JP3419312B2 - Light receiving element and light receiving element module - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical fiber.
The present invention relates to a light receiving element used as a receiver in optical two-way communication in which optical signals of three different wavelengths λ ₁ and λ ₂ are passed in one direction or two directions and information is transmitted between a base station and a subscriber. Alternatively, the present invention relates to an optical transceiver module in which a light receiving element and a light emitting element are integrated.

[0002]

2. Description of the Related Art In wavelength division multiplexing optical communication using lights of two wavelengths, lights of λ ₁ and λ ₂ are separated by a wavelength demultiplexer and received by a light receiving element sensitive to any wavelength. . A wavelength demultiplexer that splits light into λ ₁ and λ ₂ is proposed using an optical fiber, an optical waveguide, a dielectric mirror, or the like. However, in both cases, the wavelength selectivity is insufficient and the extinction ratio is insufficient. In addition, since light of different wavelengths is divided into different optical paths, the device becomes bulky. The wavelength demultiplexer itself is an expensive element and increases the cost of optical communication.

The wavelength of light used for optical communication is determined by the wavelength dependence of the loss of the quartz fiber. 1.
3 μm, 1.55 μm, etc. For example, λ ₁ is 1.3
Two wavelengths are determined such that μm and λ ₂ are 1.55 μm. There are two types of light receiving elements, a front-illuminated type and a back-illuminated type.

FIG. 1 is a cross-sectional view of a surface incident light receiving element (PD) according to a conventional example. On the n ⁺ -InP substrate 1,
An n-InP buffer layer 2, an n ^- InGaAs light receiving layer 3, and an n-InP window layer 4 are epitaxially grown.
The n-InP window layer and the light-receiving layer have a p-type due to Zn diffusion in the central portion.
Region 5 is formed. The p-electrode 6 is formed on a part of the upper surface thereof. A passivation film 7 is formed in the peripheral portion to protect the pn junction. The central portion is an opening and is covered with a transparent antireflection film 8. The incident light enters from the surface side, and hole-electron pairs are formed in the depletion layers that sandwich the pn junction. Since photocurrent flows, light can be detected.

FIG. 2 is a sectional view of a back illuminated type light receiving element according to a conventional example. On the n ⁺ -InP substrate 1, n-In
P buffer layer 2, n ^-- InGaAs light receiving layer 3, n--I
The nP window layer 4 is epitaxially grown. n-InP
The p region 5 is formed in the central portion of the window layer and the light receiving layer by Zn diffusion. Since no light enters from the surface, the p electrode 16 covers almost the entire surface of the p region 5. The boundary is in contact with the passivation film 17. The peripheral portion of the back surface of the substrate 1 becomes the n-electrode 19.
The central part becomes an opening. The antireflection film 20 is attached here.
Incident light enters through the back opening. This is the substrate, the buffer layer,
It passes through the light-receiving layer to reach the depletion layer, where electron-hole pairs are formed.

Which wavelength of light can be received? Because, it depends on the crystal composition of the absorption layer. The InGaAs light receiving layer can receive light of 1.3 μm and 1.55 μm. Conventionally, a light receiving element having sensitivity in such a wide wavelength range has been used.

When such a PD chip is housed in an appropriate package, it becomes a photodiode. A PD module is obtained by attaching the tip of the optical fiber to the package. The PD chip may be used in an LD module that is a light emitting device. The monitor PD is provided behind the LD and monitors the light emission amount of the LD.

FIG. 3 is a perspective view showing an example of a coaxial type PD module according to a conventional example. Here, the front incidence type PD chip 22 is used. The PD chip 22 is die-bonded to the submount 23, and the submount 23 is fixed to the central portion of a circular package 24 made of metal. Insert the submount 23 from the package (case) potential, P
This is because it is necessary to float the D cathode potential. The package 24 includes an anode pin 25, a cathode pin 26,
The case pin 27 is attached. A sleeve 28 is put around the package 24 and fixed.

A cylindrical cap 28 is fixed to the upper surface of the package 24. At the center of the cap 28 is a spherical lens 29. A cylindrical ferrule holder-30 is fixed to the sleeve 28. The ferrule 33 fixed to the tip of the optical fiber 32 is inserted into the center axis hole of the ferrule holder-30 and aligned and fixed. There is a wavelength demultiplexer at the end of the optical fiber 32, which separates λ ₁ and λ ₂ and guides only the light of any wavelength to this PD module. Such P
Since the D module has a three-dimensional structure and has many parts and many alignment points, it cannot be placed on the automation line.
Cost reduction is difficult. Eliminating the wavelength demultiplexer This is one issue.

There are still problems. Recently, it has been required to mount an optical device on a flat package by surface mounting. This flattening of the entire device makes the module small, thin and compact. Moreover, like general electronic components, optical components (PD module, LD module) can be mounted on a printed circuit board by solder reflow. Then, optical parts can be put on the automation line. For surface mounting, the optical fiber should not be perpendicular to the package surface as shown in FIG. The optical fiber should be parallel to the package surface. If the chip is mounted parallel to the package, the beam must be bent 90 degrees somewhere. Several flat package PD modules and LD modules having such a device have been proposed. Let me give you some examples.

Y. Oikawa, H. Kuwatsuka, T. Yamamoto,
T.Ihara, H.Hamano & T.Minami, "Packing Technology f
or a 10-Gb / s Photoreceiver Module ", Journal of lig
htwaveTechnology, vol.12, no.2, p343 (1994)

This proposes a planar package having a structure in which light from an optical fiber parallel to the PD surface direction is introduced into the PD without using a lens. FIG. 4 is an example of a top-illuminated PD module using a Si platform.

FIG. 4A is a plan view and FIG. 4B is a vertical sectional view. Si bench 3 made by processing a Si wafer into a rectangle
Reference numerals 5 and 36 are substrates for planar mounting. Lower Si
An upper Si bench 36 is fixed to the front half of the bench 35. The upper Si bench 36 has a V groove 37 cut in the axial direction. An optical fiber 38 is inserted and fixed in the V groove 37. The second half of the lower Si bench 35 is covered with the insulating layer 39. Metallization pattern 4 on the insulating layer 39
0 is printed. The PD chip 42 is bonded thereon. This PD chip 42 is a front-illuminated type. The rear end of the optical fiber 38 is cut at an oblique angle of 45 degrees, and the signal light transmitted through the core is reflected by the oblique cut surface 45 and enters the p region 43 of the PD 42. The p electrode of PD is wire 4
6 is connected to the metallization 47. Metallized 4
7 is connected to the anode pin 48 by a wire 49.
The back surface of the PD chip is an n-electrode, which is bonded to the metallized pattern 40 over the entire surface. The metallized pattern 40 is connected to the cathode pin 51 by the wire 50.

Thus, the PD has an n-electrode on the InP substrate side, which is die-bonded to the metallized pattern. With such a circuit board, the metallized pattern 40 must be formed in advance for the cathode. The n-electrode cannot be wire-bonded after reflow. The back surface n electrode is the most common design in the case of a light receiving element, but is not suitable for planar mounting.

FIG. 5 shows a planar mounting type module using a back illuminated PD. An optical waveguide 53 is formed at the center of the Si bench 52 in the longitudinal direction. The upper surface of the Si bench 52 is covered with the insulating layer 54. A metallized pattern 55 is printed on the insulating layer 54. Back-illuminated P
Fix D56. An optical fiber (not shown) is fixed to the front end of the optical waveguide 53, and the light of the optical fiber is transmitted through the optical waveguide 5.
3. It enters the PD 56 through the mirror 58. The p electrode 57 of the PD 56 is connected to the metallization 59 by the wire 60. The metallization 59 is connected to the pin 63 by the wire 62. The n-electrode is on the back surface and is die-bonded to the metallization 55. The one using such a waveguide is, for example,

B. Hillerich, A. Geyer, "Self-aligned
flat-pack fiber-photodiode coupling ", ELECTRONICS
LETTERS, Vol.24, No.15, p918 (1988)

Have been proposed by This also does not require a lens. The light traveling direction is parallel to the PD chip surface. There is such an advantage. However, a metallized pattern for attaching the n-electrode is still required. Not optimal for planar mounting.

[0018]

SUMMARY OF THE INVENTION It is an object of the present invention to fabricate a light receiving element sensitive only to λ ₂ and omit a wavelength demultiplexer in optical communication using light of two wavelengths λ ₁ and λ ₂ . This is the first purpose. It is a second object of the present invention to provide a light receiving element structure suitable for planar mounting. The third aspect of the present invention is to prevent the tailing of the signal due to the light entering the peripheral portion of the PD.
Is the purpose of.

[0019]

A light-receiving element of the present invention is a back-illuminated type, has a wavelength-selective layer having a band gap between λ ₁ and λ ₂ as a filter, and is provided in the center of an epitaxial growth layer. In addition to the provided pn junction, an annular second pn junction surrounding the second pn junction is provided, and an n electrode (or p electrode) is formed so as to straddle the n region adjacent to the p region of the second pn junction.
The feature is that the electrodes are provided.

That is, there are three characteristics. One is a filter
Intervening layers λ₁It means that I tried to drop it.
Therefore λ₁<Λ_g<Λ_TwoBandgap as is
Wavelength λ _gA filter layer having λ₁Is shorter
Semiconductor band gap energy in the middle
If you put a thin film of crystal somewhere λ₁Will be absorbed, so λ
_TwoIt becomes an element that can sense only the light of. λ₁Against
It is desirable that the Luther effect has a transmittance of 3% (-15 dB) or less.
Yes.

The second is to provide an annular second pn junction in the peripheral portion. This has the effect of absorbing electron-hole pairs created by light entering the peripheral portion and preventing a response delay. The annular p region (or n region) is referred to as a diffusion blocking layer. There is such a name because it blocks the diffusion of holes and electrons.

Thirdly, an n electrode (p electrode) is provided so as to extend over the p region and the n region of the pn junction in the peripheral portion. Since the p region and the n region inside and outside the diffusion shielding layer are short-circuited, the electron-hole pairs formed by the light incident on the peripheral portion are immediately extinguished. Further, there is an advantage in implementation. Since both the p electrode and the n electrode are on the front surface side, the metallization pattern for the bottom n electrode is unnecessary. The n-electrode and p-electrode on the surface are connected to patterns and pins by wire bonding. However, a metallized surface may be provided in a ring shape on the bottom surface of the board for soldering (bonding) to the circuit board or the package surface. Even then it is not an electrode. Alternatively, the chip may be adhered to the circuit board or the package with an adhesive material without attaching the metallization to the bottom surface.

[Characteristic 1: Filter layer] In the case of InP substrate, if λ ₁ = 1.3 μm and λ ₂ = 1.55 μm,
For example, a semiconductor mixed crystal having a bandgap wavelength λ _g between them may be provided as a filter layer between the incident surface and the InGaAs light receiving layer. For example, InGa having a λ _g of 1.42 μm
The AsP layer can be the filter layer. InGaAsP having a band gap of 1.42 μm is a quaternary mixed crystal of In _0.66 Ga _0.34 As _0.76 P _{0.24 in} a detailed composition. It absorbs 1.3 μm and transmits 1.55 μm. Not limited to 1.42 μm, any crystal having a λ _g between 1.3 μm and 1.55 μm has such a property. When this InGaAsP mixed crystal is placed on the light receiving side,
A product that absorbs 1.3 μm and passes 1.55 μm is obtained.

The filter layer may be provided on the front surface side (the one on which the epitaxial layer is stacked) or the back surface side of the InP substrate. In any case, the light has to pass through the filter layer to reach the light receiving layer, so that it is a back-illuminated type. The filter layer may be n-type, p-type, or semi-insulating. When the epitaxial layer is n-type, the back-side metallization is insulated by using a p-type filter, so that the insulating film is unnecessary. When both the substrate and the epitaxial layer are n-type, an insulating film is required when using an n-type filter. No insulating film is required when using a semi-insulating filter.

[Characteristic 2: Diffusion Shielding Layer on Ring] A ring-shaped pn junction is provided so as to surround the pn junction in the central portion, and an electrode is attached thereto. An electrode is formed over the diffusion shield layer surrounded by the peripheral pn junction and the outer portion.
A reverse bias is also applied to the peripheral pn junction to expand the depletion layer. Light entering the peripheral depletion layer forms electron-hole pairs, and photocurrent flows. This is short-circuited by the electrode across the pn junction in the peripheral portion and disappears. Since it does not enter the signal current, there is no signal delay.

[Characteristic 3: Electrode traversing pn junction] Since an electrode traversing the junction of the ring-shaped second pn junction is provided, and this and the central electrode form a pair of electrodes, the electrode is attached to the bottom surface of the substrate. No need. Therefore, it is not necessary to provide the metallization pattern in the package when mounting. The structure is suitable for surface mounting.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a semi-insulating InP substrate,
It can be applied to both an n-type InP substrate and a p-type InP substrate. The best is the semi-insulating substrate (SI-In
P substrate). For the three types of substrates, the epitaxial layer (first conductivity type), the central conductivity type (second conductivity type)
Conductivity type), diffusion shield layer (second conductivity type) conductivity type, center electrode, peripheral electrode conductivity type, filter conductivity type, and the like.

[A. Semi-insulating InP substrate and n-type epitaxial layer] n-type epitaxial layer. Surface center =
p region. Diffusion shielding layer = p region. Filter = n-type, p-type or SI-type. Center electrode = p electrode. Peripheral electrode = n electrode.

[B. In case of n-type InP substrate and n-type epitaxial layer] n-type epitaxial layer. Surface center part = p region. Diffusion shielding layer = p region. Filter = n-type, p-type or S
Type I. Center electrode = p electrode. Peripheral electrode = n electrode.

[C. In the case of p-type InP substrate and p-type epitaxial layer] p-type epitaxial layer. Surface center = n region. Diffusion shielding layer = n region. Filter = n-type, p-type or S
Type I. Center electrode = n electrode. Peripheral electrode = p electrode.

[D. Semi-insulating InP substrate and p-type epitaxial layer] p-type epitaxial layer. Surface center =
n region. Diffusion shielding layer = n region. Filter = n-type, p-type or SI-type. Center electrode = n electrode. Peripheral electrode = p electrode.

FIG. 6 shows an SI-InP substrate or an n-type substrate I.
1 shows a schematic PD structure for nP. The InP substrate 66 includes both a semi-insulating InP substrate and an n-type InP substrate. One surface of the InP substrate 66 (referred to as the front surface)
An n-InGaAs light receiving layer 67 is epitaxially grown on it. This may be a single layer, or may be a stack of several epitaxial layers as will be described later in detail. A filter layer 68 is also epitaxially grown on the opposite surface of the substrate 66. As described above, the wavelength corresponding to the band gap is 1.3 μm and 1.
It is an InGaAsP mixed crystal that is in the middle of 55 μm. As described above, if 1.42 μm, In _0.66 Ga _0.34 As
_0.76 P _0.24 . InGa for other wavelengths
AsP may also be used. Since it is a quaternary mixed crystal and has two parameters, it has a lattice matching with InP and an absorption edge wavelength of 1.3 μm
InGaAsP having a thickness of 1.55 μm can be freely designed.

A central p region 69 is formed in the central portion of the InGaAs light receiving layer 67 by diffusion of a p-type dopant and ion implantation. A p electrode 72 is formed on the central p region 69. Since it is a back-illuminated type, the p electrode 72 may widely cover the p region 69. Ring-shaped p on the periphery
Region 70 is formed. The central p region 69 is also the peripheral p region 7
0 can also be manufactured in the same process. The solid line is p
It is an n-junction. Pn across the peripheral p region and n region 67
An annular n-electrode 73 is formed across the junction. The portion other than the p-electrode 72 and the n-electrode 73 is the passivation film 7.
4 is covered and protected. The n-electrode 73 is the cathode electrode to be reverse biased. I like a normal PD
No n electrode is formed on the bottom surface of the nP substrate.

On the back surface of the substrate, a metallization 75 for bonding is formed in the peripheral portion under the filter layer 68. This is not an n-electrode. It is simply metallization for fixing to a package or circuit board. An antireflection film 76 is formed on the center of the back surface. Incident light 77 is incident on the back surface of the chip from the antireflection film 76. This is the light of λ ₁ + λ ₂ ,
Λ ₁ drops in the filter layer 68, and only λ ₂ is n-InG
The vicinity of the depletion layer of the aAs light receiving layer 67 is reached.

The reverse bias is applied between the n-electrode 73 in the peripheral portion and the p-electrode 72 in the central portion. InGaAs light receiving layer is n
Although it is a type, it has a low dopant concentration and high resistance. When the InP substrate is an n-type, the InP substrate has a low resistance, so that an electric field can be generated between the p electrode, the substrate and the n electrode. When the InP substrate is semi-insulating, a low resistance buffer layer is provided on the substrate.
So the electric field direction is still vertical. Since the n electrode is biased positively and the p electrode is biased negatively, an electric field is generated from the substrate toward the p electrode. Electrons formed in the central depletion layer flow to the n region, and holes flow to the p region, and photocurrent flows.

When light enters the peripheral portion, a hole-electron pair is formed in a normal PD, but it progresses by diffusion and enters the n region or p region, causing a signal delay. This is sometimes called a trailing current. The present invention can also solve the problem of trailing current due to stray light entering such a peripheral portion.

It is assumed that electron-hole pairs are formed in the depletion layer near the peripheral p region 70. The holes enter the nearby p region 70.
The electrons go to the n region. At that time, a current flows through the electrode 73, but since the n region and the p region are short-circuited by the n electrode 73, the current flows through the electrode 73 and immediately disappears. No external current. The trailing current disappears. The n-region and the p-region are short-circuited to immediately erase the photocurrent causing the signal delay.

A light receiving element in which a p region is provided in the peripheral portion to form a pn junction to eliminate a signal delay was first proposed by the present application. Japanese Patent Application No. 2-230208 "Photodetector"
This is Ichiro Karauchi (Japanese Patent Laid-Open No. 4-111479). This is p
The end of the n-junction is exposed on the side surface of the chip and self-shorts. Japanese Patent Application No. 10-174227 "Light receiving element and light receiving device" Miki Kohara and Hitoshi Terauchi go one step further to expose the peripheral pn junction termination to the surface and attach electrodes to the peripheral p region. As a result, a reverse bias can be applied to the peripheral pn junction. USP 5,420,4
18, Yasushi Fujimura, Ichiro Karauchi proposed a photodetector in which an n electrode is attached to the peripheral p region and the adjacent n region and a reverse bias is applied between the central p electrode and the peripheral n electrode. There is. Both are in the hands of the applicant.

[0039]

[Embodiment 1] A more detailed structure will be described with reference to FIG. The InP substrate 66 is an n-type InP substrate. n
N-InP buffer layer 78, n on the InP substrate 66
An epitaxial wafer is used in which the -InGaAs light receiving layer 67 and the n-InP window layer 79 are epitaxially grown and the filter layer 68 is formed on the back surface. Compared with the basic form of FIG. 6, the buffer layer 78 and the window layer 79 are increased. The InP window layer 79 has a wider bandgap than the InGaAs light receiving layer, but does not pass light having an energy larger than the bandgap. Therefore, the front-illuminated type often uses a window layer. A window layer may be attached even when the light is incident on the back surface. The dopant concentration of the n-type InP window layer is InGaAs
Since it is higher than the dopant concentration of, the resistance to the electrode can be reduced.

An antireflection film 80 is further formed on the filter layer 68. This is on the entire surface and has the function of both insulation and antireflection. The element needs an insulating film because it needs to be insulated from the package. Further, the metallization 75 is provided only in the peripheral portion. This is not an n-electrode but only for bonding. Incident light 77 of (λ ₁ + λ ₂ ) which is incident on the back surface and passes through the antireflection film 80 on the bottom surface.
Comes in. λ ₁ is absorbed by the filter layer 68.
Only λ ₂ is the InP substrate 66, the InP buffer layer 78, I
It reaches the depletion layer through the nGaAs light receiving layer 67.

A plan view of FIG. 8 is shown in FIG. This is a plan view common to the devices of FIGS. There is a p-region 69 in the center circle (surrounded by a broken line). There is also a circular p region 70 in the peripheral portion (sandwiched by a broken line). There are n regions between them. P in the central p region 69
An electrode 72 and an n electrode 73 are provided in the peripheral p region and the adjacent n region. The p electrode 72 covers most of the central p region 69. The peripheral n-electrode 73 is mainly on the n-region. The composition is also the material of the n-electrode. Even the n-electrode material makes almost ohmic contact with the p region. The p electrode is made of AuZn alloy. The n-electrode is of AuGeNi / Au / Ti / Au system. These electrodes have excellent ohmic contact and adhesion. The n-electrode 73 is reverse biased so that it becomes positive and the p-electrode 72 becomes negative. The electric field is also generated in the lateral direction in the light receiving layer, but since it has high resistance, the electric field is strongly generated mainly in the vertical direction from the substrate to the light receiving layer. Not much different from the case where there is an n-electrode on the bottom. Even if light enters the periphery and electron-hole pairs are created, n
Only the current flows around the electrode 73, and the trailing current disappears.

[Embodiment 2 (using a semi-insulating InP substrate)] A semi-insulating substrate does not need to care for insulation more than an n-type substrate. FIG. 8 shows a light receiving element structure when a semi-insulating InP substrate is used. Iron-doped SI-InP substrate 83
I used. The resistivity is 10 ⁷ Ωcm. The substrate shape is 0.5 mm × 0.5 mm × 0.3 mm. The resistance in the thickness direction is 100 MΩ or more. The n ⁺ -InP buffer layer 84, n-I is formed on one surface (front surface) of the SI-InP substrate.
nP buffer layer 85, InGaAs light receiving layer 67, n-I
The nP window layer 79 is epitaxially grown. An InGaAsP filter layer 68 is epitaxially grown on the back surface side. The parameters of the epitaxial layer are as follows. n ⁺ -InP buffer layer ... S-doped, n = 10 ¹⁸ cm ^-3 , d = 2 μm to 4 μm n-InP buffer layer ... n = 1 to 5 × 10 ¹⁵ cm ^-3 , d = 2 μm to 4 μm n-InGaAs (InGaAsP) light receiving layer ... n = 1 to 5 × 10 ¹⁵ cm ⁻³ d = ^{3 to 4} μm n-InP window layer ... n = 2 to 5 × 10 ¹⁵ cm ⁻³ d = 2 to 3 μm InGaAsP filter layer ... λ _g = 1.4 μm The p region 69 is formed in the central portion of the InP window layer, and the second p region 69 is formed in the peripheral portion.
Region 70 is created by zinc diffusion. A p electrode 72 is provided in the central p region. An n electrode 73 is formed so as to straddle an n region 79 adjacent to the p region 70 in the peripheral portion. The filter layer 68 is provided with a bonding metallization 75 at the peripheral portion and an antireflection film 76 at the central portion.

Since the substrate 83 is insulating, n just above⁺
-InP buffer layer 84 is an n-type with high carrier concentration
ing. Dopant concentration is 10¹⁸cm^-3And above
It The n-electrode 73 has a high voltage and the p-electrode 72 has a low voltage.
, The electric field is n⁺-InP buffer layer
It is formed in the direction from 84 to the central p region 69. λ
₁+ Λ_TwoEven if the signal light 77 of₁Is Phil
Is absorbed by the data layer. λ_TwoOnly reaches the light receiving layer and is perceived
It Since the substrate is insulative, metallize 75 and filter layer
No need to insulate.

[Embodiment 3 (Semi-insulating substrate)] FIG. 9 shows an example in which a semi-insulating substrate is used and an insulating film is provided on the entire surface. N ⁺ -InP is formed on one side of the SI-InP substrate 83.
Buffer layer 84, n-InP buffer layer 85, n-In
The GaAs light receiving layer 67 and the n-InP window layer 79 are epitaxially grown, and the InGaAsP filter layer 68 is epitaxially grown on the opposite surface. On the surface side, there are a central p region 69 and a peripheral p region 70 due to Zn diffusion. A p electrode 72 is provided in the central p region 69, and an n electrode 73 is provided in the peripheral p region 70. An antireflection film 80 is attached to the entire surface of the filter layer 68 on the back surface. A metallization 75 for die bonding is attached to the peripheral portion thereof. The antireflection film 80 serves not only as antireflection but also as insulation. SiON, Si
It is made of N, SiO _2, etc. However, since the substrate is insulating, there is no need for insulation.

[Fourth Embodiment (Coupling with Amplifier)] A basic circuit in which a light receiving element and an amplifier are combined will be described with reference to FIG.
A voltage of 3.3 V, for example, is applied to Vpd connected to the n-electrode 73. The p-electrode 72 is connected to the input terminal of the amplifier 86. As the amplifier 86, an IC of Si or GaAs is used. p
A low voltage is applied to the electrode and a high voltage is applied to the n-electrode, and the pn junction is reverse biased. The amplified signal appears at Vout. Incident light 77 enters from the bottom surface. Λ ₁ drops at the filter layer 68,
Only ₂ reaches the light receiving layer 67.

[Embodiment 5 (Waveguide type)] In the light-receiving element chip of the present invention, the n-electrode is on the front surface side and not on the bottom surface. When mounted in a package, a metallization pattern for fixing the n-electrode is unnecessary. 12 and 13 show a waveguide type light receiving element module which realizes the circuit of FIG. S
An optical waveguide 89 having a high refractive index is formed along the center line of the i bench 88. A mirror 92 is formed in the middle of the optical waveguide 89. This can be made by inserting a mirror plate into the groove. Or S
It can also be made by anisotropically etching i.

The PD chip 8 of the present invention is provided directly above the mirror 92.
Fix 7 The bottom surface is not an n-electrode and does not require metallization. It may be fixed by resin. The amplifier chip 86 is fixed behind it. P-electrode 72 is connected by wire 95 to the input of amplifier 86. n-electrode is wire 93
Connected to Vpd pin 94 by. The ground pad of amplifier 86 is connected to ground pin 99 by wire 98. The power pad connects to Vcc pin 97 by wire 96. The amplified signal is taken out from the wire 102 through the output pin 103. Optical fiber 9
The tip of 0 is joined to the beginning of the optical waveguide 89. The signal light passes from the optical fiber, passes through the optical waveguide, and is reflected by the mirror 92.
Enter the chip 87 from the back side. Although the signal light is λ ₁ + λ ₂ , λ ₁ is dropped by the filter layer 68 and only λ ₂ reaches the light receiving layer. Since there is no n-electrode on the bottom surface, a metallized pattern for Vpd cannot be inserted. The n-electrode is also connected by a wire.

In this example, the PD has a light receiving diameter of 80 μm. The mirror was formed by etching the (111) surface of Si to form a surface having an angle of 45 degrees. The optical fiber is a single mode fiber. The optical fiber surface and the waveguide are bonded by a transparent resin. The package 104 is made of metal.

Vcc = Vpd = 3V was applied. 155
Laser light modulated by a digital signal of Mbps was incident from an optical fiber. The BER was measured in this state. The error rate is 10 ^-8 and the minimum receiving sensitivity is -35 dB.
m, and the maximum receiving sensitivity was 0 dBm. Since there is no tailing current, the alignment tolerance of the fiber is wide and all the fibers have good characteristics. Since all wiring between the electrodes is made by wires on the upper surface, the number of assembling steps is also shortened.

[Embodiment 6 (Embedded Optical Fiber Type)] FIGS. 14 and 15 show an embedded optical fiber type light receiving element module for realizing the circuit of FIG. Si bench 105
The V-groove 106 is cut out in the shape of the center line. The optical fiber 90 is inserted and fixed in the V groove 106. The tip is cut so as to form an inclination angle of 45 degrees. Light is reflected upward by the cut surface 107 and enters from the lower surface of the PD 87. As in the previous example, the amplifier 86 is fixed behind the PD chip 87. In this case, unlike the example of FIG. 4, it is not necessary to arrange the Si bench in two stages. This is an advantage of the back-thinned type.

[0051]

Since a filter layer having a bandgap satisfying the relationship of λ ₁ <λ _g <λ ₂ is provided and a signal of two wavelengths is passed therethrough and only λ ₂ is passed therethrough, the light receiving element itself has high wavelength selectivity. Is given. No need for wavelength demultiplexer. The electron-hole pairs that are incident on the peripheral portion and are generated by light are short-circuited at the electrodes that cross the pn junction in the peripheral portion and disappear, so that there is no signal delay. The mounting tolerance of the optical system is relaxed. Since both n-electrode and p-electrode are on the surface, they are most suitable for surface mounting.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a front-illuminated light receiving element according to a conventional example.

FIG. 2 is a cross-sectional view of a backside incident type light receiving element according to a conventional example.

FIG. 3 is a partially longitudinal perspective view of a light receiving element module according to a conventional example.

FIG. 4 is a diagram of a surface-mounted light-receiving element module according to a conventional example. (1) is a plan view and (2) is a sectional view.

FIG. 5 is a diagram of a surface-mounted light-receiving element module using a waveguide according to a conventional example. (1) is a plan view and (2) is a schematic sectional view.

FIG. 6 is a sectional view showing a basic configuration of a light receiving element of the present invention.

FIG. 7 is a sectional view showing a first type of a light receiving element of the present invention using an n-type InP substrate.

FIG. 8 is a cross-sectional view showing a second type of light receiving element of the present invention using a semi-insulating InP substrate.

FIG. 9 is a sectional view showing a third type of light receiving element of the present invention using a semi-insulating InP substrate.

FIG. 10 is a circuit diagram when the light receiving element of the present invention and an amplifier are connected.

FIG. 11 is a plan view of a light receiving element chip of the present invention.

FIG. 12 is a schematic plan view showing a state where a light receiving element of the present invention is mounted on a Si bench having an optical waveguide and housed in a package.

FIG. 13 is a schematic cross-sectional view of a light receiving element of the present invention mounted on a Si bench having an optical waveguide.

FIG. 14 is a schematic plan view showing a state in which an optical fiber is inserted into a Si bench having a V groove and the light receiving element of the present invention is mounted and housed in a package.

FIG. 15 is a schematic cross-sectional view showing a state in which an optical fiber is inserted into a Si bench having a V groove and the light receiving element of the present invention is mounted.

[Explanation of symbols]

1 n ⁺ -InP substrate 2 n-InP buffer layer 3 n-InGaAs light receiving layer 4 n-InP window layer 5 p region 6 p electrode 7 passivation film 8 antireflection film 9 n electrode 16 p electrode 17 passivation film 19 n electrode 20 Antireflection film 22 PD chip 23 Submount 24 Package 25 Anode pin 26 Cathode pin 27 Case pin 28 Sleeve 29 Ball lens 30 Ferrule holder-31 Cap 32 Optical fiber 33 Ferrule 34 Bend limiter 35 Si lower bench 36 Si upper bench 37 V groove 38 Optical Fiber 39 Insulating Layer 40 Metallized Pattern 42 PD Chip 45 Diagonal Cut Surface 46 Wire 47 Metallized 48 Pin 49 Wire 50 Wire 51 Pin 52 Si Bench 53 Optical Waveguide 54 Insulating Layer 55 Metallized Pattern 56 PD Chip 5 p electrode 59 metallization 60 wire 62 wire 63 pin 64 wire 65 pin 66 InP substrate 67 n-InGaAs light receiving layer 68 filter layer 69 central p region 70 peripheral p region 72 p electrode 73 n electrode 74 passivation film 75 bonding metallization film 76 reflection Prevention film 77 Incident light 78 n-InP buffer layer 79 n-InP window layer 80 Antireflection film 83 Semi-insulating InP substrate 84 n ⁺ -InP buffer layer 85 n-InP buffer layer 86 Amplifier 87 PD chip 88 Si bench 89 Optical Waveguide 90 Optical fiber 92 Mirror 93 Wire 94 pin 95 Wire 96 wire 97 pin 98 Wire 99 pin 102 Wire 103 pin 104 Package 105 Si bench 106 V groove 107 Inclined surface

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 4-111479 (JP, A) JP 4-92479 (JP, A) JP 5-129638 (JP, A) JP 10- 104473 (JP, A) JP 53-99889 (JP, A) JP 59-63779 (JP, A) JP 62-230065 (JP, A) T.P. P. lee et. al, Dual-channel 1.5 Mb / s Lightwave receive receiving emulsification anInGa AsP wavelength-demulturing detector, Electronics, USA, 389, 1983, 1983, 1983, 1983, 15/13, 1983, 13/15. Int.Cl. ⁷ , DB name) H01L 31/00-31/12

Claims (12)

(57) [Claims] _1. A light having a _first wavelength λ _{1 and} a second light longer than that
Is a light-receiving element for sensing only the light of the second wavelength λ _{2 in} the optical communication using the light of the wavelength λ ₂ (λ ₁ <λ ₂ ), which is either semi-insulating or n-type or p-type. The first
A filter layer made of a conductive semiconductor substrate and an n-type or p-type semiconductor crystal having a band gap lower than the energy of light of wavelength λ ₁ and higher than the energy of light of wavelength λ ₂ epitaxially grown on one surface of the semiconductor substrate. And a first-conductivity-type absorption layer epitaxially grown on the filter layer or on a substrate opposite to the filter layer, and a part of the first-conduction-type absorption layer is doped with a second-conductivity-type impurity. A second conduction type central light receiving region which is either p-type or n-type, a first pn junction formed at a boundary between the second conduction type central light receiving region and the first conduction type semiconductor layer, and a second conduction type A second conductive type electrode formed on the central light receiving region; a second conductive type diffusion shielding layer provided by doping the peripheral portion with a second conductive type impurity so as to surround the central light receiving region;
A second pn junction formed at a boundary between the second conduction type diffusion shield layer and the first conduction type semiconductor layer; and a diffusion conduction layer, a second pn junction, and a first conduction type electrode provided over the first conduction type layer. Signal light of wavelengths λ ₁ and λ ₂ enters from the substrate side,
₁ is absorbed by the filter layer, and λ ₂ is a back-illuminated type in which the filter layer, the first-conductivity-type substrate, the first-conductivity-type light-receiving layer, and the first pn junction reach the second-conductivity-type central light-receiving region. In addition, the first conduction type electrode has a function of short-circuiting the second pn junction. 2. A light having a _first wavelength λ _{1 and} a second light longer than that
Is a light-receiving element for sensing only the light of the second wavelength λ _{2 in} the optical communication using the light of the wavelength λ ₂ (λ ₁ <λ ₂ ), which is either semi-insulating or n-type or p-type. The first
A conductive semiconductor substrate and a band gap lower than the energy of light of wavelength λ ₁ and higher than the energy of light of wavelength λ ₂ epitaxially grown on one surface of the semiconductor substrate, and the transmittance of light of λ ₁ is 3% or less. A filter layer made of an n-type or p-type semiconductor crystal having a certain thickness, a first-conduction-type light-receiving layer epitaxially grown on the filter layer or on a substrate opposite to the filter layer, and a first-conduction-type light-receiving layer P formed by doping a part of the layer with impurities of the second conductivity type
-Type or n-type second-conduction-type central light-receiving region, a first pn junction formed at the boundary between the second-conduction-type central light-receiving region and the first-conduction-type semiconductor layer, and second-conduction-type central light-receiving region A second conductivity type electrode formed on the region, a second conductivity type diffusion shield layer provided by doping the peripheral part with a second conductivity type impurity so as to surround the central light receiving region, and a second conductivity type diffusion shield layer. A second pn junction formed at the boundary between the first diffusion type semiconductor layer and the diffusion barrier layer, and a first conduction type electrode provided over the diffusion shielding layer, the second pn junction and the first conduction type layer,
Signal light of wavelengths λ ₁ and λ ₂ is incident from the substrate side, λ ₁ is absorbed by the filter layer, and λ ₂ is the filter layer, the first conductivity type substrate, the first conductivity type light receiving layer, and the first pn junction. A light-receiving element, which is of a back-illuminated type so as to reach a central conduction region of the second conduction type via the first conduction type electrode and has a function of short-circuiting the second pn junction. 3. The light receiving element according to claim 1, wherein the semiconductor substrate has a metallizing surface for bonding on a part of the back surface. 4. The light receiving element according to claim 1, wherein a window layer of the first conductivity type is provided between the light receiving layer and the electrode. 5. The light receiving element according to claim 1, wherein a first conductivity type filter layer is provided between the semiconductor substrate and the first conductivity type light absorption layer. 6. The light receiving element according to claim 1, wherein a dielectric antireflection film is provided on the whole or a part of the back surface of the substrate. 7. The first conductivity type is n-type, the second conductivity type is p-type, the semiconductor substrate is a semi-insulating InP substrate, and the buffer layer is divided into two first buffer layers. Is sulfur-added low-resistance n-InP, the second buffer layer is high-resistance n-InP, the light-receiving layer is n-InGaAs or n-InGaAsP, and the window layer is n-InP. The light receiving element according to claim 1 or 2, wherein the two-conductivity type region is formed by Zn diffusion. 8. The first conductivity type is n-type, the second conductivity type is p-type, the semiconductor substrate is an n-InP substrate, the buffer layer is n-InP, and the light-receiving layer is n-. InGaA
s or n-InGaAsP and the window layer is n-InP
The light receiving element according to claim 1 or 2, wherein the second conductivity type region is formed by Zn diffusion. 9. The first conductivity type is n-type, the second conductivity type is p-type, the p electrode is AuZn-based, and the n electrode is A.
The light-receiving element according to claim 1 or 2, which is a uGeNi / Au / Ti / Au system. 10. In optical communication using light having a _first wavelength λ ₁ and light having a second wavelength λ ₂ longer than that (λ ₁ <λ ₂ ), only light having a _second wavelength λ ₂ is sensed. And a semiconductor substrate of the first conductivity type which is semi-insulating or is either n-type or p-type and lower than the energy of light of wavelength λ ₁ epitaxially grown on one surface of the semiconductor substrate. N having a band gap higher than the energy of light of wavelength λ ₂ and a thickness of 3% or less of transmittance of light of λ ₁
Type or p type semiconductor crystal, a first conductive type light receiving layer epitaxially grown on the filter layer or on a substrate opposite to the filter layer, and a part of the first conductive type light receiving layer A second conductive type central light receiving region, which is either p-type or n-type formed by doping a second conductive type impurity, and a first conductive type semiconductor layer formed at the boundary between the second conductive type central light receiving region and the first conductive type semiconductor layer. 1 pn junction, an electrode for the second conduction type formed on the second conduction type central light receiving region, and a peripheral portion so as to surround the central light receiving region by being doped with a second conduction type impurity. A second conductive diffusion barrier layer, a second pn junction formed at the boundary between the second conductive diffusion barrier layer and the first conductive semiconductor layer, and the diffusion barrier layer, the second pn junction and the first conductive layer A first conductivity type electrode provided,
Signal light of wavelengths λ ₁ and λ ₂ is incident from the substrate side, λ ₁ is absorbed by the filter layer, and λ ₂ is the filter layer, the first conductivity type substrate, the first conductivity type light receiving layer, and the first pn junction. It is a back-illuminated type that reaches the second conduction type central light receiving region via the first conduction type electrode, and the first conduction type electrode has a function of short-circuiting the second pn junction. A light-receiving element module characterized by this. 11. An optical waveguide is provided on a Si bench, a mirror is formed on a part of the optical waveguide, the light receiving element is bonded or soldered to a position on the mirror, and an amplifier is fixed on the upper surface of the Si bench. The light-receiving element module according to claim 10, wherein the bench is housed in a package. 12. A V-shaped groove is provided on a Si bench, an optical fiber whose tip is cut into a 45 ° inclined surface is inserted into the V-shaped groove, and the light-receiving element is bonded or soldered to a position directly above the cut surface of the optical fiber. Then, fix the amplifier on the upper surface of the Si bench, and
The light receiving element module according to claim 10, wherein the i bench is housed in a package.