconductor layer is an AlGaN layer,

[0180] The atomic concentration of Al in the second portion is higher than the atomic concentration of Al in the first portion.

[0181] In the light-emitting device, it is possible to easily make the bandgap of the second portion higher than the bandgap of the first portion.

[0182] In one form of the light-emitting device, it may also be:

[0183] The first semiconductor layer has:

[0184] A third portion; and

[0185] A fourth portion that surrounds the third portion when viewed from above in the stacking direction, and has a larger bandgap than the third portion,

[0186] The fourth portion constitutes the side surface of the columnar portion.

[0187] According to the light-emitting device, the current flowing through the side surface of the columnar portion can be further reduced.

[0188] In one form of the light-emitting device, it may also be:

[0189] The first semiconductor layer is an AlGaN layer,

[0190] The atomic concentration of Al in the fourth portion is higher than the atomic concentration of Al in the third portion.

[0191] According to the light-emitting device, it is possible to easily make the bandgap of the fourth portion higher than the bandgap of the third portion.

[0192] In one form of the light-emitting device, it may also be:

[0193] The light-emitting layer has a well layer and a blocking layer.

[0194] The blocking layer has:

[0195] A fifth part; and

[0196] A sixth part that surrounds the fifth part and has a larger bandgap than the fifth part when viewed from above in the stacking direction.

[0197] The sixth part constitutes the side surface of the columnar part.

[0198] According to the light-emitting device, the current flowing on the side surface of the columnar part can be further reduced.

[0199] In one form of the light-emitting device, it may also be:

[0200] The blocking layer is an AlGaN layer.

[0201] The atomic concentration of Al in the sixth part is higher than the atomic concentration of Al in the fifth part.

[0202] According to the light-emitting device, it is easy to make the bandgap of the sixth part higher than the bandgap of the fifth part.

[0203] One form of the projector has one form of the light-emitting device.

Claims

1. A light-emitting device, wherein, Comprising a laminate having a plurality of columnar portions, Each of the plurality of columnar portions has: A first semiconductor layer; A second semiconductor layer having a conductivity type different from that of the first semiconductor layer; and A light-emitting layer disposed between the first semiconductor layer and the second semiconductor layer, The second semiconductor layer has: A first portion; And A second portion that surrounds the first portion when viewed from above in the stacking direction of the first semiconductor layer and the light-emitting layer, and has a larger bandgap than the first portion, The second portion constitutes the side surface of the columnar portion, The first portion is an AlGaN layer, The second portion 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.

2. The light-emitting device according to claim 1, wherein, The first semiconductor layer has: A third portion; And A fourth portion that surrounds the third portion when viewed from above in the stacking direction, and has a larger bandgap than the third portion, The fourth portion constitutes the side surface of the columnar portion.

3. The light-emitting device according to claim 2, wherein, The first semiconductor layer is an AlGaN layer, The atomic concentration of Al in the fourth portion is higher than the atomic concentration of Al in the third portion.

4. The light-emitting device according to claim 1, wherein, The light-emitting layer has a well layer and a barrier layer, The barrier layer has: A fifth portion; and A sixth portion that surrounds the fifth portion when viewed from above in the stacking direction, and has a larger bandgap than the fifth portion, The sixth portion constitutes the side surface of the columnar portion.

5. The light-emitting device according to claim 4, wherein, The barrier layer is an AlGaN layer, The atomic concentration of Al in the sixth portion is higher than the atomic concentration of Al in the fifth portion.

6. A projector, wherein, Comprising a light-emitting device according to any one of claims 1 to 5.

Images