JPS63108790A - Semiconductor laser with optical output monitor - Google Patents

Abstract

PURPOSE:To form one layer in buried layers in a photodetector corresponding to the buried layer limiting a light-emitting section in upper and lower electrodes having different conductivity, to increase a light-receiving area and to reduce dark currents resulting from the buried layers by giving energy smaller than the band gap energy of a light-emitting layer to one layer in the buried layers in the photodetector. CONSTITUTION:A laser section 53 and a light-receiving section 54 isolated by an isola tion trench 52 are formed onto an N-type InP substrate 44, and P-type InGaAsP layers 41, 41' are shaped to each of the sections 53 and 54. P-type InP clad layers 42, 42' are formed, and an InGaAsP light-emitting layer 43 is shaped to the section 53 and an InGaAsP layer 43 to the light-receiving section 54. P-type InP layers 49, 49', N-type InP layers 48, 48' and a P-type InGaAsP gap layer 47 and a P-type InGaAsP light- receiving layer 47 are formed to each of the sections 53, 54. A laser electrode+45 and a laser electrode-46 are shaped to the light-emitting layer 43 emitting laser beams 50, and a light-receiving section electrode+51 and a light-receiving section electrode-45 are formed to the light-receiving section 54. The band gap energy of one layer in the light-receiving section is made smaller than that of the light-emitting layer 43.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a highly stable and economical monolithic light emitting/light receiving device for optical fiber transmission.

[Conventional technology]

Conventionally, a semiconductor laser with a monitor as shown in FIG. 5 is an example in which a laser and a receiver for monitoring the laser light output are monolithically formed from the same wafer (Iga et al., "
GaInAsP/InP lamar withmo
Nolithically integrated
monltorlng d@tector”.

Electron Lett, vot, 16.
P, 342.1980).

In Fig. 5, 1 is a laser part, 2 is a monitor diode part, 3 is a laser electrode (+), y' is a monitor diode electrode (-), 4 is a p-type InP cladding layer, 5 is InGaAsP Light emitting layer, 6 is n-type InP cladding layer, 7
1 is an n-type 1nP substrate, 81'i is a common electrode (earth), 9 is an etching groove portion, 10 and 10' are emitted light, and 11 is a photodetection layer. When manufacturing these semiconductor lasers with a monitor, etching is performed by chemically or physically perpendicular to the laser stripe-shaped implantation region, approximately perpendicular to the top surface of the wafer (usually the Vi (100) plane). The laser resonator end face was formed at the same time as element isolation. Therefore, the device structures of the laser and the photoreceiver were the same, and the light-receiving layer of the photoreceiver corresponded to the light-emitting layer of the laser. However, the layer is between 0.1 and 0.
It is as thin as 2 μm, and its emission width is several μm. In a normal laser, the emitted light spreads over an angle of several tens of degrees vertically and horizontally due to the phenomenon of light diffraction. However, the layer that receives the emitted light is 0.1
The thickness and width of ~0.27a are several μm, and the area that receives light is extremely small, making it difficult to obtain a sufficient function as a receiver for monitoring laser light. Distributed feedback W(D
FB) For lasers, methods are used to increase the coupling efficiency of the laser emitted light to the monitoring receiver by extending the laser's light-emitting layer to the monitor part or by slanting the laser end face with respect to the stripe (Murata) Others,' DFB laser/
"PD Monolithic Integrated Device", Proceedings of the 1985 National Conference of the Institute of Electronics and Communication Engineers, 931. P, 4-55:
JP-A-59-125659, Moni integrated semiconductor light emitting device). However, these methods have the disadvantage that the etching process for element isolation and the element grossing process are complicated, and they can only be applied to DFB type lasers.

Furthermore, not only these DFB lasers but also current communication lasers generally use an embedded structure as shown in FIG. In FIG. 6, 2 is an InGaAsP cap layer, 22 is a p-type InP cladding layer, and 23 is an InGaAsP cap layer.
GaAsP light emitting layer, 24 is n-type InP cladding layer, 25
is an n-type InP substrate, 26 is a laser electrode (+), 27#i
Laser electrode (-), 28 is n-type InGaAsP layer, 29
is an n-type InP layer, and 30 is a p-type InP layer. The laser first grows crystals of each layer 21 to 24 on an n-type InP substrate 25, and then etches them into a mesa shape.
It is fabricated by crystal growth of 8 to 30 layers. If this buried structure is used as it is as a light receiving section, leakage current will be large due to the buried structure, noise (dark current) as a light receiver will be large, it will be difficult to obtain a highly sensitive light receiver, and the yield will be low. Disadvantages - [Problems to be Solved by the Invention] The present invention solves the problems in the prior art, such as low detection sensitivity due to the small light-receiving area of the monitor light receiver, and large noise in the light receiver due to increased dark current. The purpose of this invention is to provide a light source for optical fiber transmission with high yield.

[Next method to solve the problem]

In order to achieve the above object, the present invention provides a semiconductor laser with an optical output monitor in which a semiconductor laser and a semiconductor photodetector for monitoring the optical output of the semiconductor laser are formed on the same wafer substrate, and the laser emitting part is limited. At least one layer of the buried layer of the photodetector corresponding to the buried layer has a bandgap energy less than or equal to the bandgap energy of the light emitting layer,
A layer having a bandgap energy lower than that of the light-emitting layer is characterized in that it has a conductivity type different from that of the layer above or below it.
Another invention is characterized in that, in addition to these features, a reflecting mirror and/or a prism is provided between the semiconductor laser and the light receiver for guiding monitor light from the semiconductor laser to the light receiver. It is.

[Function] The first invention is: (1) Among the buried layers for limiting the laser emitting part, the band gap energy of at least one layer (light receiving layer) is made smaller and thicker than that of the light emitting layer, thereby increasing the light receiving area. By increasing the amount of light received and using only the relevant layer and the conductor layer with a different conductivity type from the relevant layer for light detection,
This reduces the 9l1lf current due to the buried structure.

Moreover, in addition to the first invention, the second invention forms a reflecting mirror and/or a prism between the laser and the light receiver, and efficiently guides the light from the laser to the light receiver, thereby increasing the amount of light received. It will further enhance your well-being.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 (container) is a perspective view illustrating a case in which a layer having a conductivity different from that of the light-receiving layer is provided below the light-receiving layer among the embodiments of the invention described in the first claim of the present invention. , is an example in which a P-embedded laser in an InGaAsP crystal is used as a light emitter. %41 and 4 in Figure 1 6)
1' is a p-type I nGaAsP layer, 42 and 42' F
ip type InP cladding layer, 43 rnGaAsP light emitting layer, 43' InGaA+sP layer, 44 n type InP substrate, 45 laser electrode (→, 45' light receiving part electrode (to),
46 is a laser electrode (→, 47 is a p-type 1 nGaA@P cap layer, 47' is a p-type InGaAsP light-receiving layer, 48 and 48' are n-type InP layers, 49 and 49' are p-type I
thP layer, 50 is a laser beam, 5) is a light receiving part electrode (→, 5
2 is a separation groove, 53 is a laser portion, and 54 is a light receiving portion.

Here, a voltage is applied between the p@N electrode 4 and the upper 5@electrode 46.
When a current is injected into the InGaAsP light emitting layer 43 from the p@electrode 45 of the light emitting part, laser light 50 is emitted at an angle of about 20' to 40° vertically and horizontally. Since this emitted light is emitted to the outside from both sides of the laser portion 53, the laser light is incident on the light receiving portion 54 with the element arrangement of the embodiment. Here, since the laser light spreads as described above, the laser emitting layer of the receiver is also made of p-type InGaA, which has a small band gap energy.
The light is incident on the aP light-receiving layer 47'. The light incident on this layer 47' is efficiently absorbed into the light receiving layer 47' by reflection at the electrode 45' and the refractive index difference between the light receiving layer 47' and the n-type InP layer 48'. , and generates electron-hole pairs. Here, the light-receiving layer 47' is p-type, t), I
Since the diffusion length of electrons in nGaAsP crystal is usually 2 to 3 μm, the electron diffusion length occurs within about 21a'n from the p-n junction between 47' and 48' in the light-receiving layer 47', and the
It reaches the n-junction and becomes a photo-induced current. In this way, according to this embodiment, it is possible to increase the amount of light received by the monitoring light receiver. Element isolation @ 52 i It can be easily formed by 1J active ion etching or the like. Further, according to this embodiment, by providing a p-n junction between layers 47' and 48', the electrode arrangement is changed to 45' and 51p, and each layer 41', 42', 4j' constituting the laser is and each layer 47', 4g', 49' corresponding to the buried layer
This eliminates the influence of leakage current between the photodetectors, making it possible to reduce the noise due to the dark current of the photoreceiver by more than an order of magnitude, and at the same time making it possible to achieve high yields.

FIG. 1(b) shows a light receiver (laser) in which a layer having a conductivity different from that of the light-receiving layer is provided on the light-receiving layer among the embodiments of the invention described in the first vf of the present invention. FIG. Although the order of the buried layers and the electrode arrangement of the photodetector are different, the operation is the same as the embodiment shown in FIG. 1(&). In FIG. 1(b), 55 is n-type InGaA, s
This is the P layer.

Note that Figures 1(a) and 1(b) have a three-layer structure and a four-layer structure, respectively, but if the structure is such that a reverse bias is applied to the PN junction, for example, a two-layer structure may be used. It's fine just by itself.

However, the laminated laser part and light receiving part have the same layer structure.

Of course, f'';i 47' having different conductivity types may be placed in the position.

Although the above explanation is an example using an n-type substrate, it goes without saying that the present invention can be applied even if a p-type substrate is used, and that the present invention is effective regardless of whether the light-receiving layer is a p-type or an n-type. .

2 to 4 show embodiments of the invention described in the second claim of the present invention, in which the monitor light from the laser portion 53 is reflected by the reflective surface 58 or refracted by the prism entrance surface 59. , the light is efficiently incident on the light-receiving layer 47' in FIG.

These figures correspond to the top view of FIG. 1 except for the shape of the light receiving section. Here, the reflected light 56 on the reflective surface 58 or the refracted light 57 on the incident surface 59 can be detected separately by using the shape and electrode arrangement of the light receiving section as shown in FIGS. 2 and 3. The second invention is to make the shape of the container part as shown in FIG. 4 and to use them at the same time. The light emitted from the laser spreads vertically and horizontally, but the light intensity is highest in the light emitting layer 43.
is on the linear extrapolation of . However, the light-receiving layer 47' is not on this extrapolation. Therefore, by providing a plane of 58.59 and bending the laser light from the linear extrapolation of the light emitting layer 43, the amount of light received by the light receiving layer 47' can be further increased. Furthermore, by providing surfaces 58 and 59 and adjusting the angle of incidence of the laser beam on the surfaces, it is possible to remove the return light from the light receiver to the laser emitting layer 43. According to the present invention, it is possible to provide a semiconductor laser with a light output monitor that eliminates noise due to returned light. In the embodiment, the reflecting mirror and prism are incorporated into the light receiver, but the same effect can be obtained even if the reflecting mirror or prism is formed independently in the groove 52.

The above explanation uses an InGaAsP/InP-based 7-apple-Perot type buried laser as an example.Next, the present invention is of course effective for lasers made of other materials and elements of other structures, It is also applicable to light sources other than those for use. Furthermore, by combining the following embodiments shown in FIGS. 2 and 3, it is also possible to operate two light receivers simultaneously.

〔Effect of the invention〕

As explained above, the present invention is a semiconductor laser with an optical output monitor that can efficiently receive monitor light from a laser and has a light receiver with a small dark current, so it can be used as a monolithic light source for optical fiber transmission. . Furthermore, it is possible to manufacture a wafer for an embedded laser, a laser, and a light receiver with a simple structure, and the device manufacturing and process are simple, so it is possible to provide an economical device with a high yield.

[Brief explanation of the drawing]

FIG. 1 (&) is a perspective view showing an outline of an embodiment of the present invention;
Fig. 1(b) is a sectional view showing an outline of another embodiment of the present invention, Figs. 2 to 4 are sectional views showing an outline of another embodiment of the invention, and Fig. FIG. 6 is a perspective view schematically showing a conventional laser with a monitor, and FIG. 6 is a cross-sectional view schematically showing a conventional embedded laser. 41 and 41' = p-type InGaAsP layer, 42 and 42' = p-type InP cladding layer, 43...
InGaAsP light emitting layer, 43' = InGaAsP layer, 44- n-type 1nP substrate, 45... laser electrode (+
), 45'... Light-receiving part electrode (-), 46-... Laser emitting layer (-), 47 = p-type InGaAsP gear layer, 47'... p-type 1nGaAsP light-receiving layer, 48
and 419' - n-type InP layer, 49 and 49'
...p-type 1nP layer, 50...laser light, 51...
Light receiving part electrode (+), 52... Separation groove, 53... Laser part, 54... Light receiving part. Applicant's agent Patent attorney Takehiko Suzue 41 41'
: PiInGaAsP layer 4
7: P'l! InGaAsPty-Nof 81%42
．． 42: Pi InP 7 Futu and J
47': Pt1nGaAsρ light reception・-43:
InGaAsP light emitting layer 48.48
': n-type 1nP gu45: t-t 'Eji)F
(+) 51% wheat 'r15
Draw the layer (10) 45' two xuanyu average (-)
52:Kaibinomizo Figure 1 Figure 2 Figure 3 Figure 5

Claims (2)

[Claims] (1) In a semiconductor laser with an optical output monitor in which a semiconductor laser and a semiconductor optical receiver for monitoring the optical output of the semiconductor laser are formed on the same wafer substrate, the buried layer of the optical receiver corresponds to the buried layer that limits the laser emitting part. At least one layer of the layer has a bandgap energy less than or equal to the bandgap energy of the light emitting layer, and the layer having a bandgap energy less than or equal to the bandgap energy of the light emitting layer has a conductivity type different from that of the layer above or below it. A semiconductor laser with an optical output monitor featuring: (2) In a semiconductor laser with an optical output monitor in which a semiconductor laser and a semiconductor optical receiver for monitoring the optical output of the semiconductor laser are formed on the same wafer substrate, the buried layer of the optical receiver corresponds to the buried layer that limits the laser emitting part. At least one layer of the layer has a bandgap energy less than or equal to the bandgap energy of the light-emitting layer, and the layer having a bandgap less than or equal to the bandgap energy of the light-emitting layer has a conductivity type different from that of the layer above or below it, and A semiconductor laser with an optical output monitor, characterized in that a reflecting mirror and/or a prism for guiding monitor light from the semiconductor laser to the light receiver is provided between the semiconductor laser and the light receiver.