JP2524595B2 - Method for manufacturing solid laser - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a solid-state laser, and more particularly to a solid-state laser using an electroluminescence phenomenon.

[Prior art and its problems]

A laser is a light wave of a single frequency, with its straightness and
Due to its features such as good coherence and narrow spectrum width, its use in various fields such as communication, measurement, and information recording in optical memory has been drawing attention.

In particular, in the field of information recording, one that emits light of a short wavelength is required in order to increase the recording density.

However, even the shortest wavelength lasers currently in practical use are about 687 nm of aluminum gallium indium phosphide (AlGaInP), and shorter wavelength lasers are required.

Therefore, the present inventors have faced a light emitting layer formed by injecting impurities serving as a light emitting center into a base material layer made of a semiconductor such as zinc sulfide (ZnS), calcium sulfide (CaS), and strontium sulfide (SrS). The two surfaces are used as reflecting surfaces, and the two
A solid-state laser device is proposed in which, except for the surface, other surfaces are surrounded by an insulator having a refractive index smaller than that of the light emitting layer, and a desired voltage is applied through the insulator to generate light emission. (Japanese Patent Application No. 61-236009) This laser device uses electroluminescence (EL).
This phenomenon is utilized, and the principle of light emission is exactly the same as that of the thin film EL element. Electrons trapped in the interface state are extracted and accelerated by the electric field induced in the light emitting layer by applying a voltage, and sufficient energy is obtained. This electron collides with the orbital electron of the impurity atom at the luminescence center, excites it, and emits light when the excited luminescence center returns to the state of lower energy. It reciprocates in a resonator formed of a reflective surface to cause stimulated emission, and light is enhanced like an avalanche to emit laser light.

By the way, since the electric field excitation type laser using such electroluminescence intensively extracts the energy accumulated in the electrons and molecules as light, the property of the laser light is that the distribution of the electron molecules is uniform. Strongly depends on. That is, in order to make the light-emitting layer emit light effectively, the accelerated electrons are prevented from being scattered by the crystal grain boundaries before they collide with the emission center impurities and contribute to the light emission, and the light is emitted efficiently. Must be composed of layers.

 By the way, one example of a conventional laser device is shown in FIG.

This solid-state laser includes a first electrode 2 made of an aluminum thin film formed on a glass substrate 1 and a second electrode 3 also made of a striped pattern of the aluminum thin film. Emitting layer 5 consisting of striped pattern of ZnS: 1 wt% Tb (terbium) thin film covered with insulating film 4 (4a, 4b, 4c, 4d)
The light-emitting layer 5 has opposite end surfaces perpendicular to the glass substrate 1 and is coated with a silver film to form total reflection and translucent mirror surfaces 6a and 6b, respectively. Laser light is output from the translucent mirror surface 6b.

 Next, a method of manufacturing this solid-state laser will be described.

First, as shown in FIG. 11 (a), on the glass substrate 1,
First made of aluminum thin film by electron beam evaporation method
The electrode 2 is formed.

Next, as shown in FIG. 11 (b), a silicon oxide film is formed by the sputtering method to form the lower insulating film 4a.

Subsequently, as shown in FIG. 11C, a ZnS: 1 wt% Tb layer is formed by a sputtering method, and then patterned in a stripe shape by using a photolithography method to form a light emitting layer 5.

Then, as shown in FIG. 11D, a silicon oxide film is formed by a sputtering method so as to cover the side surface and the upper surface of the light emitting layer, and insulating films 4b, 4c, 4d are formed.

After that, an aluminum thin film is formed by an electron beam evaporation method through a metal mask to form the second electrode 3. (FIG. 11 (e)) Finally, the light emitting layer 5 is cut so as to be perpendicular to the laminated surface, the cut surface is mirror-polished, and then a silver film is applied to form a mirror surface 6a as a reflective surface. , 6b are formed to complete the solid-state laser shown in FIG.

According to this method, a solid laser having a simple structure and a very small size is formed, but on an insulating film such as a silicon oxide film,
When stacking the light emitting layers, there is a problem that it is difficult to grow the single crystal layer, crystal defects are likely to occur, and the film formation rate cannot be increased.

The present invention has been made in view of the above circumstances, and an object thereof is to form a solid-state laser having high emission efficiency and high reliability.

[Means for solving problems]

Therefore, according to the method of the present invention, a single crystal thin film forming a light emitting layer on a single crystal substrate and a surface side insulating film in the production of a solid-state laser in which two side surfaces of the light emitting layer are reflective surfaces and the other surface is surrounded by an insulating layer. Are sequentially grown, the substrate is etched from the back surface side to expose the single crystal thin film, and an insulating layer is formed on the exposed surface.

Further, according to the method of the present invention, when manufacturing a solid-state laser in which two side surfaces of the light emitting layer are reflection surfaces and the other surface is surrounded by an insulating layer,
After sequentially growing a single crystal thin film forming a light emitting layer and an insulating film on the front surface side on a single crystal substrate, the substrate is etched from the back surface side to a predetermined thickness, and an insulating layer is formed on this etched surface. I am trying.

[Action]

That is, it was made paying attention to the fact that a single crystal thin film is easily epitaxially grown on a single crystal substrate such as gallium arsenide (GaAs). Since the light emitting layer can be directly grown on the single crystal substrate. It is possible to obtain a single crystal thin film having extremely good crystallinity.

Further, in the present invention, when the substrate is etched from the back surface side to form the insulating layer on the back surface side, the substrate is left slightly without exposing the light emitting layer. A good condition is maintained without being contaminated by the etching liquid or the outside air. Moreover, since the substrate is left, the device strength is also improved.

Furthermore, when ZnS: Tb is used for the light-emitting layer, it has a problem that it is easily damaged when the surface is exposed because it is particularly vulnerable to chemicals, but by leaving the substrate slightly, it is possible to maintain a good state. .

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, as shown in FIG. 1, a ZnS: Tb layer is grown as a light emitting layer 12 on a GaAs (single crystal) substrate 11 by a MOCVD method, an MBE method, or the like, patterned by a photolithography method, and then sputtered. Tantalum pentoxide (Ta ₂ O
_A first insulating film 13 composed of ₅ ) is formed. Then, an aluminum layer is formed by the vapor deposition method and is patterned by the photolithography method to form the first electrode 14.

Then, a resist pattern (not shown) is formed on the back surface of the GaAs substrate 11 by photolithography,
Using this as a mask, the GaAs substrate 11 is etched to form electrode extraction holes 15 to expose a part of the light emitting layer 12 (FIG. 2).

After that, a second insulating film 16 made of a Ta ₂ O ₅ layer and a second electrode 17 made of an Al layer are formed on the back side of the GaAs substrate in the same manner as the front side (FIG. 3). Then, as shown in FIG. 4, by inserting a scribe line from the back side of the GaAs substrate and applying stress,
The two side surfaces facing each other are cleaved to form reflecting surfaces 18a and 18b.

In this way, as shown in the perspective view of FIG. 5, a solid-state laser having a light-emitting layer made of a single crystal having good crystallinity and having high emission efficiency and high reliability can be obtained.

That is, ZnS: Tb is easily epitaxially grown on the GaAs single crystal substrate, and a single crystal thin film layer having extremely excellent crystallinity is formed as compared with the conventional growth on an insulating film.

As described above, since the light emitting layer is made of a good single crystal, the obtained laser light has good coherence and a narrow spectral width.

The light emitting layer uses a zinc sulfide (ZnS) layer as a light emitting base material to which terbium (Tb) is added as an emission center. Therefore, the electron accelerated by the external electric field collides with the valence electron of the ground state of Tb, and the valence electron is excited to the excited state of the ⁵ D ₄ level, and this excited valence electron is ⁷ F ₅ When it transits to the level, it emits light with a short wavelength of 550 nm.

Tb has a long electron lifetime in the ⁵ D ₄ level, so
When excited strongly, an inversion distribution in which the number of electrons in the ⁵ D ₄ level is larger than the number of electrons in the ⁷ F ₅ level is easily formed. Therefore, the electrons that have naturally transitioned from the high level to the low level emit light (spontaneous emission), and this light reciprocates between the reflecting surfaces 18a and 18b, which are the cleavage planes, to cause stimulated emission. As described above, the light is enhanced and output as a powerful laser light.

 Next, a second embodiment of the present invention will be described.

Light emitting layer on GaAs (single crystal) substrate 11 as shown in FIG.
The process up to the step of sequentially stacking the ZnS: Tb layer as 12 and the Ta ₂ O ₅ layer as the first insulating film 13 is exactly the same as that of the first embodiment, but etching is performed from the back surface side of the GaAs substrate 11. When forming the electrode take-out hole 15 ', the GaAs substrate is left below the light emitting layer 12 with a thickness of about 1 .mu.m without exposing the light emitting layer 12 as shown in FIG.

Then, after that, as in the first embodiment, the GaAs
A second insulating film 16 and a second electrode 17 are formed on the back surface side of the substrate (FIG. 8) and the side surfaces are cleaved to complete the solid-state laser as shown in FIG.

In this method, when the GaAs substrate is etched to form the electrode lead-out holes, the GaAs substrate is left slightly without exposing the light emitting layer.
A good interface can be maintained without being contaminated by being exposed to the etching liquid or the outside air.

 Further, the element strength can be improved.

Further, it goes without saying that it has the same effect as that of the first embodiment.

In each of the above two examples, ZnS: Tb was used as the light emitting layer, but the light emitting base material was calcium sulfide (CaS), zinc selenide (ZnSe), strontium sulfide (SrS), or the like. It goes without saying that it may be made of a material. In addition, thulium (T
m), europium (Eu), cerium (Ce) samarium (Sm), manganese (Mn), praseodymium (Pv), holmium (Ho), dysprosium (Dy), francium (F)
It can be appropriately selected from r), neodymium (Nd) and the like.

In addition, although the GaAs substrate is used in the embodiment, any single crystal substrate that facilitates epitaxial growth may be used depending on the substance used for the light emitting layer.
P) and silicon (Si) are also effective.

〔The invention's effect〕

As described above, according to the method of the present invention, in the production of a solid-state laser in which both surfaces of the light emitting layer are sandwiched by electrodes via insulating films, after the light emitting layer is epitaxially grown on the single crystal substrate, Etching is performed from the back surface of the single crystal substrate to expose at least a part of the light emitting layer, and an insulating film and an electrode are formed on the back surface side as well. It is possible to obtain an efficient and highly reliable short wavelength laser.

Further, in the method of the present invention, when the single crystal substrate is etched from the back surface side, the substrate is left thin without exposing the light emitting layer, and the insulating film and the electrode are formed in the same manner as described above. In addition to the above effects, contamination of the interface of the light emitting layer can be prevented, the device strength can be increased, and the reliability can be improved.

[Brief description of drawings]

1 to 5 are views showing a manufacturing process of a solid-state laser according to a first embodiment of the present invention, and FIGS. 6 to 9 are manufacturing processes of a solid-state laser according to a second embodiment of the present invention. FIG. 10 is a view showing a conventional solid-state laser, and FIG. 11 is a manufacturing process drawing of the same solid-state laser. 1 ... Glass substrate, 2 ... First electrode, 3 ... Second electrode, 4a, 4b
... Insulating film, 5 ... Light emitting layer, 6a, 6b ... Mirror surface, 11 ... (GaAs) substrate, 12 ... Light emitting layer, 13 ... First insulating film, 14 ... First electrode,
15, 15 '... Electrode take-out hole, 16 ... Second insulating film, 17 ... Second electrode, 18a, 18b ... Reflective surface.

Claims (6)

(57) [Claims] 1. A solid-state laser in which electrodes are formed on two opposite surfaces of a light-emitting layer formed by adding an emission center impurity in a light-emitting base material via insulating films and the other two surfaces are used as reflection surfaces. In the method, a light emitting layer forming step of forming a single crystal thin film as a light emitting layer on a single crystal substrate by an epitaxial growth method, and forming a first electrode on the surface of the light emitting layer via an insulating film
Electrode forming step, a substrate etching step of etching the single crystal substrate from the back surface side to expose the light emitting layer, and a second electrode formed on the exposed light emitting layer back surface through an insulating film. 2. A method of manufacturing a solid-state laser, comprising: 2. The light emitting layer comprises terbium (Tb) as an emission center impurity in zinc sulfide (ZnS) as a light emitting base material.
The method for producing a solid-state laser according to claim (1), wherein the solid-state laser is composed of a single-crystal thin film obtained by adding Al. 3. The method of manufacturing a solid-state laser according to claim 1, wherein the reflecting surface is a cleavage surface formed by applying stress to the light emitting layer to cause cleavage. 4. A method for manufacturing a solid-state laser in which electrodes are formed on both surfaces of a light-emitting layer formed by adding a light-emitting center impurity in a light-emitting base material through insulating films and the other two surfaces are used as reflective surfaces. A light emitting layer forming step of forming a single crystal thin film as a light emitting layer on a single crystal substrate by an epitaxial growth method, and a first electrode for forming a first electrode on the surface of the light emitting layer via an insulating film.
Electrode forming step, a substrate etching step of etching the single crystal substrate from the back surface side to a predetermined thickness, and a second electrode forming step of forming an electrode on the etched surface with an insulating layer interposed therebetween. A method for manufacturing a solid-state laser, characterized in that the method includes: 5. The light emitting layer comprises terbium (T) as an emission center impurity in zinc sulfide (ZnS) as a light emitting base material.
The method for producing a solid-state laser according to claim (4), characterized in that the method comprises a single crystal thin film formed by adding b). 6. The method of manufacturing a solid-state laser according to claim 4, wherein the reflecting surface is a cleavage surface formed by applying a stress to the light emitting layer to cause cleavage.