JP2561004B2 - Semiconductor laser and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser and its manufacturing method, and more particularly to a semiconductor laser having a diffraction grating and its manufacturing method.

[0002]

2. Description of the Related Art A distributed feedback semiconductor laser (Distributed
Feedback LASER Diode (hereinafter abbreviated as DFB-LD) stability and yield of single axis mode oscillation are mainly determined by the phase of the optical standing wave at the end face of the cavity, that is, the phase of the diffraction grating adjacent to the active layer. Is well known. When using the DFB-LD for analog transmission, the DFB-LD
Good linearity between the LD current and light output is essential, and the light distribution in the active layer of the DFB-LD greatly affects the characteristics. Since this light distribution is largely influenced by the phase of the diffraction grating on the end face of the active layer of the DFB-LD, it is necessary to control the phase of the diffraction grating on the end face of the active layer.

FIG. 2 shows the structure of a DFB-LD element.
The diffraction grating (21) is formed on the n-type InP substrate (23) by using the interference exposure technique and the etching technique. On the diffraction grating (21), for example, a metalorganic vapor phase epitaxy method (Metalorganic
Vapor Phase Epitaxy (hereinafter abbreviated as MOVPE) is used to form an n-InP buffer layer (26), an InGaAsP active layer (22), and a p-InP layer (27). For confining current and light, a p-InP layer (211) and an n-InP layer (210) are formed by etching and MOVPE, and a p-InP layer (28) and a p-InGaAsP layer (29) are formed. After the n-side electrode (24) and the p-side electrode (25) are vapor-deposited on the substrate, a laser emitting end face is formed perpendicular to the active layer by cleavage. A non-reflective film (2
12) and a reflective film (213) are formed. Active layer (22)
The light inside is diffracted by the diffraction grating (21) and oscillates in the single longitudinal mode in the mode having the smallest oscillation threshold gain among the fixed modes determined by the grating period. The laser light is mainly output from the non-reflection film (212) side.

The conventional DFB-LD manufacturing method has the following drawbacks. That is, when the light emitting end face is formed by the cleavage, the grating phase of the diffraction grating end face is cleaved without any control, and the reflection loss significantly changes depending on the state of the phase of the grating at the end face. Elements that do not uniaxially oscillate are also generated. Further, since the light density in the resonator varies depending on the element, I−
Some L characteristics have poor linearity. Conventionally, this I-
The L characteristic having poor linearity was dealt with by measuring and selecting the DFB-LD after manufacturing. Therefore, it takes a lot of man-hours for selection, and the DFB-L has a reduced yield.
However, there is a drawback that the manufacturing cost of D is increased. In order to make up for these drawbacks, a countermeasure as described below has been proposed.

In the known example 1 described in JP-A-61-220496, after forming the diffraction grating pattern (32) on the substrate (31) of FIG. 3 (a), a focused ion beam apparatus is used. The position of the phase of the diffraction grating that is scheduled to cleave the diffraction grating pattern (32) is detected, and the groove (33) indicating the position is formed by irradiating the ion beam. On this substrate (31), layers (34) to (37) constituting the laser shown in FIG. 3 (b) are epitaxially grown. At this time, InP and InGaAsP are deposited in a polycrystalline state (33A) on the groove (33). This polycrystalline deposition (33
A) is selectively etched to form a groove indicating the cleavage position. On this substrate, the electrodes (38), (3
After forming 9), cleavage is performed using the groove (33) as a guide to control the phase of the diffraction grating at the light emitting end face. (310) is an antireflection film.

A known example 2 described in JP-A-64-81383 will be described. DFB-L by conventional method
D is manufactured and attached to the focused ion beam etching apparatus shown in FIG. The light from the DFB-LD is observed using the optical fiber (413) and the spectrum analyzer (414). Ga liquid metal ion source (41), extraction electrode (42), converging lens (43), deflection electrode (44)
Thus, the Ga ion beam is focused on the end surface of the active layer of the DFB-LD. The portion irradiated with the Ga ion beam is selectively etched using Cl ₂ gas or the like. Etching is performed until the phase of the diffraction grating at the light emitting end face is optimized so that the spectrum oscillates in a single longitudinal mode. In FIG. 4, (45) is a secondary electron detector, (46) is a secondary electron image monitor, (47) is an etching gas blowing nozzle,
(48) is a Ga ion beam, (49) is a laser driving power source, (410) is a DFB laser, (411) is a laser chip mount, and (412) is a stage.

[0007]

In the case of the known example 1, it is practically extremely difficult to provide the groove indicating the cleavage position sufficiently deep so that the cleavage with the initial dimensional accuracy is easy and the surface accuracy is vertical. The drawback is that it is difficult. For example 1.
DFB using InGaAsP of 3 μm wavelength band for active layer
-In the case of LD, the period of the diffraction grating is about 0.4 μm,
About 0.1 μ of FIG. 3A described in the known example 1
The width dimension accuracy of the groove (33) having a width of m is
It is extremely difficult to form the groove (33A) shown in (b) by etching. Further, in mechanical cleavage, it is difficult to maintain the accuracy by cleaving the groove exactly according to its position. Therefore, there is a drawback that the yield for obtaining a DFB-LD with desired characteristics is low. In the case of the known example 2, since the etching is performed while observing the light, the device is complicated and the number of man-hours is increased, such as the connection of the fiber for the light and the wiring for passing the current to the laser diode are required, and the manufacturing cost is increased. There is a drawback that Moreover, it is unrealistic to use an optical fiber, an electrode, or the like in Cl ₂ gas.

[0008]

The present invention solves the above-mentioned drawbacks of the prior art. In a semiconductor laser having a diffraction grating, the conductivity type is determined for one of the semiconductor crystals forming the diffraction grating. The semiconductor laser is characterized in that a portion containing an impurity different from the above-mentioned impurities is provided separately from the above-mentioned impurities, and the emission end face of the semiconductor laser is etched by ion irradiation to perform mass analysis of secondary ions. The semiconductor laser manufacturing method is characterized in that the phase of the diffraction grating is determined by performing the measurement of the impurity concentration to control the phase of the diffraction grating at the light emitting end face.

[0009]

Embodiments of the present invention will be described with reference to the drawings. [Embodiment 1] FIG. 1 illustrates Embodiment 1 of the present invention. As shown in FIG. 1A, impurities other than Sn, such as Te and Si, are ion-implanted near the surface of the n-type InP substrate (3) using Sn as a donor impurity. (1
4) shows a region where the impurities are ion-implanted near the surface of the n-type InP substrate (3). As shown in FIG. 1B, a diffraction grating is formed by interference exposure and etching. Impurity region (1
5) remains. As shown in FIG. 1C, the active layer (2) and other DFB-LDs are formed as in the prior art. The depth of the ion-implanted region (14) into the n-type InP substrate (3) from the substrate surface is 100 Å with a depth centered at about 1/2 of the diffraction grating, assuming that the depth is 250 Å. 15
0Å is suitable.

As shown in FIG. 1E, the emission end face of the laser diode is sputtered by using, for example, a secondary ion mass spectrometer, and the concentration of the ion-implanted element is observed.
The primary ion beam (16) emitted from the primary ion source (18) is irradiated near the light emitting end surface of the DFB-LD (20), and the vicinity of the light emitting end surface is sputtered. Impurities implanted in the peaks of the diffraction grating are 2
It becomes the secondary ion (17), is detected by the secondary ion detector (19), and the concentration of target impurities (Te and Si) on the sputtered light emitting end face is measured. When the concentration of the ion-implanted impurity is the highest, the peak portion of the diffraction grating is formed, and when the concentration is the lowest, the valley portion is formed.

The phase position of the diffraction grating on the light emitting end face can be determined and adjusted by the high and low concentration of the ion-implanted impurities (FIG. 1 (d)). After that, a non-reflection film and a reflection film are formed on the light emitting end face, and the manufacturing of the DFB-LD is completed. According to the present invention, it becomes possible to control the phase position of the diffraction grating on the light emitting end face, which is a problem of the prior art, with an accuracy of several tens of Å. Further, since optical coupling and electrode wiring are not required, the number of steps can be reduced and the cost can be reduced.

[Embodiment 2] As Embodiment 2, Embodiment 1
It is possible to control the end face phase of a plurality of devices at once by performing the operation of Example 1 in the state of the bar after the end face cleaving, instead of the single element described in 1. above.

[0013]

As described above, according to the present invention, the phase of the diffraction grating at the light emitting end face can be controlled accurately and at low cost, and therefore the light distribution in the active layer can be controlled. The DFB-LD can be manufactured well, and the phase of the diffraction grating on the light emitting facet can be controlled by the impurity concentration to improve the stability of the oscillation mode and the yield for the current-light output linearity. It is a thing. For example,
When the DFB-LD is used for analog modulation, the linearity between the light output and the current is required. DFB-as in the present invention
If the LD is manufactured, the linear yield can be greatly improved to about 90% as compared with the conventional technology of about 30%. Further, when the method of Example 2 of the present invention is used, a time reduction of 70% or more can be expected as compared with Example 1.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an example of the present invention.

FIG. 2 is a diagram illustrating a structure of a conventional DFB-LD.

FIG. 3 is a diagram illustrating a known example 1 of the related art.

FIG. 4 is a diagram illustrating a known example 2 of the related art.

[Explanation of symbols]

 2 Active Layer 3 n-type InP Substrate 14 Impurity-Implanted Region 15 Ion-Implanted Impurity Region after Diffraction Grating Formation 16 Primary Ion Beam 17 Secondary Ion 18 Primary Ion Beam Source 19 Secondary Ion Detector 20 DFB-LD 21 Diffraction grating 22 GaInAsP active layer 23 n-type substrate 24 n-side electrode 25 p-side electrode 26 n-type InP 27 p-type InP 28 p-type InP 29 p-type GaInAsP 210 n-type InP 211 p-type InP 212 non-reflective film. Reference numeral 213 Reflective film 31 InP substrate 32 Diffraction grating pattern 33 Groove 34 n-type InGaAsP guide layer 35 InGaAsP active layer 36 p-type InP clad layer 37 p-type InGaAsP 38 p-side electrode 39 n-side electrode 310 antireflection film 311 substrate 312 Laser element structure Formation area 313 Cleavage guide 41 Ga Liquid Metal Ion Source 42 Extraction Electrode 43 Focusing Lens 44 Deflection Electrode 45 Secondary Electron Detector 46 Secondary Electron Image Monitor 47 Etching Gas Blowing Nozzle 48 Ga Ion Beam 49 Laser Driving Power Supply 410 DFB Laser 411 Laser Chip Mount 412 Stage 413 Optical fiber 414 spectrum analyzer

Claims (4)

(57) [Claims] 1. A semiconductor laser having a diffraction grating, wherein one semiconductor crystal forming the diffraction grating is provided with a portion containing an impurity different from the impurity in addition to the impurity for determining the conductivity type. A semiconductor laser characterized by: 2. A semiconductor laser, wherein the impurity-containing portion according to claim 1 has the impurity in a concentration distribution synchronized with a phase of a diffraction grating. 3. The phase of the diffraction grating is determined by etching the light emitting end surface of the semiconductor laser by ion irradiation, measuring the concentration of the impurities by performing mass analysis of secondary ions, and determining the phase of the diffraction grating at the light emitting end surface. 3. The method for manufacturing a semiconductor laser according to claim 1, wherein the phase of the diffraction grating is controlled. 4. The phase of the diffraction grating is discriminated by etching the light emitting end surface of the semiconductor laser by ion irradiation, measuring the concentration of the impurities by mass spectrometry of secondary ions, and determining the phase of the light emitting end surface. 3. The semiconductor laser according to claim 1, which has a diffraction grating whose phase is controlled.