JPS63283080A - End-face photodetecting-type photodiode - Google Patents

Abstract

PURPOSE:To guide the incident light from an end part of a device to a photodetecting part efficiently by a method wherein a heterostructure light waveguide route composed of a clad part and a core part which have a forbidden band width bigger than the photodetecting part is formed as a window part at an end part on the incident side of the photodetecting part. CONSTITUTION:A core layer 47 has a forbidden band width which is smaller than a lower-part clad layer 46 and an upper-part clad layer 49, i.e. has a refractive index which is bigger than these layers. Because these three layers have the forbidden band width which is bigger than the energy corresponding to the wavelength of the incident light, they constitute a plasma waveguide route which is transparent with reference to the incident light 52. The core layer 47 forms a core part; the lower-part clad layer 46 and the upper-part clad layer 49 form clad parts. The incident light 52 is guided to a photodetecting part by the planar waveguide route composed of the core layer and the clad layers and is photodetected at a photodetecting part 51.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an edge-light receiving photodiode for a hybrid optical integrated circuit.

[Prior art/problems to be solved by the invention] In recent years, optical components used in the fields of optical communication and optical information processing have been replaced by conventional mirrors, lenses,
Bulk components based on prisms are progressing to optical integrated circuits based on optical waveguides. For optical integrated circuits, semiconductor films are laminated on a ■-V group semiconductor substrate,
There are monolithic optical integrated circuits in which a light emitting/receiving element and an optical waveguide are integrally formed, and hybrid optical integrated circuits in which various individual optical components such as a light receiving/emitting element are added to a quartz and dielectric waveguide. Hybrid optical integrated circuits have the advantage of being able to obtain highly functional and multifunctional optical components by selecting the most suitable material for the required optical function and combining the optical elements and optical waveguide circuits manufactured using these materials. be.

Light receiving elements used in such hybrid optical integrated circuits include pin photodiodes and avalanche photodiodes. FIG. 4 shows an InGaAsP-pin photodiode as an example of a conventional planar photodiode used as a light receiving element for a wavelength of 1 cm or more. In the figure, 1 is an n'-1nP substrate, 2 is an n-1nP buffer layer, 3 is an n-InGaAsP light absorption layer, 4 is an n-InP window layer, 5 is a p-diffusion region, and 6 is a 5L
3Na insulating film, 7 is an upper electrode, and 8 is a lower electrode. In addition, as an external circuit, 9 is a drive power supply, 10 is a load resistance,
11 is a coupling capacitor, 12 is an output terminal, 13
is the incident light.

When the incident light 13 containing a signal component is introduced into the pin photodiode to which a reverse bias is applied by the drive power supply 9, electron-hole pairs are generated in the n-1nGaAsP light absorption layer 3, resulting in a photocurrent and the load resistor 10 and An electrical signal is output from the output terminal 12 via the coupling capacitor 11.

The conventional method for hybrid integration of such a planar photodiode into an optical waveguide circuit is shown in Fig. 5(a).
Shown in (b). In the figure, 14 is a planar photodiode, 1
5 is a substrate, 16 is an optical waveguide constituting an optical waveguide circuit, 17
18 is a core portion, 18 is a cladding portion, 19 is a reflecting mirror block, 20 is a refractory surface, and 21 is a guided light. The reflective mirror block 19 has a reflective surface 20 in which a film 45 of the glass block is deposited on the slope. This reflective mirror block 19 is pressed against and fixed to the end of the waveguide 16, and a planar photodiode 14 is placed above it with the light-receiving surface facing downward, thereby performing hybrid integration. Waveguide light 21
is reflected by the reflective surface 20 and the planar photodiode 14
and is converted into an electrical signal. However, with this method, it is necessary to prepare the reflective mirror block 19, and it is necessary to precisely align and fix the optical waveguide 16, the reflective mirror block 19, and the planar photodiode 14; The disadvantages are that the process is complicated and cannot be mass-produced, the structure is complicated, and it is difficult to miniaturize.

As a method to solve these drawbacks, a method of hybrid-integrating an edge-receiving photodiode by direct bonding to the end of an optical waveguide can be considered. FIG. 6(a) is a perspective view for explaining the direct bonding of the edge-light receiving type photodiode to the end of the optical waveguide, and FIG. 3(b) is a sectional view thereof. In the figure, reference numeral 22 indicates an edge-light receiving type photodiode, and reference numeral 23 indicates a low melting point metal vapor-deposited thin film (for example, Au-5n) for fixing the photodiode. The edge-receiving photodiode 22 receives light from its end surface.

This edge-receiving photodiode 22 is placed on the substrate 15, and after alignment with the optical waveguide 16, the substrate 15 is heated.
By melting the low melting point metal vapor deposited thin film 23, the edge receiving type photodiode is fixed. The use of such a hybrid integration method has the advantage of being highly mass-producible and capable of miniaturization. As such an edge-light receiving type photodiode, Z-C di-wavelength 1.3tIJn band 1nGaAsP is used.
Edge-receiving pin photodiode (1, E, Bowe
rs and C, A, Burrus old gh-spee
d zero bias waveguide pho
todetectors, Electron, L
ett,, 1986, Vol 22, No.
17, p905-906) and wavelength 1.3'' band Ge,
SLl,/Si superstructure edge-sensitive avalanche photodiode (T, P, Pearsall,
H, Temkin, John, C, Bean an.
d Serge Luryi, AualanCll
e (la:n In Geχ5L1-χ/SL I
nfrared WaVe(ILI!de Detec
tors IEEE Electron Device
e Lett, Vol, EDL-7, No5. 1
986, p330-332), etc. have been reported.

- As an example, 1. TnGaAsP reported by E. Bowers and C. BurruS.
The structure of an edge-receiving pin photodiode is shown. In the figure, 24 is an n+-InP layer, 25 is a 1-1nGaAsP light absorption layer, 26 is a p-1nP layer, and 27 is a p'' InGaA layer.
sP key p-tube layer; 28, S02 film; 29, insulating resin; 30, lower electrode; 31, upper electrode; and 32, incident light.

However, in these reported devices, the pn junction surface is exposed at the end surface where light enters. Therefore, these elements require extreme handling, are unreliable due to an increase in end face leakage current over time, and require non-reflective coating on the end face where the light enters in order to efficiently receive the incident light. This method had the disadvantage of not being able to add a membrane, and was far from practical.

In order to solve this drawback, InG
aAsP edge-receiving p1n photodiode (patent application 1986)
1-182995) has been reported.

The structure is shown in FIGS. 8(a), (b), and (c). Figure (a) is a perspective view, and figure (b) is a perspective view of A-
A sectional view taken along line A', Figure (C) is a perspective view (a
) is a sectional view taken along line BB' of FIG. 3 in the diagram
3 is an n''-1nP substrate, 34 is an n-1np buffer layer,
35 is a 1-1nGaASP light absorption layer, 36 is a leaf diffusion region, 37 is an n-1nP window layer, 38 is a 5i3Na insulating film, 3
9 is an upper electrode, 40 is a lower electrode, 41 is a non-reflective coating film, 42 is an incident light, and 43 is an n-1nP upper layer. The leaf diffusion region 36 is composed of the n-1nP upper layer 43 and the n-
They are formed in each part of the 1nP window layer 37. Further, 44 indicates a light receiving portion of the giant 1nGaAsP light absorption layer 35 which forms a depletion layer by applying a reverse bias to the device and actually receives light.

However, in this edge-light receiving type photodiode, the incident light 42 incident through the optical waveguide 16 is transmitted through the n-1nP window layer 37.
The light receiving section 44 spreads by the radiation angle of the waveguide 16.
The disadvantages are that the coupling efficiency to the photoreceptor decreases and the light-receiving sensitivity tends to deteriorate. In other words, in order to guarantee the light-receiving sensitivity of an edge-receiving photodiode with such a window, the length of the window must be made as short as possible, and extremely advanced manufacturing technology is required to control the length of the window. was needed. Therefore,
There was a problem that the device cost was high.

An object of the present invention is to solve the problem that the light receiving sensitivity decreases due to an increase in the length of the window in an edge-receiving photodiode having a window. Receives sufficient light entering from the end of the optical waveguide,
The object of the present invention is to provide a new structure of an edge-receiving photodiode that achieves high light-receiving sensitivity and high yield rate.

[Means for solving problems]

The present invention provides a semiconductor optical waveguide comprising a conductive type cladding part and a conductive type core part having a composition having a forbidden band width smaller than the forbidden band width of the cladding part and larger than the energy corresponding to the wavelength of incident light. a conductive type light absorption part embedded in the core part and having a composition having a forbidden band width smaller than the energy corresponding to the wavelength of the incident light, and a depletion region formed in at least a part of the light absorption part; A conductivity type region formed in a part of the core part and cladding part on one side with respect to the light absorption part so that the boundary thereof is not exposed to the end of the waveguide, and a pair of electrodes. ≧

A feature of the present invention is that a heterostructure optical waveguide is formed as a window portion at both ends or one side (the side where light enters) of the light receiving portion, and is made of a core portion and a cladding portion made of the same type of semiconductor material as the light receiving portion. This is because we have established the following.

FIG. 1 shows the basic structure of an edge-light receiving type photodiode according to the present invention. Figure (a) is a perspective view, Figure (b) is a cross-sectional view taken along line AA' in perspective view (a), where 46 is a lower cladding layer, 47 is a core layer, and 48 49 is a light absorption layer, 49 is an upper cladding layer, 50 is a p-diffusion region for forming a pn junction, and 51 is a light absorption layer, which forms a depletion layer by applying a reverse bias to the element, and actually A light receiving section 52 that receives light is incident light.

Here, the core layer 47 has a smaller forbidden band width, that is, a larger refractive index, than the lower cladding layer 46 and the upper cladding layer 49. These three layers have a forbidden band width larger than the energy corresponding to the incident light wavelength, so the incident light 52
The planar waveguide is transparent to the outside. Also,
The light absorption layer 48 is embedded in the core layer 47, and its forbidden band width is a value smaller than the energy corresponding to the wavelength of the incident light. That is, the core layer 47 forms a core part,
The lower cladding layer 11.6 and the upper cladding layer 49 form a cladding section (in this configuration example, a planar waveguide consisting of the core layer and cladding layer is shown as an optical waveguide section; (This includes, but is not limited to, a channel waveguide in which the core portion is rectangular and is surrounded by a cladding portion.) The incident light 52 is guided by the planar waveguide to the light receiving section and is received by the light receiving section 51 . A conventional edge-light receiving type photodiode has a structure in which a window layer made of a single semiconductor material is provided at both ends of a light-receiving portion, and this window layer does not have the function of guiding light.

In contrast, in the present invention, a waveguide structure having a hair structure is provided as the window portion.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Second
The figure shows a 1nG wavelength 1.3 band end-receiving type optical waveguide having a Brener waveguide structure consisting of a core layer made of a semiconductor material and cladding layers above and below the core layer at both ends of the light receiving section.
FIG. 2 is a diagram for explaining the aAsP pin photodiode, where (a) is a perspective view, and (b) is a perspective view of the AAsP pin photodiode.
- A cross-sectional view taken along line A', Figure (C) is the same figure (a
) is a cross-sectional view taken along line B-8' in FIG. In the figure, 53 is an n-1nP substrate, 54 is an n-1nP lower cladding layer (7 buffer layers), and 55 is n-InGaAsP.
Lower core layer, 56 1-1nGaAsρ light absorption layer, 57
is n-1nGaAs that protects the InGaAsP light absorption layer.
P protective layer, 58 is n-InGaAsP upper core layer, 59
is an n-1nP upper cladding layer, 60 is a Si, 3N4 insulating film, 61 is an upper electrode, 62 is a lower electrode, 63 is a non-reflection coating film, 64 is a p-diffusion region, 65 is a light receiving part,
Reference numeral 66 indicates an optical waveguide, and reference numeral 67 indicates incident light.

In the optical waveguide 66 (Z direction thickness 5 to 15), n-I
The nGaAsP upper core layer 58 and the lower core layer 55 are used as core layers, the n-1nP upper cladding layer 59 is used as the upper cladding layer, and the n-InP lower cladding layer (buffer layer) 54.
A planar waveguide is formed with the lower cladding layer (see figure (d)). Also, inside the device, InGaA
sP light absorption layer 56 light absorption layer end 6sP lower core Pji55
A planar waveguide is formed with the InGaAsP protective layer 57, the TnGaAsP upper core layer 5, the upper core layer 58n-1nP lower cladding layer (buffer '1l) 54, and the n-InP cladding layer 59 as cladding (see Figure (C)). The structure of the photodiode of this example is shown in FIG. 2(b), in which an n-1n layer with a chirelia density of 10''/c-m' is placed above an n''-InP substrate 53 with a carrier density of 10+8/c-at'.
P lower cladding layer (buffer layer) 54 (3uR thickness) n-InGaAsP lower core layer 55 with carrier density 1017/cm" (2 cap thickness at the center of the element, optical waveguide 6
6, it is thinner due to etching)
1-1 n GaAsP light absorption layer 56 (2 cm thick) with a chytria density of 10/cvl', n- with a chytria density of 10+6/d
InGaAsP protective layer 57 (1 gath thickness), carrier density 1
016/cm' n-InGaAsP upper core layer 58 (2 thick at the center of the device, 5 layers M thick at the optical waveguide 66), n-1 nP upper cladding layer 59 (3IiR thick) with chitria density 1016/cm' by laminating n-In
P cladding layer 59 and n-InGaAsP upper core layer 58
This structure has a p- diffusion region 64 having a chirelia density of 10'8/cil' in a part of the n-InGaAsP protective layer 57. Here, InGaAsP light absorption layer 56 light absorption layer end 61
．． 551a, InO, 590, 410, 92PO,
08 mixed crystal ratio, and n-InGaGaA
s AsP upper core layer 58, lower core layer 55, and protective layer 57 have a light absorption edge of 1.05za, and are made of InGaO,8
A mixed crystal ratio of 90,1 10,2S PO,75 was used.

As Therefore, the incident light 67 of the 1.3-layer M band is transmitted to the optical waveguide 66, where the core portion has the optical absorption edge LO5 and the band 0InGaAsP.
The cladding part is made of InP with a light absorption edge of 0°92
Since the light is formed by the InGaAsP light absorption layer 56, the light propagates through the optical waveguide without absorption, and the light absorption edge 6 of the InGaAsP light absorption layer 56 is 1.55 m.

Furthermore, n-InP is used to protect the top surface of the device and to electrically insulate it.
A 5L3Na insulating film 60 is formed on the upper part of the upper cladding layer 59 and at the end of the p- diffusion region 64.

An upper electrode 61 of Au--Zn is provided above the p- diffusion region 64, including a part of the 3N4 insulating film 60. Also n+-In
An Au-3n lower electrode 62 is provided on the bottom surface of the P substrate 53. A non-reflective coating film 63 is deposited on the side where the incident light 67 is incident. n-InGaAsP of optical waveguide 66
The refractive index of the upper and lower core layers 55.58 is Ns The refractive index of air is N
If a(=1), then (Na-Ns) the film thickness with a refractive index value of 0.5 at 0°5 is λ/(4・(Na-Ns))
It is optically known that when a film is added, the reflectance can be minimized. Here, λ is the wavelength of the incident light. In manufacturing this device, since it is used at a wavelength of 1.31, the S0A film with a refractive index of 1.789 is used at a wavelength of approximately 0.182.
It was deposited to a thickness of a. The structure of the p-diffusion region 64 formed by diffusing Zn is to diffuse Zn over the entire surface of the n-1nGaAsP light absorption layer 56 as shown in Figure (C) in order to minimize the junction capacitance caused by the pn junction. Rather, the width was kept to the minimum necessary to sufficiently receive the light that passed through the optical waveguide section. Specifically, it was made 20m wide. In addition, regarding the depth direction and the Y direction), the interface of the p-diffusion region 64 is n-1
It was made to coincide with the top surface of the nGaASP light absorption layer.

Next, the effect will be explained. The incident light 67 passes through the non-reflection coating film 63 and the optical waveguide section 66 and is coupled to the light receiving section 65, and then propagates therein while being gradually absorbed. Light reception is performed only in the light receiving portion 65 of the light absorption layer 56, which is a depletion region formed by a pn junction. The optical waveguide section 66 is transparent to incident light in the 1.3 band, and the light is efficiently guided to the light receiving section 65.
In the light receiving section 65, the electron-hole pairs emitted by the light become a photocurrent and are detected as an electrical signal.

Figure 3 shows the ideal state when the length of the light receiving section 65 is changed (
Calculated light sensitivity (solid line) when all electron-hole pairs generated by light passing through the light absorption part are converted into photocurrent (solid line) and that of a conventional edge-sensing photodiode with a window part. The variation value of the light receiving characteristics (measured value, indicated by diagonal line P1 in the figure) and the variation value of the present invention (measured value, indicated by diagonal line P2 in the figure) are shown. The light receiving efficiency of each measured value is lower than the calculated light receiving efficiency, but this is mainly due to the fact that some of the electron-hole pairs generated in the light receiving section recombine and do not contribute to the photocurrent. The light-receiving sensitivity of a normal planar photodiode is about 80%. It has been found that, compared to the edge-light receiving type photodiode having a window shown in the figure, the present invention has a characteristic of having small variations in device characteristics and saturating at a high light receiving efficiency (0.6 to 0.7 A/W). In other words, it can be seen that the yield rate is improved. The length of the light receiving section is determined by the capacitance due to the pn junction formed by the p-diffusion region 64.
It is proportional to the length of the light receiving section 65. For this reason, the light receiving section 6
Increasing the length of 5 deteriorates the response speed characteristics of the element. Therefore, this device was fabricated with the shortest length of the light receiving section 65 at which saturation of the light receiving efficiency occurs with respect to the length of the light receiving section 65, 120 cm, and the pn junction capacitance was 1.51) F (reverse bias 10 V). Package 16 has a capacitance of 1flo, 5pF, and 50Ω
The transmission system also achieved high-speed response of 1.5 GHz.

Next, the manufacturing method will be described.

On the (100) plane n''-1nP substrate 53, an n-InP lower cladding layer (buffer layer) 54 and an n-1nGaAsP lower core layer 55.1-
An absorption layer 56 and an n-1nGaAsP protective layer 57 are laminated on the 1nGa8sP layer. Next, in order to form the optical waveguide 66, the above shrimp film is etched along the <110> direction using an etching solution (potassium dichromate + acetic acid + water).
A groove reaching the lower core layer 55 is created. Next, this groove is filled with an n-InGaAsP upper core layer 58 by liquid phase epitaxial method, and an n-1nP upper cladding layer 59 is roughly laminated. Next, a 5L3N4 insulating film 60 is deposited on the top surface of the device by the CVD method to form a 5L3N4 insulating film 60 as shown in FIGS.
A 3Na insulating film 60 is formed using a photoresist mask pattern and a buffered hydrofluoric acid etching solution. This 5j3Na insulating film 60 is ultimately used as an electrical insulating film to prevent voltage from being applied to the end of the element, but is also used as a mask for forming the p- diffusion region 64 at the same time. The 5i3Na insulating film 60 is formed so as to cover the end of the light receiving section 65 in consideration of the expansion length of Zn. After forming the 5L3Na insulating film 60, the device is vacuum sealed in a glass tube containing Zn and P, and Zn is thermally diffused in an electric furnace. During this step, the base diffusion layer formed on the bottom of the 1nP substrate 53 by Zn diffusion is removed by polishing.

Next, Au--Zn is deposited on the top of the element to form the top electrode 61. In order to align the core 17 of the optical waveguide 16 shown in FIG. 6 with the light receiving section 65, if necessary, the Au--Zn electrode is further plated with Au to a desired thickness by a plating method. (With the upper electrode 61 facing downward, the optical waveguide 16
(This is for direct bonding to the end face of the element.) Next, Au-8n is vapor deposited on the lower part of the element to form a lower part 1wA62.

Next, the optical waveguide section 66 is cut into pieces by cleavage. The element is also cut into hybrid fiber widths (usually 50 to 100 degrees) by cleavage in the Y direction. Next, an SLO film is deposited on the input light side by vapor deposition.

Through the above steps, an edge-receiving photodiode having an optical waveguide can be manufactured.

As shown in FIG.
As a conventional method, the end surface direct bonding method described above is used.

In the above embodiment, the edge-receiving type 1nG with a wavelength of 1.3° is used.
Although the n-type as the first conductivity type and the p-type as the second conductivity type have been described for the aASP pin photodiode, the present invention is not limited to this.
The conductivity type may be P type, and the second conductivity type may be n type.Furthermore, an edge-lighting 1nGaAsP avalanche A diode, an edge-lighting pin photodiode and an edge-lighting avalanche photodiode using GaAs-based semiconductor materials may be used. can also be produced, and the wavelength band is not limited to 1.3 myo.

In addition, the structure of the optical waveguide can be not only a Brener waveguide but also a channel waveguide, and the manufacturing method is not limited to liquid phase epitaxial method [but is not limited to metal organic vapor phase epitaxy].
MOCVD), molecular beam epitaxy cell method, etc. can also be used.

〔Effect of the invention〕

As explained above, the edge-light receiving type photodiode according to the present invention includes a cladding portion having a larger forbidden band width than the light receiving portion at the end of the light receiving portion made of a semiconductor material on the light incident side. Since the heterostructure optical waveguide consisting of the core part is provided as a window layer, incident light can be efficiently introduced from the element end to the light receiving part, and a highly sensitive edge-receiving photodiode can be stably manufactured. Therefore, the processing accuracy with respect to the length of the window layer is significantly relaxed, so the yield is significantly improved, and a low-cost edge-receiving photodiode can be provided.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are diagrams showing the basic structure of an edge-light receiving type photodiode according to the present invention, in which FIG. 1(a) is a perspective view, and FIG. 1(b) is a perspective view. (a) (7)
There is a sectional view taken along the line AA'. 2(a) to 2(d) are diagrams showing an embodiment of the present invention, in which FIG. 2(a) is a perspective view, and FIG. 2(b) is a diagram illustrating an embodiment of the present invention. 'Line view new surface view,
Figure 2(c) is a sectional view taken along line B-8' of Figure 2(a),
Figure (d) is a sectional view taken along the line c-c' of Figure 2 (a). FIG. 3 is a diagram for explaining the present invention in detail, and is a diagram showing variations in the characteristics of a conventional edge-receiving photodiode having a window portion and variations in the characteristics of the present invention. FIG. 4 is a configuration diagram of a conventional planar photodiode. FIGS. 5(a) and 5(b) are diagrams showing a method of hybrid integration of planar photodiodes. Figure 6 (a
). (b) is a diagram showing a method of hybrid integration of edge-light receiving type photodiodes by direct bonding. FIG. 7 is a configuration diagram of a conventional edge-receiving photodiode. FIGS. 8(a) to 8(C) are diagrams showing the configuration of a conventional edge-receiving photodiode having a window portion, in which FIG. 8(a) is a perspective view, and FIG. 8(b) is a perspective view of an Figure (a) A-A'
8(C) is a sectional view taken along line BB' in FIG. 8(a). 46... Lower cladding layer, 47... Core layer, 48.
...Light absorption layer, 49... Upper cladding layer, 50...
p-diffusion region, 51... light receiving section, 52... incident light, 53... n''-1nP substrate, 54... n-InP
Lower cladding layer (buff 7B), 55-n-1n
GaAsPT core layer, 56...1-1nGaAs
P light absorption layer, 57 ・n-1nGaAsP protective layer, 58
-n-1nGaAsP upper core layer, 59 ・n-1nP
Upper cladding layer, 60...Si3N4 insulating film, 61.
...Top electrode, 62...Bottom electrode, 63...Non-reflection coating film, 64...p-diffusion region, 65...
Light receiving section, 66... Optical waveguide, 67... Incident light. Figure 3 Figure 4 °゛-°・5 9.・, -4,;:j゛,2,,:f':,
4th knife - Figure 5 (a) (b)

Claims (1)

[Scope of Claims] A semiconductor optical waveguide comprising a conductive type cladding part and a conductive type core part having a composition having a forbidden band width smaller than the forbidden band width of the cladding part and larger than the energy corresponding to the wavelength of incident light. A conductive type light absorption part embedded in the core part and having a composition having a forbidden band width smaller than the energy corresponding to the wavelength of the incident light, and a depletion region formed in at least a part of the light absorption part. , a conductivity type region formed in a part of the core part and cladding part on one side with respect to the light absorption part so that the boundary thereof is not exposed to the end of the waveguide, and a pair of electrodes. An edge-receiving photodiode featuring: