JPH036079A - semiconductor light source - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure and manufacturing method of a device for generating second harmonics of semiconductor laser light, which is characterized by being integrated.

[Conventional technology 1] Conventionally, second harmonic generation (hereinafter SH) of semiconductor laser light has been
For example, Applied Physics
Letters) Vo 1, 35. No,
6 (1979) p, 461-p, 463 and Nikkei New Material April 20, 1987 issue p, 96-p10
As shown in 5, a module has been devised that combines a semiconductor laser and a waveguide type SHG element.1 For example, A.
An lGaAs-based semiconductor laser beam with a wavelength of 0.84 nm is focused onto the waveguide end face of a waveguide type SHG element made of LxNbOs single crystal using a collimator lens for optical pickup (numerical aperture 0.3) and a focusing lens (numerical aperture 06). , and generate SHG within the LINbO8 single crystal waveguide. An example of the overall dimensions of the module is:
10X10X10X30''.

[Problems to be Solved by the Invention] However, the above-mentioned module has the following problems.

1. Due to the modular system, it is essentially impossible to integrate the brainer as a component of an optoelectronic integrated circuit.

2. Since the SHG element requires a large crystal of extremely high quality, the manufacturing cost of the single crystal becomes high.

3. Since the optical waveguide is usually a thin layer on the order of lu,
Strictness is required for center alignment of the semiconductor laser optical resonator waveguide and the 5T (G element waveguide, parallelism adjustment, etc.), and the work is complex and delicate, and workability is poor.

4. The optical coupling efficiency between the semiconductor laser and the SHG element is low, and the overall SHG conversion efficiency is low, so the optical output is below the 1 mW level.

5. LiNb0a single crystal is susceptible to optical damage in the visible wavelength range.

The present invention is intended to solve this problem, and its purpose is to fully utilize semiconductor epitaxial technology to obtain a Brenna integrated device.

[Means for Solving the Problems 1] The integrated second harmonic generation device of the present invention is characterized by having the following structural requirements as means for solving the above problems.

1. Select a compound semiconductor as the SHG crystal material.

2. The compound semiconductor has MO on the semiconductor laser substrate surface.
CVD epitaxial growth is possible.

3. The epitaxial growth includes selective formation.

4. The SHG function section has an optical waveguide structure.

5. The optical waveguide is constructed on a plane that includes the optical resonator, that is, the active layer of the semiconductor laser.

6. The semiconductor laser optical resonator forms a ring-shaped resonator. Moreover, it has two independent resonators.

7. The SHG functional section forms a ring-shaped resonator.

8. The three resonators are formed on the same plane and placed close to each other so as to be optically coupled.

9. In the SHG functional section optical resonator waveguide.

The phase matching between the excitation laser beam and the SHG light utilizes the mode dispersion of the optical waveguide, and the low-order mode of the excitation laser beam and the SHG beam are matched.
The effective refractive indexes of higher-order modes of light are set to match.

10 Extraction of SHG light from the ring resonator is as follows:
Wavelength separation is achieved by DBR grating.

Introduced into the optical waveguide.

With the above configuration, laser light can be confined within the ring resonator, increasing the SHG conversion efficiency, and by planar integration, an extremely compact and short wavelength semiconductor light source can be realized. Example 1 The following case will be described as an example of the present invention.

The excitation laser beam is In, Ga+-y As (3”
) Light with an oscillation wavelength of 11000n depending on the composition of the active layer.

2. A compound semiconductor superlattice structure film is used as the SHG crystal material.

3. The compound semiconductor film is formed by MO on the semiconductor laser substrate.
CVD or MOMBE evixial growth is performed to form a superlattice structure.

4. Phase matching between the basic excitation laser beam and the SHG light is performed using the S
The effective refractive index is matched by controlling the thickness of the HG optical waveguide.

5. Both the laser beam resonator and the SHG function waveguide are ring-shaped resonators, and the laser oscillation part and the SHG part are optically coupled in the lateral direction.

6. The SHG optical waveguide is made by depositing a metal film on its top surface.
It is assumed that a Schottky barrier is formed and an optical waveguide is included in the depletion layer.

Next, the function and structure will be explained. FIG. 1 is a diagram showing a schematic planar structure of this embodiment as viewed from above. On the substrate 1, optical waveguides 23-1 and 3-2 are formed coplanarly and in a square shape so that light can be propagated and reflected many times. That is, a square ring-shaped resonator is formed. However, the laser resonator 3-2 has one corner missing, and has a resonator function due to reflection from the end face.

The light wave repeats reflection and propagation approximately as indicated by the dotted lines and arrow lines in FIG. 1, and propagates within the ring-type optical oscillator many times. Laser oscillation occurs within the optical waveguides of the ring-shaped optical resonator 3-1 and the resonator 3-2, and laser light is transmitted within the optical waveguide of the ring resonator 2 optically coupled to the two resonators. Propagate energy. In order to realize optical coupling, the optical waveguides of each of the three resonators are arranged in parallel and close to each other, with the optical waveguide of the resonator 3-1 being sandwiched between the other resonators 2 and 3-2. It is arranged as follows.

Therefore, the laser beam propagated to the resonator 2 causes SMC, that is, second harmonic generation, within the resonator 2. At this time, it is important that the laser light induced by optical coupling is almost completely confined within the resonator 2.

The optical waveguide 2 is formed, for example, by repeatedly laminating ultrathin films of two materials Z and nS/2nSe, which are II-Vl group compound semiconductors. The optical waveguide 3-1.3-2 is +11-
The laser active layer is composed of V group compound semiconductor mixed crystal In and Gap-y As.

Since it is necessary to phase match the laser beam and the SMC light in the optical waveguide 2, the film thickness and film composition of the optical waveguide 2 are adjusted.

For example, the film thickness and film composition are controlled so that the effective refractive indexes of the zero-order mode of the laser beam and the second-order mode of the SHG beam are made equal.

For optical confinement in the lateral direction of the optical waveguide, that is, in the direction parallel to the substrate 1, the lateral parts 4.5, 6 of the optical waveguide are connected to the optical waveguide 2.
．． 3-1.3-2, it may be filled with a material having a lower refractive index than 3-2. In this example, for the sake of simplicity, a space is left as it is etched during the process of forming the ring laser resonator 3-1, 3-2 (therefore, an air layer with a refractive index of Or, if the device is finally sealed with nitrogen, it becomes a nitrogen layer.

The SMC light is extracted to the outside of the optical resonator 2, as shown in FIG.
A means to use it as a light source is required.

For this reason, a DBR diffraction grating is formed on the surface 1, for example, at a portion 8 of the corner portion of the optical waveguide 2 where the SMC light is generated. Shallow etching, ion implantation, and
The diffraction grating is formed by epitaxial or vapor deposition methods. At this time, 100% of the laser beam with a wavelength of 11000n is reflected.

For SMC light with a wavelength of 500 nm, the period of the diffraction grating is set so that the reflectance is extremely low. As a result, the laser light induced in the resonator 2 is reflected at the four corners and confined within the resonator, whereas the generated SMC light is transmitted through the diffraction grating 8 and the optical waveguide 10. It is guided to the part, adjusted to the eigenmode, and taken out as light 7 to the outside.

Both the excitation laser light and the SMC light exist as light waves in two directions, clockwise and counterclockwise, but by designing the diffraction grating to be incident and reflected at 45 degrees, both directions can be transmitted. The above-mentioned conditions for reflection and transmission can be simultaneously satisfied for both light waves in the direction.

The ring laser 3 is a metal thin film ohmic 'r4rrA
It is driven by current injection from 11.

Metal thin film electrode 12 arranged and formed on the upper surface of the optical waveguide 2
For example, platinum (PT), gold (Au), or aluminum (A1) is selected to form a Schottky barrier for the n--ZnS/Zn5e superlattice pool optical waveguide 2. By applying a reverse bias to the electrode 12, a depletion layer is formed, the optical waveguide 2 is included in the depletion layer, and the generated strong electric field causes the refractive index of the optical waveguide to be influenced by the electro-optic effect. Accept it and change. Thereby, the phase matching conditions of the laser beam and the SMC light and the optical coupling conditions of the resonator 2 and the resonator 3-1, 3-2 can be precisely controlled. However, a feature of the present invention is that it can be adjusted by an external power source after all the above configurations are formed and completed.

As mentioned above, a ring-shaped optical resonator dedicated to SHG excitation is
By forming the ring resonator independently and confining the excitation laser within the ring resonator, SHG conversion can be performed effectively, and the overall 5t-IG conversion efficiency can be increased, and when the loOmW laser light is output, 3
A SHG optical output of 0mW was achieved.

Next, a manufacturing method for the structure of the present invention will be described.

FIG. 2 is a diagram showing the structure of the semiconductor laser section of FIG. 1, ie, a cross section taken along line A-A', showing an embodiment of the present invention. 20 is n −
GaAs substrate, 21 is n-GaAs buffer layer, 22
is n-Alx Gap-x As (X=O1l),
23 is n-In, Gap-y As (y=0.0
5), 24 is n-Al, lGa+-x As (X
:0. l) -25 is p-Al, Gap-++A
s (XJ,l), 26 is an n-GaAs cap layer, and 27 is a 5102 film. 28 indicates a 2n diffusion region, n
-AlxGa+-x Diffused to a depth up to the boundary between the As layer 22 and the n-GaAs buffer layer 21. As a result, n-In, Ga+-y As (y・0.05)
A portion of the layer 23 in which Zn is diffused and becomes p-type forms an active layer. Each of the aforementioned layers is evixaxially grown on the substrate 20 by MOCVD. The MOCVD conditions are roughly as follows.

Substrate temperature ・760℃～820℃ Pressure
-: 760 TorrV group/Ill group ratio:
50-100 Growth rate 0.07um/min
MOCVD source gases are trimethylgallium, trimethylaluminum, trimethylindium, and arsine. The Zn diffusion region is formed by a well-known diffusion method. A 2μXl 50u window is opened in the S10□ membrane 27, and diffusion is performed at a temperature of 600°C to 650°C. The Zn concentration is l
IO"/crn'.

Next, in order to form the SHG functional part shown in FIG.
Figure 2 n-G by etching other than the laser oscillation part.
Remove up to 21 layers of aAs buffer. The exposure n −G
On the aAs21 surface, there is a Z
Ecxitically grow the n5x 5et-m cladding layer and waveguide layer. The etching is performed by the RTBE method using an ECR type plasma apparatus. Etching gas is CCL
It was adopted. Compared to the chemical etching process, the RIBE process produces a much smoother etched surface, and some corners are formed at right angles, resulting in a more desirable shape. Therefore, a good epitaxial growth surface is obtained. Using this surface as a substrate, an SHG functional section is formed. A method of epitaxial growth of the SH5 functional section in cross section B-B' in FIG. 1 will be explained with reference to FIG. First, SiO□ of the mask 34 is deposited on the GaAs substrate 34 by thermal CVD or the like. This state is shown in FIG. 3(a). Next, patterning of SiO is performed by photolithography. At this time, 810. of the portion forming the waveguide layer. is removed by etching. This state is shown in FIG. 3(b). By selective epitaxial growth using the patterned 5xO2 as a mask, 2nSx Se+ of the cladding layer was formed.
-x 32 and a waveguide layer 33 thereon are successively formed in the same growth furnace. At this time, 5iOa of the mask
There is no deposit on the top, and the state is as shown in FIG. 3(C).

The selective epitaxial growth can be achieved by the following method.

Using organic compounds of Zn, S and Se as raw materials, the growth pressure is 1 oOTor or less, growth i = degree hs 4
Low pressure MOCVD method or M
This will be carried out using the OMBE method. The ZnS/Zn5e superlattice epitaxial film can be produced one after another with a thickness of 10 to 100 angstroms per layer by alternately supplying raw material organic compound vapors of S and Se according to a sea fence for a preset time. Stack. After forming the film layer, the SiO□ is removed using a hydrofluoric acid etchant to complete the optical waveguide as shown in FIG. 3(d). In the above example, a 5iOz film was used as the mask material, but Si
Other dielectric thin films such as 3N4 or metal thin films such as W can be used as well. Furthermore, as superlattice epitaxial films, in addition to Zn3/Zn5e superlattice epitaxial films, CdS/CdSe superlattice, ZnTe/Zn5p
Superlattice, CdSe/Zn5e superlattice, CdSe/Zn
S superlattices, CdS/ZnS Ml lattices are also applicable.

In the above embodiment, the composition of the semiconductor laser active layer is Iny Ga+-yAs, but
AIX Ga+-x As type and In++ Ga1-x
Py ASI-X system can be realized for other wavelength ranges,
TnP can also be applied to the substrate.

Further, in the above embodiment, the P-N junction is formed by a diffusion process, but it can also be realized by an in-implantation method as another method.
The N-type dopant can be towed from the gas phase at the same time, and the PN junction made by this method has better laser oscillation efficiency than the diffused process junction. P-N junction using a liquid phase epitaxial film is also possible.

In addition, in the above-mentioned embodiment, the region shown in FIG. 1, 4.5.6 is used as the etching removal space, but the entire surface of this region is made of the same material as the optical waveguide 2 and is grown epitaxially at the same time, after which the laser beam is removed. The resonator 3-1, 3-2, the optical waveguide 2, and the optical waveguide 10 are protected by a mask, and the remaining portions can be implanted with proton ions. That is, as a result, all the lateral sides of the optical waveguide are covered by the proton (H)-doped ZnS/Zn5e superlattice layer,
Optical confinement is achieved by the difference in refractive index depending on the presence or absence of proton doping. This has the advantage that there are no steps on the surface of the chip, a flat surface is formed, and other elements or electrodes/wirings can be easily integrated.

Next, the DBR diffraction grating shown in FIG. 18 is formed by the following method. FIG. 4 shows a schematic diagram of the principle in which photoelectrochemical etching is performed while irradiating with laser light. Reference numeral 40 denotes a processing laser beam, and 41 a beam splitter, which separates the monitor light reflected from the grading 43 to be processed and introduces it to a photodetector 42, so that the processing status of the grating 43 can be determined by on-site observation. A reflecting mirror 44 deflects the laser beam at right angles and causes it to interfere with other laser beams on the surface to be processed, that is, the surface of 43, thereby forming a holographic grating pattern. The area irradiated with the laser beam is etched, but the dark area is not etched. 45 is an etching liquid in which the workpiece is immersed. An electric bias is applied to the workpiece to form a depletion layer on its surface.

The laser light is excimer laser light with a wavelength of 257 nm. The etching solution is H,5O4=H,O.

H20=l:l, 100 (volume ratio) or H
It is a liquid of N0xH20=1+20 (volume ratio). Reagent concentrations are: HISO, = 98% (weight), HNO,:
70% (weight) and 8.0□: 30% (weight). By rotating the table on which the reflecting mirror 43 and the workpiece 43 are set, the grating period can be changed continuously.

Furthermore, the photoelectrochemical etching method is extremely suitable for etching the side surface of the optical waveguide described above, and a smooth plane that is perpendicular to the substrate is formed.

As described above, the light source of the present invention formed under optimal conditions was able to extract 30 mW of SHG light output at a wavelength of 500 nm.

[Effect of the invention] As explained above, the present invention has the following effects.

lIt is extremely compact and can be handled in the same way as a conventional LD chip.

It has the potential to be integrated as a component of a 24 optoelectronic integrated circuit.

3. High-quality large single crystals are not required.

4.30mW class semiconductor laser can be realized, and 100mW class semiconductor laser can be realized.
We can also expect mW class.

5 Conventional IC technology can be used.

6. Therefore, mass production is possible and manufacturing costs can be reduced.

7. Since the SHG crystal is grown by MOCVD epitaxial growth, high quality of integrity can be ensured, resulting in high conversion efficiency.

The 8-layer pitaxial superlattice film layer provides extremely high nonlinear optical constants and high conversion efficiency.

9. Due to the structure in which multiple ring-shaped resonators are combined, laser light can be effectively confined within the SHG resonator, and can contribute as light energy for SHG until it is attenuated.

As mentioned above, it has a very wide range of useful effects,
It is particularly useful as a light source for magneto-optical recording systems and laser beams.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view showing an embodiment of the semiconductor light source of the present invention. FIG. 2 is a schematic cross-sectional structural diagram of a semiconductor laser section in an embodiment of the semiconductor light source of the present invention. FIGS. 3(a) to 3(d) are diagrams illustrating the outline of a process for manufacturing an SHG functional light guide waveguide in an embodiment of the semiconductor light source of the present invention. FIG. 4 shows a DBR in an embodiment of the semiconductor light source of the present invention.
A diagram explaining a method for manufacturing a diffraction grating. l ・ ・ ・ ・ ・ ・ ・ ・ ・GaAs substrate 2...SHG 18 Nobe ring resonator optical waveguide 3-1.3-2...Ring laser oscillation part optical waveguide 4. ...... Lateral light confinement layer 5 ...
・・・・・・Same as above 6・・・・・・・・・Same as above 7・・・・・・Output SHG light 8・・・・・・DBR diffraction grating function section】0...
...... Optical waveguide 11 ...... Ohmic electrode 12 ...
・・・Schottky barrier electrode 20・ ・ ・ ・ ・ ・ ・ ・ ・n-GaA
s board 21・ ・ ・ ・ ・ ・ ・ ・n-G
aAs buffer layer 22 - - - - - -
・ ・ n-AlxGa, -xAs23---
-- ・InyGa+-yAs (including active stone) 24-----=-n-AlxGa+-xAs25 ・
・ ・ ・ ・ ・ ・ ・ ・ p-A1 Ga
, -1l AS26 ・ ・ ・ ・ ・ ・ ・ ・
・ n -GaAs27・ ・ ・ ・ ・ ・
・・S10. Film 28...Zn diffusion region 31...GaAs substrate 32...Zn Sx 5el-x cladding layer 33... ...Superlattice structure optical waveguide 34...
・・・・・・5i02 Mask 40・ ・ ・ ・・ ・
・ ・ ・Laser beam 41...Beam splitter 42... ・Detector 43...Liquid addition nigerating 44...
・・・・・・Reflector 45・・・・・More than etching liquid

Claims (1)

[Claims] A semiconductor light source configured on a plane includes two ring-shaped optical resonators having a laser oscillation function and one ring-shaped optical resonator having a second harmonic generation function, and the former optical waveguide is the latter optical waveguide. A semiconductor light source characterized by being placed closely on both sides of an optical waveguide.