WO2018008381A1

WO2018008381A1 - Optical element, active layer structure, and display device

Info

Publication number: WO2018008381A1
Application number: PCT/JP2017/022624
Authority: WO
Inventors: 義昭渡部; 河角　孝行
Original assignee: ソニー株式会社
Priority date: 2016-07-04
Filing date: 2017-06-20
Publication date: 2018-01-11
Also published as: JP7147560B2; JPWO2018008381A1; DE112017003372T5

Abstract

[Problem] To provide an optical element with which light having a high output and a wide spectrum width can be emitted, and to provide an active layer structure and a display device. [Solution] An optical element of the present technology comprises a first conductivity-type layer, a second conductivity-type layer, and an active layer. The first conductivity-type layer has a current constriction structure that is configured so as to constrict an injection region of a current. The active layer is provided between the first conductivity-type layer and the second conductivity-type layer, and includes a single quantum well layer or multiple quantum well layers. The thickness of the single quantum well layer is 10 nm or less, and the total thickness of the multiple quantum well layers is 10 nm or less.

Description

Optical element, active layer structure, and display device

This technology relates to the technology of super luminescent diode (SLD).

A super luminescent diode (SLD) is a light-emitting element that has a characteristic of emitting light with a narrow emission angle and strong intensity, such as the emission state of a semiconductor laser, while having a broad emission spectrum width relatively close to that of a light-emitting diode. is there. This SLD is applied to the field of interferometers such as fiber gyros. In recent years, application to displays is also expected as a light source for image projection with low interference noise due to its low coherence.

For example, Patent Document 1 discloses an SLD including a linear ridge waveguide followed by a curved waveguide. Light generated in the active layer immediately below the ridge waveguide travels through the curved waveguide and is emitted in a direction non-perpendicular to the end face of the SLD. This prevents the reflected light from the end face from returning to the waveguide.

In short, the SLD does not have a structure in which light is reciprocated by a mirror provided on both end faces and resonates (laser oscillation) unlike a normal laser diode (LD), but light is made to pass through the waveguide in one direction. It has a structure to be amplified (stimulated emission is performed). The first light generation source is spontaneous emission light generated in the active layer near the rear end face of the SLD (end face opposite to the light exit end face). The SLD has a structure in which light having a wide spectral width is directly amplified by a waveguide to increase the intensity and output.

JP-A-2-310975

In the above-described SLD, output light output is required to be improved for application to a display or the like. However, the output of the emitted light and the spectral width are in a trade-off relationship, and it is not easy to increase the output of the emitted light and realize a wide spectral width.

In view of the circumstances as described above, an object of the present technology is to provide an optical element, an active layer structure, and a display device that can emit light with high output and a wide spectrum width.

In order to achieve the above object, an optical element according to an embodiment of the present technology includes a first conductivity type layer, a second conductivity type layer, and an active layer.
The first conductivity type layer has a current confinement structure configured such that a current injection region is constricted.
The active layer is an active layer provided between the first conductivity type layer and the second conductivity type layer, and has one quantum well layer or a plurality of quantum well layers. The thickness of the quantum well layer is 10 nm or less, and the total thickness of the plurality of quantum well layers is 10 nm or less.

According to this configuration, by reducing the thickness of the quantum well layer, the light confinement effect in the quantum well is reduced, and the utilization efficiency of spontaneous emission light is reduced. For this reason, the carrier density required to start light emission increases, and the amount of spontaneous emission light emitted per unit volume increases. Also in the gain region where the spontaneous emission light is amplified, the carrier density is high, so that the gain and the spectral width are also increased. As a result, the light emitted from the optical element can be made to have a high output and a wide spectrum width.

The one quantum well layer or the plurality of quantum well layers may be made of AlInGaP.

When the quantum well layer is made of AlInGaP, red light is emitted from the optical element.

The active layer has the one quantum well layer,
The one quantum well layer may be made of AlInGaN.

When the quantum well layer is made of AlInGaN, blue-violet to green light is emitted from the optical element.

The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The thickness of the first guide layer is 10 nm or more and 500 nm or less,
The thickness of the second guide layer may be 10 nm or more and 500 nm or less.

The light confinement ratio in the quantum well can be adjusted by the thickness of the first guide layer and the second guide layer. Specifically, by setting the thickness of these layers to 10 nm or more and 500 nm or less, the optical confinement ratio in the quantum well can be 3% or less.

The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The difference in refractive index between the first cladding layer and the first guide layer is 0.03 or more and 0.50 or less,
The difference in refractive index between the second cladding layer and the second guide layer may be not less than 0.03 and not more than 0.50.

When the quantum well layer is made of AlInGaP and the emission color is red, the refractive index difference between the first cladding layer and the first guide layer and the refractive index difference between the second cladding layer and the second guide layer are 0.03 or more and 0.50. By making it below, the light confinement rate in the quantum well can be made 3% or less.

The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The refractive index difference between the first cladding layer and the first guide layer is 0.01 or more and 0.10 or less,
The difference in refractive index between the second cladding layer and the second guide layer may be not less than 0.01 and not more than 0.10.

When the quantum well layer is made of AlInGaN and the emission color is from violet to green, the refractive index difference between the first cladding layer and the first guide layer and the refractive index difference between the second cladding layer and the second guide layer are 0.01 or more. By setting it to 0.10 or less, the light confinement ratio in the quantum well can be set to 3% or less.

The active layer may have a light confinement rate of 3% or less in the quantum well.

By setting the light confinement ratio in the quantum well to 3% or less, the light emitted from the optical element can be output with high output and wide spectrum width as described above.

In order to achieve the above object, an optical element according to an embodiment of the present technology includes a first conductivity type layer, a second conductivity type layer, and an active layer.
The first conductivity type layer has a current confinement structure configured such that a current injection region is constricted.
The active layer is an active layer provided between the first conductivity type layer and the second conductivity type layer, and has one quantum well layer or a plurality of quantum well layers. The light confinement rate is 3% or less.

The thickness of the first guide layer is 50 nm or more and 200 nm or less,
The thickness of the second guide layer may be 50 nm or more and 200 nm or less.

Considering the control of the light emission pattern (spreading of the emitted light) and the confinement of carriers, the thickness of the first guide layer and the second guide layer is more preferably 50 nm or more and 200 nm or less.

The refractive index difference between the first cladding layer and the first guide layer is 0.06 or more and 0.30 or less,
The difference in refractive index between the second cladding layer and the second guide layer may be not less than 0.06 and not more than 0.30.

When the emission color is red, taking into consideration the control of the emission pattern (spreading of emitted light) and the confinement of carriers, the refractive index difference between the first cladding layer and the first guide layer and the refraction of the second cladding layer and the second guide layer. The rate difference is preferably 0.06 or more and 0.30 or less.

The refractive index difference between the first cladding layer and the first guide layer is 0.02 or more and 0.06 or less,
The refractive index difference between the second cladding layer and the second guide layer may be not less than 0.02 and not more than 0.06.

When the emission color is blue violet to green, considering the control of the emission pattern (spreading of the emitted light) and the confinement of carriers, the difference in refractive index between the first cladding layer and the first guide layer and the second cladding layer and the second guide layer The refractive index difference is preferably 0.02 or more and 0.06 or less.

The optical element may be a super luminescence diode.

The optical element may be an optical amplifier.

In order to achieve the above object, an active layer structure according to an embodiment of the present technology includes a first conductivity type layer having a current confinement structure configured to confine a current injection region, a second conductivity type layer, It is an active layer structure of an optical element comprising an active layer provided between the first conductivity type layer and the second conductivity type layer.
The active layer has one quantum well layer or a plurality of quantum well layers, the thickness of the one quantum well layer is 10 nm or less, and the total thickness of the plurality of quantum well layers is 10 nm. It is as follows.

In order to achieve the above object, a display device according to an embodiment of the present technology includes an optical element and an image generation unit.
The image generation unit can scan the light emitted from the optical element in a two-dimensional manner, and can control the luminance of the projected light based on the image data.
The optical element includes a first conductivity type layer, a second conductivity type layer, and an active layer.
The first conductivity type layer has a current confinement structure configured such that a current injection region is constricted.
The active layer is an active layer provided between the first conductivity type layer and the second conductivity type layer, and has one quantum well layer or a plurality of quantum well layers. The thickness of the quantum well layer is 10 nm or less, and the total thickness of the plurality of quantum well layers is 10 nm or less.

As described above, according to the present technology, it is possible to provide an optical element, an active layer structure, and a display device that can emit light with high output and a wide spectrum width. Note that the effects described here are not necessarily limited, and may be any of the effects described in the present disclosure.

It is the perspective view and top view which show the optical element which concerns on one Embodiment of this technique. It is sectional drawing of the optical element shown in FIG. It is a schematic diagram which shows the band structure of the optical element shown in FIG. It is a graph which shows the relationship between the well width and spectrum width of a quantum well. It is a table | surface which shows the characteristic of the optical element of embodiment of this technique, and the optical element of conventional structure. It is a graph which shows the relationship between the wavelength by a carrier density, and a gain. It is a graph which shows the relationship between the electric current by the well width of a quantum well, and an output. It is a graph which shows the relationship between the wavelength by the well width of a quantum well, and intensity | strength. It is a graph which shows the relationship between the optical confinement rate to a quantum well, and a spectrum width. It is a schematic diagram which shows the band structure of the optical element which has multiple quantum well layers. It is sectional drawing which shows the layer structure of the active layer of the optical element shown in FIG. It is a mimetic diagram showing a display concerning one embodiment of this art.

(Optical element structure)
FIG. 1A is a schematic perspective view showing an optical element 100 according to an embodiment of the present technology, and FIG. 1B is a plan view thereof. 2 is a cross-sectional view taken along the line CC in FIG. 1B. This optical element is, for example, a ridge type superluminescent diode (SLD) having a ridge portion 10 in a p-type or n-type conductive layer.

The optical element 100 includes a p-type electrode layer (or a contact layer in contact with a p-type electrode layer not shown) 11 from the top in FIG. 2, a p-type first conductivity type layer 13 among the semiconductor layers, an active layer 20, and a semiconductor. Among the layers, an n-type second conductivity type layer 14, an n-type semiconductor substrate 15, and an n-type electrode layer (or a contact layer in contact with an n-type electrode layer not shown) 12 are provided.

The first conductivity type layer 13 includes a p-type cladding layer 131 and a p-type guide layer 132 formed in this order from the p-type electrode layer 11 side. The second conductivity type layer 14 includes an n-type cladding layer 141 and an n-type guide layer 142 formed in this order from the substrate 15 side. For example, the ridge portion 10 is configured by the p-type electrode layer 11 and the p-type cladding layer 131. An n-type buffer layer may be provided between the substrate 15 and the second conductivity type layer 14. As shown in FIG. 1B, the optical element 100 includes a light exit end face 33 and a rear end face 35 that is an end face opposite to the light exit end face 33.

As shown in FIG. 1B, the ridge portion 10 has a linear portion 10a and a curved portion 10b. The linear portion 10a is linearly extended along a direction perpendicular to the rear end surface 35, and the curved portion 10b is extended in a curved shape continuously to the linear portion 10a. The ridge portion 10 does not necessarily have the linear portion 10a and the curved portion 10b, and may be configured linearly from the rear end surface 35 to the light emitting end surface 33.

The first conductivity type layer 13 has a current confinement structure 32 as shown in FIG. Specifically, the current confinement structure 32 configured to confine the current injection region from the p-type electrode layer 11 to the active layer 20 is formed by the structure of the ridge portion 10. Thereby, an optical waveguide along the longitudinal direction of the ridge portion 10 is formed near the ridge portion 10 in the active layer 20.

An insulating layer (not shown) is formed on the p-type guide layer 132 and around the ridge portion 10.

Note that the lower end of the p-type cladding layer 131 coincides with the lower end of the ridge portion 10, but this need not be the case, and the lower end of the ridge portion 10 includes a part of the p-type guide layer 132. Also good.

As shown in FIG. 1B, a low reflection mirror film 18 is provided on the light emitting end face 33, and a high reflection mirror film 19 is provided on the rear end face 35 on the opposite side.

When a current is applied between the p-type electrode layer 11 and the n-type electrode layer 12, spontaneous emission light is generated in the active layer 20 near the rear end face 35. Spontaneous emission light is amplified by stimulated emission while traveling through the optical waveguide toward the light exit end face 33. Of the spontaneously emitted light, the light traveling toward the rear end face 35 is reflected by the highly reflective mirror film 19 and amplified while traveling toward the light exit end face 33. The amplified light is emitted from the light emitting end face 33 through the low reflection mirror film 18. 1A and 1B show the emitted light L of the optical element 100. FIG.

When the ridge portion 10 includes the linear portion 10a and the curved portion 10b, the light emitted from the active layer 20 is emitted in a direction inclined from the vertical direction with respect to the light emitting end surface 33. Thereby, the reflected light slightly generated in the low reflection mirror film 18 is prevented from returning to the active layer 20. This is because laser oscillation occurs when the reflected light from the low reflection mirror film 18 returns to the active layer 20.

Note that, as described above, the ridge portion 10 may be composed of only a linear portion. Further, a low reflection mirror film may be provided instead of the high reflection mirror film 19. In this case, the light emitted from the optical element 100 is emitted from both ends of the optical element 100.

The optical element 100 can be used as an SLD, but can also be used as an amplifier for amplifying light generated by another light source. In this case, an antireflection film is provided in place of the high reflection mirror film 19. Light generated by another light source enters the optical waveguide through the antireflective film and is amplified while traveling through the optical waveguide.

(Active layer structure)
The active layer structure of the optical element 100 will be described. FIG. 3 is a schematic diagram showing the band structure of each layer. The horizontal direction indicates energy (E in the figure), and indicates that the energy is higher toward the left side. The vertical direction indicates the stacking direction of the layers constituting the optical element 100. The lower energy band is a valence band (VB), and the higher energy band is a conduction band (CB).

The active layer 20 has a single quantum well layer 20a. As shown in FIG. 3, the quantum well layer 20a is a layer having a smaller band gap than the surrounding layers (p-type guide layer 132 and n-type guide layer 142). When a current is applied between the p-type electrode layer 11 and the n-type electrode layer 12, electrons existing in the conduction band (CB) are transferred to holes in the valence band (VB) through the band gap of the quantum well layer 20a. Recombine with each other to produce light emission. The band gap of the quantum well layer 20a is called a light emission recombination level energy gap.

(About the thickness of the quantum well layer)
The thickness T of the quantum well layer 20a is the width of the quantum well formed by the quantum well layer 20a. The well width T is preferably 10 nm or less.

FIG. 4 is a graph showing the relationship between the well width T and the SLD spectrum width (left axis) and the relationship between the well width T and the PL spectrum width (right axis). The SLD spectral width is the spectral width of light (SLD) emitted from the optical element 100, and the PL spectral width is the spectral width of spontaneous emission light (PL: Photoluminescence) generated in the quantum well layer 20a.

As shown in the figure, when the well width T is reduced, the PL spectrum width is reduced. This is because the transition level in the quantum well contributing to light emission decreases as the well width T decreases. For this reason, there has been no reason to use a single-layer thin quantum well layer for SLD in the past.

For example, as a conventional SLD structure, there is a structure including an active layer having a plurality of thin quantum wells (hereinafter, conventional structure 1). In this structure, in order to widen the spectrum width, the wavelength of each quantum well is changed variously to obtain a wide spectrum width. On the other hand, in a structure including a plurality of quantum wells, injected carriers are dispersed in the plurality of quantum wells, the carrier distribution is likely to be non-uniform, and high gain is difficult to obtain.

For this reason, an SLD (hereinafter, conventional structure 2) having an active layer having a single layer and a thick quantum well has been developed. In this structure, carriers are concentrated in a single-layer quantum well, and light of various wavelengths is emitted at many energy levels contained therein. However, even with this structure, the output is insufficient, and is not particularly suitable for display applications.

On the other hand, the active layer 20 according to the present embodiment has a single quantum well layer 20a as described above. When the well width T is reduced, the PL spectrum width is reduced, so that the SLD spectrum width is also expected to be reduced (broken line in the figure).

However, in practice, it has been found that when the well width T is reduced, the SLD spectral width is improved as shown in box A in the figure. FIG. 5 is a table showing the characteristics of the SLD having the conventional structure and the SLD according to the present embodiment.

As shown in the “present embodiment” in the figure, when the well width T is reduced, the optical confinement effect in the quantum well is reduced, and the coupling ratio of spontaneously emitted light (light that is the source of SLD light emission) to the optical waveguide is reduced. Therefore, the utilization efficiency of spontaneously emitted light is reduced.

Therefore, in order to start SLD light emission, a carrier density several times higher than that of the conventional structure is required. As a result, since the carrier density is high at the start of SLD light emission, the amount of spontaneous emission light emitted per unit volume increases. Also in the gain region where spontaneous emission light is amplified (region where spontaneous emission light is amplified), the carrier density is high, so the gain and spectral width are also large.

FIG. 6 is a graph showing the relationship between the spectrum width and the gain depending on the carrier density. As shown in the figure, when the carrier density at the start of SLD light emission is large, both the spectrum width and the gain are improved.

Furthermore, since the well width T is small and the carrier density is large, the quantum effect of the quantum well is increased, the use efficiency of injected carriers is promoted, and the output and temperature characteristics are improved. Moreover, the active layer loss is also reduced by reducing the volume of the active layer 20.

As a result, it is possible to achieve a wide spectrum width which has been considered difficult when the well width T is small, and to achieve high output and high efficiency at the same time.

FIG. 7 is a graph showing the relationship between the current supplied to the optical element 100 and the output of the emitted light from the optical element 100, and shows the calculation results when the well width T is 6 nm and 15 nm. As shown in the figure, when the well width T is 6 nm, the output of the emitted light is improved by 30% or more compared to the case of 15 nm.

In the vicinity of the maximum current in the graph, output saturation is observed at 15 nm, whereas output saturation is not observed at 6 nm. For this reason, the difference between the two is expected to increase further at higher currents. Further, in this calculation, the self-heating effect is also taken into consideration, and from the result that the output in the operation in the high current region is particularly improved, the operation at the high temperature is advantageous in the case of 6 nm.

FIG. 8 is a graph showing the relationship between the wavelength and intensity of the emitted light from the optical element 100, and shows the calculation results when the well width T is 6 nm and 15 nm. As shown in the figure, when the well width T is 6 nm, the spectral width and the spectral shape are the same as in the case of 15 nm.

In addition, when the well width T is 6 nm, the temperature characteristics are improved compared to the case of 15 nm, and the beam shape is equivalent to that of 15 nm. As described above, by setting the well width T to 10 nm or less, it is possible to reduce the rising current of the SLD light, maintain the spectral width of the SLD light, improve the light emission efficiency, and improve the temperature characteristics.

The well width T is preferably 10 nm or less. However, in order to improve the characteristics, it is effective to promote the effective use of carriers by further thinning the film, and the crystallinity is impaired in the process of epitaxial growth when the optical element 100 is manufactured. It is desirable to make it extremely thin at no level. In particular, when the well width T is 7 nm or less, the effect is large and suitable.

In addition, it is known that the well width T is reduced, that is, the optical loss of the active layer light absorption in the non-excitation region is reduced by the amount that the volume of the active layer 20 is reduced, and the heat source around the active layer is reduced. Further, it is effective in further improving the light emission efficiency or energy efficiency, lowering the temperature inside the device, and thus improving the reliability.

(About optical confinement ratio in quantum well)
The light confinement ratio in the quantum well formed by the quantum well layer 20a is preferably 3% or less. The light confinement rate in the quantum well means the ratio of the light density confined in the quantum well. Conventionally, the light confinement rate in the quantum well is generally 4% or more.

As described above, when the well width T is reduced, the light confinement rate in the quantum well is reduced, and the spectrum width of the spontaneous emission light generated in the quantum well layer 20a is reduced. FIG. 9 is a graph showing the relationship between the optical confinement rate in the quantum well and the SLD spectrum width (left axis), and the relationship between the confinement rate and the PL spectrum width (right axis).

As shown in the figure, when the light confinement ratio in the quantum well is reduced, the PL spectrum width is reduced, so that the SLD spectrum width is also expected to be reduced (broken line in the figure). However, in practice, it has been found that when the light confinement ratio in the quantum well is reduced, the SLD spectrum width is improved as shown by a box B in the figure.

As shown in FIG. 5, when the light confinement rate in the quantum well is small and the utilization efficiency of spontaneous emission becomes small, a high carrier density is required at the start of SLD light emission. This is because the effect is increased and the active layer loss is reduced. Thus, by setting the light confinement ratio in the quantum well to 3% or less, it is possible to realize a wide spectrum width and simultaneously achieve high output and high efficiency.

(Concerning conditions for quantum well layers)
As described above, the thickness (well width T) of the quantum well layer 20a is preferably 10 nm or less, and the optical confinement ratio in the quantum well formed by the quantum well layer 20a is preferably 3% or less. The optical element 100 according to the present embodiment only needs to satisfy at least one of the condition that the thickness of the quantum well layer 20a is 10 nm or less and the condition that the light confinement ratio in the quantum well is 3% or less. .

(About material of quantum well layer)
The material of the quantum well layer 20a is not particularly limited, but the emission color of the optical element 100 varies depending on the material of the quantum well layer 20a. For example, when the quantum well layer 20a is made of AlInGaP, red light having an emission wavelength of 550 to 900 nm (practical range of 630 to 680 nm) is generated. When the quantum well layer 20a is made of AlInGaN, blue-violet to green light having an emission wavelength of 400 to 1000 nm (practical range of 400 to 550 nm) is generated.

In addition, the materials of the quantum well layer 20a include AlGaN (emission wavelength ultraviolet region to 400 nm), AlGaAs (emission wavelength 750 to 850 nm, infrared region), InGaAs (emission wavelength 800 to 980 nm, infrared region), InGaAsP (emission wavelength 1.2). To 1.6 μm, infrared region) and the like.

(Guide layer and cladding layer)
Depending on the thickness of the p-type guide layer 132 and the n-type guide layer 142, the light confinement ratio in the quantum well can be adjusted to 3% or less. The thicknesses of the p-type guide layer 132 and the n-type guide layer 142 are each preferably 10 nm to 500 nm, and more preferably 50 nm to 200 nm.

The above 10 nm to 500 nm is a numerical range that can be taken in the device design of SLD, and 50 nm to 200 nm is a numerical range that considers not only light confinement but also light emission pattern control (spreading of emitted light) and carrier confinement. is there.

Further, the refractive index difference between the p-type cladding layer 131 and the p-type guide layer 132 (hereinafter referred to as p-type refractive index difference) and the refractive index difference between the n-type cladding layer 141 and the n-type guide layer 142 (hereinafter referred to as n-type refractive index difference). ) Can also adjust the light confinement rate in the quantum well to 3% or less.

Specifically, when the quantum well layer 20a is made of AlInGaP and the emission color is red, the p-type refractive index difference and the n-type refractive index difference are each preferably 0.03 to 0.50, and 0.06 More than 0.30 is more suitable.

The above 0.03 to 0.50 is a numerical range that can be taken in the device design of the SLD, and 0.06 to 0.30 is not only the confinement of light but also the control of the light emission pattern (spreading of the emitted light) This is a numerical range that also considers the confinement of carriers.

When the quantum well layer 20a is made of AlInGaN and the emission color is from violet to green, the p-type refractive index difference and the n-type refractive index difference are each preferably 0.01 or more and 0.10 or less, and 0.02 More preferred is 0.06 or less.

The range from 0.01 to 0.10 is a numerical range that can be taken in the device design of the SLD, and the range from 0.02 to 0.06 is not only the confinement of light but also the control of the light emission pattern (spreading of the emitted light) This is a numerical range that also considers the confinement of carriers.

The materials of the p-type cladding layer 131, the p-type guide layer 132, the n-type cladding layer 141, and the n-type guide layer 142 are not particularly limited. For example, the p-type cladding layer 131 is Al _0.5 In _0.5 P doped with Mg, the p-type guide layer 132 is Ga _x In _1-x P, and the n-type cladding layer 141 is Ga _x In _1-x P. The n-type guide layer 142 may be made of Al _0.5 In _0.5 P doped with Si.

(Effects of optical elements compared with conventional structures)
In order to improve the output of the SLD, it is conceivable to inject a large amount of current, increase the waveguide length, or increase the width of the ridge waveguide.

However, when a large amount of current is injected, the upper limit value is limited by the thermal saturation of the output. Therefore, in order to increase the output, the heat radiation burden on the mounting or package becomes large. In addition to increasing the cost, laser oscillation is likely to occur due to slight end surface reflection. Therefore, it is necessary to use a current much lower than the limit due to thermal saturation.

Also, when the waveguide length is increased, the light intensity is increased because the light is amplified through a longer path until the light is emitted. On the other hand, by receiving more light amplification by stimulated emission, it is strongly influenced by the gain spectrum (wavelength dependence), and the emission spectrum width is narrowed. For this reason, low coherence property falls. That is, the output and coherence have a trade-off relationship. Further, when the waveguide length is long, the size of the SLD becomes large, which is not suitable for downsizing of the package, the influence of the entire waveguide loss is increased, and the light change efficiency is also lowered.

Also, when the width of the ridge waveguide is increased, the output can be increased by reducing the concentration of current density and increasing the light emitting area. However, it becomes difficult to use as a light source because the width of the emitted beam becomes wider and a special optical system is required. Furthermore, increasing the width of the ridge waveguide increases the number of modes that can be guided, which causes output instability.

There are other methods to increase the spectral width at the stage of spontaneous emission before amplification, but for this purpose, the injection electrode is divided or the material and structure of the active layer are divided into parts. Need to change. In the former case, it is necessary to drive the divided electrodes with separate drivers, which is expensive. In the latter case, it is difficult to manufacture, for example, since crystal regrowth is required, and the cost is high.

In addition, since the current consumed by any of the above methods increases, the efficiency as a light source decreases.

On the other hand, in the optical element 100 according to the present embodiment, light having a high output and a wide spectral width can be obtained by setting the thickness of the quantum well layer 20a to 10 nm or less or setting the optical confinement ratio to the quantum well to 3% or less. Can be emitted.

As described above, in the conventional structure, there is a trade-off relationship between the spectral width expansion and the output improvement, and the element design that considers a compromise between both characteristics has been used. However, this technology is not subject to this limitation. It is possible to design at the same time, and both higher performance can be achieved.

In addition, the structure is suitable for SLD using a unique operation principle in which the waveguide coupling of spontaneous emission light near the rear end face directly affects the device characteristics, and does not require a special active layer deposition method. The film formation method can be used.

Furthermore, the optical gain is improved by increasing the quantum effect due to the thinning of the quantum well element, so that the SLD output can be greatly increased and the deterioration of characteristics at high temperatures can be suppressed. Further, the added process is only a partial process change in the epitaxial growth, and the influence on the entire manufacturing process is small.

The composition and film thickness of the active layer can be sufficiently detected by EDX (Energy Dispersive X-ray Spectrometry) analysis or WDX (Wavelength Dispersive X-ray Spectroscopy) analysis after TEM (Transmission Electron Microscope) analysis. Further, not only the film thickness but also the optical confinement ratio can be calculated by combining optical waveguide calculation.

Furthermore, it is possible to adjust the output to the required spectral width and output by adjusting the output according to the resonator length according to the application. In addition, by using a thin quantum well layer, it is easy to make the spectrum unimodal, and even in applications using interference such as OCT (Optical Coherence Tomography), measurement results with little disturbance can be obtained.

In addition, even when used as an amplifier, the same effect can be expected. By using the same structure, it is possible to improve functions such as widening the amplification wavelength band and increasing efficiency.

(Regarding the number of quantum well layers)
In the above embodiment, the active layer 20 has the single quantum well layer 20a. However, the active layer 20 may have a plurality of quantum well layers 20a. FIG. 10 is a schematic diagram showing a band structure in the active layer 20 having a plurality of quantum well layers 20a.

As shown in the figure, the active layer 20 has a plurality of quantum well layers 20a, and a barrier layer 20b is provided between the quantum well layers 20a. Note that the number of the quantum well layers 20a included in the active layer 20 is not limited to three, and may be two or four or more. Here, a description will be given by taking the three quantum well layers 20a as an example.

When the thickness of each quantum well layer 20a is defined as thickness T1, thickness T2, and thickness T3, the total thickness of the quantum well layers 20a, that is, the total thickness T1, thickness T2, and thickness T3 is preferably 10 nm or less. Similarly, when the number of quantum well layers 20a is two or four or more, the total thickness of the quantum well layers 20a is preferably 10 nm or less.

Thereby, the optical element 100 can emit light having a high output and a wide spectral width according to the same principle as that in the case where the active layer 20 has the single quantum well layer 20a. The thicknesses of the respective quantum well layers 20a may be the same or different from each other. Further, the band gaps of the respective quantum well layers 20a may be the same or different from each other.

Further, the light confinement rate in the quantum well formed by the quantum well layer 20a is preferably 3% or less. By setting the optical confinement ratio in the quantum well to 3% or less, it is possible to realize a wide spectral width and simultaneously achieve high output and high efficiency.

Even when the active layer 20 has a plurality of quantum well layers 20a, among the conditions that the total thickness of the quantum well layers 20a is 10 nm or less and the light confinement ratio in the quantum wells is 3% or less, What is necessary is just to satisfy | fill at least any one.

FIG. 11 is a schematic diagram showing a specific configuration of the active layer 20 including a plurality of quantum well layers 20a. In the figure, the illustration of components other than the active layer 20, the p-type guide layer 132, and the n-type guide layer 142 is omitted. As shown in the figure, the active layer 20 is configured by alternately stacking quantum well layers 20a and barrier layers 20b.

The quantum well layer 20a is made of a material such as AlInGaAlP (red) or AlInGaN (blue purple to green) as described above. Further, the materials may be different between the quantum well layers 20a. The barrier layer 20b can be made of, for example, AlGaSs.

The configuration other than the active layer 20 can be the same as the structure in which the active layer 20 includes a single quantum well layer 20a. That is, the thicknesses of the p-type guide layer 132 and the n-type guide layer 142, the refractive index difference between the p-type cladding layer 131 and the p-type guide layer 132, and the refractive index difference between the n-type guide layer 142 and the n-type cladding layer 141 are within the above ranges. By doing so, the light confinement rate in the quantum well can be made 3% or less.

(Display device)
FIG. 12 schematically shows a configuration of a display device that uses an SLD that is an optical element according to the embodiment as a light source. The display device 200 is a raster scan projector.

The display device 200 includes an image generation unit 70. The image generation unit 70 can scan light emitted from an optical element as a light source in a two-dimensional manner, for example, raster scan, and is based on light projected on an irradiation surface 105 such as a screen or a wall surface based on image data. The brightness can be controlled.

The image generation unit 70 mainly includes a horizontal scanner 103 and a vertical scanner 104, for example. Each of the beams from the red light emitting optical element 100R, the green light emitting optical element 100G, and the blue light emitting optical element 100B is combined into one beam by the

dichroic prisms

102R, 102G, and 102B. This beam is scanned by the horizontal scanner 103 and the vertical scanner 104 and projected onto the irradiation surface 105 to display an image.

It should be noted that at least one of the light sources for emitting light of RGB colors may be an SLD having the configuration of the optical element 100 according to the present embodiment, and the other elements may be ordinary LDs.

The horizontal scanner 103 and the vertical scanner 104 are configured by a combination of a polygon mirror and a galvano scanner, for example. In this case, as the luminance control means, for example, a circuit for controlling the current injected into the optical element is used.

Alternatively, as the horizontal scanner and the vertical scanner, for example, a two-dimensional light modulation element such as a DMD (Digital Micro-mirror Device) manufactured using MEMS (Micro Electro Mechanical System) technology may be used.

Alternatively, the image generation unit 70 may be configured by a combination of a one-dimensional light modulation element such as a GLV (Grating Light Valve) element and the above-described one-dimensional scan mirror.

Alternatively, the image generation unit 70 may be configured by a refractive index modulation type scanner such as an acousto-optic effect scanner or an electro-optic effect scanner.

(Other embodiments)
The present technology is not limited to the embodiments described above, and other various embodiments can be realized.

The current confinement structure 32 configured to constrict the current injection region is not limited to the structure constituting the ridge portion 10. For example, the current confinement structure may be a buried type or a buried ridge type structure.

In the above embodiment, an n-type substrate is used as the substrate 15. However, a p-type substrate may be used, and the semiconductor layer constituting the current confinement structure may be n-type. In this case, the “first conductivity type” is n-type, and the “second conductivity type” is p-type.

The optical element according to the above embodiment has a configuration in which the current confinement structure 32 is disposed on the opposite side of the substrate 15 with the active layer 20 as the center. However, a current confinement structure may be disposed on the same side as the substrate (which may be n-type or p-type) with the active layer 20 as the center. However, the optical element of the above embodiment has a merit that the heat dissipation is high in structure as compared with the optical element having the configuration in which the current confinement structure is arranged on the same side as the substrate.

Among the feature portions of the other embodiments described above, it is possible to combine at least two feature portions.

In addition, this technique can also take the following structures.
(1)
A first conductivity type layer having a current confinement structure configured to confine a current injection region;
A second conductivity type layer;
An active layer provided between the first conductivity type layer and the second conductivity type layer, the active layer having one quantum well layer or a plurality of quantum well layers, An optical element comprising: an active layer having a thickness of 10 nm or less and a total thickness of the plurality of quantum well layers being 10 nm or less.

(2)
The optical element according to (1) above,
The one quantum well layer or the plurality of quantum well layers is made of AlInGaP.

(3)
The optical element according to (1) above,
The active layer has the one quantum well layer,
The one quantum well layer is an optical element made of AlInGaN.

(4)
The optical element according to any one of (1) to (3) above,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The thickness of the first guide layer is 10 nm or more and 500 nm or less,
The thickness of the said 2nd guide layer is 10 nm or more and 500 nm or less.

(5)
The optical element according to any one of (1) to (4) above,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The difference in refractive index between the first cladding layer and the first guide layer is 0.03 or more and 0.50 or less,
An optical element, wherein a difference in refractive index between the second cladding layer and the second guide layer is 0.03 or more and 0.50 or less.

(6)
The optical element according to any one of (1) to (4) above,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The refractive index difference between the first cladding layer and the first guide layer is 0.01 or more and 0.10 or less,
The optical element has a refractive index difference between the second cladding layer and the second guide layer of 0.01 or more and 0.10 or less.

(7)
The optical element according to any one of (1) to (6) above,
The optical element has an optical confinement ratio of 3% or less in the quantum well.

(8)
A first conductivity type layer having a current confinement structure configured to confine a current injection region;
A second conductivity type layer;
An active layer provided between the first conductivity type layer and the second conductivity type layer, having one quantum well layer or a plurality of quantum well layers, and having an optical confinement ratio in the quantum well An optical element comprising: an active layer that is 3% or less.

(9)
The optical element according to (8) above,
The one quantum well layer or the plurality of quantum well layers is made of AlInGaP.

(10)
The optical element according to (8) above,
The active layer has the one quantum well layer,
The one quantum well layer is an optical element made of AlInGaN.

(11)
The optical element according to any one of (8) to (9) above,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The thickness of the first guide layer is 10 nm or more and 500 nm or less,
The thickness of the said 2nd guide layer is 10 nm or more and 500 nm or less.

(12)
The optical element according to (11) above,
The thickness of the first guide layer is 50 nm or more and 200 nm or less,
The thickness of the second guide layer is 50 nm or more and 200 nm or less.

(13)
The optical element according to any one of (8) to (12) above,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The difference in refractive index between the first cladding layer and the first guide layer is 0.03 or more and 0.50 or less,
An optical element, wherein a difference in refractive index between the second cladding layer and the second guide layer is 0.03 or more and 0.50 or less.

(14)
The optical element according to (13) above,
The refractive index difference between the first cladding layer and the first guide layer is 0.06 or more and 0.30 or less,
The optical element has a refractive index difference between the second cladding layer and the second guide layer of 0.06 or more and 0.30 or less.

(15)
The optical element according to any one of (8) to (12) above,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The refractive index difference between the first cladding layer and the first guide layer is 0.01 or more and 0.10 or less,
The optical element has a refractive index difference between the second cladding layer and the second guide layer of 0.01 or more and 0.10 or less.

(16)
The optical element according to (15) above,
The refractive index difference between the first cladding layer and the first guide layer is 0.02 or more and 0.06 or less,
The optical element has a refractive index difference between the second cladding layer and the second guide layer of 0.02 or more and 0.06 or less.

(17)
The optical element according to any one of (1) to (16) above,
An optical element that is a super luminescence diode.

(18)
The optical element according to any one of (1) to (16) above,
An optical element that is an optical amplifier.

(19)
Provided between a first conductivity type layer having a current confinement structure configured to confine a current injection region, a second conductivity type layer, and between the first conductivity type layer and the second conductivity type layer An active layer structure of an optical element comprising an active layer,
The active layer has one quantum well layer or a plurality of quantum well layers, the thickness of the one quantum well layer is 10 nm or less, and the total thickness of the plurality of quantum well layers is 10 nm. The active layer structure is:

(20)
An optical element;
The light emitted from the optical element can be scanned two-dimensionally, and based on image data, an image generation unit capable of controlling the luminance by the projected light,
The optical element is
A first conductivity type layer having a current confinement structure configured to confine a current injection region;
A second conductivity type layer;
An active layer provided between the first conductivity type layer and the second conductivity type layer, the active layer having one quantum well layer or a plurality of quantum well layers, A display device comprising: an active layer having a thickness of 10 nm or less and a total thickness of the plurality of quantum well layers being 10 nm or less.

DESCRIPTION OF SYMBOLS 11 ... p-type electrode layer 12 ... n-type electrode layer 13 ... 1st conductivity type layer 131 ... p-type clad layer 132 ... p-type guide layer 14 ... 2nd conductivity type layer 141 ... n-type clad layer 142 ... n-type guide layer 20 ... Active layer 20a ... Quantum well layer 20b ... Barrier layer 32 ... Current confinement structure

Claims

A first conductivity type layer having a current confinement structure configured to confine a current injection region;
A second conductivity type layer;
An active layer provided between the first conductivity type layer and the second conductivity type layer, the active layer having one quantum well layer or a plurality of quantum well layers, An optical element comprising: an active layer having a thickness of 10 nm or less and a total thickness of the plurality of quantum well layers being 10 nm or less.
The optical element according to claim 1,
The one quantum well layer or the plurality of quantum well layers is made of AlInGaP.
The optical element according to claim 1,
The active layer has the one quantum well layer,
The one quantum well layer is an optical element made of AlInGaN.
The optical element according to claim 1,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The thickness of the first guide layer is 10 nm or more and 500 nm or less,
The thickness of the second guide layer is 10 nm or more and 500 nm or less.
The optical element according to claim 2,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The refractive index difference between the first cladding layer and the first guide layer is 0.03 or more and 0.50 or less,
An optical element, wherein a difference in refractive index between the second cladding layer and the second guide layer is 0.03 or more and 0.50 or less.
The optical element according to claim 3,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The refractive index difference between the first cladding layer and the first guide layer is 0.01 or more and 0.10 or less,
The optical element has a refractive index difference between the second cladding layer and the second guide layer of 0.01 or more and 0.10 or less.
The optical element according to claim 1,
The optical element has an optical confinement ratio of 3% or less in the quantum well.
A first conductivity type layer having a current confinement structure configured to confine a current injection region;
A second conductivity type layer;
An active layer provided between the first conductivity type layer and the second conductivity type layer, having one quantum well layer or a plurality of quantum well layers, and having an optical confinement ratio in the quantum well An optical element comprising: an active layer that is 3% or less.
The optical element according to claim 8,
The one quantum well layer or the plurality of quantum well layers is made of AlInGaP.
The optical element according to claim 8,
The active layer has the one quantum well layer,
The one quantum well layer is an optical element made of AlInGaN.
The optical element according to claim 8,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The thickness of the first guide layer is 10 nm or more and 500 nm or less,
The thickness of the second guide layer is 10 nm or more and 500 nm or less.
The optical element according to claim 11,
The first guide layer has a thickness of 50 nm to 200 nm,
The optical element having a thickness of the second guide layer of 50 nm or more and 200 nm or less.
The optical element according to claim 9,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The refractive index difference between the first cladding layer and the first guide layer is 0.03 or more and 0.50 or less,
An optical element, wherein a difference in refractive index between the second cladding layer and the second guide layer is 0.03 or more and 0.50 or less.
The optical element according to claim 13,
The refractive index difference between the first cladding layer and the first guide layer is 0.06 or more and 0.30 or less,
The optical element has a refractive index difference between the second cladding layer and the second guide layer of 0.06 or more and 0.30 or less.
The optical element according to claim 10,
The first conductivity type layer includes a first cladding layer, and a first guide layer provided between the first cladding layer and the active layer,
The second conductivity type layer includes a second cladding layer, and a second guide layer provided between the second cladding layer and the active layer,
The refractive index difference between the first cladding layer and the first guide layer is 0.01 or more and 0.10 or less,
The optical element has a refractive index difference between the second cladding layer and the second guide layer of 0.01 or more and 0.10 or less.
The optical element according to claim 15,
The refractive index difference between the first cladding layer and the first guide layer is 0.02 or more and 0.06 or less,
The optical element has a refractive index difference between the second cladding layer and the second guide layer of 0.02 to 0.06.
The optical element according to claim 1 or 8,
An optical element that is a super luminescence diode.
The optical element according to claim 1 or 8,
An optical element that is an optical amplifier.
Provided between a first conductivity type layer having a current confinement structure configured to confine a current injection region, a second conductivity type layer, and between the first conductivity type layer and the second conductivity type layer An active layer structure of an optical element comprising an active layer,
The active layer has one quantum well layer or a plurality of quantum well layers, the thickness of the one quantum well layer is 10 nm or less, and the total thickness of the plurality of quantum well layers is 10 nm. The active layer structure is:
An optical element;
The light emitted from the optical element can be scanned two-dimensionally, and based on image data, an image generation unit capable of controlling the luminance by the projected light,
The optical element is
A first conductivity type layer having a current confinement structure configured to confine a current injection region;
A second conductivity type layer;
An active layer provided between the first conductivity type layer and the second conductivity type layer, the active layer having one quantum well layer or a plurality of quantum well layers, A display device comprising: an active layer having a thickness of 10 nm or less and a total thickness of the plurality of quantum well layers being 10 nm or less.