JP3089584B2 - Semiconductor laser with monitor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser with a monitor in which a monitoring photodiode for monitoring output light of a semiconductor laser and a semiconductor laser are integrated on the same substrate.

[Conventional technology]

Conventionally, a semiconductor laser with a monitor in which a monitoring photodiode and a semiconductor laser are integrated on the same substrate is, for example, the sixth type.
As shown in the cross-sectional view of the figure, there is a nitride stripe laser in which a separation groove is provided by chemical etching to integrate a semiconductor laser and a monitoring photodiode on the same substrate (K. Iga and BIMiller: Electron Lett. 16 pp342-3
43 (1983)). In FIG. 6, reference numeral 16 denotes an n-type InP substrate;
Is an n-type InP cladding layer, 18 is a GaInAsP active layer, 19 is a p-type InP
The P cladding layer 20 is a p ⁺ -type GaInAsP contact layer. Reference numeral 6 denotes a p-type electrode, 7 denotes an n-type electrode, 8 denotes a laser portion, 9 denotes a photodiode portion, and 13 denotes an etching separation groove.

In such a semiconductor laser with a monitor, since the etched end face of the laser section 8 facing the photodiode section 9 and the etched end face of the photodiode 9 facing the laser section 8 are substantially parallel, multiple reflection of laser output light is performed. Occurs
There is a disadvantage in that the light receiving efficiency of the photodiode varies significantly due to a slight variation in the etching groove width between the elements. This issue is discussed in detail in the following document (H. Sa
ito and Y. Noguchi: Electron Lett. 25 pp719-720 (198
9)).

FIG. 7 is a plan view of a semiconductor laser with a monitor devised for the purpose of increasing the light receiving efficiency of a photodiode (Kitamura, Kobayashi, Sugimoto: JP-A-58-84486). In FIG. 7, 8 is a laser portion, 9 is a photodiode portion, 13 is an etching separation groove, 21 is a stripe-shaped active region, and 22 is a light receiving region of a photodiode having a rounded light receiving surface.

Such a structure has the advantage that the reflection at the end face of the photodiode facing the laser section 8 is small and the light receiving area of the photodiode section 9 is wide, so that the light receiving efficiency is high.

However, it is practically difficult to manufacture semiconductor lasers having various embedded structures, which are generally used in optical communication, by changing the stripe width of the laser portion and the stripe width of the photodiode.

That is, in a buried semiconductor laser, when the stripe width is changed, the transition region of the stripe width change becomes relatively long, and as a result, the separation groove width between the laser part and the photodiode part must be widened. However, there is a disadvantage that the light receiving efficiency is reduced.

Due to the manufacturing difficulties described above, the conventional example of manufacturing a semiconductor laser with a monitor shown in FIG.

In addition, a groove is provided beside the stripe-shaped active region of the buried structure laser to reduce the parasitic capacitance and form the end face of the photodiode facing the laser portion obliquely with respect to the stripe-shaped active region. A semiconductor laser with a monitor that suppresses the adverse effects of reflection was recently announced (1989 IEICE Autumn National Convention: Ueki, Yamamoto, Oishi, Kaminishi, Nakano, Tsuzuki, C-192).

This is shown in the plan view of FIG. In FIG. 8, 8 is a laser section, 9 is a photodiode section, 10 is a stripe-shaped current path, 11 is a mesa including a stripe-shaped active region, 12
Is a protective mesa, and 13 is an etching separation groove. In this structure, since the grooves on both sides of the stripe-shaped active region are not vertical, the effect is merely to reduce the parasitic capacitance but not to increase the light receiving efficiency of the photodiode.

[Problems to be solved by the invention]

As described above, in the conventional structure shown in FIG. 6, the etched end face of the laser section 8 facing the photodiode section 9 and the etched end face of the photodiode section 9 facing the laser section 8 are substantially parallel to each other. Multiple reflection of the output light occurs, and there is a problem that the light receiving efficiency of the photodiode is remarkably fluctuated by a slight change in the etching groove width between the elements.

In addition, in the structure shown in FIG. 7, it is necessary to change the stripe width of the laser section 8 and the stripe width of the photodiode 9, so that the manufacture is extremely difficult. In addition, when the stripe width is changed, the transition region of the change in the stripe width becomes relatively long. Therefore, there is a problem that the separation groove width between the laser unit 8 and the photodiode unit 9 must be widened, and the light receiving efficiency decreases. There was a problem.

Further, the structure shown in FIG. 8 has a problem that the light receiving efficiency of the photodiode cannot be increased merely by reducing the parasitic capacitance because the grooves on both sides of the stripe-shaped active region are not vertical.

The present invention has been made in view of the above points, and its object is to solve the problem of reflection of laser light on the end face of the photodiode facing the laser portion and the problem of low light receiving efficiency of the photodiode, which is easy to manufacture and It is to provide a new semiconductor laser with a monitor.

[Means for solving the problem]

In order to achieve the above object, a semiconductor laser with a monitor according to the present invention is provided on both sides of a stripe-shaped active region having the same width with an etching groove provided at least until reaching a cladding layer on the substrate side, and is formed on the same substrate. The width of the mesa including the active region of the photodiode portion having a stripe-shaped active region having the same width is formed in a tapered shape in such a manner that a portion closer to the laser portion is wider and a portion farther from the laser portion is narrower. Angle θ in the range of 0 <θ ≦ 80 °,
The main feature is that the side surface of the mesa including the active region is formed perpendicular to the plane of the substrate.

(Operation)

ADVANTAGE OF THE INVENTION According to this invention, while using a complicated process, the reflection of the laser beam in the photodiode end surface facing a laser part can be prevented, and the light receiving efficiency of a photodiode can be made high. That is, even if the stripe-shaped active regions of the laser portion and the photodiode portion are linear, the light receiving efficiency of the photodiode can be easily increased by using a vertical etching technique such as dry etching, and the photodiode end face facing the laser portion can be easily obtained. A novel semiconductor laser with a monitor, which suppresses the adverse effect of the reflected light of the laser at the time, can be obtained.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 is a perspective view illustrating a semiconductor laser with a monitor according to a first embodiment of the present invention. In FIG. 1, 1 is a p-type
InP substrate, 2 is p-type InP cladding layer, 3 is u-type InGaAsP active region, 4 is n-type InP cladding layer, 5 is n-type InGaAsP contact layer, 23 is n-type InP buried layer, 24 is p-type InP buried layer It is. Reference numeral 6 denotes a p-type electrode, 7 denotes an n-type electrode, 8 denotes a laser portion, 9 denotes a photodiode portion, 10 denotes a stripe-shaped current path, 11 denotes a mesa including a stripe-shaped active region, 13 denotes an etching separation groove, and 14 denotes a photodiode. The tapered portion of the mesa 11 including the stripe-shaped active region of the portion 9.

That is, in the semiconductor laser with a monitor of this embodiment, as shown in FIG. 1, a laser section 8 having a buried structure having a stripe-shaped active region on a substrate 1 and a monitoring photodiode section 9 are integrally formed. The laser section 8 and the photodiode section 9 are electrically separated by a separation groove 13 having a laser-side end face and a photodiode-side end face, and at least on the substrate side substantially parallel to the stripe on both sides of the mesa 11 including the stripe-shaped active region. The etching groove 13 is provided to a depth reaching the cladding layer 2. Then, a taper portion 14 is formed in which the width of the mesa 11 including the stripe-shaped active region of the photodiode portion 9 is formed wider in a direction closer to the laser portion 8 and narrower in a direction farther from the laser portion 8. The taper angle θ of the tapered portion 14 is set in a range of 0 <θ ≦ 80 °,
In addition, the side surfaces of the mesas 11 are formed perpendicular to the substrate plane by using a vertical etching technique such as RIE or the like by dry etching. Further, by covering the side surface of the mesa 11 including the stripe-shaped active region of the photodiode section 9 with a high-reflection film (not shown) made of an insulating film and a metal film, the output light from the laser end face can be used. The light is reflected on the side surface and enters the active region of the photodiode section 9.

FIG. 2 is a plan view showing a schematic structure of a semiconductor laser with a monitor according to a second embodiment of the present invention. This embodiment is different from that of FIG. 1 in that protective mesas 12 separated by etching grooves 13 are provided on both sides of a laser portion 8 having a stripe-shaped active region and a monitoring photodiode portion 9, respectively. That is. In FIG. 2, reference numeral 15 denotes a laser output light, and the same reference numerals in the drawing denote the same or corresponding parts.

Thus, according to the structure of the above embodiment, the laser unit 8
Out of the output light incident on the photodiode portion 9 from the laser beam, the output light 15 of the laser that does not directly enter the stripe-shaped active region of the photodiode portion 9 is reflected by the tapered portion 14 of the mesa 11 including the stripe-shaped active region and is reflected by the photodiode. The light can enter the active region of the portion 9 and contribute to the photocurrent of the photodiode. That is, the light receiving efficiency of the photodiode can be increased. Furthermore, the side surface of the mesa 11 including the stripe-shaped active region of the photodiode section 9 is perpendicular to the substrate plane, and although not shown, is covered with a highly reflective film made of an insulating film and a metal film. The efficiency is high, and the light receiving efficiency of the photodiode can be further increased.

Further, in the embodiment of FIG. 1, the entire outside of the mesa 11 including the stripe-shaped active region on the substrate is etched, which is advantageous in reducing the parasitic capacitance. In the embodiment shown in FIG. 2, the protection mesas 12 are provided on both sides of each mesa 11 via a groove, which is effective for protecting the active region.

FIG. 3 is a plan view corresponding to FIG. 2 according to a third embodiment of the present invention. This embodiment differs from that of FIG.
The end face of the photodiode 9 facing the laser portion 8 is formed obliquely to the stripe-shaped active region and perpendicular to the plane of the substrate so that the reflected light of the laser at the end face of the photodiode does not return to the laser side. It was done. At this time, the taper angle θ of the tapered portion 14 differs on both sides of the tapered portion, and is indicated by θ ₁ and θ ₂ , respectively.

According to the structure of such an embodiment, as shown in FIG. 3, the end face of the photodiode facing the laser section 8 is formed obliquely to the stripe-shaped active region and perpendicular to the substrate plane. Since the etched end face of the laser section 8 facing the photodiode section 9 and the etched end face of the photodiode 9 facing the laser section 8 are not parallel, multiple reflection of laser output light does not occur between the laser end face and the photodiode end face. Therefore, even if the separation groove width between the laser section 8 and the photodiode section 9 varies between the elements,
Variations in the light receiving efficiency of the photodiode among the elements can be suppressed.

Next, the calculation result of the relationship between the taper angle θ of the tapered portion 14 of the mesa 11 including the stripe-shaped active region of the photodiode portion 9 and the improvement rate of the light receiving efficiency in the above-described embodiment is shown in FIG.
FIG. 5 and FIG. FIG. 4 shows the calculation results when the output light of the laser is assumed to be a Gaussian beam and the phase plane is approximated to a spherical surface. FIG. 5 shows the calculation when the phase plane is approximated to a plane similarly to the Gaussian beam. The result.

Here, beam wavelength λ = 1.3 μm, beam width w _o = 0.6 μ
m, beam angle width θ ₀ = 35 °, refractive index n = 3.2, active area width 2a = 2 μm, thickness 2c = 0.3 μm, distance d between laser part and photodiode part d = 5 μm, maximum width of mesa 2b = 6
Calculated as μm, 10 μm, 16 μm. However, curves I, II and III in FIG. 4 indicate that the maximum width 2b of the mesa is 6 μm, 1
0 μm, 16 μm, and the characteristics when all other parameters are the same. Curves IV, V, and VI in FIG. 5 also have the maximum mesa width 2b of 6 μm, 10 μm, 16 μm, and the other parameters are the same. The characteristics at the same time are shown below. As is apparent from FIGS. 4 and 5, the optimum value of the taper angle θ depends on these structural parameters, but a value around 60 ° is considered appropriate.

〔The invention's effect〕

As described above, the present invention provides an etching groove on both sides outside the stripe-shaped active region at least until reaching the cladding layer of the substrate, and reduces the width of the mesa including the stripe-shaped active region of the photodiode portion by laser. The part closer to the part is wider and the part farther from the laser part is narrower and tapered, and the mesa side surface is formed perpendicular to the substrate plane. Even the light that does not directly enter the stripe-shaped active region is reflected on the side surface of the mesa, enters the stripe-shaped active region of the photodiode portion, and contributes to the photocurrent of the photodiode. That is, there is an advantage that the light receiving efficiency of the photodiode is increased.

Further, since the end face of the photodiode facing the laser portion is formed obliquely to the stripe-shaped active region and perpendicular to the plane of the substrate, multiple reflection between the etched end face of the photodiode and the etched end face of the laser is performed. This is advantageous in that variations in the light receiving efficiency among the elements of the semiconductor laser with monitor can be reduced.

Furthermore, since the mesa side surface including the stripe-shaped active region of the photodiode portion is covered with a high-reflection film made of an insulating film and a metal film, the reflectivity on the mesa side surface is increased and the light receiving efficiency of the photodiode can be increased. is there.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a semiconductor laser with a monitor according to a first embodiment of the present invention, FIG. 2 is a schematic plan view of a semiconductor laser with a monitor according to a second embodiment of the present invention, and FIG. FIGS. 4 and 5 are schematic plan views of a semiconductor laser with a monitor according to a third embodiment of the present invention, and FIGS. 4 and 5 show the taper angle and the taper angle of a mesa including a stripe-shaped active region of a photodiode section, respectively. FIG. 6 is a diagram showing a calculation result of a relationship with light receiving efficiency, FIG. 6 is a schematic sectional view of a conventional semiconductor laser with a monitor, FIG. 7 is a schematic plan view of another conventional semiconductor laser with a monitor, and FIG. It is a schematic plan view of another semiconductor laser with a monitor. 1 .... p-type InP substrate, 2 .... p-type InP cladding layer, 3 ....
u-type InGaAsP active region, 4... n-type InP cladding layer, 5.
... n-type InGaAsP contact layer, 6 ... p-type electrode, 7 ...
n-type electrode, 8 laser part, 9 photodiode part,
10 ... stripe current path, 11 ... mesa including stripe active region, 12 ... protective mesa, 13 ... etching separation groove, 14 ... taper portion of mesa including stripe active region, 15 ... laser output light, 23 ... n-type InP buried layer, 24 ... p-type InP buried layer.

Claims (5)

(57) [Claims] 1. A monitor-equipped semiconductor wherein a laser having a stripe-shaped active region having the same width and a monitoring photodiode formed on the same substrate are electrically separated by a separation groove having a laser-side end face and a photodiode-side end face. In the laser, an etching groove is provided on both sides outside the stripe-shaped active region substantially parallel to the stripe to a depth reaching at least the cladding layer on the substrate side, and the width of the laser stripe-shaped active region and the width of the photodiode part are reduced. The width of the mesa including the active region of the same stripe shape is tapered so that the width closer to the laser portion is wider and the width farther from the laser portion is narrower, and the angle θ of this taper is 0 <θ ≦
A semiconductor laser with a monitor, wherein the semiconductor laser has a range of 80 ° and a side surface of the mesa is formed perpendicular to a plane of the substrate. 2. The semiconductor laser with a monitor according to claim 1, wherein the end face of the photodiode facing the laser portion is formed obliquely to the stripe-shaped active region and perpendicular to the plane of the substrate. 3. A semiconductor laser with a monitor according to claim 1, wherein a side surface of the mesa including the stripe-shaped active region of the photodiode portion is covered with a high reflection film made of an insulating film and a metal film. 4. A semiconductor laser with a monitor according to claim 1, wherein the entire mesa including the stripe-shaped active region is entirely etched. 5. The semiconductor laser with a monitor according to claim 1, wherein protective mesas separated by etching grooves are provided on both sides outside the stripe-shaped active region.