JP6258815B2 - Nitride semiconductor light emitting device - Google Patents

Description

  The present invention relates to a nitride semiconductor light emitting device.

AlN, GaN, and InN have band gap energies of about 6.0 eV, about 3.4 eV, and about 0.6 eV, respectively. Therefore, a nitride semiconductor light emitting device using these mixed crystals as the material of the light emitting layer can generate light having a wavelength from the ultraviolet region to the infrared region (for example, Patent Document 1), and is used for illumination. It is being applied to various uses such as a light source or a backlight of a liquid crystal display. In particular, a nitride semiconductor light emitting device capable of generating light having a wavelength in the ultraviolet region is made of Al _a Ga _b N (0 ≦ a, b ≦ 1, a + b = 1), which is _a mixed crystal of AlN and GaN. Light emitting diodes having layers as light emitting layers are being realized.

  Each crystal structure of AlN and GaN is a wurtzite structure. Each valence band of AlN and GaN is split into three states by the crystal field and the spin-orbit interaction.

  In GaN, the splitting energy of the valence band due to the crystal field is 11 meV, and the splitting energy of the valence band due to the spin-orbit interaction is 11 meV. Therefore, the valence band near the Γ point is divided into a heavy hole band, a light hole band, and a hole band due to the crystal field in order from the top of the valence band. Therefore, the emission of GaN is dominated by the optical transition between the heavy hole band and the conduction band described above. Such a transition is allowed when the electric field vector E of the light is perpendicular to the c-axis ([0001]) (E⊥c polarized light is generated), so that light emission from the C plane becomes strong.

  On the other hand, in AlN, the splitting energy of the valence band due to the crystal field is −217 meV, and the splitting energy of the valence band due to the spin-orbit interaction is 36 meV. Therefore, the valence band near the Γ point is divided into a hole band due to the crystal field, a heavy hole band, and a light hole band in order from the top of the valence band. Therefore, the light emission of AlN is dominant due to the optical transition between the hole band and the conduction band due to the crystal field. Such a transition is allowed when the electric field vector E of the light is parallel to the c-axis (E || c-polarized light is generated), so that light emission from the C-plane is weakened.

Thus, the polarization plane of the generated light is different between GaN and AlN. Therefore, in a light emitting diode including a light emitting layer including a polar surface as a main surface and made of Al _s Ga _1-s N (0 <s ≦ 1), when the Al composition s is increased from 0 to 1, the light emitting layer The light generated in E changes from E⊥c polarized light to E || c polarized light. In this specification, the (0001) plane is represented as “+ C plane”, the (000-1) plane is represented as “−C plane”, and includes a (0001) plane and a (000-1) plane { The 0001} plane is represented as “C plane”. The “polar plane” includes, for example, a plane having a plane orientation with an off angle of ± 5 ° with respect to a specific plane orientation.

  The Ec-polarized light travels predominantly in a direction perpendicular to the main surface of the light emitting layer. For this reason, since light emission from the C plane becomes strong, it is advantageous for taking out from the surface of the light emitting diode (the surface of the light emitting diode extending in parallel to the main surface of the light emitting layer). On the other hand, E || c-polarized light travels predominantly in a direction parallel to the main surface of the light emitting layer. For this reason, light emission from the C plane is weakened, which is disadvantageous for extraction from the surface of the light emitting diode. In the vicinity where the light generated in the light emitting layer switches from E⊥c polarized light to E || c polarized light, the energy of the hole band due to the crystal field and the energy of the heavy hole band are close, so both optical transitions are taken. Can do. That is, the light generated in the light emitting layer includes E⊥c polarized light and E || c polarized light.

JP 2008-91664 A

  The E || c-polarized light travels predominantly in a direction parallel to the main surface of the light-emitting layer, but part of it travels in a direction inclined at a predetermined angle from the main surface of the light-emitting layer. Here, the “predetermined angle” is generally light that is generated in the main surface of the light-emitting layer and light that is generated in the light-emitting layer and totally reflected at the interface between the nitride semiconductor layer and the medium located above and below it. This means the angle formed by the direction of travel. Therefore, light traveling in a direction inclined at a predetermined angle from the main surface of the light emitting layer repeats total reflection inside the light emitting diode, and thus is absorbed by the absorption layer (layer that absorbs the light), and thus the light emitting diode. It is hard to be taken out to the outside.

As described above, the light emitting diode including the active layer made of AlGaN and emitting E || c-polarized light has a problem that the light extraction efficiency is low. Considering that the light generated in the light emitting layer is changed from E⊥c polarized light to E || c polarized light by increasing the Al composition of the light emitting layer, the above problem is the case where the light emitting layer does not contain Al ( For example, it cannot occur when the patent document 1) and the light emitting layer are Al _x Ga _1-x N (0 ≦ x <0.3) layers, and the light emitting layer is Al _x Ga _1-x N (0.3 ≦ 3). It occurs for the first time in the case of x ≦ 1) layer.

The present invention has been made in view of the above points, and an object of the present invention is to provide light from a nitride semiconductor light emitting device when the light emitting layer is an Al _x Ga _1-x N (0.3 ≦ x ≦ 1) layer. It is to increase the extraction efficiency.

The nitride semiconductor light emitting device includes a light emitting layer and at least one nitride semiconductor layer different from the light emitting layer. The light emitting layer has a polar surface as a main surface, and is made of Al _x Ga _1-x N (0.3 ≦ x ≦ 1). The at least one nitride semiconductor layer is in contact with the first medium having a lower refractive index than the nitride semiconductor in a direction parallel to the c-axis of the nitride semiconductor crystal, and at least one of the interfaces with the first medium. The part has a light extraction surface. On the light extraction surface, a plurality of protrusions are formed that protrude from the nitride semiconductor layer having the light extraction surface toward the first medium. The following formula 1 and the following formula 2 are satisfied. In the following formula 1 and the following formula 2, D represents the interval between adjacent convex portions, H represents the height of the convex portion, θ ₁ represents the inclination angle of the side surface of the convex portion, and α represents the c axis. It represents the spread angle of E || c-polarized light around the vertical direction, and θ _t represents the total reflection angle of E || c-polarized light.
D ≧ H (1−tan θ ₁ × tan α) / tan α (Formula 1)
0 <θ ₁ <θ _t Expression 2

Preferably, in Formula 1, D is 200 μm or less. More preferably, in Formula 1 and Formula 2 above, when 0 <α ≦ 40 °, θ ₁ is 20 ° or more and 40 ° or less, and H is 0.1 μm or more and 10 μm or less.

  The convex portion preferably has a conical shape.

In the present invention, when the light emitting layer is an Al _x Ga _1-x N (0.3 ≦ x ≦ 1) layer, the light extraction efficiency of the nitride semiconductor light emitting device is increased.

It is sectional drawing which shows a mode that E || c polarized light propagates the inside of the conventional nitride semiconductor light-emitting device. It is a graph which shows the result of the simulation with respect to the conventional nitride semiconductor light-emitting device. (A) is a graph showing the relationship between the incident angle and the transmittance T when E || c-polarized light enters the air from an n-type nitride semiconductor layer or a p-type nitride semiconductor layer, and (b) is a graph. , E || c polarization is a graph showing the relationship between the incident angle and the transmittance T when the polarized light enters the sapphire substrate from the n-type nitride semiconductor layer or the p-type nitride semiconductor layer. It is sectional drawing of the nitride semiconductor light-emitting device of one Embodiment of this invention. FIG. 6 is a cross-sectional view illustrating light propagation when E || c-polarized light is incident on a light extraction surface in the nitride semiconductor light emitting device of one embodiment of the present invention. In the nitride semiconductor light emitting device of one embodiment of the present invention, it is a cross-sectional view illustrating the propagation of light when E⊥c polarized light enters the light extraction surface. (A) And (b) is sectional drawing which shows the manufacturing method of the nitride semiconductor light-emitting device of one Embodiment of this invention in order of a process. It is sectional drawing of the nitride semiconductor light-emitting device of one Embodiment of this invention. It is sectional drawing of the nitride semiconductor light-emitting device of one Embodiment of this invention. It is sectional drawing of the nitride semiconductor light-emitting device of one Embodiment of this invention. It is sectional drawing of the nitride semiconductor light-emitting device of one Embodiment of this invention. It is sectional drawing of the nitride semiconductor light-emitting device of one Embodiment of this invention. It is sectional drawing of the nitride semiconductor light-emitting device of one Embodiment of this invention.

[Details of assignment]
The inventors have performed the following simulations to form a conventional nitride semiconductor light emitting device (including a light emitting layer made of AlGaN having a C surface as a main surface and a high Al composition, and forming the light extraction surface of the present invention) It was confirmed that the light extraction efficiency of the nitride semiconductor light emitting device (not yet) was lowered.

As described above, E || c-polarized light travels predominantly in a direction parallel to the main surface of the light-emitting layer, but part of the light travels in a direction inclined at a predetermined angle from the main surface of the light-emitting layer. . FIG. 1 is a cross-sectional view showing how E || c polarized light propagates inside a conventional nitride semiconductor light emitting device. Here, a nitride semiconductor light emitting device in which an active layer and a p-type nitride semiconductor layer 5 (thickness 400 nm) are sequentially formed on an n-type nitride semiconductor layer (thickness 500 nm) is assumed. The active layer has three quantum well layers 3 and three barrier layers, and is configured by alternately stacking one quantum well layer 3 and one barrier layer. Each of the quantum well layers 3 includes a C plane as a main surface, is made of undoped Al _s Ga _1-s N (0 <s ≦ 1), and has a thickness of 3 nm. Each of the barrier layers contained an n-type dopant and had a thickness of 6 nm. In FIG. 1, for simplicity of explanation, the n-type nitride semiconductor layer 1 and the three barrier layers are collectively shown as an n-type nitride semiconductor layer 1 (having a thickness of 518 nm).

Further, it was assumed that only the quantum well layer 3 absorbs E || c-polarized light L01 (hereinafter, “quantum well layer 3” may be referred to as “absorbing layer 3”). One side of the nitride semiconductor light emitting device was 1 mm, and the left end P of the nitride semiconductor light emitting device was the origin, and the x axis was taken to the right. That is, the right end Q of the nitride semiconductor light emitting device is a point where x = 10 ⁶ .

Θ _out shown in FIG. 1 means the exit angle of E || c-polarized light L01, that is, parallel to the traveling direction of E || c-polarized light L01 and the c-axis of the nitride semiconductor crystal at an arbitrary point x = x1. This means an angle formed with a certain direction (a direction perpendicular to the growth surface). The E || c-polarized light L01 is incident on the lower surface 1A of the n-type nitride semiconductor layer 1 at θ _out , totally reflected by the lower surface 1A, and then incident on the upper surface 5B of the p-type nitride semiconductor layer 5 at θ _out . . In this way, the E || c-polarized light L01 is repeatedly reflected from the lower surface 1A of the n-type nitride semiconductor layer 1 and the upper surface 5B of the p-type nitride semiconductor layer 5, and from the left end P of the nitride semiconductor light emitting device. Proceed to the right end Q of the nitride semiconductor light emitting device. Therefore, the E || c-polarized light L01 passes through the absorption layer 3, and is thus absorbed by the absorption layer 3.

In such a nitride semiconductor light emitting device, when the intensity of light generated at an arbitrary point x = x1 is assumed to be 1, the right end of the nitride semiconductor light emitting device repeats total reflection from the arbitrary point. The light intensity at the arrival point when the point on the Q side was reached was calculated. In this calculation, the refractive indexes of the n-type nitride semiconductor layer 1, the quantum well layer 3, and the p-type nitride semiconductor layer 5 were not taken into consideration. Also, E || c polarization L01 is assumed to be totally reflected by the upper surface 5B of the lower surface 1A and p-type nitride semiconductor layer 5 of n-type nitride semiconductor layer 1 irrespective of the theta _out. FIG. 2 shows a calculation result when the absorption coefficient of the absorption layer 3 is assumed to be 5000 / cm. The horizontal axis “distance [nm] to the light emitting point (x = x1)” in FIG. 2 means the distance from the left end P of the nitride semiconductor light emitting element to the light emitting point. Therefore, “the distance to the light emitting point (x = x1) is 0 nm” means that light is generated at the left end P of the nitride semiconductor light emitting device. “The distance to the light emitting point (x = x1) is 1 × 10 ⁶ nm” means that light is generated at the right end Q of the nitride semiconductor light emitting device. The vertical axis “incident angle [°]” in FIG. 2 represents the incident angle when E || c-polarized light L01 is incident on the lower surface 1A of the n-type nitride semiconductor layer 1 or the upper surface 5B of the p-type nitride semiconductor layer 5. That is, θ _out .

  In practice, the total reflection angle needs to be taken into account. The total reflection angle is determined by the refractive index of the n-type nitride semiconductor layer 1 and the refractive index of the medium in contact with the n-type nitride semiconductor layer 1, and the refractive index of the p-type nitride semiconductor layer 5 and the p-type nitride thereof. It is determined by the refractive index of the medium in contact with the semiconductor layer 5. FIG. 3A shows the relationship between the incident angle and the transmittance T when E || c-polarized light enters the air from the n-type nitride semiconductor layer or the p-type nitride semiconductor layer, and FIG. ) Shows the relationship between the incident angle and the transmittance T when E || c-polarized light enters the sapphire substrate from the n-type nitride semiconductor layer or the p-type nitride semiconductor layer. 3A and 3B, Ts represents the transmittance for S-polarized light, and Tp represents the transmittance for P-polarized light. The incident angle when the transmittance T is 0 is the total reflection angle.

When the n-type nitride semiconductor layer 1 or the p-type nitride semiconductor layer 5 is in contact with air (FIG. 3A), the refractive index of the nitride semiconductor is 2.5, and the refractive index of air is 1. Therefore, the total reflection angle is 24 °. That is, if θ _out > 24 °, the E || c-polarized light L01 is incident on the interface between the n-type nitride semiconductor layer 1 and air (the lower surface 1A of the n-type nitride semiconductor layer 1) at θ _out. It is totally reflected at the interface, is incident at θ _out to the interface between the p-type nitride semiconductor layer 5 and air (the upper surface 5B of the p-type nitride semiconductor layer 5), and is totally reflected at the interface. Focusing on the region where the incident angle is larger than 24 ° in FIG. 2, the longer the distance from the left end P of the nitride semiconductor light emitting element to the light emitting point (x = x1), the standardized intensity (nitride semiconductor light emitting element) It can be seen that the intensity of light observed on the right end Q side of is large. From this, the following can be said. The E || c-polarized light L01 advances from the left end P side of the nitride semiconductor light emitting device to the right end Q side of the nitride semiconductor light emitting device while repeating total reflection inside the nitride semiconductor light emitting device. Therefore, the longer the distance from the left end P of the nitride semiconductor light emitting element to the light emitting point (x = x1), the shorter the distance from the light emitting point to the right end Q. Therefore, the optical path length of the light propagating through the absorption layer 3 while repeating total reflection inside the nitride semiconductor light emitting device is shortened. Therefore, the intensity of light absorbed by the absorption layer 3 is reduced, and finally the light intensity observed at the right end Q is increased.

Further, when the n-type nitride semiconductor layer 1 or the p-type nitride semiconductor layer 5 is in contact with the sapphire substrate (FIG. 3B), the refractive index of the nitride semiconductor is 2.5 and the refractive index of air is 1. .8, and the total reflection angle is 47 °. That is, if θ _out > 47 °, the E || c-polarized light L01 is incident on the interface between the n-type nitride semiconductor layer 1 and the sapphire substrate at θ _out and is totally reflected at the interface, and the p-type nitride semiconductor. It is incident on the interface between the layer 5 and the sapphire substrate at θ _out and is totally reflected at the interface.

When the maximum value of the smaller one of the angles formed by the direction perpendicular to the c-axis and the traveling direction of E || c-polarized light L01 is defined as angle β, θ _out > 24 ° is rewritten using angle β. The angle β <66 ° (= 90 ° -24 °). That is, when the n-type nitride semiconductor layer 1 or the p-type nitride semiconductor layer 5 is in contact with air, the light existing in the range of the angle β <66 ° is the interface between the n-type nitride semiconductor layer 1 and air or Total reflection occurs at the interface between the p-type nitride semiconductor layer 5 and air. Therefore, most of the light traveling in the direction inclined at a predetermined angle from the main surface of the light emitting layer (direction perpendicular to the c-axis) is the interface between the n-type nitride semiconductor layer 1 and air or the p-type nitride semiconductor. Total reflection occurs at the interface between the layer 5 and air.

Actually, in a nitride semiconductor light emitting device, one side is larger than 300 μm (3 × 10 ⁵ nm). Therefore, while light traveling in a direction inclined at a predetermined angle from the main surface of the light emitting layer travels from the left end P of the nitride semiconductor light emitting device to the right end Q of the nitride semiconductor light emitting device, most of the light is absorbed by the absorbing layer. 3 is absorbed. Therefore, the light extracted from the end face of the nitride semiconductor light-emitting element mainly includes E || c-polarized light L01 generated in the vicinity of the end face of the nitride semiconductor light-emitting element, and is centered in a direction perpendicular to the c-axis. The E || c-polarized light L01 generated in the vicinity is hardly included. The E || c-polarized light L01 generated near the center in the direction perpendicular to the c-axis travels through the nitride semiconductor light emitting device while repeating total reflection, and is absorbed by the absorption layer 3 in the nitride semiconductor light emitting device. Therefore, it is difficult to take out the nitride semiconductor light emitting device. Therefore, the light extraction efficiency is reduced.

Based on such considerations, the present inventors have improved the light extraction efficiency of the nitride semiconductor light emitting device when the light emitting layer is an Al _x Ga _1-x N (0.3 ≦ x ≦ 1) layer. Successful. Hereinafter, the present invention will be specifically described with reference to the drawings. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

[First Embodiment]
<Structure of nitride semiconductor light emitting device>
FIG. 4 is a cross-sectional view of the nitride semiconductor light emitting device according to the first embodiment of the present invention. The nitride semiconductor light emitting device 20 of this embodiment includes a first n-type nitride semiconductor layer 25, a second n-type nitride semiconductor layer 27, an active layer 31, a carrier barrier layer 33, and a first p-type nitride semiconductor layer. 35 and a second p-type nitride semiconductor layer 37. Thus, the nitride semiconductor light emitting device 20 includes the n-type nitride semiconductor layer 29 including the first n-type nitride semiconductor layer 25 and the second n-type nitride semiconductor layer 27, the first p-type nitride semiconductor layer 35, and the like. A p-type nitride semiconductor layer 39 including a second p-type nitride semiconductor layer 37 and an active layer 31 provided between the n-type nitride semiconductor layer 29 and the p-type nitride semiconductor layer 39 are provided. The n-type nitride semiconductor layer 29 may be a single layer or may be configured by stacking three or more n-type nitride semiconductor layers. The same can be said for the p-type nitride semiconductor layer 39.

The active layer 31 has a light emitting layer, and preferably has a multiple quantum well structure in which quantum well layers (functioning as a light emitting layer) and barrier layers are alternately stacked. The quantum well layer has a polar surface (C surface in the present embodiment) as a main surface, and is made of Al _x Ga _1-x N (0.3 ≦ x ≦ 1). The Al composition x of the quantum well layer is preferably 0.5 or more, more preferably 0.7 or more. The closer the Al composition x of the quantum well layer is to 1, the more the light emitted from the E || c-polarized light L02 becomes dominant. Therefore, the effect of the present embodiment can be effectively obtained. The “polar plane” is a plane having a plane orientation with an off angle of ± 5 ° with respect to the plane orientation (0001) in addition to the plane having the plane orientation (0001) and the plane having the plane orientation (000-1). And a plane having a plane orientation with an off angle of ± 5 ° with respect to the plane orientation (000-1) is also included.

  A part of the second p-type nitride semiconductor layer 37, the first p-type nitride semiconductor layer 35, the carrier barrier layer 33, the active layer 31, and the second n-type nitride semiconductor layer 27 is etched. An n electrode 41 is provided on the first exposed surface of the second n-type nitride semiconductor layer 27 (the surface of the second n-type nitride semiconductor layer 27 exposed by etching), and the upper surface of the second p-type nitride semiconductor layer 37. Is provided with a p-electrode 43.

FIG. 5 is a cross-sectional view for explaining the propagation of light when E || c-polarized light enters the light extraction surface. In the nitride semiconductor light emitting device 20, the first n-type nitride semiconductor layer 25 is first in a direction parallel to the c-axis ([0001]) of the nitride semiconductor crystal (hereinafter referred to as “c-axis direction”). The light extraction surface 60 is in contact with the medium and at the interface with the first medium. The first medium has a refractive index n ₂ lower than the refractive index n ₁ of the nitride semiconductor, and is air 51 in this embodiment.

A plurality of convex portions 61 are formed on the light extraction surface 60 at intervals. Each of the protrusions 61 protrudes from the first n-type nitride semiconductor layer 25 (a nitride semiconductor layer having a light extraction surface) toward the first medium (air 51), and an interval D between adjacent protrusions 61 is as follows. Formula 1 and the following formula 2 are satisfied.
D ≧ H (1-tan θ ₁ × tan α) / tan α Formula 1
0 <θ ₁ <θ _t Expression 2

In Equation 1 and Equation 2, D, H, θ ₁ , α, and θ _t are as shown in FIG. The interval D between the adjacent convex portions 61 means the size of the flat portion 65 in the c-axis direction. Here, the “flat portion 65” is a portion of the light extraction surface 60 that is located between the adjacent convex portions 61 and on which the convex portions 61 are not formed. H represents the height of the convex portion 61 and means the size of the convex portion 61 in the protruding direction of the convex portion 61, that is, the size of the convex portion 61 in the c-axis direction. θ ₁ represents the inclination angle of the side surface 63 of the convex portion 61, and means the smaller one of the angles formed by the c-axis direction and the side surface 63 of the convex portion 61. α represents the divergence angle of E || c-polarized light L02 centered on a direction perpendicular to the c-axis direction, and E || c-polarized light L02 emitted from the direction perpendicular to the c-axis direction and the quantum well layer. It means the maximum value of the smaller angle among the angles formed by the traveling direction. θ _t represents the total reflection angle of the E || c-polarized light L02, and the incident angle of the E || c-polarized light L02 on the light extraction surface 60 when the E || c-polarized light L02 is totally reflected on the light extraction surface 60. means.

If Expression 1 and Expression 2 are satisfied, at least part of the E || c-polarized light L02 generated in the quantum well layer is incident on the light extraction surface 60 at an angle less than θ _t and is emitted from the light extraction surface 60. Exit. That is, at least part of the E || c-polarized light L02 emitted obliquely from the quantum well layer toward the n-type nitride semiconductor layer 29 side is taken out from the lower portion of the first n-type nitride semiconductor layer 25. Therefore, at least a part of the E || c-polarized light L02 emitted obliquely from the quantum well layer toward the n-type nitride semiconductor layer 29 side can be extracted to the outside of the nitride semiconductor light emitting element 20.

It is known that a part of the E || c-polarized light enters the interface between the nitride semiconductor layer and the first medium as p-polarized light. The transmittance Tp for P-polarized light is larger than the transmittance Ts for S-polarized light, and is 1.0 when the incident angle is a Brewster angle (for example, FIGS. 3A and 3B). Therefore, E || c polarization L02 incident at an angle less than theta _t to the light extraction surface 60 is further easily retrieved to the outside of the nitride semiconductor light emitting device 20.

  In addition, if the above formulas 1 and 2 are satisfied, the E || c-polarized light L02 extracted from the nitride semiconductor light emitting element 20 re-enters the first n-type nitride semiconductor layer 25 from the light extraction surface 60. Can be prevented. As described above, the light extraction efficiency of the nitride semiconductor light emitting device 20 can be increased as compared with the conventional nitride semiconductor light emitting device.

In addition, in the nitride semiconductor light emitting device 20, the light extraction efficiency of E || c-polarized light can be increased without causing a decrease in the light extraction efficiency of E⊥c-polarized light. FIG. 6 is a cross-sectional view for explaining the propagation of light when E⊥c polarized light enters the light extraction surface. Consider the case where the E⊥c polarized light L03 is inclined by θ ₂ from the c-axis direction and is emitted from the quantum well layer and incident on the convex portion 61. In the following, it is assumed that the E⊥c polarized light L03 is inclined to the right with respect to the c axis and is incident on the side surface 63 of the convex portion 61 (FIG. 6). The same can be said for the case where it is inclined to the left and incident on the side surface 63 of the convex portion 61.

When 90 ° −θ ₁ + θ ₂ <θ _t , the E⊥c polarized light L03 is emitted from the light extraction surface 60 to the first medium (air 51) when entering the light extraction surface 60 for the first time. After passing through the first medium with transmittance, it is taken out of the nitride semiconductor light emitting device 20. The light that has not passed through the first medium in the E⊥c polarized light L <b> 03 is reflected by the light extraction surface 60.

When 90 ° −θ ₁ + θ ₂ ≧ θ _t , the E⊥c polarized light L03 is totally reflected by the light extraction surface 60 when incident on the light extraction surface 60 for the first time. If the incident angle θ ₃ <θ _t to the light extraction surface 60 incident after total reflection, the light is extracted from the light extraction surface 60 to the first medium (air 51) and transmitted through the first medium with a specific transmittance. Then, the nitride semiconductor light emitting device 20 is taken out. On the other hand, if the incident angle θ ₃ ≧ θ _t , the light is totally reflected on the light extraction surface 60 and is incident on another light extraction surface (not shown). Here, the incident angle θ ₃ depends on θ ₁ . When (90 ° + θ ₂ )> 3θ ₁ , θ ₃ = (90 ° + θ ₂ ) −3θ ₁ . When (90 ° + θ ₂ ) <3θ ₁ , θ ₃ = 3θ ₁ − (90 ° + θ ₂ ).

The total reflection of the E⊥c polarized light L03 on the light extraction surface 60 is the (n−1) th (where n is a positive integer), and (90 ° + θ ₂ )> (2n−1) θ ₁ , The incident angle when the E⊥c polarized light L03 is incident on the light extraction surface 60 for the nth time is (90 ° + θ ₂ ) − (2n−1) θ ₁ and (90 ° + θ ₂ ) −. When (2n−1) θ ₁ <θ _t , the light exits from the light extraction surface 60 to the first medium (air 51) and passes through the first medium. Similarly, when the total reflection of the E⊥c polarized light L03 on the light extraction surface 60 is the (n−1) th and (90 ° + θ ₂ ) <(2n−1) θ ₁ , the E⊥c The incident angle when the polarized light L03 enters the light extraction surface 60 for the nth time is (2n−1) θ ₁ − (90 ° + θ ₂ ), and (2n−1) θ ₁ − (90 ° + θ ₂ ) < emitted from the light extraction surface 60 to the first medium (air 51) in the case of theta _t, it passes through the first medium. As described above, in this embodiment, it is possible to prevent a decrease in the light extraction efficiency of the polarized light L03 of E 低下 C.

  In summary, if the above formula 1 and formula 2 are satisfied, the E || c-polarized light L02 emitted obliquely from the quantum well layer toward the n-type nitride semiconductor layer 29 side is converted into the first n-type nitride semiconductor. It can be taken out from the lower part of the layer 25 to the outside of the nitride semiconductor light emitting device 20. Furthermore, if the above formula 1 and the above formula 2 are satisfied, the re-incidence of the E || c polarized light L02 extracted from the nitride semiconductor light emitting element 20 can be prevented. For these reasons, the light extraction efficiency of the nitride semiconductor light emitting device 20 can be increased as compared with the conventional nitride semiconductor light emitting device. Further, it is possible to prevent the light extraction efficiency of the E⊥c polarized light L03 from being lowered due to the increased light extraction efficiency of the E || c polarized light L01. Below, each component of the nitride semiconductor light-emitting device 20 is shown concretely.

(First n-type nitride semiconductor layer)
The first n-type nitride semiconductor layer 25 is preferably a layer made of Al _t1 Ga _{1 -t1} N (0 <t1 ≦ 1) and doped with an n-type dopant, more preferably Al _t1 Ga _{A layer made of 1-t1} N (0.6 ≦ t1 ≦ 0.9) is doped with an n-type dopant. Examples of the n-type dopant include Si, Ge, or Sn.

The n-type dopant concentration of the first n-type nitride semiconductor layer 25 is preferably 5 × 10 ¹⁶ / cm ³ or more and 1 × 10 ²¹ / cm ³ or less, more preferably 5 × 10 ¹⁷ / cm ³ or more and 2 × 10. ¹⁹ / cm ³ or less. The thickness of the first n-type nitride semiconductor layer 25 is preferably 0.5 μm or more and 20 μm or less, and more preferably 3 μm or more and 10 μm or less.

(Convex)
In the present embodiment, the lower surface of the first n-type nitride semiconductor layer 25 functions as the light extraction surface 60. Therefore, the convex portion 61 is formed on the lower surface of the first n-type nitride semiconductor layer 25.

  As long as the above formula 1 and the above formula 2 are satisfied, the shapes of the convex portions 61 formed on the light extraction surface 60 may be the same or different from each other. The convex portions 61 may be formed in a stripe shape on the light extraction surface 60, but may be arranged on the light extraction surface 60 in a lattice shape. When the convex part 61 is arrange | positioned at the light extraction surface 60 at the grid | lattice form, it is preferable that the convex part 61 is a cone shape and may be a pyramid shape, but it is more preferable that it is a cone shape.

  If the convex portion 61 is conical, the following effects can be obtained. According to the optical transition selection rule, E || c-polarized light radiates in all directions around the c-axis. That is, according to the selection rule of optical transition, the radiation of E || c-polarized light has no anisotropy when the c-axis is the center. Therefore, if the convex portion 61 has a conical shape, the E || c-polarized light L02 emitted in all directions around the c-axis can be extracted to the outside of the nitride semiconductor light emitting element 20. Therefore, the orientation of the light extracted outside the nitride semiconductor light emitting element 20 becomes omnidirectional around the c axis.

  If the above formula 1 and the above formula 2 are satisfied, the outer shape of the convex portion 61 in the side view may be a triangle or a trapezoid. The side surface 63 of the convex portion 61 in the side view may have a curvature, for example, may be curved or may draw a parabola.

So as to satisfy the above formula 1 and the formula 2, and, E || c as divergence angle alpha of polarization L02 is _{0 <α ≦ 90-θ t} , spacing of the protrusions 61 adjacent D, the convex portion 61 It is preferable to set the height H and the inclination angle θ ₁ of the side surface 63 of the convex portion 61. For example, D is preferably 200 μm or less. As a result, a plurality of convex portions 61 are formed on the light extraction surface 60, so that the effect obtained by providing the convex portions 61 can be obtained. That is, the light extraction efficiency of the nitride semiconductor light emitting device 20 can be effectively increased.

Effective light extraction efficiency of E || c-polarized light existing in the range of 0 <α ≦ 40 ° out of E || c-polarized light obliquely emitted from the quantum well layer toward the n-type nitride semiconductor layer 29 side In order to increase the thickness, θ ₁ is preferably 20 ° or more and 40 ° or less, and H is preferably 0.1 μm or more and 10 μm or less. As a result, most of the E || c-polarized light emitted obliquely from the quantum well layer toward the n-type nitride semiconductor layer 29 side can be extracted from the nitride semiconductor light emitting device 20. At this time, D is 8.3 μm or more and 200 μm or less.

Considering that E || c-polarized light obliquely emitted from the quantum well layer toward the n-type nitride semiconductor layer 29 side is concentrated in the range of 0 <α ≦ 5 °, n It is preferable to effectively enhance the light extraction efficiency of E || c-polarized light existing in the range of 0 <α ≦ 5 ° out of E || c-polarized light emitted obliquely toward the type nitride semiconductor layer 29 side. . For that purpose, θ ₁ is preferably 20 ° or more and 40 ° or less, and H is preferably 0.1 μm or more and 10 μm or less. At this time, D is 111 μm or more and 200 μm or less. In addition, θ ₁ , H, and D can be obtained using a non-contact type step measuring device such as a stylus step meter, a laser microscope, or a scanning electron microscope.

In addition, the number of the convex parts 61 is not limited to the number shown in FIG. Further, in one light extraction surface 60, θ ₁ may be the same or different from each other. For example, in one convex portion 61, one θ ₁ and the other θ ₁ may be different from each other. Further, the adjacent θ ₁ across the flat portion 65 may be different from each other. In either case, θ ₁ may be regularly different or irregularly different. In addition, if the convex part 61 is formed according to the method shown below, the dispersion | variation in (theta) ₁ can be prevented.

  Moreover, in one light extraction surface 60, H may be the same or different from each other. When H is different from each other, H may be regularly different or irregularly different. In addition, if the convex part 61 is formed according to the method shown below, the dispersion | variation in H can be prevented.

  In one light extraction surface 60, D may be the same or different from each other. When D is different from each other, D may be regularly different or irregularly different.

When θ ₁ is different between adjacent convex portions 61, it is preferable to substitute the smaller value for θ ₁ in Equation 1 above. When the adjacent convex portions 61 are different from each other, it is preferable to substitute the larger value for H in Equation (1).

  The connection part of the convex part 61 and the flat part 65, or the front-end | tip of the convex part 61 may be rounded by the restrictions of the manufacturing process of the convex part 61, etc., and has a plane part in part. Also good.

(First medium)
The first medium is not limited to the air 51 as long as it has a refractive index smaller than that of the nitride semiconductor, and may be an inert gas such as nitrogen, argon, or helium. As will be described in a third embodiment described later, the first medium may be a substrate 21 (see FIG. 9 and the like). The first medium may be a dielectric layer or a metal layer formed on the nitride semiconductor layer after the growth of the nitride semiconductor layer, or may be a sealing resin or a fixing resin.

  The first medium may be one type or two or more types. For example, two or more types of first media may be in contact with the light extraction surface 60.

(Second n-type nitride semiconductor layer)
The second n-type nitride semiconductor layer 27 functions as an n-type contact layer. As the second n-type nitride semiconductor layer 27, a layer made of Al _t2 Ga _{1 -t2} N (0 <t2 ≦ 1) and an n-type dopant is preferably used, and more preferably, A layer made of Al _t2 Ga _{1 -t2} N (0.4 ≦ t2 ≦ 0.8) is used in which an n-type dopant is doped.

The n-type dopant concentration of the second n-type nitride semiconductor layer 27 is preferably 5 × 10 ¹⁶ / cm ³ or more and 1 × 10 ²¹ / cm ³ or less, more preferably 5 × 10 ¹⁷ / cm ³ or more and 2 × 10. ¹⁹ / cm ³ or less. The thickness of the second n-type nitride semiconductor layer 27 is preferably 1 μm or more and 20 μm or less, and more preferably 4 μm or more and 10 μm or less.

(Active layer)
The number of quantum well layers and barrier layers in the active layer 31 is not particularly limited, and is preferably 1 or more and 20 or less, more preferably 3 or more and 6 or less.

  The thickness of the quantum well layer of the active layer 31 is preferably 1 nm or more and 15 nm or less, and more preferably 3 nm or more and 12 nm or less.

The barrier layer of the active layer 31 preferably has a band gap energy larger than that of the quantum well layer, and is preferably made of, for example, Al _y Ga _1-y N (0 <y ≦ 1). Is made of Al _y Ga _1-y N (0.7 ≦ y ≦ 0.9). The thickness of the barrier layer is preferably 1 nm or more and 25 nm or less, and more preferably 3 nm or more and 10 nm or less. The barrier layer may contain an n-type dopant and may be undoped.

(Carrier barrier layer)
The carrier barrier layer 33 is a layer provided to prevent electrons injected from the n-type nitride semiconductor layer 29 into the active layer 31 from overflowing into the p-type nitride semiconductor layer 39. The carrier barrier layer 33 preferably includes a p-type dopant, but may be an undoped layer. This p-type dopant may be intentionally doped or may be mixed by diffusion from the p-type nitride semiconductor layer 39.

The carrier barrier layer 33 is preferably made of Al _t3 Ga _{1 -t3} N (0 <t3 ≦ 1), more preferably made of Al _t3 Ga _{1 -t3} N (0.7 ≦ t3 ≦ 0.9). The thickness of the carrier barrier layer 33 is preferably 1 nm or more and 30 nm or less, and more preferably 5 nm or more and 25 nm or less.

(First p-type nitride semiconductor layer)
As the first p-type nitride semiconductor layer 35, a layer in which a p-type dopant is doped in a layer made of Al _t4 Ga _{1 -t4} N (0 <t4 ≦ 1) is preferably used, and more preferably Al _t4 Ga. _{A layer made of 1-t4} N (0.7 ≦ t4 ≦ 0.9) is used in which a p-type dopant is doped. Examples of the p-type dopant include Mg.

The p-type dopant concentration of the first p-type nitride semiconductor layer 35 is preferably 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²⁰ / cm ³ or less, more preferably 5 × 10 ¹⁸ / cm ³ or more and 1 × 10. ²⁰ / cm ³ or less. The thickness of the first p-type nitride semiconductor layer 35 is preferably 0.01 μm or more and 5 μm or less, and more preferably 0.05 μm or more and 1 μm or less.

(Second p-type nitride semiconductor layer)
The second p-type nitride semiconductor layer 37 is preferably a layer made of Al _t5 Ga _{1 -t5} N (0 <t5 ≦ 1) and doped with a p-type dopant, more preferably Al _t5 Ga. _{A layer made of 1-t5} N (0.7 ≦ t5 ≦ 0.9) is used in which a p-type dopant is doped.

The p-type dopant concentration of the second p-type nitride semiconductor layer 37 is preferably 5 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less, more preferably 5 × 10 ¹⁹ / cm ³ or more and 5 × 10. ²⁰ / cm ³ or less. The thickness of the second p-type nitride semiconductor layer 37 is preferably 0.01 μm or more and 0.1 μm or less, and more preferably 0.01 μm or more and 0.05 μm or less.

(N electrode, p electrode)
Each of the n electrode 41 and the p electrode 43 may be a transparent electrode or a non-transparent electrode. Examples of the material for the transparent electrode include metal oxides containing at least one of In, Ga, Zn, and Sn. Examples of the material for the non-transparent electrode include metals such as Al and Ag. Each thickness of the n electrode 41 and the p electrode 43 is preferably 1 nm or more and 10,000 nm or less.

<Manufacture of nitride semiconductor light emitting device>
7A and 7B are cross-sectional views illustrating a method for manufacturing the nitride semiconductor light emitting device 20 in the order of steps. Below, an example of the method of manufacturing the nitride semiconductor light-emitting device 20 shown in FIG. 4 through a dicing process is shown.

(Formation of laminate)
A buffer layer 23, a first n-type nitride semiconductor layer 25, a second n-type nitride semiconductor layer 27, an active layer 31, a carrier barrier layer 33, and a first layer are formed on the upper surface of the substrate 21 (for example, the C surface of a sapphire substrate). A 1p type nitride semiconductor layer 35 and a second p type nitride semiconductor layer 37 are formed in this order. For example, it is preferable to form these layers by MOCVD (Metal Organic Chemical Vapor Deposition). As the substrate 21, a substrate made of sapphire, ZnO, diamond, graphite, graphene, quartz glass, glass other than quartz glass containing SiO ₂ as a main component, or the like can be used. In this way, the laminate shown in FIG. 7A is obtained.

(Peeling the substrate)
The substrate 21 is removed from the obtained laminate. For example, when laser light is irradiated from the substrate 21 side, the laser light is absorbed by the buffer layer 23. As a result, the energy of the laser beam is converted into thermal energy, so that at least a part of the buffer layer 23 evaporates, and the substrate 21 is peeled off. Therefore, the buffer layer 23 or the first n-type nitride semiconductor layer 25 is exposed.

(Formation of light extraction surface)
For example, the mask 45 is formed on the peeling surface (the lower surface of the first n-type nitride semiconductor layer 25 in FIG. 7B. The surface that becomes the light extraction surface 60) by photolithography. Thereafter, the portion of the first n-type nitride semiconductor layer 25 exposed from the mask 45 is removed by, for example, RIE (Reactive Ion Etching). Thereby, the some convex part 61 is formed. At this time, the mask 45 is preferably formed so as to satisfy the above formula 1 and the above formula 2, and the etching condition of the first n-type nitride semiconductor layer 25 is optimized so as to satisfy the above formula 1 and the above formula 2. Is preferred. For example, physical etching may be performed instead of chemical etching, or chemical etching and physical etching may be used in combination.

(Activation of p-type dopant)
Heat treatment is performed to activate the p-type dopant. The p-type dopant doped in the nitride semiconductor crystal is located at the group III atom site by substitution with a group III atom, but is located at the group III atom site in a state bonded to hydrogen. Inactive. Therefore, it is preferable to perform a heat treatment to break the bond between hydrogen and the p-type dopant.

  In this heat treatment, the laminate shown in FIG. 7B is preferably heated at a temperature of 800 ° C. to 900 ° C. for 10 minutes or less. Thereby, unnecessary damage to the nitride semiconductor layer due to this heat treatment (for example, surface roughness of the nitride semiconductor layer due to this heat treatment) can be prevented. This heat treatment is preferably performed in a nitrogen atmosphere or a mixed gas atmosphere of nitrogen and oxygen, but may be performed in a rare gas atmosphere such as Ar or a mixed gas atmosphere of a rare gas and oxygen. When heat treatment is performed in an atmosphere containing oxygen, a reaction between the oxygen and hydrogen bonded to the p-type dopant occurs, so that the bond between hydrogen and the p-type dopant can be effectively cut. However, if the oxygen concentration in the atmosphere is too high, adverse effects such as the formation of an oxide film on the surface of the laminate shown in FIG. Therefore, the oxygen concentration in the atmosphere is preferably 50 ppm or less. For example, this heat treatment is preferably performed using a heat treatment furnace capable of rapid temperature increase / decrease by resistance heating or halogen lamp heating.

(Formation of electrodes)
After etching part of the second p-type nitride semiconductor layer 37, the first p-type nitride semiconductor layer 35, the carrier barrier layer 33, the active layer 31, and the second n-type nitride semiconductor layer 27, the second n-type exposed by this etching is exposed. An n-electrode 41 is formed on the surface of the type nitride semiconductor layer 27. A p-electrode 43 is formed on the upper surface of the second p-type nitride semiconductor layer 37. Thereafter, heat treatment for alloying is performed as necessary, and then dicing is performed to divide the chip. In this way, the nitride semiconductor light emitting device 20 can be obtained.

[Second Embodiment]
FIG. 8 is a cross-sectional view of the nitride semiconductor light emitting device according to the second embodiment of the present invention. Hereinafter, points different from the first embodiment will be mainly described.

  In the nitride semiconductor light emitting device 120, at least a part of the interface between the second p-type nitride semiconductor layer 37 and the first medium (air 51) also functions as the light extraction surface 60. That is, a plurality of convex portions 61 are formed on at least a part of the interface between the second p-type nitride semiconductor layer 37 and the first medium. Each of the protrusions 61 protrudes from the second p-type nitride semiconductor layer 37 (a nitride semiconductor layer having a light extraction surface) toward the first medium. Furthermore, the above formula 1 and the above formula 2 are satisfied.

  In such a nitride semiconductor light emitting device 120, at least part of E || c-polarized light emitted obliquely from the quantum well layer toward the n-type nitride semiconductor layer 29 side is the first n-type nitride semiconductor layer 25. At least part of the E || c-polarized light extracted from the lower part and obliquely emitted from the quantum well layer toward the p-type nitride semiconductor layer 39 side is extracted from the upper part of the second p-type nitride semiconductor layer 37. Thus, since at least part of the E || c-polarized light emitted obliquely from the quantum well layer toward the p-type nitride semiconductor layer 39 side can also be extracted to the outside of the nitride semiconductor light emitting device 120, nitriding The light extraction efficiency of the semiconductor light emitting device 120 can be higher than the light extraction efficiency of the nitride semiconductor light emitting device 20.

At least one of the height H of the convex portion 61, the distance D between the adjacent convex portions 61, the inclination angle θ ₁ of the side surface 63 of the convex portion 61, and the shape of the convex portion 61 includes one light extraction surface 60 and the other light. The take-out surface 60 may be different from each other. In addition, according to the method described in (Formation of light extraction surface) of the first embodiment, the convex portion 61 is formed on at least a part of the interface between the second p-type nitride semiconductor layer 37 and the first medium. Can do.

  As shown in a fifth embodiment to be described later, the first medium may be different from each other on one light extraction surface 60 and the other light extraction surface 60.

  The p-electrode 43 may be provided at a part of the interface between the second p-type nitride semiconductor layer 37 and the first medium (FIG. 8) or may be provided at the entire interface.

  When the p electrode 43 is a transparent electrode, the convex portion 61 may be formed also in a portion where the p electrode 43 is provided in the interface between the second p-type nitride semiconductor layer 37 and the first medium.

  When the p electrode 43 is a non-transparent electrode, the thickness of the p electrode 43 is preferably 50 nm or less, more preferably 20 nm or less. As a result, the E || c polarized light emitted obliquely from the quantum well layer toward the p-type nitride semiconductor layer 39 can be prevented from being absorbed by the p electrode 43. Therefore, the E || c polarized light can be efficiently extracted outside the nitride semiconductor light emitting device 120. However, from the viewpoint of increasing the light extraction efficiency of the nitride semiconductor light emitting device 120, it protrudes at least at a part of the interface between the second p-type nitride semiconductor layer 37 and the first medium where the p-electrode 43 is not provided. It is preferable that the part 61 is formed.

In the case where the convex portion 61 is also formed in the portion where the p-electrode 43 is provided in the interface between the second p-type nitride semiconductor layer 37 and the first medium, the adjacent convex portions are formed as follows. It is preferable to determine the interval D of 61, the height H of the convex portion 61, and the inclination angle θ ₁ of the side surface 63 of the convex portion 61. In the portion where the p-electrode 43 is provided, D, H, and θ ₁ are determined so that the above formulas 1 and 2 are satisfied by using the p-electrode 43 as the first medium. In a portion where the p-electrode 43 is not provided, D, H, and θ ₁ are determined so that the above formulas 1 and 2 are satisfied using the air 51 as the first medium.

Note that the ratio of the interface between the second p-type nitride semiconductor layer 37 and the first medium covered by the p electrode 41 (the coverage of the p electrode 41) is greater than 50%, and In the case of (refractive index) <(refractive index of the second p-type nitride semiconductor layer 37), D, H, and θ ₁ are determined so that the above formulas 1 and 2 are satisfied using the p-electrode 43 as the first medium. It is preferable.

[Third Embodiment]
FIG. 9 is a cross-sectional view of the nitride semiconductor light emitting device according to the third embodiment of the present invention. Hereinafter, points different from the first embodiment will be mainly described.

  In the nitride semiconductor light emitting device 220, the buffer layer 23 (not shown, between the substrate 21 and the first n-type nitride semiconductor layer 25 is actually disposed between the substrate 21 and the first n-type nitride semiconductor layer 25). 7A) functions as the light extraction surface 60. That is, a plurality of convex portions 61 are formed at the interface between the substrate 21 and the first n-type nitride semiconductor layer 25. Each of the protrusions 61 protrudes from the first n-type nitride semiconductor layer 25 toward the substrate 21. Furthermore, the above formula 1 and the above formula 2 are satisfied.

  In such a nitride semiconductor light emitting device 220, the effects described in the first embodiment can be obtained. Therefore, even when the substrate 21 is used as the first medium, the light extraction efficiency of the nitride semiconductor light emitting device 220 can be increased as compared with the conventional nitride semiconductor light emitting device.

Further, in the nitride semiconductor light emitting element 220, since the total reflection angle theta _t is larger than that of the nitride semiconductor light emitting device 20, the inclination angle theta ₁ of the side surface 63 of the convex portion 61 can be made larger than that of the nitride semiconductor light emitting device 20 ( Formula 2) above. Thereby, E || c-polarized light having a larger spread angle α can be extracted from the interface between the substrate 21 and the first n-type nitride semiconductor layer 25 to the substrate 21 side. Therefore, the light extraction efficiency of the nitride semiconductor light emitting device 220 can be higher than the light extraction efficiency of the nitride semiconductor light emitting device 20.

  Note that when a nitride semiconductor layer is grown on a sapphire substrate, a gap may be generated near the interface between the sapphire substrate and the nitride semiconductor layer serving as a light extraction surface depending on the growth conditions of the nitride semiconductor layer. Even in such a case, it is preferable to consider light guiding in the nitride semiconductor light emitting device 20 assuming that no void is generated.

  According to the method described in (Formation of light extraction surface) of the first embodiment, a concave portion is formed on the main surface (C surface in the present embodiment) of the substrate 21, and then the main portion of the substrate 21 on which the concave portion is formed. A first n-type nitride semiconductor layer 25 is formed on the surface. Thereby, a convex portion 61 protruding from the first n-type nitride semiconductor layer 25 to the substrate 21 is formed.

[Fourth Embodiment]
<Configuration of nitride semiconductor light emitting device>
FIG. 10 is a cross-sectional view of the nitride semiconductor light emitting device according to the fourth embodiment of the present invention. In the following, points different from the third embodiment will be mainly shown.

  In the nitride semiconductor light emitting device 320, the third nitride semiconductor layer 26 is provided on the upper surface of the substrate 21 with a buffer layer (not shown) interposed therebetween, and the second n-type nitride is formed on the upper surface of the third nitride semiconductor layer 26. A physical semiconductor layer 27, an active layer 31, and the like are sequentially provided.

As the third nitride semiconductor layer 26, a layer made of Al _t6 Ga _1-t6 N (0 <t6 ≦ 1) is preferably used, and more preferably Al _t6 Ga _1-t6 N (0.1 ≦ t6). ≦ 0.9) is used. The third nitride semiconductor layer 26 is preferably an undoped layer, but may contain an n-type dopant diffused by heat treatment or the like. The thickness of the third nitride semiconductor layer 26 is preferably 0.5 μm or more and 20 μm or less, and more preferably 3 μm or more and 10 μm or less.

  The light extraction surface 60 is also formed on the p-type nitride semiconductor layer 39 side. Specifically, the third nitride semiconductor layer 26 and the substrate are formed on the first exposed surface of the second p-type nitride semiconductor layer 37 (the portion of the upper surface of the second p-type nitride semiconductor layer 37 exposed from the p-electrode 43). 21 are stacked in this order, and the interface between the third nitride semiconductor layer 26 and the substrate 21 functions as the light extraction surface 60. That is, a plurality of convex portions 61 are formed at the interface between the third nitride semiconductor layer 26 and the substrate 21. Each of the protrusions 61 protrudes from the third nitride semiconductor layer 26 toward the substrate 21. Furthermore, the above formula 1 and the above formula 2 are satisfied.

  In such a nitride semiconductor light emitting device 320, at least part of E || c-polarized light emitted obliquely from the quantum well layer toward the n-type nitride semiconductor layer 29 side is the first n-type nitride semiconductor layer 25. At least part of the E || c-polarized light extracted from the lower part and obliquely emitted from the quantum well layer toward the p-type nitride semiconductor layer 39 side is extracted from the upper part of the second p-type nitride semiconductor layer 37. As described above, since at least part of the E || c-polarized light emitted obliquely from the quantum well layer toward the p-type nitride semiconductor layer 39 side can also be extracted to the outside of the nitride semiconductor light emitting device 320, nitriding The light extraction efficiency of the semiconductor light emitting device 320 can be higher than the light extraction efficiency of the nitride semiconductor light emitting devices 20 and 220.

  Note that the third nitride semiconductor layer 26 provided between the substrate 21 and the second n-type nitride semiconductor layer 27 may intentionally contain an n-type dopant, but nitride is formed according to a method described later. When manufacturing the semiconductor light emitting device 320, an undoped layer is preferable.

<Manufacture of nitride semiconductor light emitting device>
According to the method described in the third embodiment, a recess is formed in the main surface (C surface in the present embodiment) of the substrate 21. Thereafter, a buffer layer (not shown) and a third nitride semiconductor layer 26 are sequentially formed on the main surface of the substrate 21 on which the recesses are formed in accordance with the method described in (Formation of laminated body) in the first embodiment. To do. The obtained base material substrate is diced to obtain a first substrate and a second substrate having a substrate area smaller than that of the first substrate.

  Next, the second n-type nitride semiconductor layer 27, the active layer 31 and the like are formed on the upper surface of the third nitride semiconductor layer 26 of the first substrate according to the method described in (Formation of stacked body) of the first embodiment. Are formed in order. Thereafter, (activation of the p-type dopant) and (formation of the electrode) described in the first embodiment are sequentially performed. Thereafter, the second substrate is placed on the first exposed surface of the second p-type nitride semiconductor layer 37 so that the third nitride semiconductor layer 26 of the second substrate contacts the first exposed surface of the second p-type nitride semiconductor layer 37. Provide. In this way, the nitride semiconductor light emitting device 320 can be obtained.

[Fifth Embodiment]
FIG. 11 is a cross-sectional view of a nitride semiconductor light emitting device according to the fifth embodiment of the present invention. In the following, differences from the second and third embodiments will be mainly described.

  In the nitride semiconductor light emitting device 420, at least a part of the interface between the second p-type nitride semiconductor layer 37 and the first medium (air 51) also functions as the light extraction surface 60. That is, as described in the second embodiment, a plurality of convex portions 61 are formed on at least a part of the interface between the second p-type nitride semiconductor layer 37 and the first medium. Protrudes from the second p-type nitride semiconductor layer 37 toward the first medium, and Expression 1 and Expression 2 are satisfied.

  In such a nitride semiconductor light emitting device 420, at least part of E || c-polarized light emitted obliquely from the quantum well layer toward the n-type nitride semiconductor layer 29 side is the first n-type nitride semiconductor layer 25. At least part of the E || c-polarized light extracted from the lower part and obliquely emitted from the quantum well layer toward the p-type nitride semiconductor layer 39 side is extracted from the upper part of the second p-type nitride semiconductor layer 37. As described above, since at least part of the E || c-polarized light emitted obliquely from the quantum well layer toward the p-type nitride semiconductor layer 39 side can also be extracted to the outside of the nitride semiconductor light emitting device 420, nitriding The light extraction efficiency of the semiconductor light emitting device 420 can be higher than the light extraction efficiency of the nitride semiconductor light emitting devices 20 and 220.

  In the nitride semiconductor light emitting device 420, one light extraction surface 60 is in contact with the air 51, while the other light extraction surface 60 is in contact with the substrate 21. Even in such a case, the same effect as that of the nitride semiconductor light emitting device 320 can be obtained.

  The positional relationship between the p-electrode 43 and the convex portion 61 described in the second embodiment can also be said in this embodiment.

[Sixth Embodiment]
<Configuration of nitride semiconductor light emitting device>
FIG. 12 is a cross-sectional view of the nitride semiconductor light emitting device according to the sixth embodiment of the present invention. The nitride semiconductor light emitting device 520 is a vertical structure nitride semiconductor light emitting device, and includes a second n-type nitride semiconductor layer 27, an active layer 31, a carrier barrier layer 33, a first p-type nitride semiconductor layer 35, and a second p-type. Nitride semiconductor layers 37 are sequentially stacked. A p-electrode 43 is provided on the upper surface of the second p-type nitride semiconductor layer 37.

  In the nitride semiconductor light emitting device 520, at least part of the interface between the second n-type nitride semiconductor layer 27 and the first medium (air 51) functions as the light extraction surface 60. That is, a plurality of convex portions 61 are formed on at least a part of the interface between the second n-type nitride semiconductor layer 27 and the first medium. Each of the convex portions 61 protrudes from the second n-type nitride semiconductor layer (nitride semiconductor layer having a light extraction surface) 27 toward the first medium. Furthermore, the above formula 1 and the above formula 2 are satisfied.

  In such a nitride semiconductor light emitting device 520, at least part of E || c polarized light emitted obliquely from the quantum well layer toward the second n-type nitride semiconductor layer 27 side is the second n-type nitride semiconductor layer 27. It is taken out from the lower part. Therefore, the light extraction efficiency of the nitride semiconductor light emitting device 520 can be increased as compared with the conventional nitride semiconductor light emitting device. Such an effect becomes more prominent than when the light extraction surface 60 is formed in a lateral structure nitride semiconductor light emitting device (for example, the nitride semiconductor light emitting device 20).

  Specifically, the nitride semiconductor light emitting device having a vertical structure is thinner than the nitride semiconductor light emitting device having a horizontal structure. For this reason, the vertical structure nitride semiconductor light emitting device has a larger number of times of total reflection of E || c-polarized light in the nitride semiconductor light emitting device than the lateral structure nitride semiconductor light emitting device, so that the light extraction efficiency is increased. It is easy to cause a drop in However, as shown in the first embodiment and the like, when the light extraction surface 60 is formed, it is possible to prevent a decrease in light extraction efficiency. Therefore, the effect obtained by forming the light extraction surface 60 is more remarkable in the nitride semiconductor light emitting device having the vertical structure than in the nitride semiconductor light emitting device having the horizontal structure.

  The n electrode 41 may be formed at a part of the interface between the second n-type nitride semiconductor layer 27 and the first medium (FIG. 12), or may be provided over the entire interface.

  When the n electrode 41 is a transparent electrode, the convex portion 61 may be formed also in a portion where the n electrode 41 is provided in the interface between the second n-type nitride semiconductor layer 27 and the first medium.

  When the n electrode 41 is a non-transparent electrode, the thickness of the n electrode 41 is preferably 50 nm or less, and more preferably 20 nm or less. As a result, the E || c polarized light emitted obliquely from the quantum well layer toward the second n-type nitride semiconductor layer 27 can be prevented from being absorbed by the n electrode 41. Therefore, the E || c polarized light can be efficiently extracted outside the nitride semiconductor light emitting device 520. However, from the viewpoint of increasing the light extraction efficiency of the nitride semiconductor light-emitting device 520, at least a portion of the interface between the second n-type nitride semiconductor layer 27 and the first medium where the n-electrode 41 is not provided is projected. It is preferable that the part 61 is formed.

When the convex part 61 is formed also in the part in which the n electrode 41 is provided among the interfaces between the second n-type nitride semiconductor layer 27 and the first medium, adjacent convex parts as shown below. It is preferable to determine the interval D of 61, the height H of the convex portion 61, and the inclination angle θ ₁ of the side surface 63 of the convex portion 61. In the portion where the n-electrode 41 is provided, D, H, and θ ₁ are determined so that the above formulas 1 and 2 are satisfied with the n-electrode 41 as the first medium. In a portion where the n-electrode 41 is not provided, D, H, and θ ₁ are determined so that the above formulas 1 and 2 are satisfied using the air 51 as the first medium.

The ratio of the interface between the second n-type nitride semiconductor layer 27 and the first medium that is covered by the n electrode 41 (the coverage of the n electrode 41) is greater than 50%, and (the n electrode 41 In the case of (refractive index) <(refractive index of the second n-type nitride semiconductor layer 27), D, H, and θ ₁ are determined so that the above formulas 1 and 2 are satisfied with the n electrode 41 as the first medium. It is preferable.

  Further, at least a part of the interface between the second n-type nitride semiconductor layer 27 and the first medium may function as the light extraction surface 60. In this case, the n-electrode 41 is preferably a reflective electrode.

<Manufacture of nitride semiconductor light emitting device>
After the stacked body is formed according to the method described in (Formation of stacked body) of the first embodiment, the substrate 21, the buffer layer 23, and the first n-type nitride semiconductor layer 25 are removed by RIE. Thereby, the second n-type nitride semiconductor layer 27 is exposed. Thereafter, the nitride semiconductor light emitting device 520 is manufactured according to the method described in (Formation of light extraction surface), (Activation of p-type dopant), and (Formation of electrode) of the first embodiment.

[Seventh Embodiment]
FIG. 13 is a cross-sectional view of a nitride semiconductor light emitting device according to the seventh embodiment of the present invention. In the following, points different from the sixth embodiment will be mainly shown.

  In the nitride semiconductor light emitting device 620, at least a part of the interface between the second p-type nitride semiconductor layer 37 and the first medium (air 51) also functions as the light extraction surface 60. That is, a plurality of convex portions 61 are formed on at least a part of the interface between the second p-type nitride semiconductor layer 37 and the first medium. Each of the protrusions 61 protrudes from the second p-type nitride semiconductor layer 37 toward the first medium. Furthermore, the above formula 1 and the above formula 2 are satisfied.

  In such a nitride semiconductor light emitting device 620, at least part of the E || c-polarized light emitted obliquely from the quantum well layer toward the n-type nitride semiconductor layer 29 side is the second n-type nitride semiconductor layer 27. At least part of the E || c-polarized light extracted from the lower part and obliquely emitted from the quantum well layer toward the p-type nitride semiconductor layer 39 side is extracted from the upper part of the second p-type nitride semiconductor layer 37. As described above, since at least part of the E || c-polarized light emitted obliquely from the quantum well layer toward the p-type nitride semiconductor layer 39 side can also be extracted to the outside of the nitride semiconductor light emitting device 620, nitriding is performed. The light extraction efficiency of the semiconductor light emitting device 620 can be higher than the light extraction efficiency of the nitride semiconductor light emitting device 520.

  The positional relationship between the p-electrode 43 and the convex portion 61 described in the second embodiment can also be said in this embodiment.

[Summary of Embodiment]
For example, the nitride semiconductor light emitting device 20 shown in FIG. 4 includes a light emitting layer and at least one nitride semiconductor layer 27 different from the light emitting layer. The light emitting layer has a polar surface as a main surface, and is made of Al _x Ga _1-x N (0.3 ≦ x ≦ 1). At least one nitride semiconductor layer 27 is in contact with a first medium having a refractive index lower than that of the nitride semiconductor in a direction parallel to the c-axis of the nitride semiconductor crystal, and at least at the interface with the first medium. A part has a light extraction surface 60. The light extraction surface 60 is formed with a plurality of convex portions 61 that protrude from the nitride semiconductor layer 27 having the light extraction surface 60 toward the first medium. The following formula 1 and the following formula 2 are satisfied. In the following formula 1 and the following formula 2, D represents the interval between the adjacent convex portions 61, H represents the height of the convex portion 61, θ ₁ represents the inclination angle of the side surface 63 of the convex portion 61, and α represents c The divergence angle of E || c polarization centered on the direction perpendicular to the axis is represented, and θ _t represents the total reflection angle of E || c polarization. Thereby, when the Al composition of the light emitting layer is high, the light extraction efficiency of the nitride semiconductor light emitting device 20 can be increased.
D ≧ H (1−tan θ ₁ × tan α) / tan α (Formula 1)
0 <θ ₁ <θ _t Expression 2

In Formula 1 and Formula 2, D is preferably 200 μm or less. In the above formulas 1 and 2, when 0 <α ≦ 40 °, θ ₁ is preferably 20 ° or more and 40 ° or less, and H is preferably 0.1 μm or more and 10 μm or less.

  The convex portion 61 preferably has a conical shape. Thereby, the orientation of the light extracted outside the nitride semiconductor light emitting device 20 becomes omnidirectional around the c-axis.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Example 1>
In Example 1, the nitride semiconductor light emitting device shown in FIG. 1 was manufactured.

(Formation of laminate)
First, etching was performed at 1250 ° C. for 10 minutes on the C surface of the sapphire substrate in a hydrogen atmosphere.

  Next, after carrying the sapphire substrate into the reactor of the MOCVD apparatus and placing it on the susceptor in the reactor, the temperature of the sapphire substrate was lowered to 900 ° C. An AlN buffer layer (thickness: 300 nm) was grown on the C surface of the sapphire substrate using hydrogen as a carrier gas and TMA (trimethylaluminum) and ammonia as source gases. Then, after raising the temperature of the sapphire substrate to 1175 ° C., an AlN layer (thickness of 5 μm) is grown on the upper surface of the AlN buffer layer using hydrogen as a carrier gas and TMA and ammonia as source gases. It was.

  Subsequently, using hydrogen as a carrier gas, TMA, trimethylgallium (TMG), ammonia and silane (silane diluted with hydrogen (40 ppm)) as source gases, an n-type AlGaN layer (thickness of 2 μm) is formed. It was grown on the top surface of the AlN layer.

Subsequently, Al _0.9 Ga _0.1 N layer (thickness 10 nm, barrier layer) and Al _0.6 Ga _0.4 N layer (thickness 5 nm, using TMA, TMG and ammonia as source gases) A multiple quantum well structure (active layer, 3 periods) composed of (quantum well layer) was grown on the upper surface of the n-type AlGaN layer.

  Subsequently, an AlN layer (thickness: 10 nm, carrier barrier layer) was grown on the upper surface of the multiple quantum well structure using hydrogen as a carrier gas and TMA and ammonia as source gases.

Subsequently, using hydrogen as a carrier gas and using TMA, TMG, ammonia and Cp ₂ Mg (cyclopentadienylmagnesium), a p-type Al _0.8 Ga _0.2 N layer (thickness: 100 nm) is formed on the upper surface of the AlN layer. Grown up. Thereafter, after the supply of TMA was stopped, a p-type GaN layer (thickness: 50 nm) was grown on the upper surface of the p-type Al _0.8 Ga _0.2 N layer. In this way, a laminate was obtained.

(Peeling the substrate)
The obtained laminated body was taken out from the MOCVD apparatus. The lower surface of the sapphire substrate of the laminate was irradiated with laser light from an ArF excimer laser to peel off the sapphire substrate.

(Formation of light extraction surface)
A mask made of SiO ₂ (line width: 2 μm, interval: 60 μm, stripe shape) was formed on the peeling surface (surface generated by peeling off the sapphire substrate) by photolithography. At this time, the longitudinal direction of the mask was parallel to the m-axis direction of the AlN layer. Thereafter, the portion where the mask was not formed was etched by RIE to a depth of about 2 μm using Cl ₂ and SiCl ₄ . Thereafter, the mask was removed using an HF-based etchant. Thereby, the convex portion (the height H of the convex portion is about 2 μm, the interval D between the adjacent convex portions is about 60 μm, and the inclination angle θ ₁ of the side surface of the convex portion is about 20 °) is the peeling surface (light extraction surface). Been formed.

When the interface between the AlN layer and air is the light extraction surface, the total reflection angle θ _t is 24 ° (described above). Here, assuming that α = 10 °, D ≧ 10.5 μm from the above equation 1. Therefore, in the present embodiment, the above Equation 1 is satisfied.

(Activation of p-type dopant)
The laminated body on which the convex portions were formed was heat-treated at 850 ° C. for 2 minutes in a mixed gas atmosphere containing nitrogen and 5 ppm oxygen. Thereby, the p-type dopant was activated.

(Formation of electrodes)
After forming an electrode pattern and an etching pattern by photolithography, etching was performed by RIE. Thereby, a part of the n-type AlGaN layer was exposed.

  Next, an n-electrode was formed on the exposed surface of the n-type AlGaN layer, and a p-electrode was formed on the upper surface of the p-type GaN layer. Thereafter, after heat treatment, dicing was performed to divide the chip. Thus, the nitride semiconductor light emitting device of this example was obtained.

<Example 2>
The nitride semiconductor light emitting device of this example was manufactured according to the method described in Example 1 except that a recess was formed on the C surface of the sapphire substrate and then crystal growth was performed on the C surface.

Specifically, a mask (line width: 60 μm, interval: 2 μm, stripe shape) made of SiO ₂ was formed on the C surface of the sapphire substrate by photolithography. Thereafter, the portion where the mask was not formed was etched by RIE to a depth of about 2 μm using Cl ₂ and SiCl ₄ . Thereafter, the mask was removed using an HF-based etchant. As a result, a concave portion (the depth of the concave portion is about 2 μm, the interval between adjacent concave portions is about 60 μm, and the inclination angle of the side surface of the concave portion is about 40 ° is formed on the peeling surface (light extraction surface). Was formed on the C surface of the sapphire substrate.

Next, an AlN buffer layer was formed on the C surface of the sapphire substrate in which the recesses were formed. Thus, a convex portion (the height H of the convex portion is about 2 μm, the interval D between adjacent convex portions is about 60 μm, and the inclination angle θ ₁ of the side surface of the convex portion is about 40 °) is formed on the lower surface of the AlN buffer layer. Been formed.

When the interface between the AlN layer and the sapphire substrate is the light extraction surface, the total reflection angle θ _t is 47 ° (described above).

<Example 3>
A nitride semiconductor light emitting device of this example was manufactured according to the method described in Example 1 except that the conical convex portion was formed. Specifically, after peeling the sapphire substrate, a mask made of SiO ₂ (diameter: 2 μm, interval: 60 μm) was formed in a lattice shape on the peeling surface (the surface generated by peeling the sapphire substrate) by photolithography. Thereafter, etching was performed according to the method described in Example 1 above. As a result, the conical convex portion (the height H of the convex portion is about 2 μm, the interval D between the adjacent convex portions is about 60 μm, the inclination angle θ ₁ of the side surface of the convex portion is about 20 °), and the peeling surface (light extraction) Surface).

<Comparative Example 1>
According to the method described in Example 1, except that the nitride semiconductor light emitting device was manufactured without performing (the formation of the light extraction surface) described in Example 1, the nitride semiconductor light emitting of Comparative Example 1 A device was manufactured.

<Comparative Examples 2-5>
Except that the convex portions are formed on the light extraction surface so that the interval D between the adjacent convex portions, the height H of the convex portions, and the inclination angle θ ₁ of the side surfaces of the convex portions have the values shown in Table 1. According to the method described in Example 1, the nitride semiconductor light emitting devices of Comparative Examples 2 to 5 were manufactured.

(Discussion)
The light extraction efficiency was measured for the nitride semiconductor light emitting devices of Examples 1 to 3 and Comparative Examples 1 to 5. The results are shown in Table 1.

In Table 1, “D (μm)” represents the interval between adjacent convex portions, “H (μm)” represents the height of the convex portion, and “θ ₁ (°)” represents the inclination angle of the side surface of the convex portion. “Θ _t (°)” represents the total reflection angle of E || c-polarized light. The “lower limit value (μm) of D in Formula 1” represents the lower limit value of D calculated by substituting H, θ _1, and α (α = 5 °) into Formula 1 above.

  As shown in Table 1, in Examples 1 to 3, the light extraction efficiency was higher than that of Comparative Example 1. The reason is that the light extraction surface is formed in Examples 1 to 3, whereas the light extraction surface is not formed in Comparative Example 1.

  In Examples 1 to 3, the light extraction efficiency was higher than those of Comparative Examples 2 to 5. As the reason, in Examples 1-3, the said Formula 1 and the said Formula 2 are satisfy | filled, but in the Comparative Examples 2-5, the said Formula 1 and the said Formula 2 are not satisfy | filled.

  In Example 2, the light extraction efficiency was higher than in Example 1. The reason is that in Example 2, since the first medium is a sapphire substrate, E || c-polarized light having a larger spread angle α is extracted outside the nitride semiconductor light emitting device.

  In Example 3, the light extraction efficiency was higher than in Example 1. The reason is that in Example 3, since the convex portion has a conical shape, the E || c polarized light radiated in all directions around the c-axis is taken out of the nitride semiconductor light emitting device.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1,29 n-type nitride semiconductor layer, 1A lower surface, 3 quantum well layer, 5,39 p-type nitride semiconductor layer, 5B upper surface, 20, 120, 220, 320, 420, 520, 620 nitride semiconductor light emitting device, 21 substrate, 23 buffer layer, 25 1st n-type nitride semiconductor layer, 26 3rd nitride semiconductor layer, 27 2nd n-type nitride semiconductor layer, 31 active layer, 33 carrier barrier layer, 35 1st p-type nitride semiconductor layer 37 second p-type nitride semiconductor layer, 41 n electrode, 43 p electrode, 45 mask, 51 air, 60 light extraction surface, 61 convex portion, 63 side surface, 65 flat portion.

Claims (4)

A nitride semiconductor light emitting device comprising a light emitting layer and at least one nitride semiconductor layer different from the light emitting layer,
The light emitting layer has a polar surface as a main surface, and is made of Al _x Ga _1-x N (0.3 ≦ x ≦ 1).
The at least one nitride semiconductor layer is in contact with a first medium having a lower refractive index than the nitride semiconductor in a direction parallel to the c-axis of the nitride semiconductor crystal, and an interface with the first medium Having a light extraction surface on at least a part of
The light extraction surface is formed with a plurality of protrusions protruding from the nitride semiconductor layer having the light extraction surface toward the first medium,
A nitride semiconductor light emitting device satisfying the following formula 1 and the following formula 2.
D ≧ H (1−tan θ ₁ × tan α) / tan α (Formula 1)
0 <θ ₁ <θ _t・ ・ ・ Formula 2
In Formula 1 and Formula 2, D represents the interval between the adjacent convex portions, H represents the height of the convex portion, θ ₁ represents the inclination angle of the side surface of the convex portion, and α represents the c The divergence angle of E || c polarization centered in a direction perpendicular to the axis is represented, and θ _t represents the total reflection angle of the E || c polarization.   The nitride semiconductor light-emitting element according to claim 1, wherein D in Formula 1 is 200 μm or less. 3. The nitriding according to claim 2, wherein in the above formulas 1 and 2, when 0 <α ≦ 40 °, θ ₁ is 20 ° or more and 40 ° or less, and H is 0.1 μm or more and 10 μm or less. Semiconductor light emitting device.   The nitride semiconductor light emitting element according to claim 1, wherein the convex portion has a conical shape.