Light-emitting element

Abstract

[Problem] The present disclosure provides a light-emitting element capable of increasing the conductivity of a conductive film and suppressing a decrease in light transmissivity. [Solution] To solve the problem, the present disclosure provides a light-emitting element comprising: a first compound semiconductor layer having a first surface and a second surface on the opposite side to the first surface; an active layer facing the second surface of the first compound semiconductor layer; and a second compound semiconductor layer having a first surface facing the active layer and a second surface on the opposite side to the first surface, the second compound semiconductor layer having a different conductivity type from the first compound semiconductor layer, wherein the impurity concentration profile, which shows a position along the stacking direction of the first compound semiconductor layer, the active layer, and the second compound semiconductor layer, and the concentration of the position, has a low-doped region showing a localized decrease.

Description

Light-emitting element

[0001] The present disclosure relates to light-emitting devices.

[0002] In a light-emitting device consisting of a vertical cavity surface-emitting laser (VCSEL), laser oscillation is typically generated by resonating laser light between two optically reflective layers (Distributed Bragg Reflector layer, DBR layer). In such a light-emitting device, for example, a stacked structure is formed in which a first compound semiconductor layer, a light-emitting layer (active layer) consisting of a compound semiconductor, and a second compound semiconductor layer are stacked. A second electrode consisting of a light-transmitting conductive film is then formed on the second compound semiconductor layer, and a second optically reflective layer consisting of a thin-film stacked structure is formed on the second electrode. In order to improve light-emitting efficiency, it is necessary to increase the light transmittance.

[0003] International Publication No. 2018 / 083877

[0004] However, increasing the light transmittance may result in a decrease in the electrical conductivity of the laminated structure.

[0005] Therefore, the present disclosure provides a light-emitting element that can increase light transmittance and suppress a decrease in the conductivity of the laminated structure.

[0006] In order to solve the above-mentioned problems, the present disclosure provides a light-emitting device comprising: a first compound semiconductor layer having a first surface and a second surface facing the first surface; an active layer facing the second surface of the first compound semiconductor layer; and a second compound semiconductor layer having a first surface facing the active layer and a second surface facing the first surface, the second compound semiconductor layer having a conductivity type different from that of the first compound semiconductor layer, wherein the light-emitting device has a lightly doped region at a position along a stacking direction of the first compound semiconductor layer, the active layer, and the second compound semiconductor layer, and an impurity concentration profile indicating the impurity concentration at the position locally decreases.

[0007] The lightly doped region may have a minimum point indicating a lowest concentration, the first compound semiconductor layer may be made of an n-type semiconductor, and the second compound semiconductor layer may be made of a p-type semiconductor.

[0008] The peak position of the optical field intensity of the standing wave of the oscillated light in the first compound semiconductor layer, the active layer, and the second compound semiconductor layer may correspond to the lightly doped region of the impurity concentration profile.

[0009] The peak position of the optical field intensity may correspond to the minimum point of the low-doped region.

[0010] The impurity concentration in the lightly doped region may linearly decrease and linearly increase along the stacking direction.

[0011] The impurity concentration profile in the lightly doped region may be configured as a curve in which the differential of the change in concentration with respect to the change in the position along the stacking direction is continuous.

[0012] The impurity concentration in the lightly doped region may decrease and increase stepwise along the stacking direction.

[0013] The lightly doped region may be in at least one of the first compound semiconductor layer and the second compound semiconductor layer.

[0014] The minimum impurity concentration of the lightly doped region in the first compound semiconductor layer may be equal to or less than half the average impurity concentration in the first compound semiconductor layer.

[0015] The minimum value of the impurity concentration of the lightly doped region in the second compound semiconductor layer may be equal to or less than half of the average impurity concentration in the second compound semiconductor layer.

[0016] The lightly doped regions may be plural, and the interval between the lightly doped regions may be within ±10% of an integral multiple of the length obtained by dividing the oscillation wavelength of the element by twice the refractive index.

[0017] The device may further include a first reflective layer on the first surface side of the first compound semiconductor layer, and a second reflective layer facing the second surface of the second compound semiconductor layer, wherein a distance from an interface of at least one of the first reflective layer and the second reflective layer to the lightly doped region may be within ±10% of an integer multiple of a length obtained by dividing an oscillation wavelength of the device by four times a refractive index.

[0018] The width of the lightly doped region along the stacking direction may be configured to be thinner than the thickness divided by eight times the refractive index of the oscillation wavelength of the element.

[0019] In the impurity concentration profile, a width of a portion where the impurity concentration is one order of magnitude higher than the minimum value of the impurity concentration of the lightly doped region may be 30 nm or less.

[0020] The width may be 10 nm or less.

[0021] The n-type impurity in the first compound semiconductor layer may be at least one of Si, Ge, Se, SnC, Te, S, O, Pd, and Po, and the p-type impurity in the second compound semiconductor layer may be at least one of Mg, Zn, Cd, Be, Ca, Ba, C, Hg, and Sr.

[0022] The semiconductor device may further include a compound semiconductor substrate facing the first surface in the first compound semiconductor layer, and the material of the compound semiconductor substrate may be a III-V group compound semiconductor containing at least any one of GaN, GaAs, and InP.

[0023] The semiconductor device may further include a compound semiconductor substrate facing the first surface in the first compound semiconductor layer, and the compound semiconductor substrate may be a polar or semi-polar substrate.

[0024] The optical element may further include a first reflective layer on the first surface side of the first compound semiconductor layer, and the first reflective layer may have a concave mirror structure.

[0025] The resonator may further include a first reflective layer on the first surface side of the first compound semiconductor layer, and a second reflective layer facing the second surface of the second compound semiconductor layer, wherein the resonator in which the standing wave exists is composed of a region of the first optical reflective layer from the first surface of the first compound semiconductor layer to a certain depth, the first compound semiconductor layer, the active layer, and the second compound semiconductor layer, and a region of the second optical reflective layer from the second surface of the second compound semiconductor layer to a certain depth, and may have a length of 5 μm or more.

[0026] 10 is a schematic partial cross-sectional view showing an example configuration of a light-emitting device according to an embodiment of the present disclosure; FIG. 11 is a diagram showing an impurity concentration profile in a first compound semiconductor layer; FIG. 12 is a diagram showing the intensity of a standing wave in a resonator; FIG. 13 is a diagram showing a simulation result showing the output characteristics of a light-emitting device; FIG. 14 is a diagram showing an impurity concentration profile in a first compound semiconductor layer according to a second embodiment; FIG. 15 is a diagram showing an impurity concentration profile in a first compound semiconductor layer according to a third embodiment; FIG. 16 is a diagram showing an impurity concentration profile in a first compound semiconductor layer according to a fourth embodiment; FIG. 17 is a diagram showing an impurity concentration profile in a first compound semiconductor layer according to a fifth embodiment; FIG. 18 is a diagram showing an impurity concentration profile in a second compound semiconductor layer; and FIG. 19 is a schematic cross-sectional view showing a part of a stack according to a seventh embodiment.

[0027] Hereinafter, embodiments of a light-emitting device will be described with reference to the drawings. The following description will focus on the main components of the light-emitting device, but the light-emitting device may include components and functions not shown or described. The following description does not exclude components and functions not shown or described. Furthermore, when the first light-reflecting layer is cut along a virtual plane including the stacking direction of the stacked structure, the figure drawn by the interface of a portion of the concave mirror portion of the first light-reflecting layer facing the stacked structure can be a portion of a circle or a parabola. The figure may not strictly be a portion of a circle or a parabola. In other words, even if the figure is roughly a portion of a circle or a parabola, it is still included in the definition of "a figure being a portion of a circle or a parabola." Such a portion (region) of the first light-reflecting layer that is a portion of a circle or a parabola may be referred to as the "effective area of ​​the concave mirror portion of the first light-reflecting layer." The figure drawn by the interface of a portion of the concave mirror portion facing the stacked structure can be determined by measuring the shape of the interface with a measuring instrument and analyzing the obtained data using the least squares method.

[0028] 1 is a schematic partial cross-sectional view showing an example of the configuration of a light-emitting device 1 according to an embodiment of the present disclosure. In this embodiment, an axis passing through the center of a resonator formed by two light-reflecting layers is defined as the Z-axis, and an imaginary plane perpendicular to the Z-axis is sometimes referred to as the XY plane. In addition, in this embodiment, a semiconductor laser element formed from a surface-emitting laser element is referred to as a "light-emitting element."

[0029] The light-emitting element 1 according to this embodiment is configured by laminating a first optical reflection layer 41, a compound semiconductor substrate 11, a stacked structure 20, and a second optical reflection layer 42. The stacked structure 20 is configured by laminating, from the first optical reflection layer 41 side, a first compound semiconductor layer 21, a light-emitting layer (active layer 23) 23, and a second compound semiconductor layer 22. That is, the light-emitting element 1 according to this embodiment is a surface-emitting laser element (vertical cavity laser, VCSEL) that emits laser light from the top surface of the second compound semiconductor layer 22 via the second optical reflection layer 42.

[0030] More specifically, the light-emitting element 1 according to this embodiment includes: (A) a stacked structure 20 made of GaN-based compound semiconductors, in which a first compound semiconductor layer 21 having a first surface 21 a and a second surface 21 b facing the first surface 21 a and having a first conductivity type (specifically, n-type), an active layer 23 (light-emitting layer) 23 facing the second surface 21 b of the first compound semiconductor layer 21, and a second compound semiconductor layer 22 having a first surface 22 a facing the active layer 23 and a second surface 22 b facing the first surface 22 a and having a second conductivity type (specifically, p-type), (B) a first light-reflecting layer 41 disposed on the first surface 21 a side of the first compound semiconductor layer 21; and (C) a second light-reflecting layer 42 disposed on the second surface 22 b side of the second compound semiconductor layer 22. The first light reflecting layer 41 has a concave mirror portion 43, and the second light reflecting layer 42 has a flat shape. A compound semiconductor substrate 11 is disposed between the first surface 21a of the first compound semiconductor layer and the first light reflecting layer 41. The compound semiconductor substrate 11 is made of a GaN substrate. For example, the material of the compound semiconductor substrate 11 is a III-V group compound semiconductor containing at least one of GaN, GaAs, and InP.

[0031] A resonator is formed by the region of the first light reflecting layer 41 extending from the first surface 21 a of the first compound semiconductor layer 21 to a certain depth, the stacked structure 20 (the first compound semiconductor layer 21, the active layer 23, and the second compound semiconductor layer 22), and the region of the second light reflecting layer 42 extending from the second surface 22 b of the second compound semiconductor layer 22 to a certain depth. Here, when the resonator length is Lor, the resonator is configured to satisfy, for example, the resonator length Lor > 5 micrometers (μm), and the emission wavelength is, for example, 445 nm. Note that this configuration is merely an example and is not limiting.

[0032] When the first light reflecting layer 41 is cut along an imaginary plane including the stacking direction of the stacked structure 20, the figure drawn by the interface of a part of the concave mirror portion 43 of the first light reflecting layer 41 (the effective area of ​​the concave mirror portion 43 of the first light reflecting layer 41) facing the stacked structure 20 is a part of a circle or a part of a parabola. Note that the shape (cross-sectional figure) of the part of the concave mirror portion 43 located outside the effective area does not have to be a part of a circle or a part of a parabola.

[0033] The first compound semiconductor layer 21 is made of an n-type semiconductor, and the impurity concentration profile along the Z-axis has a region where it locally decreases. A detailed configuration example of the first compound semiconductor layer 21 will be described later. The active layer 23 has a five-layer multiple quantum well structure in which, for example, In0.04Ga0.96N layers (barrier layers) and In0.16Ga0.84N layers (well layers) are stacked, and the second compound semiconductor layer 22 is made of a p-type semiconductor.

[0034] The first electrode 31 is formed on the third surface 21c of the first compound semiconductor layer 21. The first electrode 31 is made of, for example, Ti / Pt / Au. A pad electrode (not shown) made of, for example, Ti / Pt / Au or V / Pt / Au is formed on or connected to the edge of the first electrode 31 for electrical connection to an external electrode or circuit.

[0035] On the other hand, the conductive film (second electrode) 32 is formed on the second compound semiconductor layer 22, and the second light-reflecting layer 42 is formed on the conductive film 32. The second light-reflecting layer 42 on the conductive film 32, which is the second electrode, has a flat shape. The conductive film 32 is made of a transparent conductive material, specifically, ITO. That is, the conductive film 32 is made of a material such as ITO (Indium Tin Oxide), ITiO (Indium Titanium Oxide), AZO (Al ２ O3-ZnO), IGZO (InGaZnO ｘ ) A second pad electrode 33 is formed on or connected to the peripheral region of the conductive film 32 for electrical connection to an external electrode or circuit.

[0036] The first light-reflecting layer 41 and the second light-reflecting layer 42 are made of Ta ２ O ５ layer and SiO ２ The first electrode 31, the first light reflecting layer 41, the second light reflecting layer 42, and the insulating layer (current confinement layer) 34 each have a multi-layer structure (for example, 20 layers in total). Although the first light reflecting layer 41 and the second light reflecting layer 42 each have a multi-layer structure, they are shown as a single layer for the sake of simplicity. The openings provided in the first electrode 31, the first light reflecting layer 41, the second light reflecting layer 42, and the insulating layer (current confinement layer) 34 each have a circular planar shape.

[0037] FIG. 2 is a diagram showing the profile of the impurity concentration in the first compound semiconductor layer 21. FIG. 2( a) is a schematic cross-sectional view showing a portion of the stack 20. For ease of explanation, the Z axis represents the stacking direction of the stack 20, and the side from the second compound semiconductor layer 22 toward the first compound semiconductor layer 21 is indicated as positive. FIG. 2( b) shows the impurity concentration in a portion of the range of line Lpn in FIG. 2( a). The horizontal axis represents the distance in the Z direction along line Lpn, and the vertical axis represents the concentration of n-type impurities (n-type dopants). In this embodiment, the change in impurity concentration with respect to position is referred to as the impurity concentration profile. Line Lpn is a line parallel to the Z axis that passes through the center of the resonator and extends along the stacking direction of the stacked structure 20. As such, the impurity concentration profile showing the position along the stacking direction of the stacked structure 20 and the impurity concentration at this position has a lightly doped region where the impurity concentration locally decreases.

[0038] For example, the n-type impurity in this embodiment is silicon (Si). As shown in Figure 2A, for example, the concentration decrease starts in the Z-axis direction at a position, for example, 267 nanometers (nm) from the end of the active layer 23. This start position can also be set based on the maximum value of the optical field.

[0039] As shown in FIG. 2B, the lightly doped regions in the first compound semiconductor layer 21, where the concentration of n-type impurities (n-type dopants) locally decreases, have minimum points min. These lightly doped regions are configured to have a predetermined periodicity. For example, the interval in the stacking direction between the minimum points min, where the concentration in the lightly doped regions is minimum, is set to 64.5 nanometers (nm). In addition, the impurity concentration at the minimum points min is set to, for example, 3E+17 (m- ３ ), which is approximately half the average impurity concentration in the first compound semiconductor layer 21. The width of the region where the concentration is one order of magnitude higher than the minimum concentration value at the minimum point min is referred to as the "width" of the low-concentration region. This width is, for example, 30 nanometers (nm) or less, and preferably 10 nanometers (nm) or less. Thus, the region where the concentration locally decreases is composed of one or more regions, including one. That is, the region where the concentration locally decreases may be a single region or multiple regions. In addition, a linear increase and decrease in the impurity concentration profile may be referred to as a linear type. As mentioned above, the minimum point min may also be referred to as a minimum point.

[0040] FIG. 3 is a diagram showing the strength of standing waves in a resonator. The horizontal axis represents the distance in the z-direction within a partial range of the line Lpn in FIG. 2( a), and the vertical axis schematically represents the strength of the optical field (electric field strength). For convenience of explanation, the amplitude of the optical field is illustrated with the same width, but this is not limiting. FIG. 3 also shows the minimum point min shown in FIG. 2( b). As described above, the resonator according to this embodiment is composed of a region of the first optical reflecting layer 41 extending from the first surface 21 a of the first compound semiconductor layer 21 to a certain depth, the stacked structure 20 (the first compound semiconductor layer 21, the active layer 23, and the second compound semiconductor layer 22), and a region of the second optical reflecting layer 42 extending from the second surface 22 b of the second compound semiconductor layer 22 to a certain depth.

[0041] 3 , the minimum points min where the concentration is minimum are determined according to the position where the standing wave intensity is maximum. That is, the interval of 64.5 nanometers (nm) between the minimum points min in the stacking direction of the stack 20 corresponds to half the wavelength of the standing wave. In this way, the interval between the minimum points min where the concentration is minimum is determined based on the length Lor of the resonator, the structure of the stacked structure 20 (the first compound semiconductor layer 21, the active layer 23, and the second compound semiconductor layer 22), and the oscillation wavelength.

[0042] More specifically, the spacing between regions where the impurity concentration decreases (low-doped regions) is within ±10% of an integer multiple of the length obtained by dividing the oscillation wavelength of the element by twice the refractive index. The length obtained by dividing the oscillation wavelength of the light-emitting element 1 by twice the refractive index corresponds to the spacing between the maximum values ​​of the optical field. This ±10% value takes into account fluctuations in the wavelength of standing waves in the resonator. In other words, the spacing between regions where the impurity concentration decreases may be the length obtained by dividing the oscillation wavelength by twice the refractive index, or an integer multiple such as 2, 3, or 4 times the length. It may also be a combination of 1, 2, 3, or 4 times. As described above, in this embodiment, the regions where the impurity concentration decreases may be referred to as low-doped regions. In the following description, the term "integer multiple" may refer to a combination of 1, 2, 3, or 4 times, or a combination of multiples of 2 such as 2, 4, 6, or 8 times.

[0043] The interval between the maximum values ​​of the optical field generally varies depending on the distance from the interface of the first optical reflecting layer 41 of the resonator. Therefore, the interval between the minimum points min where the concentration is minimum from the interface of the first optical reflecting layer 41 of the resonator is within ±10% of an integer multiple of the length obtained by dividing the oscillation wavelength of the light-emitting element 1 by four times the refractive index. This ±10% range takes into consideration fluctuations in the region of the first optical reflecting layer 41 from the first surface 21a of the first compound semiconductor layer 21 to a certain depth, and in the region of the second optical reflecting layer 42 from the second surface 22b of the second compound semiconductor layer 22 to a certain depth, fluctuations in the wavelength of standing waves, etc.

[0044] The standing wave also depends on the position of the active layer 23. Therefore, the distance between the minimum points min where the concentration is minimum is within ±10% of an integer multiple of the length from the active layer 23 to the oscillation wavelength of the light-emitting element 1 divided by four times the refractive index.

[0045] Reducing the concentration of n-type impurities (n-type dopants) reduces the current conducted to the active layer 23. For this reason, the thickness of the lightly doped region is set to be thinner than the thickness obtained by dividing the refractive index of the oscillation wavelength of the element by eight times. This suppresses the reduction in current.

[0046] On the other hand, the lower the concentration of n-type impurities (n-type dopants), the better the light propagation. Thus, the concentration of n-type impurities (n-type dopants) has a trade-off relationship between light propagation and current conductivity. Therefore, for example, by lowering the concentration of n-type impurities (n-type dopants) to match the position where the standing wave intensity is maximum, it is possible to more efficiently increase light propagation and also to suppress a decrease in the concentration of n-type impurities (n-type dopants).

[0047] 4A and 4B are graphs showing the results of a simulation illustrating the output characteristics of the light-emitting element 1. Fig. 4A shows a comparative example in which a low-impurity-concentration region is not formed in the first compound semiconductor layer 21, and Fig. 4B shows a case in which a low-impurity-concentration region according to this embodiment is formed. The horizontal axis represents the current flowing between the first electrode 31 and the second electrode 32, one vertical axis represents the voltage between the first electrode 31 and the second electrode 32, and the other vertical axis represents the power of the light-emitting laser.

[0048] The voltage Lva of the comparative example and the voltage Lvb of the present embodiment show almost the same tendency with increasing current. On the other hand, the voltage Lvb of the present embodiment tends to be higher than the voltage Lva of the comparative example. For example, at 7 milliamperes (mA), the voltage of the comparative example is 2.4, while the voltage of the present embodiment is 2.51, an increase of approximately 4.5 percent. In other words, the resistance between the first electrode 31 and the second electrode 32 increases slightly due to the lower concentration.

[0049] On the other hand, the power of the light-emitting laser is increased by approximately 30% when the voltage Lvb of this embodiment is 7 milliamperes (mA) compared to the power Lpa of the comparative example. In other words, by reducing the impurity concentration to match the position of the maximum optical field intensity, it is possible to increase the power by approximately 30% while maintaining approximately the same voltage-current characteristics.

[0050] As described above, according to this embodiment, the stacked structure 20 (the first compound semiconductor layer 21, the active layer 23, and the second compound semiconductor layer 22) has regions in which the impurity concentration locally decreases along the stacking direction of the stacked structure 20. This makes it possible to increase the power of laser emission for a given current value between the first electrode 31 and the second electrode 32. In particular, by configuring the spacing between the regions in which the impurity concentration locally decreases in accordance with the position where the strength of the standing wave is maximized, it is possible to increase the power of laser emission while suppressing an increase in resistance between the first electrode 31 and the second electrode 32.

[0051] Such improved performance of the light-emitting element 1 can achieve excellent effects such as improved output (low Ith, high slope efficiency). Furthermore, by configuring the spacing between the regions where the impurity concentration locally decreases according to the position where the standing wave intensity is maximized, longitudinal mode stabilization can be achieved. Furthermore, the overlap of the optical field peak and the low-doping position contributes to improved voltage characteristics. Furthermore, since this contributes to lower voltages for the same light emission, heat generation during array emission is reduced, contributing to a reduction in the number of parts. Furthermore, improved ESD (Electro-Static Discharge) resistance and improved temperature characteristics are possible. This allows for a longer lifespan and miniaturization of the light-emitting element 1. This facilitates fabrication of the light-emitting element 1, enabling improved yields.

[0052] Second Embodiment The light-emitting element 1 according to the second embodiment differs from the light-emitting element 1 according to the first embodiment in the shape of the concentration profile of the low-concentration region. The differences from the light-emitting element 1 according to the first embodiment will be described below.

[0053] 5A and 5B are diagrams showing the profile of the impurity concentration in the first compound semiconductor layer 21 according to the second embodiment. FIG. 5A is a schematic cross-sectional view showing a portion of the stacked body 20. For ease of explanation, the Z axis represents the stacking direction of the stacked body 20, and the side from the second compound semiconductor layer 22 toward the first compound semiconductor layer 21 is indicated as positive. FIG. 5B shows the impurity concentration in a partial range of line Lpn in FIG. 5A. The horizontal axis represents the distance in the z direction along line Lpn, and the vertical axis represents the concentration of n-type impurities (n-type dopants).

[0054] 5B, the first compound semiconductor layer 21 has a region where the concentration of the n-type impurity (n-type dopant) locally decreases. The region where the concentration locally decreases in the impurity concentration profile according to the second embodiment is configured as a differentially continuous curve. That is, the impurity concentration profile in the lightly doped region is configured as a curve where derivatives, which are extreme values ​​of a first-order difference of the impurity concentration with respect to a first-order difference at a position along the stacking direction, are continuous. Furthermore, an impurity concentration profile where the decrease and increase in the impurity concentration are configured as differentially continuous curves is sometimes referred to as a parabolic profile.

[0055] In addition, the impurity concentration at the minimum point min is, for example, 3E+17 (m- ３ ), which is approximately half the average impurity concentration in the first compound semiconductor layer 21. The width of the portion where the concentration is one order of magnitude higher than the minimum concentration value at the minimum point min is referred to as the "width" of the low-concentration region. This width is, for example, 30 nanometers (nm) or less, and preferably 10 nanometers (nm) or less. As indicated by arrow W2, the width of the region where the impurity concentration is reduced is widened to the vicinity of the minimum point min. This makes it possible to further increase the power of laser emission for a given current value between the first electrode 31 and the second electrode 32, in addition to achieving the same effect as the light-emitting element 1 according to the first embodiment.

[0056] Third Embodiment The light-emitting element 1 according to the third embodiment differs from the light-emitting element 1 according to the first embodiment in the shape of the concentration profile of the low-concentration region. The differences from the light-emitting element 1 according to the first embodiment will be described below.

[0057] 6A and 6B are diagrams showing the profile of the impurity concentration in the first compound semiconductor layer 21 according to the third embodiment. Fig. 6A is a schematic cross-sectional view showing a portion of the stacked body 20. For ease of explanation, the Z axis represents the stacking direction of the stacked body 20, and the side from the second compound semiconductor layer 22 toward the first compound semiconductor layer 21 is indicated as positive. Fig. 6B shows the impurity concentration in a partial range of line Lpn in Fig. 6A. The horizontal axis represents the distance in the z direction along line Lpn, and the vertical axis represents the concentration of n-type impurities (n-type dopants).

[0058] 6B, there is a region in which the concentration of n-type impurities (n-type dopants) in the first compound semiconductor layer 21 is locally decreased. The region in which the concentration is locally decreased in the impurity concentration profile according to the second embodiment is different from the light-emitting element 1 according to the first embodiment in that the width of the region in which the concentration is locally decreased is decreased stepwise from width W3 to width W4. In addition, a profile of impurity concentration in which the decrease and increase in impurity concentration are configured by changing the width stepwise is sometimes referred to as a step type.

[0059] By widening the region of width W4, it is possible to further increase the power of laser emission for a given current value between the first electrode 31 and the second electrode 32. On the other hand, the region of width S3 has a concentration distribution equivalent to that of the light-emitting element 1 according to the first embodiment. This makes it possible to further increase the power of laser emission while suppressing an increase in resistance between the first electrode 31 and the second electrode 32, in addition to achieving the same effect as the light-emitting element 1 according to the first embodiment.

[0060] (Fourth embodiment) The light-emitting element 1 according to the fourth embodiment differs from the light-emitting element 1 according to the first embodiment in that the shape of the concentration profile of the low-concentration region varies depending on the position. The differences from the light-emitting element 1 according to the first embodiment will be described below.

[0061] 7 is a diagram showing the profile of the impurity concentration in the first compound semiconductor layer 21 according to the fourth embodiment. Fig. 7 shows the impurity concentration in a partial range of the line Lpn in Fig. 2(a). The horizontal axis represents the distance in the z direction along the line Lpn, and the vertical axis represents the concentration of the n-type impurity (n-type dopant).

[0062] As shown in FIG. 7 , the first compound semiconductor layer 21 has a region where the concentration of n-type impurities (n-type dopants) locally decreases. The concentration distribution can be, for example, a mixture of linear, parabolic, and stepwise. In each case, the doping concentration at the minimum min is less than half the average doping concentration. The widths W5, W6, and W7 at the half-average doping concentration point satisfy the relationship W6 > W5 > W7. This configuration allows for a more optimal impurity concentration distribution depending on the structural characteristics of the stacked structure 20 (the first compound semiconductor layer 21, the active layer 23, and the second compound semiconductor layer 22). This not only achieves the same effects as the light-emitting device 1 according to the first embodiment, but also enables further increase in the power of laser emission while suppressing an increase in resistance between the first electrode 31 and the second electrode 32.

[0063] Fifth Embodiment The light-emitting element 1 according to the fifth embodiment differs from the light-emitting element 1 according to the first embodiment in that the semiconductor substrate 11 a is a semi-polar GaN substrate. The differences from the light-emitting element 1 according to the first embodiment will be described below.

[0064] 8A and 8B are diagrams showing the impurity concentration profile in the first compound semiconductor layer 21 according to the fifth embodiment. FIG. 8A is a schematic cross-sectional view showing a portion of the stacked body 20. For ease of explanation, the Z axis represents the stacking direction of the stacked body 20, and the side from the second compound semiconductor layer 22 toward the first compound semiconductor layer 21 is indicated as positive. The fifth embodiment differs from the light-emitting element 1 according to the first embodiment in that the semiconductor substrate 11a is a semi-polar GaN substrate. As a result, the light-emitting wavelength of the light-emitting element 1 according to the fifth embodiment is 515 nanometers (nm).

[0065] FIG. 8( b ) shows the impurity concentration in a partial range of the line Lpn in FIG. 8( a ). The horizontal axis represents the distance in the z-direction along the line Lpn, and the vertical axis represents the concentration of the n-type impurity (n-type dopant). The horizontal axis represents the distance in the z-direction along the line Lpn, and the vertical axis represents the concentration of the n-type impurity (n-type dopant). For example, the n-type impurity in this embodiment is silicon (Si). As shown in FIG. 8( a ), for example, the concentration decrease starts at a position, for example, 309 nanometers (nm) from the end of the active layer 23 in the Z-axis direction. This starting position can also be set based on the maximum value of the optical field.

[0066] As shown in FIG. 8B, the first compound semiconductor layer 21 has a region where the concentration of the n-type impurity (n-type dopant) locally decreases. This region where the concentration locally decreases is configured to have a predetermined periodicity. For example, the interval in the stacking direction of the stack 20 between minimum points min where the concentration is minimum is set to 74.5 nanometers (nm). In addition, the impurity concentration at the minimum point min is set to, for example, 3E+17 (m- ３ ) is set to about half the average impurity concentration in the first compound semiconductor layer 21. In this way, by making the emission wavelength different from that of the light-emitting element 1 according to the first embodiment, the period and position of the minimum points min at which the concentration is minimum may be changed. The shape of the concentration profile may be linear, parabolic, or stepwise. Alternatively, it may be a mixture of linear, parabolic, and stepwise shapes.

[0067] This makes it possible to obtain the same effects as those of the light-emitting element 1 according to the first to fourth embodiments even if the emission wavelength is changed.

[0068] Sixth Embodiment The light-emitting element 1 according to the sixth embodiment differs from the light-emitting element 1 according to the first embodiment in that a region in which the impurity concentration is locally reduced is formed in the second compound semiconductor layer 22 of the stacked structure 20. The differences from the light-emitting element 1 according to the first embodiment will be described below.

[0069] FIG. 9 is a diagram showing the impurity concentration profile in the second compound semiconductor layer 22. FIG. 9( a) is a schematic cross-sectional view showing a portion of the stack 20. For convenience of explanation, the Z axis represents the stacking direction of the stack 20, and the direction from the second compound semiconductor layer 22 toward the first compound semiconductor layer 21 is indicated by a positive sign. FIG. 9( b) shows the impurity concentration in a portion of the range of line Lpn2 in FIG. 9( a). The horizontal axis represents the distance in the Z direction along line Lpns, and the vertical axis represents the concentration of p-type impurities (p-type dopants). For example, the p-type impurity in this embodiment is magnesium (Mg). As shown in FIG. 9( a), for example, the concentration decrease starts at a predetermined position in the Z axis direction from the end of the active layer 23. This starting position can also be set based on the maximum value of the optical field.

[0070] As shown in FIG. 9B, the second compound semiconductor layer 22 has a region where the concentration of the p-type impurity (p-type dopant) locally decreases. This region where the concentration locally decreases is configured to have a predetermined periodicity. For example, the interval in the stacking direction of the stack 20 between minimum points min where the concentration is minimum is set to 64.5 nanometers (nm). In addition, the impurity concentration at the minimum point min is set to, for example, 3E+17 (m- ３ ) is set to about half the average impurity concentration in the second compound semiconductor layer 22. The width of the portion where the concentration is one order of magnitude higher than the minimum concentration value at the minimum point min is referred to as the "width" of the low concentration region. This width is, for example, 30 nanometers (nm) or less, and preferably 10 nanometers (nm) or less. In this way, the region where the concentration locally decreases is composed of a number equal to or greater than one, including one. In other words, the region where the concentration locally decreases may be a single region or multiple regions. The shape of the concentration profile may be linear, parabolic, or stepwise. Alternatively, it may be a mixture of linear, parabolic, and stepwise.

[0071] According to this embodiment, a region in which the impurity concentration locally decreases along the stacking direction of the stacked structure 20 is formed in the second compound semiconductor layer 22 of the stacked structure 20 (the first compound semiconductor layer 21, the active layer 23, and the second compound semiconductor layer 22). This makes it possible to increase the power of laser emission for a given current value between the first electrode 31 and the second electrode 32. In particular, by configuring the spacing between the regions in which the impurity concentration locally decreases in accordance with the position where the strength of the standing wave is maximized, it is possible to increase the power of laser emission while suppressing an increase in resistance between the first electrode 31 and the second electrode 32.

[0072] Seventh Embodiment The light-emitting element 1 according to the seventh embodiment differs from the light-emitting element 1 according to the first embodiment in that regions in which the impurity concentration is locally reduced are formed in the first compound semiconductor layer 21 and the second compound semiconductor layer 22 of the stacked structure 20. The differences from the light-emitting element 1 according to the first embodiment will be described below.

[0073] 10 is a schematic cross-sectional view showing a portion of the stack 20 according to the seventh embodiment. This view is similar to FIG. 2A, and differs from the light-emitting element 1 according to the first embodiment in that the stack 20 further includes a region in which the concentration of the p-type impurity (p-type dopant) in the second compound semiconductor layer 22 is locally reduced. The shape of the concentration profile may be linear, parabolic, or stepwise. Alternatively, the shape may be a mixture of linear, parabolic, and stepwise.

[0074] According to this embodiment, regions in which the impurity concentration locally decreases along the stacking direction of the stacked structure 20 are formed in the first compound semiconductor layer 21 and the second compound semiconductor layer 22 of the stacked structure 20 (first compound semiconductor layer 21, active layer 23, and second compound semiconductor layer 22). This makes it possible to increase the power of laser emission for a given current value between the first electrode 31 and the second electrode 32. In particular, by configuring the interval between the regions in which the impurity concentration locally decreases according to the position where the strength of the standing wave is maximized, it is possible to increase the power of laser emission while suppressing an increase in resistance between the first electrode 31 and the second electrode 32.

[0075] (Other Configuration Examples) Furthermore, in the light-emitting devices and the like of the present disclosure including the preferred forms and configurations (first to seventh embodiments) described above, it is preferable that the materials constituting the various compound semiconductor layers (including the compound semiconductor substrates 11, 11a) located between the active layer 23 and the first light-reflecting layer 41 do not have a refractive index modulation of 10% or more (no refractive index difference of 10% or more based on the average refractive index of the stacked structure 20), which makes it possible to suppress the occurrence of disturbances in the optical field within the resonator.

[0076] In the light-emitting device etc. of the present disclosure, the stacked structure 20 can be specifically configured to be made of an AlInGaN-based compound semiconductor. More specifically, AlInGaN-based compound semiconductors include GaN, AlGaN, InGaN, and AlInGaN. Furthermore, these compound semiconductors may contain boron (B) atoms, thallium (Tl) atoms, arsenic (As) atoms, phosphorus (P) atoms, and antimony (Sb) atoms, as desired. The active layer 23 desirably has a quantum well structure. Specifically, it may have a single quantum well structure (SQW structure) or a multiple quantum well structure (MQW structure). The active layer 23 having a quantum well structure has a structure in which at least one well layer and one barrier layer are stacked, and the combination of (the compound semiconductor constituting the well layer and the compound semiconductor constituting the barrier layer) may be (In ｙ Ga （１－ｙ） N, GaN), (In ｙ Ga （１－ｙ） N, In ｚ Ga （１－ｚ） N) [where y>z], (In ｙ Ga （１－ｙ）Examples of the compound semiconductor layer 21 include a compound semiconductor of a first conductivity type (e.g., n-type), and a compound semiconductor of a second conductivity type (e.g., p-type) different from the first conductivity type. The first compound semiconductor layer 21 and the second compound semiconductor layer 22 are also referred to as a first cladding layer and a second cladding layer. The first compound semiconductor layer 21 and the second compound semiconductor layer 22 may be layers of a single structure, layers of a multilayer structure, or layers of a superlattice structure. Furthermore, they may be layers having a composition gradient layer or a concentration gradient layer.

[0077] The laminated structure 20 is formed on the second surface of a substrate for manufacturing a light-emitting element, or alternatively, on the second surface of the compound semiconductor substrate 11. The substrate for manufacturing a light-emitting element may be a GaN substrate, a sapphire substrate, a GaAs substrate, a SiC substrate, an alumina substrate, a ZnS substrate, a ZnO substrate, an AlN substrate, a LiMgO substrate, a LiGaO ２ Substrate, MgAl ２ O ４Examples of the substrate include a silicon substrate, an InP substrate, and a silicon substrate, and substrates having an underlayer or buffer layer formed on the surface (main surface) of these substrates. However, the use of a GaN substrate is preferred due to its low defect density. Another example of a compound semiconductor substrate is a GaN substrate. It is known that the properties of a GaN substrate vary from polar to non-polar to semi-polar depending on the growth surface. However, any of the main surfaces (second surfaces) of a GaN substrate can be used to form a compound semiconductor layer. Furthermore, with regard to the main surface of a GaN substrate, depending on the crystal structure (e.g., cubic or hexagonal), crystal orientation planes called the A-plane, B-plane, C-plane, R-plane, M-plane, N-plane, S-plane, etc., or planes obtained by off-axis orientation of these in a specific direction, can also be used. Examples of methods for forming various compound semiconductor layers that constitute the light-emitting element include, but are not limited to, metalorganic chemical vapor deposition (MOCVD, Metalorganic-Chemical Vapor Deposition, MOVPE, Metalorganic-Vapor Phase Epitaxy), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE) in which halogen contributes to transport or reaction, atomic layer deposition (ALD, Atomic Layer Deposition), migration-enhanced epitaxy (MEE, Migration-Enhanced Epitaxy), and plasma-assisted physical vapor deposition (PPD).

[0078] Here, examples of organic gallium source gases in the MOCVD method include trimethylgallium (TMG) gas and triethylgallium (TEG) gas, and examples of nitrogen source gases include ammonia gas and hydrazine gas. When forming a GaN-based compound semiconductor layer having n-type conductivity, for example, silicon (Si) may be added as an n-type impurity (n-type dopant), and when forming a GaN-based compound semiconductor layer having p-type conductivity, for example, magnesium (Mg) may be added as a p-type impurity (p-type dopant). When aluminum (Al) or indium (In) is included as a constituent atom of the GaN-based compound semiconductor layer, trimethylaluminum (TMA) gas may be used as the Al source, and trimethylindium (TMI) gas may be used as the In source. Furthermore, monosilane gas (SiH4 gas) may be used as the Si source, and biscyclopentadienyl magnesium gas, methylcyclopentadienyl magnesium, or biscyclopentadienyl magnesium (Cp2Mg) may be used as the Mg source. Note that examples of n-type impurities (n-type dopants) other than Si include Ge, Se, Sn, C, Te, S, O, Pd, and Po, and examples of p-type impurities (p-type dopants) other than Mg include Zn, Cd, Be, Ca, Ba, C, Hg, and Sr.

[0079] The support substrate may be composed of, for example, any of the various substrates exemplified as substrates for manufacturing light-emitting elements, or may be composed of an insulating substrate such as AlN, a semiconductor substrate such as Si, SiC, or Ge, or a metal or alloy substrate. However, a conductive substrate is preferred, or a metal or alloy substrate is preferred from the viewpoints of mechanical properties, elastic deformation, plastic deformability, heat dissipation, etc. The thickness of the support substrate can be, for example, 0.05 mm to 1 mm. Known methods such as solder bonding, room-temperature bonding, bonding using adhesive tape, wax bonding, and adhesive bonding can be used to secure the second light-reflecting layer 42 to the support substrate. However, solder bonding or room-temperature bonding is preferred from the viewpoint of ensuring conductivity. For example, when a conductive silicon semiconductor substrate is used as the support substrate, it is desirable to use a method that allows bonding at a low temperature of 400°C or less to suppress warping due to differences in thermal expansion coefficients. When a GaN substrate is used as the support substrate, the bonding temperature may be 400°C or higher.

[0080] In manufacturing the light-emitting element and the like according to the present disclosure, the substrate for manufacturing the light-emitting element may be left in place, or the substrate for manufacturing the light-emitting element may be removed after the active layer 23, the second compound semiconductor layer 22, the second electrode 32, and the second light reflecting layer 42 are sequentially formed on the first compound semiconductor layer 21. Specifically, the active layer 23, the second compound semiconductor layer 22, the second electrode 32, and the second light reflecting layer 42 are sequentially formed on the first compound semiconductor layer 21, and then the second light reflecting layer 42 is fixed to a support substrate, after which the substrate for manufacturing the light-emitting element is removed to expose the first compound semiconductor layer 21 (the first surface 21 a of the first compound semiconductor layer 21). The substrate for manufacturing a light-emitting element can be removed by wet etching using an alkaline aqueous solution such as a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution, an ammonia solution + hydrogen peroxide solution, a sulfuric acid solution + hydrogen peroxide solution, a hydrochloric acid solution + hydrogen peroxide solution, a phosphoric acid solution + hydrogen peroxide solution, or the like, a chemical mechanical polishing method (CMP method), a mechanical polishing method, a dry etching method, a lift-off method using a laser, or a combination of these methods.

[0081] When the substrate for manufacturing a light-emitting element remains, the first electrode 31 may be formed on the first surface opposite to the second surface of the substrate for manufacturing a light-emitting element, or may be formed on the first surface opposite to the second surface of the compound semiconductor substrate. When the substrate for manufacturing a light-emitting element remains, the first electrode 31 may be formed on the first surface 21 a of the first compound semiconductor layer 21 constituting the stacked structure 20. In this case, since the first light reflecting layer 41 is formed on the first surface 21 a of the first compound semiconductor layer 21, the first electrode 31 may be formed so as to surround the first light reflecting layer 41, for example. The first electrode 31 preferably has a single-layer or multilayer structure containing at least one metal (including alloys) selected from the group consisting of gold (Au), silver (Ag), palladium (Pd), platinum (Pt), nickel (Ni), titanium (Ti), vanadium (V), tungsten (W), chromium (Cr), aluminum (Al), copper (Cu), zinc (Zn), tin (Sn), and indium (In). Specific examples include Ti / Au, Ti / Al, Ti / Al / Au, Ti / Pt / Au, Ni / Au, Ni / Au / Pt, Ni / Pt, Pd / Pt, and Ag / Pd. Note that the layer before the " / " in the multilayer structure is located closer to the active layer 23. This also applies to the following description. The first electrode 31 can be formed by a physical vapor deposition (PVD) method such as vacuum deposition or sputtering.

[0082] When the first electrode 31 is formed to surround the first light-reflecting layer 41, the first light-reflecting layer 41 and the first electrode 31 may be in contact with each other. Alternatively, the first light-reflecting layer 41 and the first electrode 31 may be spaced apart, i.e., offset, with a separation distance of 1 mm or less. If the current injection region located in the first light-reflecting layer 41 and the first electrode 31 are separated in plan view, the current will flow a long distance through the first compound semiconductor layer 21. Therefore, in order to keep the electrical resistance occurring in this current path low, it is preferable that the separation distance be 1 mm or less. In some cases, the first electrode 31 may be formed up to the edge of the first light-reflecting layer 41, or the first light-reflecting layer 41 may be formed up to the edge of the first electrode 31. Here, when the first light reflecting layer 41 is formed up to the edge of the first electrode 31, the first electrode 31 needs to have an opening of a certain size so as to absorb as little fundamental mode light of laser oscillation as possible. The size of the opening varies depending on the wavelength of the fundamental mode and the light confinement structure in the lateral direction (in-plane direction of the first compound semiconductor layer 21), so is not limited, but is preferably on the order of several times the oscillation wavelength λ0 or more.

[0083] The second electrode 32 can be made of a transparent conductive material. The transparent conductive material constituting the second electrode 32 can be an indium-based transparent conductive material [specifically, for example, indium-tin oxide (ITO, IndiumTinOxide, Sn-doped In ２ O ３ , including crystalline ITO and amorphous ITO), indium-zinc oxide (IZO, IndiumZincOxide), indium-gallium oxide (IGO), indium-doped gallium-zinc oxide (IGZO, In-GaZnO4), IFO (F-doped In ２ O ３ ), ITiO (Ti-doped In ２ O ３ ), InSn, InSnZnO], tin-based transparent conductive materials [specifically, for example, tin oxide (SnO ２ ), ATO (Sb-doped SnO ２), FTO (F-doped SnO ２ )], zinc-based transparent conductive materials [specifically, for example, zinc oxide (including ZnO, Al-doped ZnO (AZO), and B-doped ZnO), gallium-doped zinc oxide (GZO), AlMgZnO (aluminum oxide and magnesium oxide-doped zinc oxide)], and NiO can be exemplified. Alternatively, the second electrode 32 can be a transparent conductive film having a host layer of gallium oxide, titanium oxide, niobium oxide, antimony oxide, nickel oxide, or the like, or a transparent conductive material such as a spinel-type oxide or an oxide having a YbFe2O4 structure. However, the material constituting the second electrode 32 is not limited to transparent conductive materials, and metals such as palladium (Pd), platinum (Pt), nickel (Ni), gold (Au), cobalt (Co), and rhodium (Rh) can also be used, although this depends on the arrangement of the second light-reflecting layer 42 and the second electrode 32. The second electrode 32 may be composed of at least one of these materials. The second electrode 32 can be formed by a PVD method such as vacuum deposition or sputtering. Alternatively, a low-resistance semiconductor layer can be used as the transparent electrode layer. Specifically, an n-type GaN-based compound semiconductor layer can be used. Furthermore, when the layer adjacent to the n-type GaN-based compound semiconductor layer is p-type, the electrical resistance at the interface can be reduced by joining the two via a tunnel junction. By forming the second electrode 32 from a transparent conductive material, the current can be spread laterally (in the in-plane direction of the second compound semiconductor layer 22), allowing for efficient current supply to the current injection region.

[0084] A pad electrode may be provided on the first electrode 31 or the second electrode 32 for electrical connection to an external electrode or circuit. The pad electrode preferably has a single-layer or multilayer structure containing at least one metal selected from the group consisting of Ti (titanium), aluminum (Al), Pt (platinum), Au (gold), Ni (nickel), and Pd (palladium). Alternatively, the pad electrode may have a multilayer structure such as a Ti / Pt / Au multilayer structure, a Ti / Au multilayer structure, a Ti / Pd / Au multilayer structure, a Ti / Pd / Au multilayer structure, a Ti / Ni / Au multilayer structure, or a Ti / Ni / Au / Cr / Au multilayer structure. When the first electrode 31 is constructed from an Ag layer or an Ag / Pd layer, it is preferable to form a cover metal layer, for example, made of Ni / TiW / Pd / TiW / Ni, on the surface of the first electrode 31, and to form a pad electrode, for example, made of a multilayer structure of Ti / Ni / Au or a multilayer structure of Ti / Ni / Au / Cr / Au, on the cover metal layer.

[0085] The light-reflecting layers (distributed Bragg reflector layers, DBR layers) constituting the first light-reflecting layer 41 and the second light-reflecting layer 42 are composed of, for example, semiconductor multilayer films or dielectric multilayer films. Examples of dielectric materials include oxides, nitrides (e.g., SiNX, AlNX, AlGaNX, GaNX, BNX, etc.), or fluorides of Si, Mg, Al, Hf, Nb, Zr, Sc, Ta, Ga, Zn, Y, B, Ti, etc. Specific examples include SiOX, TiOX, NbOX, ZrOX, TaOX, ZnOX, AlOX, HfOX, SiNX, AlNX, etc. A light-reflecting layer can be obtained by alternately stacking two or more dielectric films made of dielectric materials with different refractive indices among these dielectric materials. For example, multilayer films such as SiOX / SiNY, SiOX / TaOX, SiOX / NbOY, SiOX / ZrOY, and SiOX / AlNY are preferred. To obtain the desired optical reflectance, the material, film thickness, and number of layers constituting each dielectric film can be appropriately selected. The thickness of each dielectric film can be adjusted appropriately depending on the material used, and is determined by the oscillation wavelength (emission wavelength) λ0 and the refractive index n of the material used at the oscillation wavelength λ0. Specifically, it is preferable to set the thickness to an odd multiple of λ0 / (4n). For example, in a light-emitting device with an oscillation wavelength λ0 of 410 nm, if the light-reflecting layer is made of SiOX / NbOY, the thickness can be approximately 40 nm to 70 nm. The number of layers can be 2 or more, preferably 5 to 20. The thickness of the entire light-reflecting layer can be, for example, approximately 0.6 μm to 1.7 μm. Furthermore, the light-reflecting layer desirably has an optical reflectance of 95% or more.

[0086] The light-reflecting layers 41 and 42 can be formed based on well-known methods, and specific examples thereof include PVD methods such as vacuum deposition, sputtering, reactive sputtering, ECR plasma sputtering, magnetron sputtering, ion beam assisted deposition, ion plating, and laser ablation; various CVD methods; coating methods such as spraying, spin coating, and dipping; methods combining two or more of these methods; and methods combining these methods with one or more of full or partial pretreatment, irradiation with inert gas (Ar, He, Xe, etc.) or plasma, irradiation with oxygen gas, ozone gas, or plasma, oxidation treatment (heat treatment), and exposure treatment.

[0087] The size and shape of the light-reflecting layers 41 and 42 are not particularly limited as long as they cover the current injection region or the element region. The shape of the boundary between the current injection region and the non-current injection inner region, the shape of the boundary between the non-current injection inner region and the non-current injection outer region, and the planar shape of the opening provided in the element region or the current confinement region can be specifically circular, elliptical, rectangular, or polygonal (triangle, square, hexagon, etc.). It is desirable that the shapes of the boundary between the current injection region and the non-current injection inner region, and the shape of the boundary between the non-current injection inner region and the non-current injection outer region are similar. When the shape of the boundary between the current injection region and the non-current injection inner region is circular, the diameter is preferably approximately 5 μm to 100 μm. Here, the term "element region" refers to the region into which a narrowed current is injected, or the region into which light is confined due to a refractive index difference, or the region sandwiched between the first light reflecting layer 41 and the second light reflecting layer 42 where laser oscillation occurs, or the region sandwiched between the first light reflecting layer 41 and the second light reflecting layer 42 that actually contributes to laser oscillation.

[0088] The side surfaces and exposed surfaces of the laminated structure 20 may be covered with a coating layer (insulating film). The coating layer (insulating film) can be formed based on a known method. The refractive index of the material constituting the coating layer (insulating film) is preferably smaller than the refractive index of the material constituting the laminated structure 20. Examples of materials constituting the coating layer (insulating film) include SiO2-containing SiOX-based materials, SiNX-based materials, SiOYNZ-based materials, TaOX, ZrOX, AlNX, AlOX, and GaOX, and also include organic materials such as polyimide resins. Examples of methods for forming the coating layer (insulating film) include PVD methods such as vacuum deposition and sputtering, or CVD methods, and the coating layer (insulating film) can also be formed based on a coating method.

[0089] The present technology can be configured as follows:

[0090] (1) A light-emitting device comprising: a first compound semiconductor layer having a first surface and a second surface opposite to the first surface; an active layer facing the second surface of the first compound semiconductor layer; and a second compound semiconductor layer having a first surface facing the active layer and a second surface opposite to the first surface, the second compound semiconductor layer having a different conductivity type from the first compound semiconductor layer, wherein the light-emitting device has a low-doped region at a position along a stacking direction of the first compound semiconductor layer, the active layer, and the second compound semiconductor layer, and an impurity concentration profile showing the impurity concentration at the position locally decreases.

[0091] (2) The light-emitting element according to (1), wherein the lightly doped region has a minimum point indicating a minimum concentration, the first compound semiconductor layer is made of an n-type semiconductor, and the second compound semiconductor layer is made of a p-type semiconductor.

[0092] (3) The light-emitting device according to (1) or (2), wherein a peak position of an optical field electric field intensity of a standing wave of oscillated light in the first compound semiconductor layer, the active layer, and the second compound semiconductor layer corresponds to the lightly doped region of the impurity concentration profile.

[0093] (4) The light-emitting device according to (3), wherein the peak position of the electric field strength of the optical field corresponds to the minimum point of the low-doped region.

[0094] (5) The light-emitting element according to any one of (1) to (4), wherein the impurity concentration in the lightly doped region linearly decreases and linearly increases along the stacking direction.

[0095] (6) The light-emitting element according to any one of (1) to (5), wherein the impurity concentration profile in the lightly doped region is configured as a continuous curve representing the derivative of a change in impurity concentration with respect to a change in the position along the stacking direction.

[0096] (7) The light-emitting element according to any one of (1) to (6), wherein the impurity concentration in the lightly doped region decreases and increases stepwise along the stacking direction.

[0097] (8) The light-emitting element according to any one of (1) to (7), wherein the lightly doped region is formed in at least one of the first compound semiconductor layer and the second compound semiconductor layer.

[0098] (9) The light-emitting element according to any one of (1) to (8), wherein a minimum value of the impurity concentration of the lightly doped region in the first compound semiconductor layer is equal to or less than half of an average impurity concentration in the first compound semiconductor layer.

[0099] (10) The light-emitting device according to (9), wherein the minimum value of the impurity concentration of the lightly doped region in the second compound semiconductor layer is equal to or less than half of the average impurity concentration in the second compound semiconductor layer.

[0100] (11) The light-emitting element according to (8), wherein the lightly doped regions are plural, and the spacing between the lightly doped regions is within ±10% of an integral multiple of the length obtained by dividing the oscillation wavelength of the element by twice the refractive index.

[0101] (12) The light-emitting element according to any one of (1) to (11), further comprising: a first reflective layer on the first surface side of the first compound semiconductor layer; and a second reflective layer facing the second surface of the second compound semiconductor layer, wherein a distance from an interface of at least one of the first reflective layer and the second reflective layer to the lightly doped region is within ±10% of an integral multiple of a length obtained by dividing an oscillation wavelength of the element by four times a refractive index.

[0102] (13) The light-emitting element according to any one of (1) to (12), wherein the width of the lightly doped region along the stacking direction is configured to be thinner than a thickness obtained by dividing by eight times the refractive index of the oscillation wavelength of the element.

[0103] (14) The light-emitting element according to any one of (1) to (13), wherein in the impurity concentration profile, a width of a portion where the impurity concentration is one order of magnitude higher than the minimum value of the impurity concentration of the lightly doped region is 30 nm or less.

[0104] (15) The light-emitting element according to (14), wherein the width is 10 nm or less.

[0105] (16) The light-emitting element according to any one of (1) to (15), wherein the n-type impurity in the first compound semiconductor layer is at least one of Si, Ge, Se, SnC, Te, S, O, Pd, and Po, and the p-type impurity in the second compound semiconductor layer is at least one of Mg, Zn, Cd, Be, Ca, Ba, C, Hg, and Sr.

[0106] (17) The light-emitting element according to any one of (1) to (16), further comprising a compound semiconductor substrate facing the first surface in the first compound semiconductor layer, wherein the material of the compound semiconductor substrate is a III-V group compound semiconductor containing at least any one of GaN, GaAs, and InP.

[0107] (18) The light-emitting element according to any one of (1) to (16), further comprising a compound semiconductor substrate facing the first surface in the first compound semiconductor layer, wherein the compound semiconductor substrate is a polar or semi-polar substrate.

[0108] (19) The light-emitting element according to (1), further comprising a first reflective layer on the first surface side of the first compound semiconductor layer, the first reflective layer having a concave mirror structure.

[0109] (20) The light-emitting element according to (3), further comprising: a first reflective layer on the first surface side of the first compound semiconductor layer; and a second reflective layer facing the second surface of the second compound semiconductor layer, wherein the resonator in which the standing wave exists is configured by a region of the first light-reflective layer from the first surface of the first compound semiconductor layer to a certain depth, the first compound semiconductor layer, the active layer, and the second compound semiconductor layer, and a region of the second light-reflective layer from the second surface of the second compound semiconductor layer to a certain depth, and has a length of 5 μm or more.

[0110] The aspects of the present disclosure are not limited to the individual embodiments described above, but include various modifications that may be conceived by those skilled in the art, and the effects of the present disclosure are not limited to the above-described contents. In other words, various additions, modifications, and partial deletions are possible within the scope of the conceptual idea and spirit of the present disclosure, which is derived from the contents defined in the claims and their equivalents.

[0111] 1: Light-emitting element, 11: Compound semiconductor substrate, 11a: Compound semiconductor substrate, 20: Layer structure, 21: First compound semiconductor layer, 22: Second compound semiconductor layer, 23: Active layer (light-emitting layer), 41: First light-reflecting layer, 42: Second light-reflecting layer, 43: Concave mirror portion.

Claims

1. A light-emitting device comprising: a first compound semiconductor layer having a first surface and a second surface facing the first surface; an active layer facing the second surface of the first compound semiconductor layer; and a second compound semiconductor layer having a first surface facing the active layer and a second surface facing the first surface, the second compound semiconductor layer having a conductivity type different from that of the first compound semiconductor layer, wherein an impurity concentration profile indicating a position along a stacking direction of the first compound semiconductor layer, the active layer, and the second compound semiconductor layer and an impurity concentration at the position has a low-doped region where the impurity concentration locally decreases.

2. The light-emitting device according to claim 1, wherein the low-doped region has a minimum point indicating a minimum concentration, the first compound semiconductor layer is made of an n-type semiconductor, and the second compound semiconductor layer is made of a p-type semiconductor.

3. The light-emitting device according to claim 1, wherein a peak position of an optical field electric field intensity of a standing wave of oscillating light in the first compound semiconductor layer, the active layer, and the second compound semiconductor layer corresponds to the low-doped region of the impurity concentration profile.

4. The light-emitting device according to claim 3, wherein the peak position of the optical field electric field intensity corresponds to the minimum point of the low-doped region.

5. The light-emitting device according to claim 1, wherein the impurity concentration in the low-doped region decreases linearly and increases linearly along the stacking direction.

6. The light-emitting device according to claim 1, wherein the impurity concentration profile in the low-doped region is configured as a curve in which a derivative of a change in the impurity concentration with respect to a change in the position along the stacking direction is continuous.

7. The light-emitting device according to claim 1, wherein the impurity concentration in the low-doped region decreases stepwise and increases stepwise along the stacking direction.

8. The light-emitting device according to claim 1, wherein the low-doped region is formed in at least one of the first compound semiconductor layer and the second compound semiconductor layer.

9. The light-emitting device according to claim 8, wherein a minimum value of the impurity concentration in the low-doped region in the first compound semiconductor layer is equal to or less than half of an average of the impurity concentration in the first compound semiconductor layer.

10. The light-emitting device according to claim 9, wherein a minimum value of the impurity concentration in the low-doped region in the second compound semiconductor layer is equal to or less than half of an average of the impurity concentration in the second compound semiconductor layer.

11. The light-emitting device according to claim 8, wherein there are a plurality of the low-doped regions, and the interval between the low-doped regions is within ±10% of an integral multiple of the length obtained by dividing the oscillation wavelength of the element by twice the refractive index.

12. The light-emitting device according to claim 1, further comprising a first reflective layer on the first surface side of the first compound semiconductor layer and a second reflective layer facing the second surface of the second compound semiconductor layer, wherein the interval between the low-doped regions from at least one of the interfaces of the first reflective layer and the second reflective layer is within ±10% of an integral multiple of the length obtained by dividing the oscillation wavelength of the element by four times the refractive index.

13. The light-emitting device according to claim 1, wherein the width along the stacking direction of the low-doped regions is configured to be thinner than the thickness obtained by dividing the oscillation wavelength of the element by eight times the refractive index.

14. The light-emitting device according to claim 1, wherein in the impurity concentration profile, the width of the portion where the impurity concentration is one digit higher than the minimum value of the impurity concentration in the low-doped region is 30 nm or less.

15. The light-emitting device according to claim 14, wherein the width is 10 nm or less.

16. The light-emitting device according to claim 1, wherein the n-type impurity in the first compound semiconductor layer is at least one of Si, Ge, Se, SnC, Te, S, O, Pd, and Po, and the p-type impurity in the second compound semiconductor layer is at least one of Mg, Zn, Cd, Be, Ca, Ba, C, Hg, and Sr.

17. The light-emitting device according to claim 1, further comprising a compound semiconductor substrate facing the first surface in the first compound semiconductor layer, wherein the material of the compound semiconductor substrate is a group III-V compound semiconductor containing at least one of GaN, GaAs, and InP.

18. The light-emitting device according to claim 1, further comprising a compound semiconductor substrate facing the first surface in the first compound semiconductor layer, wherein the compound semiconductor substrate is a polar or semi-polar substrate.

19. The light-emitting device according to claim 1, further comprising a first reflective layer on the first surface side of the first compound semiconductor layer, wherein the first reflective layer has a concave mirror structure.

20. Further comprising a first reflective layer on the first surface side of the first compound semiconductor layer and a second reflective layer facing the second surface of the second compound semiconductor layer, wherein the resonator in which the standing wave exists is formed by the region of the first light reflective layer from the first surface of the first compound semiconductor layer to a certain depth, the first compound semiconductor layer, the active layer, and the second compound semiconductor layer, and the region of the second light reflective layer from the second surface of the second compound semiconductor layer to a certain depth, and the length is 5 μm or more. The light-emitting element according to claim 3.

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