JP2000269538A - Waveguide type light receiving element and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waveguide type light receiving element, in which minimum light receiving sensitivity is increased by sufficiently increasing connecting efficiency with a light attenuating region monolithic integrated at the front stage of a light receiving element region. SOLUTION: An electrical element isolation layer 12 constituting a multilayer waveguide structure is grown on a substrate 11, and then the electrical element isolation layer 12 is etched partially and removed, so that the substrate 11 is exposed. Then, a waveguide type light receiving element region PD and a waveguide type light attenuating region ATT which are optically connected with the electrical element isolation layer 12 are grown with the electrical element isolation layer 12 interposed on the substrate 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-sensitivity waveguide type in which a light-attenuating region is monolithically integrated before a light-receiving element region to enhance the optical coupling efficiency between the light-receiving element region and the light-attenuating region. The present invention relates to a light receiving element and a method for manufacturing the same.

[0002]

2. Related Art Recently, high-speed, large-capacity optical information communication using light as a medium has been receiving attention. One of the optical elements that play an important role in such optical information communication is a semiconductor light receiving element, for example, a waveguide type light receiving element in which a light attenuation area is monolithically integrated in front of a waveguide type light receiving area.

A waveguide type light receiving element of this type is, for example, shown in FIG.
As schematically shown in the manufacturing process, a light receiving region and a light attenuation region were formed monolithically on a substrate, and an element isolation region for electrically separating the light receiving region and the light attenuation region was formed. It has an element structure. That is, this type of waveguide type light receiving element first has n-In, as shown in FIG.
An n-InP clad layer 2 forming a light receiving element on a P substrate 1 by using a metal organic chemical vapor deposition (MOCVD) method or the like, i-Ga
InAs light absorbing layer 3, p-InP cladding layer 4, and p-
The GaInAs contact layer 5 is grown in order. Next, as shown in FIG. 3B, using the SiNx film 6a as a mask, the region excluding the light receiving element forming region is selectively etched to the i-GaInAs light absorption layer 3, and the exposed region is formed as shown in FIG. I-GaInAsP light attenuating layer 7 forming a light attenuating region, p-
The InP cladding layer 9 and the p-GaInAs contact layer 9 are sequentially grown again.

Thereafter, using another mask made of the SiNx film 6b, as shown in FIG.
Selective etching until element is exposed
And the light receiving element region and the light attenuation region are each formed in a ridge waveguide structure. Then, in order to suppress a reactive current generated when the light receiving element region and the light attenuation region are reversely biased, a Fe-doped semi-insulating InP (abbreviated as Fe-InP) is formed in the element isolation opening.
By embedding and regrowing the separation layer 10, a separation resistance of 10 GΩ or more is realized, and thereafter, electrodes are formed through a predetermined process to manufacture the above-described waveguide type light receiving element having the above-described light attenuation region at the preceding stage.

[0005]

As described above, when the element isolation opening A is selectively formed by wet etching, the etching proceeds not only in the depth direction but also in the lateral direction. It is difficult to control the separation width with high accuracy. In addition, since a specific plane orientation is formed, it is difficult to completely bury and regrow the Fe-InP separation layer 10. For this reason, light scattering loss and diffraction loss in the element isolation region are large, and it cannot be denied that light receiving sensitivity as a light receiving element is limited.

Incidentally, the coupling efficiency between the light receiving element region and the light attenuation region largely depends on the separation width z of the element separating opening A as shown in FIG. Specifically, in the light receiving element in which the thickness _dPD of the light absorbing layer 3 is 0.1 μm, the above-described separation width is smaller than when the element isolation region is not provided (the separation width z is [0]). When z is 30 μm, the coupling efficiency is greatly reduced from [0.84] to [0.24], and the element isolation region greatly restricts the minimum light receiving sensitivity.

On the other hand, it is conceivable to form the element isolation region by dry etching. However, even if the element separation opening A having a separation width z of 4 μm or less is formed by dry etching, the narrow opening A
It is extremely difficult to bury the Fe-InP separation layer 10 in the first layer and to re-grow it. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a waveguide type light receiving element in which an optical attenuation area is monolithically integrated in a stage preceding a light receiving element area. It is an object of the present invention to provide a waveguide type light receiving element having a sufficiently high coupling efficiency with a region and an increased minimum light receiving sensitivity, and a method of manufacturing the same.

[0008]

In order to achieve the above-mentioned object, a waveguide type light receiving device according to the present invention comprises a light attenuating region monolithically integrated before a light receiving device region. Between the region and the light attenuation region,
It is characterized in that an electrical element isolation region for optically coupling the light receiving element region and the optical attenuation region is provided in a multilayer waveguide structure.

That is, the waveguide type light receiving element according to the present invention comprises:
The electrical element isolation region itself formed between the light receiving element region and the light attenuation region is realized as a multilayer waveguide structure that optically couples the light reception element region and the light attenuation region to achieve the electrical element isolation. It is characterized in that the minimum light receiving sensitivity is increased by suppressing light scattering loss and diffraction loss in the region and increasing the optical coupling efficiency between the light receiving element region and the light attenuation region.

In the method of manufacturing a waveguide type light receiving device according to the present invention, after an electrical isolation layer having a multilayer waveguide structure is grown on a substrate, the electrical isolation layer is partially removed by etching. Exposing the substrate, and sandwiching the electrical element isolation layer with a waveguide type light receiving element region and a waveguide type optical attenuation region optically coupled to the electrical element isolation layer on the substrate. It is characterized in that each is grown.

That is, after an electrical element isolation layer having a multilayer waveguide structure is first grown on a substrate, a waveguide type light receiving element region and a waveguide type optical attenuation region are sandwiched by the electrical element isolation layer. It is characterized in that a waveguide type light receiving element is manufactured by growing each monolithically.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A waveguide type light receiving device according to an embodiment of the present invention and a method for manufacturing the same will be described below with reference to the drawings. FIG. 1 is an exploded view of a method of manufacturing a waveguide type light receiving element according to the procedure of the manufacturing process, and FIG. 2 shows a schematic element structure of the waveguide type light receiving element manufactured according to this manufacturing procedure. . As shown in FIG. 2, the waveguide type light receiving element according to the present invention has a light attenuation region A before the waveguide type light receiving element region PD formed on the n-InP substrate 11.
In addition to monolithically integrating the TT, an electrical element isolation region WG having a multilayer waveguide structure is grown between the light receiving element region PD and the optical attenuation region ATT, and the element isolation region WG having the multilayer waveguide structure is grown. Has an element structure in which the light receiving element region PD and the light attenuation region ATT are optically coupled to each other.

A waveguide type light receiving element having such an element structure and a method of manufacturing the same will be described. First, an n-InP substrate 11 is prepared, and the n-InP substrate 11 is formed by MOCVD, for example, as shown in FIG. A multi-layer waveguide type element isolation layer 12 is grown on a substrate 11. The element isolation layer 12 having the multilayer waveguide structure includes, for example, an Fe-doped semi-insulating InP clad layer 12a sequentially grown on the n-InP substrate 11,
It comprises a semi-insulating GaInAsP light attenuating layer 12b doped with Fe and a semi-insulating InP cladding layer 12c doped with Fe.

Next, as shown in FIG. 1B, the element isolation layer 12 is selectively dry-etched using the SiNx film 13a formed on the element isolation layer 12 as a mask, and the n-InP As shown in FIG. 1 (c), an n-InP cladding layer 14, an i-GaInAs light absorbing layer 15, a p-InP cladding layer 16, and a p-GaInAs contact layer 17 forming a waveguide type light receiving element PD on a substrate 11 as shown in FIG. Are sequentially regrown. After that, the SiNx film 13b formed on the entire surface of the element isolation layer 12 is set to have a width z of
For example, patterning is performed by photolithography so as to have a thickness of, for example, 4 μm, and as shown in FIG.
2 is selectively dry-etched.

Next, on the n-InP substrate 11 exposed by the etching, as shown in FIG. 1D, n-InP cladding layers 18 and i forming a waveguide type optical attenuation region ATT are formed.
-GaInAsP light attenuation layer 19, p-InP cladding layer 20,
Then, the p-GaInAs contact layer 21 is regrown in order. Thereafter, through a predetermined process, a p-electrode 22 is formed on the upper surface and an n-electrode 2 is formed on the back surface of the substrate 11 as shown in FIG.
3 are formed by vapor deposition to manufacture a waveguide type light receiving element.

According to the waveguide type light receiving element thus manufactured, the light receiving element region PD and the light attenuation region A
TT and TT are optically coupled via an element isolation layer 12 having a multilayer waveguide structure, and an element structure electrically isolated. In addition, since the element isolation layer 12 previously grown on the n-InP substrate 11 is etched and the light receiving element area PD and the light attenuation area ATT are grown with the element isolation layer 12 interposed therebetween, an element structure is formed. Even when the separation width z between the light receiving element region PD and the light attenuation region ATT is reduced,
The element isolation layer 12 can be reliably positioned in the narrow area. Further, since the element isolation layer 12 itself forms a waveguide structure, light scattering loss and diffraction loss in the element isolation layer 12 can be sufficiently suppressed, and the coupling efficiency between the light receiving element region PD and the light attenuation region ATT can be improved. Can be increased to approximately [1]. As a result, it is possible to realize a highly sensitive waveguide type light receiving element having a minimum light receiving sensitivity of 0.8 A / W or more. Moreover, a highly sensitive waveguide type light receiving element can be manufactured very easily and inexpensively.
In addition, since the minimum light receiving sensitivity can be increased, the dynamic range can be widened, and effects such as low distortion operation can be achieved.

The present invention is not limited to the above embodiment. For example, even if the separation width z between the light receiving element region PD and the light attenuating region ATT by the element isolation layer 12 is set to be wider, the element isolation layer 12 itself forms a waveguide, which causes problems such as a decrease in sensitivity in practical use. Never. Further, the element isolation layer 12 may be etched not only by dry etching but also by wet etching. Of course, an insulating film other than the SiNx film can be used as the etching mask. In the embodiment, the core layer of the element isolation layer 12 is a light attenuating layer, but may be a light absorbing layer made of the same GaInAs layer as the light receiving element region PD.

Further, here, Ga is placed on the n-InP substrate 11.
Although an example of realizing an InAsP light receiving element has been described,
It is also possible to realize a light receiving element of the opposite conductivity type to the embodiment on a p-InP substrate,
The present invention can be similarly applied to the case of producing a light receiving element made of a II-V group or II-V compound semiconductor. Further, it is possible to separate the electrodes formed on the light receiving element region PD and the light attenuation region ATT so that the light attenuation region ATT functions as a modulator. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0019]

As described above, according to the present invention, the coupling efficiency between the light receiving element region and the light attenuating region is made sufficiently high so that the minimum light receiving sensitivity which is limited by the element isolation region is made sufficiently high. The waveguide type light receiving element described above can be realized. In addition, a waveguide-type photodetector with high sensitivity and high performance is obtained by a simple procedure of forming an element isolation region forming a waveguide structure in advance and forming a light receiving element region and an optical attenuation region with the element isolation region interposed therebetween. Can be realized inexpensively, for example, and a great effect can be obtained in practical use.

[Brief description of the drawings]

FIG. 1 is a view showing a manufacturing method of a waveguide type light receiving element according to an embodiment of the present invention in accordance with the process procedure.

FIG. 2 is a diagram showing a schematic element structure of a waveguide type light receiving element according to one embodiment of the present invention.

FIG. 3 is a diagram showing a conventional method for manufacturing a waveguide type light receiving element according to the process procedure.

FIG. 4 is a diagram showing a change characteristic of coupling efficiency depending on a separation width z of an element separating opening between a light receiving element region and a light attenuation region in a conventional waveguide type light receiving element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 n-InP board 12 Waveguide-type element isolation region 12a Fe-doped semi-insulating InP cladding layer 12b Fe-doped semi-insulating GaInAsP light attenuation layer 12c Fe-doped semi-insulating InP cladding layer 13a, 13b SiNx film ( Mask) 14 n-InP clad layer 15 i-GaInAs light absorbing layer 16 p-InP clad layer 17 p-GaInAs contact layer 18 n-InP clad layer 19 i-GaInAsP light attenuating layer 20 p-InP clad layer 21 p-GaInAs Contact layer 22 p-electrode 23 n-electrode PD light-receiving element area ATT light attenuation area WG waveguide-type element isolation area

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Takeharu Yamaguchi 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. F-term (reference) 5F049 MB07 NA01 NB01 PA04 PA14 QA03 QA08 QA11 RA06 SS04 SZ20 5F088 AA03 AB07 BA01 BB01 CB04 DA01 DA17 GA05 JA11

Claims (2)

[Claims] An optical attenuation region is monolithically integrated before a waveguide type light receiving element region, and a multilayer waveguide structure is formed between the light receiving element region and the light attenuation region. A waveguide type light receiving device, comprising: an electrical element isolation region for optically coupling a region and a light attenuation region. 2. After growing an electrical isolation layer having a multilayer waveguide structure on a substrate, the electrical isolation layer is partially etched away to expose the substrate, and the substrate is exposed on the substrate. A waveguide type light receiving device, wherein a waveguide type light receiving element region optically coupled to the electrical element isolation layer and a waveguide type light attenuation region are grown with the electrical element isolation layer interposed therebetween. Device manufacturing method.