JP2000353818A - Waveguide-type photodetector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a waveguide photodetector to be kept high in response speed, enhanced in quantum efficiency, and improved in coupling tolerance for an optical fiber both in the horizontal and the vertical direction. SOLUTION: A P-type diffused region 5 is formed into a shape of an unfolded fan extending inwardly from the edge face of incidence, an SiNx film 6 is formed directly on the semiconductor body except on a P-contact region 7 and an N-contact region 10, a P-electrode 8 is located in a region nearly equal to the P-contact region 7, an N electrode 11 is formed covering the N-contact region 10, whereas the P-contact region 7 is located inside the P-diffused region 5 and lessened in the space factor by it near the edge face of incidence.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type light receiving element having an asymmetric guide structure used for optical communication.

[0002]

2. Description of the Related Art A waveguide type light receiving element according to the present invention comprises:
Passive optical fiber using V groove of Si substrate
Attention has been paid to devices that can be mounted at low cost for alignment. One of the important factors for this waveguide type light receiving element is to obtain a large quantum efficiency by securing a wide coupling tolerance with the optical fiber.

For this purpose, Japanese Patent Application Laid-Open No. Hei 5-18318
In Japanese Patent Application Laid-Open No. 2005-115, a method is adopted in which the refractive index of the guide layer is graded so that light is guided to the absorption layer, thereby improving the quantum efficiency and the coupling tolerance.

On the other hand, Japanese Patent Application Laid-Open No. Hei 10-256589 discloses a planar structure in which a pn junction is formed by Zn diffusion, which is advantageous for a low dark current.

FIGS. 6 and 7 show an example of a conventional planar waveguide type light receiving element using the above-described graded guide layer. FIG. 6 is a plan view, and FIG. 7 is a cross-sectional view of the waveguide type light receiving element shown in FIG. 6 along the line AA.

As shown in FIG. 7, a laminated structure of an n-InP substrate 1, a graded guide layer 2, an absorption layer 3, and an n-InP layer 4 is provided from below. As shown in FIG. 6, p contact region 7 and n contact region 10 are opened, p electrode 8 is formed on p contact region 7, and n electrode 11 is formed on n contact region 10. I have. In addition, A
An R coat film 12 is provided.

With such an asymmetric waveguide having a graded guide structure on one side, the pn junction can be made shallower, so that p-diffusion control becomes easier and a planar type excellent in dark current can be easily manufactured. At the same time, an effect that a large quantum efficiency and a coupling tolerance can be secured can be obtained.

[0008]

However, bringing the absorbing layer 3 close to the p-electrode 8 means that the guided light
In terms of being easily applied to the electrode 8 and the p-alloy portion thereunder, there is a problem that when the optical fiber position is newly close to the p-electrode 8, sufficient quantum efficiency cannot be obtained. This problem is evident when looking at the horizontal tolerance. If you shift the optical fiber position horizontally,
It goes without saying that the quantum efficiency is reduced at a position outside the p-diffusion region 5, but the quantum efficiency is also slightly reduced in the p-diffusion region 5 when light is incident on the position inside the p-contact region 7. Specifically, when light is incident outside the p-contact region 7, a maximum quantum efficiency of 90% is obtained,
When light enters the position in the p-contact region 7, 80%
However, a problem arises that only the quantum efficiency can be obtained.

It is an object of the present invention to provide a waveguide type light receiving device having improved quantum efficiency while securing a response speed.

Another object of the present invention is to provide a waveguide type light receiving device having improved horizontal and vertical coupling tolerance with an optical fiber.

[0011]

According to the present invention, in a waveguide light receiving element having an asymmetric guide structure, in a region where the intensity of guided light is high, the ratio of arrangement of contact electrodes is reduced so as to reduce the distance between a metal and a semiconductor waveguide. Is characterized by inserting a dielectric film and increasing the arrangement of contact electrodes in a region where the intensity of guided light is low.

The waveguide type light receiving element according to the present invention has a p-diffusion region having a divergent shape from the incident end face, and a SiNx film is formed immediately above the semiconductor except for the p-contact region and the n-contact region. In contrast to the configuration in which the p-electrode is located in a region substantially equal to the p-diffusion region and the n-electrode is shaped to cover the n-contact region, the shape of the p-contact region is inside the p-diffusion region and In the vicinity of the end face, the shape is reduced.

[0013] Spreading the p-contact region in the vicinity of the incident end face has an effect that light loss due to the p-electrode or the p-alloy region can be effectively reduced in a region where the power of incident light is large. In addition, in the region surrounding the p-contact region, between the semiconductor and the p-electrode,
Due to the presence of a dielectric film having a refractive index much lower than that of a semiconductor, the guided light does not spread to the p-electrode, but instead is totally reflected by the dielectric film and reaches the light absorption layer. It plays the role of improving efficiency and power / current conversion efficiency.

The coupling tolerance between the optical fiber and the waveguide light receiving element will be described. Since the quantum efficiency is particularly remarkably improved when the position of the optical fiber is shifted to the side closer to the p-electrode, the coupling tolerance is greatly increased. The effect of doing so is also obtained.

[0015]

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

FIG. 1 is a plan view showing an embodiment of a waveguide type light receiving element of the present invention, and FIG. 2 is a cross-sectional view taken along the line AA.

On the n-InP substrate 1, a graded guide layer 2, an absorption layer 3, and an n-InP layer 4 are formed in this order from the bottom. In this crystal wafer, Zn is diffused from the incident end face into a p-diffusion region 5 having a divergent shape. Above this, p contact region 7 and n
The SiNx film 6 having the contact region 10 opened is provided. Further, p electrode 8 is formed on p contact region 7 in a region substantially equal to p diffusion region 5, and n electrode 11 is formed on n contact region 10 so as to cover n contact region 10. . An AR coating film 12 is provided on the light incident end face.

According to the present invention, the p-contact region 7 is formed inside the p-diffusion region 5 so that the occupied area is reduced near the incident end face. Specifically, p
The contact area 7 is 8 to 12 μm from the incident end face and 16
部分 20 μm and 24 μm and below.

In such a configuration, the ratio of the area where the p-electrode 8 is alloyed with the semiconductor in the area within 24 μm from the incident end face where the light power is large is 8/24. It can be kept low enough. The light loss reduced here is the light loss caused by the guided light being applied to the p-electrode 8 and the p-alloy portion. Since metal is a conductor, an electric current flows in a direction parallel to the electric field to perform work, and thus energy loss occurs.

On the other hand, in a region where the SiNx film 6 is not opened, the SiNx film 6 exists between the semiconductor and the p-electrode 8, so that no loss is caused by the p-electrode 8 here. This is because, while the refractive index of InP is about 3.2 and the refractive index of SiNx is about 1.8, the waveguide light intensity distribution is sufficiently reduced by SiNx, and the light intensity at the p-electrode 8 is reduced. Is completely negligible. Also, it can be said that light is totally reflected at the InP / SiNx interface due to the difference in refractive index.

However, in order to reduce light loss by such a method, the p-contact region 7 cannot be reduced without limit. This is because the resistance of p-InP between the light absorbing layer deviating from the p-contact region 7 and the p-electrode 8 increases, and the response speed deteriorates due to CR limitation. In order to secure the response speed required in the optical communication at 2.4 Gb / s or 10 Gb / s, the light absorption region p
At any point in the diffusion region 5, the distance from the p-contact region 7 must be within 30 μm, preferably within 10 μm. Therefore, in order to secure the response speed, it is preferable that the area excluding the p-contact is small.

Therefore, in order to maximize the response speed and the reduction of the optical loss, the omission of the p-contact may be limited to a region having a large optical power. 0-8 μm in distance, 12
~ 16μm, 20GHz only in the region of 20-24μm
, While effectively reducing the effect of optical loss. For this reason, the coupling with the flat-end fiber provides a quantum efficiency of 85% even at the center position in the horizontal direction.
A quantum efficiency of 90% or more can be obtained over the entire width of the diffusion region.

As described above, there is an effect that the quantum efficiency is improved and the coupling tolerance is improved without deteriorating the response speed.

The waveguide type light receiving element of this embodiment is manufactured as follows. First, on the n-InP substrate 1, V
The graded guide layer 2, the absorption layer 3, and the n-InP are formed by a PE (vapor phase epitaxy) method.
Layer 4 is laminated.

The graded guide layer 2 is made of InGaAsP having a total layer thickness of 4.8 μm, and has a band gap wavelength of 1.0 μm to 1.2 μm under conditions of lattice matching with InP.
m. The graded guide layer 2 includes, for example, InGaAsP having a composition of 1.0 μm,
InGaAsP having a composition of 1.1 μm and InGaAsP having a composition of 1.2 μm may be stacked with a thickness of 1.6 μm.

The composition of the absorption layer 3 is InGaAs, and the layer thickness is 1.5 μm, 10 Gb for 2.5 Gb / s application.
/ S for 1 μm. The carrier concentration of the absorption layer 3 is 1 × 10 ¹⁵ cm ⁻³ . Absorption layer 3 and n-InP
Between the layers 4, InGaAsP having a composition of 1.2 μm
2 μm may be inserted. This is for alleviating band discontinuity that hinders the traveling of hole carriers.

The n-InP layer 4 has a carrier concentration of 1 × 1
0 ¹⁶ cm ⁻³ and a layer thickness of 1.2 μm.

In this epitaxial wafer, Zn is selectively diffused into the p diffusion region 5 shown in FIG. The diffusion front is brought to a point where it enters the absorption layer 3 by 0.5 μm. Thereafter, a 200 nm SiNx film 6 is formed on the entire surface,
A p-contact region 7 is opened in the SiNx film 6. Further, AuZn is deposited and alloyed in the opening, and TiPtAu is formed.
An electrode is formed to form a p-electrode 8. Subsequently, an n-contact region 10 is opened in the SiNx film 6. AuG on opening
e-AuNi is deposited and alloyed, and a TiPtAu electrode is formed to form an n-electrode 11. The wafer is cleaved to form an SiNx AR coat film 12 on the incident end face side.

In the above-described embodiment, the Si
The Nx film 6 may be a SiO ₂ film. Further, a general dielectric film may be used.

Next, another embodiment of the present invention will be described.

In the above-described embodiment, the reduction of the p-contact region in the vicinity of the incident end face is adapted so that the p-contact is intermittent in the light propagation direction. Can also be adapted. The configuration is shown in FIG.

In FIG. 3, in the region 20 μm from the incident end face, the width of 4 μm on both sides of the region except for the width of 6 μm at the center is defined as the p-contact region 7.

With the shape of the p-contact region 7, when the optical fiber is located at the center in the horizontal direction, the loss is greatly reduced because the SiNx film 6 exists between the waveguide and the electrode for a distance of 20 μm from the incident end face. The effect of reduction can be obtained. At this time, when the fiber position is shifted in the horizontal direction, a maximum value of the quantum efficiency is obtained at the center, and a quantum efficiency of 90% or more can be obtained in the range of ± 2 μm in the horizontal direction around the center.

Also, in this case, the distance that the hole generated by light absorption reaches the p-electrode is sufficiently small, so that it can be used for applications of 10 Gb / s or more.

Next, still another embodiment of the present invention will be described.

In each of the above embodiments, the p-contact region is reduced only in the vicinity of the incident end face. However, the p-contact is not formed in the entire region where the guided light spreads, and the p-contact is formed around the region.
A configuration in which a contact is formed can be employed.
The structure is shown in FIG. 4 and FIG. FIG. 4 is a plan view, and FIG. 5 is a cross-sectional view along the line AA.

In this waveguide type light receiving element, the p-contact region 7 has a ring shape opened at the incident end face. At the incident end face, there is no p-contact over a width of 5 μm or more. In particular, considering low-speed applications of 1 Gb / s or less, the upper limit of the chip capacity is relaxed.
Since the p-diffusion region 5 can be made wider, the width at the incident end face is 10 μm
There can be no p-contact over m. In this case, as shown in the cross-sectional view of FIG. 5, since the upper part of the waveguide structure through which light passes becomes the SiNx film 6 having a low refractive index in the entire region, the InP layer thereunder also functions as a waveguide layer. become. Since the refractive index of the SiNx film 6 is sufficiently smaller than that of InP, if the thickness of the SiNx film 6 is 100 nm or more,
The light field is sufficiently attenuated there, and no light field is applied to the p-electrode 8.

As a result, the loss due to the electrodes and the alloy portion is eliminated, so that the maximum quantum efficiency becomes 95% even in the flat end fiber, and the width at the incident end face is 10 μm.
In case of no contact, 9
A quantum efficiency of 0% or more can be obtained. Further, since p-InP also functions as a waveguide layer, the coupling tolerance is expanded by 1 μm in the vertical direction.

The p-contact of this embodiment is made of InP
The contact to the surface, but the p contact region 7
May be changed to remove InP on the surface and make contact with the absorption layer. At this time, the holes generated by the light absorption reach InGaAs by the time they reach the p-electrode.
It is not necessary to pass through the heterogap between (P) and InP, and the tail of the optical response can be eliminated.

In the above embodiment, InGa
Although AsP and InGaAs-based material systems have been described, the present invention may use InAlGaAs-based materials. Of course, the same applies to other III-V compound semiconductors.

[0041]

As described above, according to the present invention, the quantum efficiency can be improved while ensuring the response speed by reducing the size of the p-contact region in the p-diffusion region near the incident end face. . Further, the present invention can improve the horizontal and vertical coupling tolerances with the optical fiber.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of a waveguide type light receiving element of the present invention.

FIG. 2 is a sectional view showing an embodiment of the waveguide type light receiving element of the present invention.

FIG. 3 is a plan view showing another embodiment of the waveguide type light receiving element of the present invention.

FIG. 4 is a plan view showing still another embodiment of the waveguide type light receiving element of the present invention.

FIG. 5 is a sectional view showing still another embodiment of the waveguide type light receiving element of the present invention.

FIG. 6 is a plan view of a conventional waveguide type light receiving element.

FIG. 7 is a sectional view of a conventional waveguide type light receiving element.

[Explanation of symbols]

 Reference Signs List 1 n-InP substrate 2 graded guide layer 3 absorption layer 4 n-InP layer 5 p diffusion region 6 SiNx film 7 p contact region 8 p electrode 10 n contact region 11 n electrode 12 AR coat film

Claims (6)

[Claims] 1. A p-contact region in a pn junction region,
A waveguide type light receiving element characterized in that the light receiving element is made small near the incident end face. 2. The waveguide type light receiving element according to claim 1, wherein a distance from any point of said pn junction region to a p-contact is within 30 μm. 3. The waveguide type light receiving device according to claim 1, wherein the distance from any point of the pn junction region to the p-contact is within 10 μm. 4. A p-contact region in a pn junction region,
A waveguide-type light receiving element, which is formed around a pn junction region excluding an incident end face. 5. The waveguide type light receiving device according to claim 1, wherein said pn junction has a planar structure formed by diffusion. 6. The waveguide type light receiving element according to claim 1, wherein the n-side has a thick guide layer and has an asymmetric waveguide structure.