JPH118406A - Surface-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-emitting element which provides both high external quantum efficiency and high response speed. SOLUTION: A plurality of barrier layers 16-28 include a second barrier layer 20 and a third barrier layer 24, which are positioned between a plurality of active layers 18-26 and have a band structure inclined in the stacking direction. Therefore, since energy Ev at the upper edge of the valence band and energy Ec at the lower edge of the conduction band are inclined in the second barrier layer 20 and the third barrier layer 24, the injected carriers are made to move quickly along the energy inclination in the barrier layers 20 and 24, and the moving speed of the carriers left in the barrier layers 20 and 24 is increased at a light emission stop, when the application of a drive voltage is stopped. Therefore, in a light-emitting diode having a multi-quantum well structure, the fall time is shortened, and a surface-emitting element that provides both high external quantum efficiency and high response speed is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light emitting diode (LED) and a vertical cavity surface emitting laser (VCSE).
L) and the like.

[0002]

2. Description of the Related Art A plurality of compound semiconductor layers including a light emitting layer having a quantum well structure in which a plurality of barrier layers (barrier layers) and a plurality of well layers are alternately arranged on a substrate are formed. 2. Description of the Related Art A surface light emitting element of a type in which light generated in a light emitting layer is extracted from a surface of a compound semiconductor layer opposite to a substrate by applying a current between a pair of electrodes provided on both surfaces of a plurality of compound semiconductor layers is known. ing. According to the surface light emitting device including the light emitting layer having such a multiple quantum well structure, there is an advantage that the response speed can be increased as compared with a surface light emitting device having a simple pn junction or a double hetero junction structure. Especially,
When a gradient layer in which the compound crystal ratio of the compound semiconductor is inclined is provided on both sides of the light emitting layer, the injected carriers are inclined because the energy of the valence band upper end and the conduction band lower end is inclined in the light emitting layer. Are quickly moved along the slope toward the light emitting layer, so that the response speed is further enhanced. For example, IEEE PHOTONICS TECHNOLOGY LETTER
S, VOL. 4, NO. 1, JANUARY 1992, pages 27-28, distorted quantum well light emitting diodes.

In a surface light emitting device having a light emitting layer having a quantum well structure as described above, a pair of reflecting layers constituting an optical resonator for reflecting light generated in the light emitting layer are provided with the light emitting layer interposed therebetween. Is known. For example, the optical semiconductor device described in Japanese Patent Application Laid-Open No. 4-167484 is such. A surface light emitting device having such an optical resonator includes a device called an RC-LED (resonant cavity light emitting diode) or VCSEL, in which an electron wave in the light emitting layer and a light wave in the optical resonator are coupled, and a resonance mode is set. Because of the so-called cavity QED effect in which only light is generated in the light emitting layer, light having a strong directivity and a narrow line width is emitted, so that there is no total reflection on the crystal surface and high external quantum efficiency (that is, light output). Is obtained.

[0004]

However, according to the experimental results of the present inventors, according to the experimental results of the present inventors, the optical resonator structure described in the above-mentioned publication has a surface provided with a light emitting layer having a multiple quantum well structure as described above. When applied to a light emitting device, it has been clarified that the effect of improving the response speed by the multiple quantum well structure cannot be sufficiently obtained even if the inclined layer is provided. That is, the rise time _tr (rise ti
While me) sufficient improvement effect on is obtained, since not obtained sufficient responsiveness is standing when returning to the bias voltage fall time t _f (fall time) is longer driving voltage in order to stop the emission is there. In order to obtain a high optical output by forming an optical resonator structure, it is necessary to position the well layer at the antinode of the standing wave formed in the optical resonator. Is increased to about several hundred (nm) which is substantially equal to a half wavelength. Therefore, since the moving speed of carriers [holes (holes) or electrons] in the light emitting layer when no driving voltage is applied depends on the diffusion speed, the carriers remaining in the barrier layer when returning to the bias voltage are reduced. time or t _f until recombined spread to the well layer is the longer.
This problem is remarkable on the valence band side where holes having a large mass of the two carriers are moved.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a surface-emitting device capable of obtaining both high external quantum efficiency and high response speed. .

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the gist of the present invention is to provide a light emitting layer having a quantum well structure in which a plurality of barrier layers and a plurality of well layers are alternately arranged. And a plurality of compound semiconductor layers including a pair of reflective layers provided to sandwich the light emitting layer and constituting an optical resonator for reflecting light generated in the light emitting layer. Surface light-emitting device of a type in which the extracted light is extracted from the surfaces of the plurality of compound semiconductor layers,
(a) The plurality of barrier layers include an inclined barrier layer located between the plurality of well layers and having a band structure inclined in a stacking direction.

[0007]

According to the present invention, the plurality of barrier layers include the inclined barrier layers located between the plurality of well layers and having the band structure inclined in the stacking direction. Therefore, since the energy at the upper end of the valence band and the energy at the lower end of the conduction band are inclined in the inclined barrier layer,
Since the injected carriers are quickly moved along the gradient of their energy, the speed of movement of the carriers remaining in the inclined barrier layer at the time of emission stop when the application of the driving voltage is stopped is increased, and The moving speed of the carrier is increased as a whole. Accordingly, the fall time t _f is shortened in the surface light emitting device with a multiple quantum well structure, high external quantum efficiency and high and response speed with both surface-emitting device can be obtained. Such an effect is remarkable at the upper end of the valence band where holes having a large effective mass among carriers and having a slower moving speed than electrons are moved.

In the conventional surface emitting device having a multiple quantum well structure, the barrier layer in the light emitting layer has a band structure, that is, the energy of the upper end of the valence band and the lower end of the conduction band is the energy of the compound semiconductor layer in the moving direction of the carrier. The lamination method was flat. Therefore, when light emission is stopped, a flat band layer is formed, and the carrier moving speed depends exclusively on the diffusion speed. Therefore, when the barrier layer located between the well layers is thickened to form the optical resonator structure, the response speed is increased. Was reduced.

[0009] The inclination direction of the energy of the inclined barrier layer is not limited to the direction in which the energy is decreased along the moving direction of the carrier when the driving voltage is applied, but is inclined in the opposite direction.
Alternatively, it may be inclined so as to become lower in both directions from the intermediate position in the stacking direction, that is, the thickness direction. That is, the inclined barrier layer is located between the well layers, the fall time t _f is dependent on the speed of movement of the carrier in the non-application of the driving voltage (time to be allowed to recombine in the well layers) . Therefore, if the carriers remaining in the inclined barrier layer move quickly into any of the well layers, an effect of improving the response speed can be obtained. Therefore, there is no problem even if the inclined direction is different from the moving direction of the carriers at the time of application. Does not occur. Further, the gradient barrier layer may have a band structure, that is, the energy of the upper end of the valence band and the energy of the lower end of the conduction band may be changed continuously or may be changed stepwise.

[0010]

In another aspect of the present invention, preferably, all of the plurality of barrier layers located between the plurality of well layers are configured as the inclined barrier layers. In this case, since the band structures of all the barrier layers located between the well layers are inclined, all of the carriers remaining in the barrier layers at the time of stopping the light emission are quickly regenerated in the well layers. Since they are combined, the response speed is further increased. More preferably, of the plurality of barrier layers, the one located outside the plurality of well layers is also configured as an inclined layer whose band structure is inclined toward an adjacent well layer. With this configuration, since the band structures of all the barrier layers provided in the light emitting layer are inclined, all the carriers remaining in the light emitting layer when light emission is stopped are promptly moved, and the well layer is formed. The speed of response is further increased because they are recombined within.

Preferably, the gradient barrier layer has a band gap energy inclined by changing a compound crystal ratio of the compound semiconductor in the laminating direction. In this manner, the band structure, that is, the energy at the upper end of the valence band and the energy at the lower end of the conduction band are inclined according to the inclination of the band gap energy formed by the inclination of the mixed crystal ratio.

Preferably, the gradient barrier layer has a band gap energy inclined by changing an impurity concentration in the laminating direction. With this configuration, the band gap energy is inclined according to the carrier concentration gradient formed by the impurity concentration gradient, and the band structure, that is, the energy at the upper end of the valence band and the energy at the lower end of the conduction band are inclined with respect to the vacuum level. , A gradient barrier layer having a tilted band structure is provided.

Preferably, the band structure of the gradient barrier layer, that is, the gradient of energy at the upper end of the valence band and the lower end of the conduction band is 0.05 to 0.1 (eV) per barrier layer in which carriers reach each of the plurality of well layers. ) Degree. In other words, the response speed is improved as the slope becomes larger. However, as the minimum value of the energy at the upper end of the valence band of the barrier layer becomes smaller and the maximum value of the energy at the lower end of the conduction band becomes larger, that is, the band gap energy becomes larger. Since the driving voltage (forward voltage) becomes higher, the above range is desirable in order to reduce the power consumption and keep the driving voltage at about 1.6 to 2.5 (V), which can ensure high reliability.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the following examples, the dimensional ratios and the like of each part are not necessarily drawn accurately.

FIG. 1 is a diagram showing a configuration of a surface emitting type light emitting diode (hereinafter, simply referred to as a light emitting diode) 10 which is an embodiment of the surface emitting element of the present invention. In the figure, a light emitting diode 10 is, for example, a MOCVD (Metal Orga
The substrate 12 is formed by an epitaxial growth technique such as a nic Chemical Vapor Deposition method.
The substrate-side reflective layer 14, the first barrier layer 16, the first active layer 18, the second barrier layer 20, and the second
The active layer 22, the third barrier layer 24, the third active layer 26, the fourth
Barrier layer 28, radiation side reflection layer 30, cladding layer 32,
And a current blocking layer 34, and a lower electrode 36 and an upper electrode 38 fixed to the lower surface of the substrate 12 and the upper surface of the current blocking layer 34, respectively.

The substrate 12 is, for example, a compound semiconductor made of n-GaAs single crystal having a thickness of about 350 (μm). Also,
The substrate-side reflection layer 14 is, for example, n-AlAs having a thickness of about 70 (nm).
A compound semiconductor composed of a single crystal and, for example, a compound semiconductor composed of an n-Al _0.2 Ga _0.8 As single crystal having a thickness of about 60 (nm),
A so-called n-type distributed reflection type semiconductor multilayer film reflection layer (DBR) is formed by alternately stacking, for example, 30 sets such that the former is on the substrate 12 side. The thickness of each layer constituting the substrate-side reflection layer 14 is the same as that of the first active layer 18 to the third active layer 2.
6 (hereinafter, referred to as active layers 18 to 26 when not particularly distinguished) is about 1/4 wavelength of the peak wavelength of light (not the peak wavelength of individual light, but the peak wavelength of synthesized light described later). It has been decided to be.

The first to fourth barrier layers 16 to 28 (hereinafter referred to as barrier layers 16 to 28 unless otherwise specified)
Are compound semiconductors composed of i-Al _x Ga _1-x As single crystals. The thickness of each layer is about 58 (nm) for the first barrier layer 16 and the fourth barrier layer 28, and 116 (n) for the second barrier layer 20 and the third barrier layer 24, respectively.
m). Thus, the active layer 18 to 26 mutual distance d _12, d ₂₃ are both in the extent 116 (nm). These intervals d ₁₂ and d ₂₃ are values of a combined peak wavelength, which will be described later, that is, about a half wavelength of the resonance wavelength. The first
The mixed crystal ratio x of Al in the barrier layers 16 to 28 is:
As shown in FIG. 2, while the first and second barrier layers 16 and 20 are each linearly reduced in the direction from the substrate-side reflection layer 14 to the radiation surface-side reflection layer 30,
The third and fourth barrier layers 24 and 28 are each linearly increased. That is, the third and fourth barrier layers 24 and 28
In the graph, the mixed crystal ratio x of Al is linearly reduced in the direction from the radiation surface side reflection layer 30 to the substrate side reflection layer 14. Specifically, the respective mixed crystal ratios x are about 0.4 at the interface between the first barrier layer 16 and the substrate-side reflection layer 14, about 0.2 at the interface with the first active layer 18, and the second barrier layer 20 is The third barrier layer 24 is about 0.2 at the interface with the second active layer 22, about 0.4 at the interface with the first active layer 18, about 0.2 at the interface with the second active layer 22, and about 0.2 at the interface with the second active layer 22. The fourth barrier layer 28 is set to about 0.2 at the interface with the third active layer 26, and about 0.4 at the interface with the radiation surface side reflection layer 30.

Each of the active layers 18 to 26 is made of i-Ga
This is a so-called quantum well composed of a compound semiconductor composed of an As single crystal. The thickness of each layer is, for example, the first active layer 18.
Is about 7.5 (nm), the second active layer 22 is about 9.0 (nm), and the third
The active layer 26 has a thickness of about 12.5 (nm). Therefore, the peak wavelengths of the emission spectra of the active layers 18, 22, 26 at room temperature are about 838 (nm), about 846 (nm), respectively.
It is about 856 (nm). In this embodiment, the active layer 18
26 to 26 and the barrier layers 16 to 28 correspond to a plurality of well layers and a plurality of barrier layers constituting the light emitting layer having the quantum well structure.

The radiation-surface-side reflection layer 30 comprises, for example, a compound semiconductor made of a p-AlAs single crystal having a thickness of about 70 (nm);
For example, the substrate is formed by alternately stacking ten sets of compound semiconductors made of p-Al _0.2 Ga _0.8 As single crystal having a thickness of about 60 (nm) such that the latter is on the fourth barrier layer 28 side. This is a DBR similar to the side reflection layer 14. In this embodiment,
The substrate-side reflection layer 14 and the radiation surface-side reflection layer 30 correspond to a pair of reflection layers, and the distance between them, that is, the optical resonator length is a value converted into the length in a vacuum (that is, the refractive index n = 1). For example, L is about 1260 (nm), that is, about 1.5 times as long as a peak wavelength (= 841 [nm]) of a combined light spectrum described later. For this reason, the light generated in the active layers 18 to 26 is repeatedly reflected by the substrate-side reflection layer 14 and the radiation-surface-side reflection layer 30, and forms a standing wave 40 as shown in FIG. Become. That is, the substrate side reflection layer 14 and the radiation surface side reflection layer 30
Constitutes an optical resonator that repeatedly reflects light generated in the light emitting layer. At this time, the optical resonator length and the barrier layers 16 to
Since the thickness of the active layer 28 is set as described above, as shown in FIG.
Located on the belly of the.

The cladding layer 32 has a thickness of, for example, 2
(μm) is a compound semiconductor composed of a single crystal of p-Al _0.2 Ga _0.8 As, and the current blocking layer 34 has a thickness of about 1 (μm), for example.
It is a compound semiconductor composed of n-Al _{0. 2} Ga _0.8 As a single crystal. The upper side of the cladding layer 32 and the current blocking layer 3
4, a high-concentration diffusion region 42 in which an impurity (eg, Zn or the like) which is a p-type dopant is diffused at a high concentration is formed in a part indicated by oblique lines. In the high concentration diffusion region 42, the cladding layer 3
2, the conductivity type of the current blocking layer 34 is reversed and the current blocking layer 34 is made a p-type semiconductor. For this reason, in the light emitting diode 10, a current constriction structure is formed in which the conduction type of the current blocking layer 34 is reversed only up to the boundary between the current blocking layer 34 and the cladding layer 32 and can be conducted only through a path passing through the central conducting region. .

The lower electrode 36 is, for example, 1 (μm)
For example, an Au—Ge alloy, Ni, and Au are sequentially formed on the entire lower surface of the substrate 12 from the substrate 12 side. The upper electrode 38 is, for example, 1 (μ
m), and the Au-Zn alloy and Au are laminated in order from the current blocking layer 34 side on the peripheral edge of the surface 44 of the current blocking layer 34 except for the central circular region. . Both the lower electrode 36 and the upper electrode 38 are ohmic electrodes.

The upper electrode 38 of the current blocking layer 34
In the circular area located on the inner peripheral side of the
m). The current-carrying area is provided with a similar diameter just below the concave portion 46, and the diameter of the light-extracting section 48 from which light is emitted is substantially the same as the diameter of the current-carrying area. The concave portion 46 is formed, for example, by etching or the like in order to increase the diffusion depth in a range where a current-carrying region is formed when impurities are diffused from the surface 44 side.

Light emitting diode 1 configured as above
0 is manufactured, for example, as follows. First, the substrate-side reflection layer 1 is formed on the substrate 12 by MOCVD, for example.
The epitaxial wafer is manufactured by sequentially growing crystals from No. 4 to the current blocking layer 34. Next, on the surface 44 of the current blocking layer 34, a resist is formed in a central portion except for a circular region having a diameter of, for example, about 50 (μm), and for example, using an etching solution containing ammonia and a hydrogen peroxide solution, Surface 4
Etching is performed from the 4 side. As a result, only the central portion of the current blocking layer 34 is selectively etched, so that the recess 46 is formed.

Thereafter, the resist is removed, and Zn is diffused from the surface 44 by, for example, thermal diffusion such as a sealed tube diffusion method, so that the portion where the recess 46 is formed has an intermediate depth of the cladding layer 32. By the way, the portion where the concave portion 46 is not formed is to the middle depth of the current blocking layer 34, respectively.
Doping with Zn forms the high concentration diffusion region 42 described above. In the sealed tube diffusion method, the epitaxial wafer is vacuum-enclosed in a quartz ampoule together with a diffusion source (for example, ZnAs ₂ ), and is placed in an electric furnace or the like at a temperature of about 600 (° C.).
It heats for about an hour. Thereafter, the lower electrode 36 and the upper electrode 38 are formed, and the light emitting diode 10 is obtained by cutting the light emitting diode into blocks corresponding to individual light emitting diodes. The light emitting diode 10 is, for example, a TO18 (not shown).
It is used in a state of being die-bonded and sealed to a flat stem or the like.

When the above-described light emitting diode 10 is used, a positive voltage is applied to the upper electrode 38 and a negative voltage is applied to the lower electrode 36, so that the light emitting diode 10 is placed on the upper side of the light emitting diode 10 through a path passing through the above-mentioned energizable region. A current flows from the bottom to the bottom, and the active layers 18, 22, and 26 are excited to emit light, and the emission of light is stopped by stopping the application of the driving voltage. At this time, as shown in FIG. 2, the barrier layers 16 to 28 constituting the light-emitting layer all have the mixed crystal ratio x of Al which is inclined, so that the band structure is shown in FIG. In the light emitting layer, the energy Ec at the lower end of the conduction band and the energy Ev at the upper end of the valence band of the barrier layers 16 to 28 are both carrier (electrons on the conduction band side and holes or holes on the valence band side). It is inclined so that it becomes lower toward any of the active layers 18 to 26 along the direction. That is,
In this embodiment, each of the barrier layers 20 and 24 located between the active layers 18 to 26 corresponds to an inclined barrier layer in which the band structure is inclined, and is located outside the active layers 18 to 26. The barrier layers 16 and 28 are also configured as inclined layers having an inclined band structure. Therefore, when the light emission is stopped, the carriers injected up to that time and accumulated in the barrier layers 16 to 28 are promptly moved to the active layers 18 to 26 along the above-described energy gradient and recombined there. , light emission stop the application of the drive voltage is actually shorter fall time t _f until stop, high response speed.

In the above band structure, the energy Ec at the bottom of the conduction band is about 3.37 to 3.22 (eV) for the first barrier layer 16 and the second barrier layer 20, respectively, and the third barrier layer 24 and the fourth barrier layer 28 are 3.22 to 3.37 (e
V). The energy Ev at the upper end of the valence band is about 1.45 to 1.55 (eV) for the first barrier layer 16 and the second barrier layer 20, and 1.55 to 1.45 (eV) for the third barrier layer 24 and the fourth barrier layer 28, respectively. )
It is inclined to the extent of the degree. That is, the tilt state of the band structure of the first to fourth barrier layers 16 to 28 is sufficiently set such that the energy gradient at the upper end of the valence band where the effective mass of carriers is large is about 0.1 (eV) per barrier layer. Also, the energy gradient at the bottom of the conduction band is in the opposite direction to the top of the valence band, so that the electrons and holes remaining in the first to fourth barrier layers 16 to 28 respectively become active layers 18.
Are set so that they can be moved to the same one of.

Moreover, the active layer 1 composed of three quantum wells
The light-emitting layer constituted by 8 to 26 is a pair of reflective layers 1
Since the active layers 18 to 26 are provided in the optical resonator (micro-resonator) formed by the light-emitting devices 4 and 30, the light having a narrow emission spectrum width having a wavelength satisfying the resonance condition can be generated in the active layers 18 to 26. Only. However, since the active layers 18 to 26 constituting the light emitting layer of the light emitting diode 10 are quantum wells provided with different thicknesses from each other, each of the above light emission peaks (that is, each of them is used alone as a light emitting layer). In this case, the emission spectrum of the emitted light is different from each other, and the emitted emission spectrum is light having a wide gain width and a high output when they are superimposed. Peak wavelength of synthesized light spectrum (synthetic peak wavelength)
That is, the peak wavelength of the gain is, for example, about 841 (nm).

In short, in the present embodiment, the plurality of barrier layers 16 to 28 correspond to the inclined barrier layers which are located between the plurality of active layers 18 to 26 and whose band structure is inclined toward the lamination direction. And a second barrier layer 20 and a third barrier layer 24. Therefore, in the second barrier layer 20 and the third barrier layer 24, the energy Ev at the upper end of the valence band and the energy Ec at the lower end of the conduction band are inclined. Since the carriers are quickly moved along the energy gradient, the moving speed of the carriers remaining in the barrier layers 20 and 24 is increased when the light emission is stopped when the application of the driving voltage is stopped. Accordingly, the fall time t _f is shortened in the light emitting diode 10 having the multiple quantum well structure, high external quantum efficiency and high and response speed with both surface-emitting device can be obtained. Moreover, in the present embodiment, since the barrier layers 16 and 28 located outside the active layers 18 to 26 are also configured as inclined layers having an inclined band structure, carriers remaining in these layers when light emission stops are reduced. Similarly, a faster response is obtained because they are also moved and recombined quickly.

On the other hand, in a conventional light emitting diode having a multiple quantum well structure, as shown in a band structure in FIG.
The barrier layers 50 and 52 located between 8 and 26 had a flat band structure, that is, the energies Ev and Ec at the upper end of the valence band and the lower end of the conduction band. Therefore, when light emission is stopped, a flat band layer is formed, and the carrier moving speed depends exclusively on the diffusion speed.
In the light emitting diode having the optical resonator structure in which the barrier layers 20 and 24 located between the six layers are thickened, the response speed is reduced. In the above conventional light emitting diode, the first barrier layer 16 and the fourth barrier layer 2
Although the energies Ev and Ec of FIG. 8 are not necessarily flattened as shown by a dashed line, they may have an inclined structure as shown by a solid line. Barrier layer (second barrier layer 50, third barrier layer
The barrier layer 52) has the above problem because the energies Ev and Ec are flat.

In this embodiment, the barrier layer 16
The energy gradient per barrier layer at the bottom of the conduction band and the top of the valence band of ~ 28 is about 0.1 (eV) in the valence band and about 0.15 (eV) in the conduction band. Therefore, the maximum value of the band gap energy is kept sufficiently low,
The increase in drive voltage is suppressed.

Next, another embodiment of the present invention will be described. In the following description, portions common to the above-described embodiment will be omitted.

FIGS. 5 to 7 each show a band structure of a light emitting layer which is a main part of a surface light emitting device of another embodiment, and correspond to FIG. 3 of the above embodiment. In FIG. 5, a barrier layer 54 located between the active layers 18 to 26,
In the barrier layer 56, for example, the mixed crystal ratio x of Al is increased from the first active layer 18 toward the second active layer 22 in the barrier layer 54, and from the second active layer 22 to the third active layer 26 in the barrier layer 56. 3, the inclination directions of the energy Ev at the upper end of the valence band and the energy Ec at the lower end of the conduction band are opposite to those in FIG. Therefore, when light emission is stopped, the barrier layer 5
3, carriers on the barrier layer 54 face the first active layer 18 and carriers on the barrier layer 56 face the third active layer 26, contrary to the case of FIG. However, even in this case, when the application of the driving voltage is stopped, the carriers are quickly moved and recombined in the active layers 18 to 26. The response speed is improved.

In the embodiment shown in FIG.
Two active layers 62 and 64 are provided in the light emitting layer,
The barrier layer 58 located therebetween has an energy Ev at the upper end of the valence band from the center in the thickness direction (stacking direction, that is, the moving direction of the carrier) toward both the active layers 62 and 64.
And the band structure is such that the energy Ec at the bottom of the conduction band is inclined. Even in this case, the carriers remaining on the barrier layer 58 when the light emission is stopped are promptly formed on the active layers 62 and 6.
4, the same effect of improving the response speed can be obtained. The present invention is applicable not only to the case where three active layers 18 to 26 are provided as shown in FIG. 3 and the like, but also to a surface emitting element having a plurality of active layers.
The same applies to the case where two active layers 62 and 64 are provided as shown in the figure and the case where four or more active layers are provided.

Further, the embodiment shown in FIG.
By changing the impurity concentration of the barrier layer 60 along the lamination direction, the band structure, that is, the energies Ec and Ev at the lower end of the conduction band and the upper end of the valence band are inclined while the band gap energy is kept constant. In this case, the inclination directions of the two are opposite to each other, but even in this case, the carriers remaining on the barrier layer 60 are quickly moved into the active layers 62 and 64 when the light emission is stopped. An improvement effect is obtained similarly. That is, the method of inclining the band structure, that is, the energy Ec, Ev of the conduction band lower end and the valence band upper end, is not limited to the method of changing the mixed crystal ratio, but may be changed by changing the impurity concentration.

While the embodiment of the present invention has been described in detail with reference to the drawings, the present invention can be embodied in still another embodiment.

For example, in the embodiment, the case where the present invention is applied to the light emitting diode 10 has been described.
For example, the present invention is similarly applied to an optical resonator of another surface emitting element such as a VCSEL.

In the embodiment, the active layer 18 and the like
The case where the present invention is applied to the AlGaAs-based light emitting diode 10 composed of GaAs has been described. However, the present invention is also applicable to a case where each semiconductor layer is composed of a compound semiconductor such as a GaAsP single crystal or an InGaAsP single crystal. The same applies.

In the embodiment, the substrate-side reflection layer 14 and the radiation-surface-side reflection layer 3 made of a semiconductor multilayer film reflection layer are used.
Although a pair of reflective layers is formed by 0, a pair of reflective layers may be formed of a dielectric thin film, a metal thin film, or the like.

In the embodiment, the case where the present invention is applied to the light emitting diode 10 for a point light source that extracts light only from the light extraction portion 48 provided at the center of the surface 44 has been described. The present invention can be similarly applied to a light emitting diode of a full-surface light emitting type that extracts light from substantially the entire surface.

Further, in the embodiment, the energy gradient of the barrier layer 16 and the like is set to be less than 0.1 per barrier layer in the valence band.
Although it was set to about 1 (eV), this value can be appropriately changed within a range where the forward voltage is not so high.

In the embodiment, the barrier layers 16 to
Although all of the barrier layers 28 and the like have an inclined structure, the effect of the present invention can be obtained if at least a part of the barrier layer located between the active layers 18 to 26 has an inclined structure. For example, each of the barrier layers 16 and 28 located outside the plurality of active layers 18 to 26 may not have an inclined structure, and only one of the barrier layers 20 and 24, that is, between the plurality of active layers, The effect of the present invention can be obtained even if only some of the plurality of barrier layers provided have an inclined structure.

In the embodiment, the active layers 18 to 2
6 have different thicknesses, so that three light emitting layers having mutually different peak wavelengths are provided in the light emitting layer. The film thickness may be set so that the peak wavelength may be different, or the film thickness may be set so that some peak wavelengths are the same and the remaining peak wavelengths are different.

Although not specifically exemplified, the present invention
Various changes can be made without departing from the spirit of the invention.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a light emitting diode as one embodiment of a surface light emitting device of the present invention.

FIG. 2 is a diagram for explaining a gradient of a mixed crystal ratio of a light emitting portion of the light emitting diode of FIG.

FIG. 3 is a diagram illustrating a main part of a band structure of the light emitting diode of FIG. 1;

FIG. 4 is a diagram corresponding to FIG. 3, illustrating a main part of a band structure of a conventional light emitting diode.

FIG. 5 is a diagram illustrating a main part of a band structure according to another embodiment of the present invention.

FIG. 6 is a diagram illustrating a main part of a band structure according to still another embodiment of the present invention.

FIG. 7 is a diagram illustrating a main part of a band structure according to still another embodiment of the present invention.

[Explanation of symbols]

10: Light emitting diode (surface emitting element) 素 子 14: substrate side reflection layer, 30: radiation surface side reflection layer｝ (a pair of reflection layers) ｛18: first active layer, 22: second active layer, 26: third Active layer (a plurality of well layers) {20: second barrier layer, 24: third barrier layer} (gradient barrier layer)

Claims (3)

[Claims] 1. A light emitting layer having a quantum well structure in which a plurality of barrier layers and a plurality of well layers are alternately arranged, and light generated in the light emitting layer is provided so as to sandwich the light emitting layer. A surface light emitting device of a type in which a plurality of compound semiconductor layers including a pair of reflective layers constituting an optical resonator are stacked and light generated in the light emitting layer is extracted from the surfaces of the plurality of compound semiconductor layers. The surface emitting device according to claim 1, wherein the plurality of barrier layers include an inclined barrier layer located between the plurality of well layers and having a band structure inclined in a stacking direction. 2. The surface-emitting device according to claim 1, wherein the gradient barrier layer has a band gap energy inclined by changing a mixed crystal ratio of the compound semiconductor in the stacking direction. 3. The surface-emitting device according to claim 1, wherein the gradient barrier layer has a band gap energy inclined by changing an impurity concentration in the stacking direction.