JPS62173785A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To improve the uniformity and the high output characteristic of a semiconductor laser operated in a single axis mode by forming a non-ion implanted region at the center in the active layer toward a resonator axis and current regulating regions made of high resistance regions at both sides of the region. CONSTITUTION:A diffraction grating having lambda/4 shift region 50 is formed substantially at the center of a resonator on a (001) azimuth substrate 1, and an optical guide layer 2, a non-doped active layer 3 and a clad layer 4 are laminated on the substrate 1. Two parallel grooves 71, 72 are formed at both sides of a mesa stripe 70 therebetween in (110) direction, a block layer 5 and a current enclosure layer 6 are further so laminated as not to grow only on the top of the stripe 70, a buried layer 7 and a cap layer 8 are so laminated as to cover the entirety to form a double channel planarly buried structure. Then, ions are implanted to the both end sides to form current regulating regions 9 made of high resistance regions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser used as a light source for optical communications or optical measuring instruments.

[Conventional technology]

Distributed feedback semiconductor lasers (hereinafter referred to as DFBLDs) or distributed Bragg reflection semiconductor lasers (hereinafter referred to as DBRLDs) that operate in a single-axis mode are used as light sources for high-speed and long-distance optical fiber communications. Because of its good unity, it is expected to be used as a light source for optical measuring instruments that incorporate coherent optical systems, and its development is progressing at a rapid pace. DF using InGaAsP/InP material
1100k at ultra high speed of 4 Gb/s in BLD
It has been used as a light source in experiments on optical fiber communication systems with transmission distances exceeding In addition, devices with good characteristics can achieve high-output CW operation of over 100 mW in single-axis mode operation and high-temperature CW operation of up to 140°C.
Almost the same characteristics as the t) type semiconductor laser were obtained.

However, unlike conventional Fabry-Perot semiconductor lasers, DFB LDs have manufacturing difficulties in controlling the oscillation axis mode to one. In other words, in the Fabry-Perot semiconductor laser, it was possible to stably fabricate a device that could almost satisfy the required conditions as long as the oscillation transverse mode was controlled, but the DFB LD
In this case, the oscillation spectrum changes in a complex manner, such as in a single axis mode or in multiple axis modes, depending on the phase of the diffraction grating at which the diffraction grating is cut at the light exit end face. It has been difficult to produce devices that operate in this mode with a high yield.

Furthermore, even FB LD can operate in single axis mode.
End-axis mode oscillation is not possible at high output.

FIG. 5 is a sectional view of the main part of a laser chip showing an example of a conventional DFB LD.

This conventional example is a DFB2L, D in which a λ/4 shift region 50 is provided that changes the phase of the diffraction rays by 1/4 wavelength with respect to the black wavelength at approximately the center of the element. In order to avoid the influence of reflection, low reflection films 30 and 31 are formed on both end faces.

It is known that the oscillation characteristics of the single-axis mode are improved in such an FB LD (for example, reported by Utaka in Proceedings of the 1981 Institute of Electronics and Communication Engineers National Conference No. 1017).

However, even in such an FB LD, if the injected current is increased in an attempt to obtain high output, the mode that oscillates at the Black wavelength or the mode at the Bragg wavelength stops oscillating and becomes secondary. mode begins to oscillate.

This phenomenon can be understood in the following way.

FIGS. 6(a) and 6(b) are characteristic diagrams for explaining the distribution of gain and electric field intensity of light in the conventional example shown in FIG.

Assuming a gain distribution of −)k in the direction of the resonance axis, as shown in FIG.

However, calculations were made assuming that the injected current density is uniform in the axial direction of the resonator4.The electric field strength is highest at one point in the λ/4 shift region 50' at the center of the element and attenuates toward the end face. The element in which the λ/'4 shift region 50 is formed oscillates at the Bragg wavelength, and has an excellent structure that allows a large difference in oscillation threshold gain with the submode. The electric field strength distribution of the light inside the cavity takes the form shown in Figure 6(a).By the way, in Figure 6(a), the gain is assumed to be uniform in the resonator axis direction.However, in reality, the resonator Since the electric field strength of the light is large near the center of the resonator, more injected carriers are consumed than at both ends of the resonator, and the gain actually saturates.

Considering this effect, the electric field strength distribution and gain distribution of light will have a shape as shown in FIG. 6(b), in which the electric field strength of light at the center is slightly smaller than that in FIG. 6(a>). By the way, when the injected current is gradually increased in an attempt to obtain high output, the electric field strength of the light inside the resonator further increases, which further increases the consumption of injected carriers near the center of the resonator. The tendency for the gain to be large at both ends of the resonator, where the consumption of injected carriers is smaller than that at As the secondary mode increases in size, it becomes easier to oscillate, and eventually the secondary mode oscillates at the same time as the mode that oscillates at the Bragg wavelength, or when the mode at the Bragg wavelength stops oscillating. The calculations were not well understood because they mostly assumed that the gain within the resonator was uniform.In fact, the inventors of the present invention used a similar structure of When we prototyped and evaluated a device with this structure, we observed sub-mode oscillation, which was different from what was initially predicted.The explanation for this is that the electric field of the light in the direction of the resonator axis as described above. It was found that it is necessary to consider the intensity distribution.

[Problem that the invention seeks to solve]

The above-mentioned conventional semiconductor lasers have a problem in that even if the laser oscillates most stably in a single-axis mode, as the injection current is increased, a sub-mode appears and the semiconductor laser no longer oscillates in the single-axis mode.

An object of the present invention is to provide a semiconductor laser that operates in a stable single-axis mode and that can be manufactured with high yield.

1. Means for Solving the Problems] The semiconductor laser of the present invention provides an injection current density distribution that at least approximately matches the electric field intensity distribution of light in the cavity axis direction within the active layer in a predetermined axial mode. It has a current adjustment area.

Embodiment] Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a laser chip showing a first embodiment of the present invention.

In this embodiment, a current adjustment region 9-1 consisting of a proton injection region provides an injection current density distribution that approximately matches the electric field intensity distribution of light in the cavity axis direction within the active layer 3 in the zero-order axial mode. .9-2.

Next, the manufacturing process of this example will be explained.

On a substrate 1 made of (001)-oriented n-type InP (So-doped, carrier concentration I x 1018 cm-'), a λ/4 shift region 50 is located approximately in the center of the resonator, and the depth is 1000. A diffraction grating 60 with a period of 2000 is formed. On this substrate 1, the emission wavelength is 1.15 μm.
A light guide layer made of n-type InGaAsP (film thickness 0.15 μry3Sn doped at the valleys of the diffraction grating, carrier concentration 7×10”cm−4) with a forbidden band width of 2° emission wavelength, 30 μm. non-doped InGa
Active layer 3 made of AsP (film thickness 0.1 μm) and p-type 1nP (Zn doped, carrier concentration 1×1()1
80. -3, film thickness 0.7 μm) is laminated. After this, in the <110> direction, the upper width is about 1 in between.
．． A depth of 3 μm, with a mesa stripe 70 of 5 μm in between.
Two parallel grooves 71 and 72 with a width of about 8 μm are formed, and p-type 1oP (Zn doped, carrier concentration 1×10 18
Current blocking layer 5 consisting of n-type 1nP (Te-doped, carrier concentration 5 x 10 "cm-', thickness 0.5 am in the flat part), CII+-3, thickness 0.5 am in the flat part)
A current confinement layer 6 consisting of a p-type 1nP (Zn doped, carrier concentration l
-3, buried layer 7 with a thickness of 1.5 μm at the flat part
, p-type 1nGaAsP (Zn doped, carrier concentration I
x 1019 cm-3, thickness 1.0 μm at the flat part) is laminated to form a double channel planar embedded structure, which was reported by Mito et al. in Proceedings 857 of the 1985 IEICE General Conference. form. Next, ions are implanted into both end faces in a width of 40 μm (the implanted ions are H+, and multiple implantations of 25 to 200 keV are performed for a total implantation of M3×10 “H”/am2). This DFBL, D
The resonator length is 200 μm, so there is a 120 μm long region in the center in the direction of the resonator where no ions are implanted;
6p side electrode 80. Current adjustment regions 9-1 and 9-2 each consisting of a high resistance region of 40 μm are formed on both sides thereof. n
After forming the side mold ff181, low reflection films 3o and 31 made of a silicon nitride film with a reflectance of 2% or less are formed on both end faces obtained by the creases.

Figure 2 shows the electric field strength distribution of light (
FIG. 4 is a characteristic diagram showing the injection current density distribution (solid line) and the injection current density distribution (broken line).

This figure is a characteristic diagram when a voltage is applied in the forward direction between the p-side electrode 80 and the n-side electrode 81, and has an injection current density distribution that approximately matches the electric field intensity distribution of light.

When we measured the characteristics of the device fabricated in this way, we found that
The oscillation threshold at 25°C is 25 mA, and the front end face is 90 mA.
The differential quantum efficiency in terms of light output from was 20-25%. Regarding the oscillation spectrum, in the devices of the same wafer lot that were not ion-implanted, many axial mode oscillations occurred and multi-axis mode oscillation was observed, but with the structure of the present invention, about 70% of the devices oscillated in multiple axial modes. One side output 3
Do not exhibit single-axis mode operation up to a high power range of about 0mW or more.

FIG. 3 is a perspective view of a laser chip showing a second embodiment of the invention.

The difference from the first embodiment is that first of all, on the rear end surface, there is a 5i02/thickness Q of 0.2 μm, and an amorph film of 1 μm.
rs Si, / 0.2 μm thick 5i02 / 0.1 μm thick
The second feature is that a high reflection film 32 with a reflectance of 90% consisting of four layers of amorphous Si of λ/m is provided.
The 4-shift region is not needed in this structure and is not formed, and as shown in FIG. 3, the current adjustment region 9-3 consisting of the proton injection region is provided only at the left end of the laser chip. be. The conditions for proton injection are the same as in the first example.

Figure 4 shows the electric field intensity distribution of light during operation of the embodiment shown in Figure 3 (
FIG. 4 is a characteristic diagram showing the injection current density distribution (solid line) and the injection current density distribution (broken line).

When the characteristics of this element were evaluated, the oscillation threshold was 20 m.
A. Maximum output of light emitted from the front end face 90 100mW
, and the differential quantum efficiency was 50% at room temperature. The stability of single-axis mode operation is also good, with most elements
It operated in a stable single-axis mode up to an optical power range exceeding 0 mW.

In the above explanation, an example is shown in which a high resistance region is formed under a single implantation condition, but the resistivity can be controlled by changing the implantation depth by changing the accelerating voltage or by changing the implantation amount. It is clear that it is possible to obtain an injection current density distribution that matches the electric field intensity distribution of light even more by combining these methods.

Further, ions other than protons may be implanted, and the method is not limited to the ion implantation method, as long as the resistance value can be substantially controlled.

For example, an insulating film having openings of an appropriate size may be provided between the cap layer and the n-side electrode.

Furthermore, although the explanation has been given using a double channel planar embedded type LD as an example, it is also applicable to other structured LDs, such as a simple embedded type LD or a guide type LD.

〔Effect of the invention〕

As explained above, by providing the current adjustment region, the present invention can realize an injection current density distribution that almost matches the electric field intensity distribution of light inside the semiconductor laser, thereby improving the uniformity of the semiconductor laser operating in a single axis mode. This has the effect of providing improved high output characteristics.

[Brief explanation of drawings]

Figure 1 is a perspective view of the laser chip, not showing the first embodiment of the present invention, and Figure 2 is the electric field intensity distribution (solid line) and injection current density during operation of the embodiment of Figure 1. 3 is a perspective view of a laser chip showing the second embodiment of the present invention, and FIG. 4 is a characteristic diagram showing the electric field intensity distribution of light during operation of the embodiment of FIG. Figure 5 is a cross-sectional view of the main diagram of a laser chip showing an example of a conventional DFB LD; Figures 6 (a>, (b)
) is a characteristic diagram for explaining the distribution of gain and electric field intensity of light in the conventional example shown in FIG. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Light guide layer, 3... Active layer,
4... Tara-sodo layer, 5... Current pro-tsuku layer, 6
... Current confinement layer, 7... Buried layer, 8... Cap layer, 9-1°9-2.9-3... Current adjustment region,
30.31...Low reflection film, 32...High reflection film, 50
...λ2/'4 shift region, 60... Diffraction grating, 7
0... Mesa stripe, 71.72... Vortex, 80.
. . . n-side electrode, 81 . . . n-side electrode, 90 . . . front end surface. Figure 1 Figure 7 Old man 30 Outside 3゛den L Fuchiyoshi? Remaining figure 4

Claims (1)

[Claims] 1. A semiconductor laser comprising a current adjustment region that provides an injection current density distribution that at least approximately matches the electric field intensity distribution of light in the cavity axis direction within an active layer in a predetermined axial mode.