JP2006245432A - Photodiode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photodiode which can restrict trailing caused by light injected between a photosensitive part and a diffusion shielding region. <P>SOLUTION: A passivation film 15 is provided on a major surface 13a of a semiconductor region 13. A reflection film 17 has a reflectance which is larger than the reflectance of the passivation film 15, and is provided on the major surface 13a of the semiconductor region 13. A second conductivity type semiconductor region 29 is provided apart from a second conductivity type semiconductor region 27 in a periphery of the second conductivity type semiconductor region 27. The second conductivity type semiconductor region 27 appears in a first area 14a of the major surface 13a. The second conductivity type semiconductor region 29 appears in a second area 14b surrounding the first area 14a of the major surface 13a. The second conductivity type semiconductor region 29 appears in the side surface 13b of the semiconductor region 13. The reflection film 17 is positioned on a third area 14c positioned between the first area 14a and the second area 14b. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photodiode.

Patent Document 1 describes a photodiode chip. This photodiode chip has a p-type anode region provided in the epitaxial layer and a p-type region provided around the anode region. The first pn junction region is formed at the interface between the p-type anode region and the epitaxial layer. The second pn junction region is formed at the interface between the p-type region and the epitaxial layer. The first pn junction region is a light receiving portion, and an electrode for outputting a photocurrent is provided thereon. There is no electrode on the second pn junction region. The second junction region reaches the end face of the photodiode chip. Carriers generated by light incident on the periphery of the first light receiving region disappear in the vicinity of the interface of the second pn junction or the portion exposed at the chip end surface. For this reason, the tailing phenomenon is suppressed, and the optical response speed of the photodiode chip is improved.
JP 2002-57363 A

In such a photodiode chip, the signal light for optical communication is incident not only on the light receiving unit but also in a region other than the light receiving unit. Although light incident on a region other than the light receiving portion also generates an electron-hole pair, this carrier is constituted by a diffusion shielding region (for example, p ⁺ region) provided so as to surround the periphery of the light receiving portion. Recombination occurs in the second pn junction region exposed at the end face. As a result, the carrier is prevented from flowing into the light receiving unit, and the output signal is prevented from being skirted.

  However, according to the inventor's observation, the tailing cannot be sufficiently reduced by this alone, and a minute tailing remains. This tailing becomes apparent particularly when a high-speed response (for example, a high-speed response of 1 GHz or higher such as 2.5 GHz or 10 GHz) is required.

As a result of studying this tailing, it was found that light is incident on the window layer between the light receiving portion made of p ⁺ semiconductor and the diffusion shielding p ⁺ region provided around the light receiving portion. In this photodiode, the light receiving portion and the p ⁺ region are formed by a single impurity introduction step using a mask for separating the two p ⁺ regions. That is, there is a gap in the window layer corresponding to the width of the mask between the light receiving portion and the p ⁺ region. The light incident on the gap also generates electron-hole pairs, and the carriers are diffused and flow into the light receiving portion, and are detected as a photocurrent as a result. The inventor has found that this extra photocurrent flowing into the light receiving portion is observed as a trailing component.

The mask needs to have a width of at least about 10 μm. This width is determined so that the depletion layer does not reach the diffusion shielding p ⁺ region when the bias voltage is applied to the light receiving portion and the depletion layer expands. When the depletion layer of the light receiving unit reaches the surrounding p ⁺ region, carriers flow from the diffusion shielding p ⁺ region to the light receiving unit. The light receiving portion and the diffusion shielding p ⁺ region are short-circuited, and current leaks through the pn junction exposed on the chip end face.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a photodiode capable of reducing tailing caused by light incident between a light receiving portion and a diffusion shielding region.

  One aspect of the present invention relates to a photodiode for receiving signal light within a predetermined wavelength band. The photodiode includes (a) a light receiving layer made of a first III-V compound semiconductor provided on a first conductivity type semiconductor substrate, and a second III-V provided on the light receiving layer. A semiconductor region having a main surface including a window layer made of a compound semiconductor; (b) a passivation film provided on the main surface of the semiconductor region; and (c) a reflectance greater than the reflectance of the passivation film. A reflective film provided on the main surface of the semiconductor region, and the semiconductor region includes a first second conductivity type semiconductor region provided in the light receiving layer and the window layer; One or a plurality of second second conductivity types provided in the light receiving layer and the window layer and spaced from the first second conductivity type semiconductor region around the first second conductivity type semiconductor region A semiconductor region, the first second conductivity type The conductor region is provided in a first area of the main surface, and the second second conductivity type semiconductor region is provided in a second area surrounding the first area of the main surface, The second second conductivity type semiconductor region is provided on a side surface of the semiconductor region, and the reflective film is located on a third area located between the first area and the second area. is doing.

  According to this photodiode, light incident toward the first second conductivity type semiconductor region in the first area generates a signal current. The light incident toward the second second conductivity type semiconductor region in the second area generates an electron hole pair near the pn junction of the second second conductivity type semiconductor region. Disappears on the side surface of the semiconductor region where the second second conductivity type semiconductor region appears without flowing into the first second conductivity type semiconductor region. For this reason, the incident light toward the second second-conductivity-type semiconductor region does not cause the tail of the photocurrent from the photodiode. Further, the light traveling toward the third area in the gap between the first second conductivity type semiconductor region and the second second conductivity type semiconductor region is reflected by the reflective film and does not substantially enter the semiconductor region. Therefore, it does not contribute to the photocurrent from the photodiode. Therefore, tailing caused by light traveling toward the third area is reduced.

  In the photodiode according to the present invention, the reflectance of the reflective film is preferably 90% or more in the predetermined wavelength band. If the reflectance of the reflective film is 90% or more, a photodiode suitable for the transmission rate of 1.3 μm band and 1.55 μm band optical communication is provided.

  In the photodiode according to the present invention, the main surface has a fourth area extending along an edge of the semiconductor region, and the second second conductivity type semiconductor region is provided in the fourth area. Preferably, the passivation film and the reflective film are provided in an area inside the fourth area.

  According to this photodiode, in order to manufacture a photodiode chip from a wafer, a part or all of the fourth area from which the passivation film is removed can be used as a scribe region. The light incident on the fourth area of the photodiode generates an electron-hole pair in the vicinity of the junction of the second second-conductivity-type semiconductor region. Do not flow into.

  In the photodiode according to the present invention, it is preferable that the passivation film includes a silicon nitride film that covers a pn junction in the main surface of the semiconductor region. Since the junction is covered with the silicon nitride film, a leakage current that may be generated on the surface of the window layer can be reduced.

  In the photodiode according to the present invention, the reflective film is formed of a dielectric multilayer film provided on the passivation film. When a dielectric multilayer film is used, a reflective film having a high reflectance can be obtained.

  In the photodiode according to the present invention, the dielectric multilayer film may include an alumina layer and an amorphous silicon layer, and the alumina layer and the amorphous silicon layer may be alternately arranged. According to this dielectric multilayer film, it is possible to provide a reflective film that exhibits a reflectance of 90% or more in a predetermined wavelength range.

  In the photodiode according to the present invention, the light receiving layer may be made of an InGaAs semiconductor, and the window layer may be made of an InP semiconductor. A photodiode suitable for optical communication in the 1.55 μm band is provided.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, an object of the present invention is to provide a photodiode that can reduce tailing caused by light incident between a light receiving portion and a diffusion shielding region.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, embodiments according to the photodiode of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

(First embodiment)
FIG. 1 is a drawing showing a photodiode according to a first embodiment. The photodiode 11 includes a semiconductor region 13, a passivation film 15, and a reflective film 17. The semiconductor region 13 includes a light receiving layer 21 and a window layer 23. The light receiving layer 21 is provided on the first conductivity type semiconductor substrate 25 and is made of the first III-V compound semiconductor. The window layer 23 is provided on the light receiving layer 21 and is made of a second III-V compound semiconductor having a forbidden band width larger than that of the first III-V compound semiconductor. The passivation film 15 is provided on the main surface 13 a of the semiconductor region 13. The reflective film 17 has a reflectance higher than that of the passivation film 15 and is provided on the main surface 13 a of the semiconductor region 13. The semiconductor region 13 includes a first second conductivity type semiconductor region 27 and one or a plurality of second second conductivity type semiconductor regions 29. The first second conductivity type semiconductor region 27 is provided in the light receiving layer 21 and the window layer 23. The second second conductivity type semiconductor region 29 is provided in the light receiving layer 21 and the window layer 23 around the first second conductivity type semiconductor region 27 so as to be separated from the first second conductivity type semiconductor region 27. ing. The first second conductivity type semiconductor region 27 appears in the first area 14a of the main surface 13a. The second second conductivity type semiconductor region 29 appears in the second area 14b surrounding the first area 14a of the main surface 13a. The second second conductivity type semiconductor region 29 appears on the side surface 13 b of the semiconductor region 13. The reflective film 17 is located on the third area 14c located between the first area 14a and the second area 14b.

FIG. 2A is a diagram showing the operation of the optical communication photodiode for receiving signal light within a predetermined wavelength band. According to the photodiode 11, the light L1 incident on the first second conductivity type semiconductor region 27 in the first area 14a is signal current in the vicinity of the junction J1 of the first second conductivity type semiconductor region 27. Is generated. The light L2 incident on the second second conductivity type semiconductor region 29 in the second area 14b generates electron-hole pairs in the vicinity of the junction J2 of the second second conductivity type semiconductor region 29. This electron-hole pair does not flow into the first second conductivity type semiconductor region 27 but disappears on the semiconductor region side surface 13b where the second second conductivity type semiconductor region 29 appears. For this reason, the light L2 (incident toward the second second conductivity type semiconductor region 29) does not cause tailing of the photocurrent from the photodiode 11. Further, the light L3 directed to the third area 14c in the gap between the first second conductivity type semiconductor region and the second second conductivity type semiconductor region is reflected by the reflection film 17 on the passivation film 15 and reflected. Since it becomes light _LR , it does not contribute to photocurrent. For this reason, the light L3 (toward the third area 14c) does not cause a tailing of the photocurrent from the photodiode 11.

  FIG. 2B is a diagram showing the operation of the optical communication photodiode having a structure different from that of the photodiode according to this embodiment. The configuration of this photodiode will be briefly described. In this photodiode 40, the light receiving layer 41 and the window layer 43 are provided on the first conductivity type semiconductor substrate 25, and are made of first and second III-V compound semiconductors, respectively. The passivation film 45 is provided on the window layer 43. The first second conductivity type semiconductor region 47 and the second second conductivity type semiconductor region 49 are provided in the light receiving layer 41 and the window layer 43. According to the photodiode 41, the light L5 incident on the first second conductivity type semiconductor region 47 generates a signal current in the vicinity of the junction J3 of the first second conductivity type semiconductor region 47. The light L6 incident on the second second-conductivity-type semiconductor region 49 generates an electron-hole pair near the junction J4 of the second second-conductivity-type semiconductor region 49. It does not flow into the first second conductivity type semiconductor region 47. Further, a part of the light L7 directed to the passivation film 45 in the gap between the first second conductivity type semiconductor region 47 and the second second conductivity type semiconductor region 49 is transmitted through the passivation film 45, and the light receiving layer Electron-hole pairs are generated in the vicinity J5 of the junction 41 and the window layer 43. A part of this electron-hole pair flows into the first second conductivity type semiconductor region 47, and as a result, a tailing occurs in the photocurrent.

  Referring again to FIG. 1, the photodiode 11 includes a first electrode 37 (for example, an anode electrode) connected to the second conductivity type semiconductor region 27 and a second electrode 39 formed on the back surface of the semiconductor substrate 25. (For example, a cathode electrode). The photodiode 11 can include an InP buffer layer 35 provided on the semiconductor substrate 25 as necessary.

  In the photodiode 11, the reflective film 17 is preferably made of a dielectric multilayer film provided on the passivation film 15. Further, as the passivation film 15, a silicon nitride film can be used for a diffusion mask. The SiN film preferably functions as a passivation film and reduces current leakage on the surface of the InP window layer. The passivation film including the SiN film can suppress an increase in dark current and can prevent deterioration of the reliability of the photodiode element. In the photodiode 11, the diffusion mask used also as the passivation film 15 is covered with a highly reflective film (HR film) so that the light does not enter the light receiving element even when the highly reflective film is exposed to light.

As shown in FIG. 1, the reflective film 17 includes a dielectric multilayer film composed of an alumina layer 31 and an amorphous silicon layer 33, and the alumina layer 31 and the amorphous silicon layer 33 are alternately arranged. it can. According to this dielectric multilayer film, it is possible to provide a reflective film that exhibits a reflectance of 90% or more in a predetermined communication wavelength band.
As an example, the structure of the dielectric multilayer film sequentially formed on the SiN passivation film includes the following structure Al ₂ O ₃ film: 180 nm
Amorphous silicon film: 90 nm
Al ₂ O ₃ film: 160 nm
Amorphous silicon film: 100 nm
Al ₂ O ₃ film: 180 nm
Can be used.

In the photodiode 11, the reflectance of the reflective film 17 is preferably 90% or more in a predetermined wavelength band including one or a plurality of wavelength components. If the reflectance of the reflective film 17 is 90% or more, a photodiode suitable for a high transmission rate of 1.3 μm band and / or 1.55 μm band optical communication is provided. FIG. 3A and FIG. 3B are diagrams showing an example of a reflection spectrum of a reflective film having a dielectric multilayer structure. As shown in FIG. 3B, according to this reflection spectrum, a reflectance of 90% or more is provided in the wavelength range of 1200 nm to 1400 nm. Since the reflectance is 90% or more, the transmitted light is 10% or less. Compared to the case where there is no reflective film, the amount of incident light can be reduced to one-tenth or less, so that the tailing can be improved by 10 dB or more. An improvement of 20 dB can be obtained by the diffusion shielding structure and 10 dB by the effect of the reflection film, and a total of 30 dB or more can be improved.
In the 1.3 μm band photodiode, for example, a reflectance of 90% or more is preferably provided in a wavelength range of 1250 nm to 1350 nm. In the 1.55 μm band photodiode, for example, it is preferable to provide a reflectance of 90% or more in a wavelength range of 1500 nm to 1600 nm.

  In the photodiode 11, the passivation film 15 appears on the main surface 13 a in the semiconductor region 13, and preferably covers the junction J <b> 0 composed of the second conductivity type semiconductor region 27 and the window layer 23 to protect the junction. If the junction is covered with a silicon nitride film, leakage current that may be generated on the surface of the window layer 23 can be reduced.

  In the photodiode 11, the passivation film 15 and the reflective film 17 are not in the fourth area 14 d extending along the edge 13 c of the semiconductor region 13, but the second conductivity type semiconductor region 29 appears in the fourth area 14 d. Yes. According to this photodiode, in order to manufacture the chip of the photodiode 11 from the wafer, a part of the fourth area 14d from which the passivation film 15 is removed can be used as a scribe region. The light incident on the fourth area 14 d of the photodiode 11 generates an electron-hole pair in the vicinity of the junction of the second conductivity type semiconductor region 29, but the electron hole pair is generated in the second conductivity type semiconductor region 27. Do not flow into.

  In the photodiode 11, the light receiving layer 21 can be made of an InGaAs semiconductor, and the window layer 23 can be made of an InP semiconductor. A photodiode suitable for 1.3 μm band and 1.55 μm band optical communications is provided.

With reference to FIGS. 4A to 4D, the fabrication of an example of a photodiode will be described. As shown in FIG. 4A, an n-type InP buffer layer 63 (Si-doped, thickness 2 μm) is formed on an n-type InP wafer (S-doped, thickness 350 μm, carrier concentration 3 × 10 ¹⁸ cm ⁻³ ) 61. , Carrier concentration 1 × 10 ¹⁷ cm ⁻³ ), non-doped InGaAs light receiving layer 65 (thickness 3 μm, carrier concentration 1 × 10 ¹⁵ cm ⁻³ ), non-doped InP window layer 67 (thickness 1.5 μm, carrier concentration 1 × 10). ¹⁵ cm ⁻³ ) is epitaxially grown by metal organic vapor phase epitaxy (MOVPE).

As shown in FIG. 4B, a SiN film 71 (thickness 60 nm) is formed by plasma CVD to form a passivation film, and the entire surface of the semiconductor region 69 is covered. Thereafter, the dielectric multilayer film 73 is coated on the entire surface of the SiN film 71 by vapor deposition. The dielectric multilayer film 73 is
Al ₂ O ₃ film: 190 nm
Amorphous silicon film: 90 nm
Al ₂ O ₃ film: 260 nm
Amorphous silicon film: 100 nm
Al ₂ O ₃ film: 160 nm
Consists of.

As shown in FIG. 4C, a mask 75 is formed using a photolithography method, and a pattern is formed on the dielectric multilayer film 73 and the SiN film 71 using the mask 75. The patterned dielectric multilayer film 73a and the SiN film 71a have a band shape (for example, a width of 20 μm) so as to surround the light receiving portion. After removing the mask 75, the dielectric multilayer film 73a and the SiN film 71a are used to selectively diffuse zinc (Zn) in the region having a light receiving diameter of 50 μm and the outer periphery thereof to diffuse with the p-type semiconductor region 81 for light reception. A p-type semiconductor region 83 for shielding is formed. Since the p-type dopant zinc is thermally diffused, the zinc atoms are also diffused in the lateral direction. As a result, as shown in FIG. 4D, the p-type semiconductor regions 81 and p are also formed under the passivation film 71a. A type semiconductor region 83 is formed. Thereafter, the anode electrode 77 and the cathode electrode 79 are formed to complete the photodiode. By setting the reflectance of the reflection film formed of the dielectric multilayer film 73a to 90% or more in a desired wavelength region, a photodiode with a tailing reduced to about one tenth can be obtained.

  As described above, light is incident on the window layer 23 that appears between the second conductive type semiconductor region 27 serving as a light receiving portion and the second conductive type semiconductor region 29 provided outside the second conductive type semiconductor region 27. By blocking, the generation of electron-hole pairs in the first conductivity type region of the window layer 23 is prevented. As a result, it is possible to suppress the minute tailing that is particularly problematic in the response when receiving a high-speed signal of 1 GHz or higher.

  On the other hand, if the entire area outside the first area 14a is covered with a highly reflective film (metal film or dielectric multilayer film) so that light enters only the second conductivity type semiconductor region 27, the second conductivity Even the incident light that does not cause tailing is reflected by the type semiconductor region 29, and unnecessary reflected light increases. As a result, the extra reflected light may be diffusely reflected on the inner wall of the optical fiber or the package and re-enter the light receiving unit. Due to the re-incident light, the photocurrent generated with a delay disturbs the response waveform. In order to prevent this, the reflective area is used only in the area where the second conductive semiconductor region 29 cannot be provided, instead of selectively covering the entire area of the peripheral portion with the light receiving portion selectively left in the semiconductor region. In addition, signal light and noise light are avoided. That is, since the area of several tens of micrometers in the outer peripheral portion in contact with the light receiving portion is covered with the reflective film, disturbance due to irregular reflection is reduced in the response waveform from the photodiode.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

FIG. 1 is a drawing showing a photodiode according to a first embodiment. FIG. 2A is a diagram showing the operation of the optical communication photodiode for receiving signal light within a predetermined wavelength band. FIG. 2B illustrates the operation of the optical communication photodiode having a structure different from that of the photodiode. 3A and 3B are diagrams showing an example of a reflection spectrum of a reflective film having a dielectric multilayer structure. 4A to 4D are diagrams for describing a method for manufacturing a photodiode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Photodiode, 13 ... Semiconductor region, 13a ... Semiconductor region main surface, 13b ... Semiconductor region side surface, 13c ... Semiconductor region edge, 14a ... 1st area, 14b ... 2nd area, 14c ... 3rd area, 14 ... 4th area, 15 ... Passivation film, 17 ... Reflective film, 21 ... Light receiving layer, 23 ... Window layer, 25 ... First conductivity type semiconductor substrate, 27 ... First second conductivity type semiconductor region, 29 ... second second conductivity type semiconductor region, 35 ... InP buffer layer, 37 ... first electrode, 39 ... second electrode, J0, J1, J2, J3, J4, J5 ... junction, L1 ... incident light , L2 ... incident light, L3 ... light, L5 ... incident light, L6 ... incident light, L7 ... light, 40 ... photodiode, 41 ... light receiving layer, 43 ... window layer, 45 ... passivation film, 47, 49 ... Second conductivity type semiconductor Pass

Claims (7)

A photodiode for receiving signal light in a predetermined wavelength band,
A first conductive type light-receiving layer provided on the first conductive type semiconductor substrate and made of the first III-V compound semiconductor; and a second III-V compound semiconductor provided on the light-receiving layer. A first conductivity type window layer comprising a semiconductor region having a major surface;
A passivation film provided on the main surface of the semiconductor region;
A reflection film having a reflectance greater than that of the passivation film and provided on the main surface of the semiconductor region;
The semiconductor region includes a first second conductivity type semiconductor region provided in the light receiving layer and the window layer, and the first second conductivity type semiconductor around the first second conductivity type semiconductor region. One or a plurality of second second-conductivity-type semiconductor regions provided in the light-receiving layer and the window layer apart from a region,
The second second conductivity type semiconductor region is provided on a side surface of the semiconductor region;
The first second conductivity type semiconductor region is provided in a first area of the main surface;
The second second conductivity type semiconductor region is provided in a second area surrounding the first area of the main surface;
The said reflecting film is a photodiode located on the 3rd area located between the said 1st area and the said 2nd area.   The photodiode according to claim 1, wherein the reflectance of the reflective film is 90% or more in the predetermined wavelength band. The main surface has a fourth area extending along an edge of the semiconductor region;
The second second-conductivity-type semiconductor region is provided in the fourth area;
The photodiode according to claim 1, wherein the passivation film and the reflective film are provided in an area inside the fourth area.   4. The photodiode according to claim 1, wherein the passivation film includes a silicon nitride film that covers a pn junction in the main surface of the semiconductor region. 5.   3. The photodiode according to claim 1, wherein the reflection film is made of a dielectric multilayer film provided on the passivation film. 4. The dielectric multilayer film includes an alumina layer and an amorphous silicon layer,
The photodiode according to claim 5, wherein the alumina layer and the amorphous silicon layer are alternately arranged. The light receiving layer is made of an InGaAs semiconductor,
The photodiode according to any one of claims 1 to 6, wherein the window layer is made of an InP semiconductor.

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