JPH08222786A - Electron beam pumping laser, manufacture of electron beam pumping laser, and drive method of electron beam pumping laser - Google Patents

Abstract

PURPOSE: To provide an electrom beam pumping laser with a high threshold level of laser oscillation by obtaining a high optical reflectively while maintaining high utilization of incident energy. CONSTITUTION: This electrom beam pumping laser is provided with an active layer 2, and optical reflecting layers 1 and 3 which are formed so as to sandwich the active layer 2. An electron beam 5 is made to enter the active layer 2 from the side surface of the active layer 2, and a laser beam is radiated perpendicularly to the active layer 2. At least one side of the optical reflecting layers 1 and 3 is provided with a plurality of very small concave mirror parts or a plurality of very small Fresnel reflecting mirror parts. The focal length of the very small concave mirror part of the very small Fresnel reflecting mirror parts or semicircular type reflecting mirror parts is set to be greater than or equal to the width of the active layer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam pumping laser, and more particularly to an electron pumping type electron beam pumping laser, which is particularly relevant to a display field such as a projection type image display device. .

[0002]

2. Description of the Related Art There are three types of electron beam excitation lasers that use semiconductors as laser cavities, and they are classified into injection laser diodes, electron beam pumping lasers, and optical pumping lasers according to their respective laser effect generation modes.

The main advantage of electron beam pumping lasers is that they can be used with all direct gap semiconductors, especially in the construction of injection laser diodes, and this advantage extends the emission wavelength from the ultraviolet to the infrared. Is possible.

[0004]

However, in the conventional electron beam pumping laser, since the incident electron beam transmits through the reflecting mirror layer and excites the active layer, it is attempted to keep the utilization efficiency of the incident energy high. In the case of a metal reflecting mirror, it was necessary to form a thin film having a thickness of about 100 nm or less, and in the case of a multilayer film reflecting mirror, it was necessary to reduce the number of layers stacked. There is a problem that a sufficiently high optical reflectance cannot be obtained with the thin reflecting mirror layer as described above, and the threshold value of laser oscillation becomes high.

The present invention is intended to solve the above-mentioned problems and obtains a high optical reflectance while maintaining a high utilization efficiency of incident energy, resulting in electron beam excitation with a high threshold of laser oscillation. The purpose is to provide a laser.

[0006]

In order to achieve the above object, the present invention has an active layer and an optical reflection layer formed so as to sandwich the active layer, and activates an electron beam from the side surface of the active layer. Characterized by emitting a laser beam in a direction perpendicular to the active layer incident on the layer, further at least one of the optical reflection layer has a plurality of micro concave concave mirror portion or a plurality of micro Fresnel type reflection mirror portion, The focal length of the minute concave mirror portion, the minute Fresnel reflecting mirror portion, or the semi-cylindrical reflecting mirror portion is equal to or more than the thickness of the active layer.

[0007]

The light emitting layer is composed of an optical resonator composed of an active layer and reflecting mirror layers formed on both the upper and lower surfaces of the active layer. It has become possible to make the thickness of the metal reflecting mirror sufficiently thick, thus solving the above problem.

Further, by injecting the electron beam from the side surface of the active layer, it becomes possible to form the reflecting mirror layers on the upper and lower surfaces of the active layer into a multi-layered structure, thereby increasing the reflectance of the reflecting mirror. It was possible to reduce the threshold value of laser oscillation.

Further, it becomes possible to scan the emitted laser light in at least one direction by scanning the incident electron beam along the side surface of the active layer.

Further, at least one of the reflecting mirror layers is a minute concave mirror, a minute Fresnel type reflecting mirror or a kamaboko type reflecting mirror, and the focal length of the minute concave mirror part, the minute fresnel type reflecting mirror part or the kamaboko type reflecting mirror part is the active state. A stable and efficient laser oscillation could be achieved by using a laser cavity structure having a layer thickness or more.

Further, the distance D from the center of the minute concave mirror portion, the center of the minute Fresnel reflecting mirror portion or the center line of the semi-circular reflecting mirror portion to the end surface of the light emitting layer on the electron beam incident side.
However, in order to match the distance at which the emission intensity when the electron beam is incident and the active layer emits light becomes the strongest, the minute concave mirror portion,
Efficient laser oscillation could be realized by making the minute Fresnel type reflecting mirror section and the kamaboko type reflecting mirror section.

Further, by making the pitch of the minute concave mirror or the minute Fresnel reflecting mirror in the scanning direction of the electron beam smaller than the beam spot diameter of the electron beam, stable and continuous laser oscillation can be realized.

The following method was used as the electron beam driving method. 1) In the scanning plane of the electron beam, the distance d between the center position of the minute concave mirror or the minute Fresnel reflecting mirror projected perpendicularly to the scanning plane and the center line of the electron beam
However, a method of irradiating an electron beam only when it approaches less than 1/2 of the pitch of the minute concave mirror or the minute Fresnel reflecting mirror, 2) a minute concave mirror portion vertically projected in the scanning plane of the electron beam, or a minute Fresnel type The beam scanning is stopped once at the point where the center position of the reflecting mirror section and the center line of the electron beam almost intersect, and after irradiating the electron beam for a predetermined time, it skips to the adjacent point where the electron beam intersects, and at that position. A method of scanning the electron beam while repeating the same cycle of irradiating the electron beam again. As a result, stable and efficient laser oscillation could be realized.

[0014]

1 shows the structure of an electron beam pumping laser according to an embodiment of the present invention. An optical resonator 7 is arranged on a substrate 4, and the active layer 2 is excited by irradiation of an electron beam 5 incident from a side surface and emits a laser beam 6 perpendicularly to the active layer 2.

The optical resonator 7 has a film thickness d of 100 nm to 10 nm.
It is composed of an active layer 2 having a thickness of about 0 μm and reflecting mirror layers 1 and 3 formed on both sides thereof.

First, the active layer 2 is formed with 1.8e as in the conventional case.
A IIb-VI group compound semiconductor such as ZnS or CdS, a manganese chalcogenide compound such as MgS, or a mixed crystal thereof having a bandgap of V or more was mainly used. Further, the reflecting mirror layer 3 provided on the substrate side has a metal reflecting mirror of Al, Ag or the like having a film thickness of about 100 to 500 nm, or SiO ₂ and TiO _2, or a band gap of an active layer having a different refractive index. Mainly used is a multi-layered film reflection mirror of a combination of two kinds of compound semiconductors or the like having a material band gap or more, while the reflection layer 1 on the laser emission side is used.
For this purpose, we mainly use metal reflectors such as Al and Ag with a film thickness of about 50 to 200 nm, or multilayer reflectors that combine SiO ₂ and TiO ₂ or two kinds of compound semiconductors with different refractive indices. I was there.

Here, the acceleration voltage of the incident electron beam is 10 kV.
In this case, when the Al film thickness is 100 nm, the electron beam transmittance is about 95%, but when the Al film thickness is 200 nm, the electron beam transmittance is about 70%.

In the case of a commonly used semiconductor laser, the cavity length is 500 μm or more. However, in the present invention, it is necessary to increase the intensity per unit area of the incident electron beam, which is an efficient laser. In order to achieve this, it is necessary to bring the distance between the mirrors and the value of the diameter of the incident fresh food closer. Therefore,
It is necessary to reciprocate between the mirrors 50 times or more as compared with a conventionally used semiconductor laser, and as a result, a mirror having a reflectance of 90% or more is required.

(Embodiment 1) Next, a method of manufacturing an electron beam pumped laser according to a first embodiment of the present invention will be specifically described with reference to FIG.

First, two kinds of ZnMgSSe films having different composition ratios are alternately formed on the sapphire single crystal substrate 4 by the molecular beam epitaxial growth method so that the thickness of each layer becomes 1/4 of the laser emission wavelength. A semiconductor multilayer film reflecting mirror 3 is formed by stacking several tens of cycles. Then, on top of that, ZnSS having a composition ratio that is lattice-matched with the underlying ZnMgSSe film is formed.
The active layer 2 made of a single crystal epitaxial film is formed by the same molecular beam epitaxial growth method so that the film thickness is an integral multiple of the laser emission wavelength. In this embodiment, the thickness of the active layer is about 10 μm, the reflectance of the semiconductor multilayer film reflecting mirror 3 is 95% or more with respect to the band edge emission wavelength of the ZnSSe, and its transmittance is about 1 to 5%. is there. Further, a semiconductor in which two kinds of ZnMgSSe films having different composition ratios are alternately laminated thereon by a molecular beam epitaxial growth method for several cycles to several tens cycles so that the film thickness of one layer becomes 1/4 of the laser emission wavelength. The multilayer film reflecting mirror 1 is formed. The reflectance of the semiconductor multilayer film reflecting mirror 1 was 92% or more with respect to the band edge emission wavelength of ZnSSe, and the transmittance thereof was about 2 to 8%.

The optical resonator obtained as described above is cleaved along the cleaving direction using a diamond cutter, and the cleaved surface of the light emitting layer 7 on which the electron beam is incident is about 5 to 30 nm. An Ag film is formed. By grounding the metal protective film made of the Ag film, it is possible to avoid a decrease in efficiency due to charge-up caused by direct irradiation of the active layer with an electron beam.

The oscillation result of the laser formed as described above will be described below. When an electron beam accelerated to an accelerating voltage of 10 to 50 kV is incident on the active layer 2 from the side surface, the minimum value of the laser oscillation threshold current density is 10 to 15 A / cm.
^{About 2} was obtained. This is the threshold current density when irradiated with electron beam into the light-emitting layer from the direction perpendicular to the conventional light-emitting layer is compared with that was 20 to 100 A / cm ^2, the threshold current by the present invention It can be seen that the density reduction effect was obtained.

The above-mentioned effects of the present invention are as follows. First, the reflectance of the reflecting mirror layer can be increased by injecting an electron beam into the active layer from the side surface. It is considered that the absorption loss in the reflecting mirror layer when the incident electron beam has been transmitted through the reflecting mirror layer has been reduced conventionally.

Next, a laser scanning method in the electron beam excitation laser of the present invention will be described. In a conventional electron beam excitation laser, when applying a single laser beam to a display or the like, it is necessary to irradiate the laser beam in a plane shape,
If a laser that cannot be normally scanned is used, it is necessary to scan the emitted laser light in the plane direction (vertical and horizontal directions) using a polygon mirror or the like. However, in the present invention, as shown in FIG. 1, since laser light is incident from the side surface of the active layer and raster-scanned along the active layer at a constant speed, laser light emitted perpendicularly to the active layer 2 is also unidirectional. Raster scanning will be performed at a constant speed. Therefore, the planar scanning of the laser light can be performed by scanning the emitted laser light in one direction using a plane mirror or the like, and the configuration of the device can be simplified.

(Embodiment 2) Next, a method for manufacturing an electron beam pumped laser having a metal reflecting mirror according to a second embodiment of the present invention will be specifically described.

As a material for the active layer, a bulk CdS single crystal is polished to about 100 nm to 100 μm, preferably about 20 μm, and the polished CdS single crystal is placed in an Ar atmosphere.
Anneal at 400 to 650 ° C., preferably about 550 ° C. for 1 hour. Because by annealing,
This is because the crystallinity can be improved, the photoluminescence (light emission) intensity can be increased, and a laser having a lower threshold value can be obtained. Also, especially 55
When it exceeds 0 ℃, the crystal begins to sublime and the mirror surface becomes messy. FIG. 2 shows the results of X-ray diffraction of the polished active layer material (CdS) having a film thickness of 70 μm after polishing by a two-crystal method after a) before annealing and b) after annealing. Here, the conditions are that the crystal plane is the (001) _H plane and the diffraction data is the (002) _H symmetrical reflection line. In the sample after polishing, in addition to the main peak of CdS, there are sub-peaks on the left and right of the main peak whose crystal axis is deviated by about 200 seconds, which is considered to be caused by polishing and the crystallinity is disturbed. The half-width of X-ray diffraction after polishing was 135 seconds after polishing, whereas it was reduced to 106 seconds after annealing, and improvement in crystallinity can be confirmed.

Next, the active layer material was cleaved along the cleavage direction using a diamond cutter. After that, on the active layer surface on the laser emission side, Al of about 30 to 300 nm,
A metal reflector such as Ag is deposited, and a metal reflector such as Al or Ag having a thickness of about 100 to 500 nm is deposited on the surface of the active layer on the substrate side. However, the metal film on the active layer surface on the substrate side must be thicker than the metal film on the laser emission side. The thin film of Ag on the laser emission side has a reflectance of 94 when the film thickness is 40 nm.
%, The transmittance is 1%, and the film thickness of the Ag thin film on the substrate side is 2
The reflectance was 97% and the transmittance was 0.1% at 00 nm. Next, an adhesive is used to adhere to a smooth substrate such as sapphire so that the reflecting mirror is in contact, and the cleavage surface of the light emitting layer 7 is charged with about 10 to 30 nm as in the first embodiment. An Ag film was vapor-deposited to prevent the increase.

When the electron beam excitation laser having the above-described structure was oscillated, an electron beam accelerated to an accelerating voltage of 10 to 50 kV was incident on the active layer 2 from the side surface, as in the first embodiment. , The threshold current density was reduced.

(Embodiment 3) Next, a method of manufacturing an electron beam pumped laser in the third embodiment having the minute concave mirror portion 8 of the present invention will be specifically described with reference to FIG.

Similar to the first embodiment, the semiconductor multilayer film reflecting mirror 3 in which two kinds of ZnMgSSe films having different composition ratios are alternately laminated is formed on the sapphire single crystal substrate 4 by the molecular beam epitaxial growth method, On top of that, a composition ratio of ZnSS that lattice-matches the underlying ZnMgSSe film
e The active layer 2 made of a single crystal epitaxial film was formed.

Further, by contact exposure and development using an exposure mask composed of a plurality of circular mask portions, a plurality of circular resist portions 10 are formed on the surface of the ZnSSe single crystal 7, as shown in FIG. It

At this time, the distance D between the center of the circular resist and the end surface of the active layer 2 on the electron beam incident side is made to coincide with the distance at which the emission intensity when the electron beam is incident and the active layer emits light becomes the strongest. Created in. Note that the above-mentioned distance at which the emission intensity becomes the strongest is about 10 μm at an acceleration voltage of 30 kV.
m.

These are heated above the softening temperature of the resist (typically about 150 to 400 ° C.), and as a result, the resist is softened, and due to the surface tension, the circular resist portion 10 is formed.
Changed to a spherical convex resist portion 8. Then, when dry etching was carried out from above on BCl ₃ using a gas in which some oxygen was mixed, the etching proceeded as indicated by the dotted line in FIG. 4 depending on the unevenness of the surface. Here, ZnSSe such as Ar or CCl ₄ is used instead of BCl _3.
A gas that can etch the surface smoothly may be used.
As described above, the minute convex surface 9 could be formed on the ZnSSe single crystal.

Finally, a semiconductor multilayer film reflecting mirror 1 in which two types of ZnMgSSe films having different composition ratios are alternately laminated for several cycles to several tens cycles by the molecular beam epitaxial growth method.
To form.

With respect to the electron beam pumped laser constructed as described above, the acceleration voltage is 10 to 50 k as in the first embodiment.
When the electron beam accelerated to V enters the active layer 2 from the side surface, the minimum value of the laser oscillation threshold current density becomes 5 to 5.
About 10 A / cm ² was obtained. This is
It can be seen that, in addition to the first embodiment, a larger effect of reducing the threshold current density was obtained.

Further, a chamfered reflecting mirror as shown in FIG. 5 can be prepared by the same method as described above, but a minute concave mirror portion, a minute Fresnel type reflecting mirror portion as shown in FIG. 6 or a kamaboko type reflecting mirror portion is formed. Another method of creating will be described below.

First, in order to form a photosensitive resist layer portion having a partially different film thickness, contact exposure using an exposure mask having a halftone or proximity exposure using an exposure mask in which a minute transmissive portion is partially disposed. The method is used. Further, the resist shape is reflected on the surface of the active layer by an etching process from the above, and as a method therefor, there is a dry etching method or a wet etching method similar to the above-mentioned embodiment.

[0038]

INDUSTRIAL APPLICABILITY By injecting the electron beam from the side surface of the active layer, firstly, the thickness of the metal reflecting mirrors on the upper and lower surfaces of the active layer can be sufficiently increased, and secondly, the metal reflecting mirrors can be formed on the upper and lower sides of the active layer. The reflecting mirror layers on both sides can be formed into a multilayer film structure, the reflectance of the reflecting mirror can be increased, and the threshold current density of laser oscillation can be reduced.

Further, the emitted laser beam can be scanned in at least one direction by scanning the incident electron beam along the side surface of the active layer.

Further, at least one of the reflecting mirror layers is a minute Fresnel type reflecting mirror, a minute concave surface reflecting mirror or a semi-concave type reflecting mirror, and the focal length of the minute Fresnel type reflecting mirror part, the minute concave reflecting mirror part or the semi-concave type reflecting mirror part is the resonator. A stable and efficient laser oscillation could be realized by using a laser cavity structure having a thickness equal to or larger than the thickness of the active layer.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an electron beam pump laser according to an embodiment of the present invention.

FIG. 2 shows X-ray diffraction results of a polished active layer material (CdS) before and after annealing.

FIG. 3 is a schematic view of an electron beam excitation laser using a minute concave mirror section or a minute Fresnel reflecting mirror section in an example of the present invention.

FIG. 4 is a schematic cross-sectional view of a process of forming a minute concave mirror section.

FIG. 5 is a schematic diagram of an electron beam excitation laser using a semi-cylindrical reflector according to an embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view of a light emitting layer of an electron beam excitation laser using a minute Fresnel reflecting mirror section in an example of the present invention.

FIG. 7 is a schematic sectional view of a conventional electron beam pumping laser.

[Explanation of reference numerals] 1, 3, 11, 13 Optical reflection mirror layer 2, 12 Active layer 4, 14 Substrate 5 Incident electron beam 6 Emitted laser light 7 Emission layer, optical resonator 8 Micro concave mirror section or micro Fresnel type reflection mirror Part 9 Kamaboko type reflecting mirror part 10 Micro Fresnel type reflecting mirror part 11 Circular resist part 12 Convex resist part 13 Convex active layer surface

Claims (17)

[Claims] 1. A direction perpendicular to the active layer, comprising an active layer and an optical reflection layer formed so as to sandwich the active layer, wherein an electron beam is incident on the active layer from a side surface of the active layer. An electron beam excitation laser, which emits laser light to 2. At least one of the optical reflection layers has a plurality of minute concave mirror portions or a plurality of minute Fresnel type reflecting mirror portions,
2. The electron beam pumped laser according to claim 1, wherein a focal length of the minute concave mirror section, the minute Fresnel reflecting mirror section, or the semi-cylindrical reflecting mirror section is equal to or more than the thickness of the active layer. 3. The distance between the center position of the minute concave mirror portion or the center position of the minute Fresnel reflecting mirror portion is substantially equal to the distance at which the emission intensity is the strongest when the electron beam is incident and the active layer emits light. The electron beam excitation laser according to claim 2. 4. At least one of the optical reflection layers has a semi-cylindrical reflection mirror portion having a central axis perpendicular or parallel to the scanning direction of the electron beam, and the micro concave mirror portion, the micro Fresnel reflection mirror portion or the semi-cylindrical reflection portion. The electron beam pumped laser according to claim 1, wherein the focal length of the mirror portion is equal to or larger than the thickness of the active layer. 5. The distance between the center line of the semi-cylindrical reflector and the end face of the active layer on the side where the electron beam is incident is approximately the distance at which the emission intensity when the electron beam is incident and the active layer emits light is the strongest. 5. The electron beam pumped lasers according to claim 4, wherein they are equal to each other. 6. The electron beam pumped laser according to claim 2, wherein the pitch of the electron beam in the scanning direction is smaller than the beam spot diameter of the electron beam. 7. A group III-V group or a material in the active layer which emits light has a band gap in the visible region or ultraviolet region.
7. The electron beam pumped laser according to claim 1, further comprising a IIb-VI group or IIa-VI group compound semiconductor, a chalcopyrite compound, or a manganese chalcogenide compound. 8. The electron beam pumped laser according to claim 1, wherein a conductive material is formed on a surface on which the electron beam is incident. 9. The electron beam pumped laser according to claim 8, wherein the thickness of the conductive material is 100 nm or less. 10. The optical reflecting mirror layer is a multilayer film, and the band gap of the multilayer reflecting mirror layer is equal to or larger than the band gap of the active layer. Electron beam excitation laser. 11. The optical reflecting mirror layer is a multilayer film, and the multilayer reflecting mirror layer has a different refractive index for each layer, and the thickness of each layer is 1 / wavelength within each layer of the emission laser. 7. The electron beam pumped laser according to claim 1, wherein the distributed reflector is No. 4. 12. The electron beam pumped laser according to claim 1, wherein the reflectance of the optical reflecting mirror layer is 90% or more. 13. An electron beam excitation laser having an active layer and an optical reflection layer formed so as to sandwich the active layer, wherein an electron beam is incident on the active layer from a side surface of the active layer. A method for driving an electron beam excitation laser that emits laser light in a direction perpendicular to an active layer, characterized in that the emitted laser light is scanned in at least one direction by scanning the electron beam in at least one direction. Driving method of electron beam excitation laser. 14. At least one of the optical reflection layers has a plurality of minute concave mirror portions, a plurality of minute Fresnel type mirror portions, or a semi-cylindrical type mirror portion having a central axis perpendicular or parallel to the electron beam scanning direction, 14. The method for driving an electron beam excitation laser according to claim 13, wherein the focal length of the minute concave mirror portion, the minute Fresnel reflecting mirror portion, or the semi-cylindrical reflecting mirror portion is equal to or greater than the thickness of the active layer. 15. In the scanning plane of the electron beam, the distance between the center position of the minute concave mirror portion or the minute Fresnel reflecting mirror portion projected perpendicularly to the scanning surface and the center line of the electron beam is the minute concave mirror portion. Alternatively, a method of driving a laser is characterized in that a beam current is caused to flow and the electron beam is irradiated only when the fine Fresnel reflecting mirror portion approaches a pitch of less than 1/2 of a scanning direction of the electron beam. 16. A center of a beam spot of an electron beam,
In the scanning plane of the electron beam, the beam scanning is once stopped at a position where the central position of the minute concave mirror portion or the minute Fresnel reflecting mirror portion projected perpendicularly to the scanning surface intersects, and after the electron beam is irradiated for a predetermined time. , Driving the laser characterized by scanning the active layer while repeating the cycle of skipping to the center position of the adjacent minute concave mirror section or minute Fresnel type reflecting mirror section and repeating the same electron beam irradiation at that position again. Method. 17. A direction perpendicular to the active layer having an active layer and an optical reflection layer formed so as to sandwich the active layer, wherein an electron beam is incident on the active layer from a side surface of the active layer. A method of manufacturing an electron beam excitation laser, comprising: emitting a laser beam to a single crystal active layer material having a film thickness of 100
After polishing or etching to nm to 100 μm,
A method of manufacturing an electron beam excitation laser, which comprises annealing at a temperature of 400 to 650 ° C.