JP2008078261A - Semiconductor photodetector and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor photodetector, having a light-receiving layer which provides a wide detecting sensitivity in the long-wavelength zone and suppresses dark current by reducing defect density, and to provide its manufacturing method. <P>SOLUTION: The semiconductor photodetector is provided with an InP substrate 11, an In<SB>x</SB>Ga<SB>1-x</SB>As buffer layer 12 (0≤x≤1) and a light-receiving layer 13 which is positioned on the In<SB>x</SB>Ga<SB>1-x</SB>As buffer layer 12 and contains nitrogen. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor light-receiving element and a method for manufacturing the same, and more specifically to a long-wavelength semiconductor light-receiving element for optical communication and a method for manufacturing the same.

Sensors used for night surveillance cameras and non-destructive inspection of foods use light-receiving elements that can detect near-infrared light. As such a light receiving element, there is one using a lattice-matched InGaAs layer grown on an InP substrate as a light receiving layer, and can detect near infrared light having a wavelength of 0.9 to 1.7 μm. However, it is desirable to detect near-infrared light (wavelength: 2 to 3 μm) in a longer wavelength region for the above-mentioned application. One of these long-wavelength light-receiving elements has been proposed to use a strained InGaAs layer as the light-receiving layer and a strain buffer layer to reduce crystal defects caused by lattice mismatch with the InP substrate ( Patent Document 1). As a light receiving element for detecting long-wavelength near-infrared light, a light receiving layer using GaInNAs has been proposed (Patent Document 2). According to the light receiving element, it is possible to detect light in a long wavelength region.
JP 2002-373999 A JP-A-9-219563

  However, the light receiving element disclosed in Patent Document 1 changes the lattice constant during epitaxial growth even if a strain buffer layer is used for strain relaxation. Therefore, crystal defects are generated during the growth of the strain buffer layer. Can not be avoided. As a result, the dark current and noise increase due to the high crystal defect density, and the sensitivity deteriorates.

On the other hand, the light receiving element disclosed in Patent Document 2 has the following problems. (1); For epitaxial growth of GaInNAs-based films, MBE (Molecular
It is desirable to use a beam epitaxy method. However, the MBE method makes it difficult to grow an epitaxial layer containing P due to the problem of the exhaust system. That is, unless the P compound or the like adhering to the inner wall of the MBE apparatus is removed for each growth, it becomes difficult to control the epitaxial growth so as to be realized repeatedly and stably. Maintenance costs are always increased due to the removal of the P compound and the like.

  (2); For the reason (1) above, an AlInAs layer is often used instead of the InP layer for the buffer layer between the InP substrate and the GaInNAs light-receiving layer. When the MBE method is used, nitrogen, which is one of GaInNAs-based materials, is supplied in the form of plasma when forming the GaInNAs light-receiving layer. Since plasma requires several minutes for generation, it must be generated prior to the growth of the GaInNAs light-receiving layer. This is because the surface of the epitaxial layer formed before the GaInNAs light-receiving layer, for example, the buffer layer, becomes rough as time passes for several minutes. For this reason, it is necessary to generate nitrogen plasma in the excitation cell while the buffer layer serving as the underlayer of the GaInNAs light receiving layer is grown. Even if nitrogen plasma is confined in a cell connected to the growth tank, a normal gate valve or the like cannot prevent a minute leak, and it becomes a large-scale apparatus for complete confinement. That is, when using a normal MBE apparatus, the excited nitrogen leaks into the growth tank. For this reason, the buffer layer is grown in a nitrogen atmosphere, and it is inevitable that nitrogen is mixed therein.

Also, MOVPE (Metalorganic) is used to form GaInNAs layers.
Even when using the Vapor Phase Epitaxy method, ammonia, dimethylhydrazine, etc. can be used to prevent the surface roughness of the buffer layer to form a GaInNAs light-receiving layer without taking time after forming the buffer layer. Since the source gas containing nitrogen atoms is flowed into the growth tank, it is inevitable that nitrogen is mixed into the buffer layer. Even when other film forming methods are used, the buffer layer is similar in that nitrogen is mixed.

  When an AlInAs layer is used for the buffer layer, aluminum nitride (AlN) or the like is formed in the buffer layer due to the mixing of nitrogen, defects are introduced into the epitaxial layer, and the defect density is increased. As a result, high-density crystal defects are inherited also in the GaInNAs layer formed on the buffer layer, and dark current is increased.

  An object of the present invention is to provide a semiconductor light-receiving element having a buffer layer that can form a light-receiving layer with good crystallinity with a high yield, and a method for manufacturing the same, particularly for receiving light in a long wavelength region. An object of the present invention is to provide a semiconductor light-receiving element having a buffer layer that enables a light-receiving layer with a low dark current while containing nitrogen, and a method for manufacturing the same.

The semiconductor light receiving device of the present invention, and the InP substrate, _In x _{Ga 1-x} As buffer layer located on an InP substrate and (0 ≦ x ≦ _1), located in the In _{x Ga 1-x} As buffer layer, And a light-receiving layer of a compound semiconductor containing nitrogen.

  With this configuration, it is possible to solve the problem that has been a major obstacle in the near-infrared light receiving element in the long wavelength region. The problems are (1) adhesion of P to the furnace wall accompanying the growth of the InP layer, and (2) the buffer layer when using the element N used to extend the detection limit of the light receiving layer to the long wavelength region. Two points are the increase in crystal defect density. The problem of (1) is that when an InP layer is used for the buffer layer, P adheres and accumulates on the inner wall (furnace wall) of the MBE device, and P spontaneously ignites when the MBE device is opened to the atmosphere for maintenance or the like. Therefore, it means that large equipment is required for removal. The problem (2) is that, as described above, when forming a compound semiconductor light receiving layer containing nitrogen, it is necessary to excite nitrogen in advance when forming the buffer layer. In the case of an AlInAs buffer layer containing strong Al or the like, nitrogen is mixed into the AlInAs buffer layer to generate a crystal that can be regarded as a foreign substance, which indicates a quality deterioration factor that greatly deteriorates the crystallinity of the buffer layer. The light-receiving layer epitaxially grown on such a buffer layer with poor crystallinity inherits a high crystal defect density from the buffer layer, and the dark current increases.

The above (1) and (2) can be solved by using In _x Ga _1-x As as the buffer layer. Moreover, the detection limit of infrared light can be extended to a long wavelength region by using the light receiving layer as a compound semiconductor containing nitrogen. Of course, the above In _x Ga _1-x As buffer layer is sufficiently useful even if it is used only to solve the P problem of (1). That is, even when the light-receiving layer of the compound semiconductor containing nitrogen is not used, it is sufficiently useful in terms of expanding the degree of freedom in selecting the material of the buffer layer not using P.

In addition, the above light-receiving layer containing nitrogen is formed by using Ga _y In _1-y N _z As _w Sb _1-zw (0 <z ≦ 1, 0 ≦ y ≦ 1, 0 ≦ w <1) or Ga _y In _{1. -y N z As w P 1-} z-w may be formed by (0 <z ≦ 1,0 ≦ y ≦ 1,0 ≦ w <1). With this configuration, the limit on the long wavelength side of detectable infrared light can be further expanded. In particular, when using Ga _y In _{1-y Nz} As _w Sb _1-z-w (0 <z <1, 0 ≦ y ≦ 1, 0 ≦ w <1) containing Sb, the light receiving layer itself is flat. Therefore, the crystallinity of the entire epitaxial stack can be made excellent. Further, in the case of Py-containing Ga _y In _1-y N _z As _w P _1-z-w (0 <z <1, 0 ≦ y ≦ 1, 0 ≦ w <1), it is not as large as the light receiving layer containing Sb. However, the surface flatness can be improved as compared with a GaInNAs light-receiving layer containing no P.

The light-receiving layer side of the In _x Ga _1-x As buffer layer may contain nitrogen. By using the In _x Ga _1-x As buffer layer, nitrogen leaks from the cell for nitrogen excitation without increasing the gate valve of the cell of the MBE device, for example, and the In _x Ga _1-x As buffer layer Even if the portion on the light receiving layer side is mixed with nitrogen, an increase in the crystal defect density of the buffer layer and the light receiving layer can be suppressed as compared with the case where AlInAs is used for the buffer layer. The same applies to film formation by the MOVPE method.

The composition ratio x in the In _x Ga _1-x As buffer layer may be changed in the thickness direction. With this configuration, the fluctuation (undesired) of the lattice constant of the buffer layer due to the mixing of nitrogen into the buffer layer is absorbed by adjusting the composition ratio x, whereby the fluctuation of the lattice constant of the buffer layer can be kept low. The change in the thickness direction of the composition ratio x may be a single step or a plurality of steps, may be linear with a constant gradient, or may be curved. Moreover, the method of the change which combined these may be sufficient.

The lattice constant of the In _x Ga _1-x As buffer layer may be adjusted to be 99.9% or more and 100.1% or less of the lattice constant of the InP substrate. As a result, the lattice constant of the buffer layer is stabilized and the lattice defect density is lowered, so that the crystallinity of the light receiving layer is improved and the dark current can be lowered.

The method of manufacturing a semiconductor light receiving device of the present invention, on an InP _substrate, and forming In _{x Ga 1-x} As buffer layer (0 ≦ x ≦ _1), the In _{x Ga 1-x} As buffer layer, And a step of forming a light-receiving layer of a compound semiconductor.

  With this configuration, since the P compound is not used as a raw material, the yield can be improved. Further, when a light-receiving layer of a compound semiconductor containing nitrogen is used, a buffer layer and a light-receiving layer having excellent crystallinity can be secured, so that dark current can be reduced. In addition, the film forming method or the components of the film forming apparatus may be anything. For example, any film formation method such as the MOVPE method or the MBE method may be used, and the film formation apparatus can be changed according to the film formation method.

Even if the above light-receiving layer is a compound semiconductor layer containing nitrogen, and the In _x Ga _1-x As buffer layer is formed, the buffer layer is exposed to nitrogen prepared for forming the light-receiving layer containing nitrogen. Good. Thereby, after extending the detection limit wavelength of a light reception layer to the long wavelength side, crystallinity can be made favorable and a dark current can be suppressed. That is, it is possible to form a light-receiving layer containing nitrogen using nitrogen excited in a short time after the formation of the buffer layer, and to increase the surface defect density or surface properties due to evaporation of a specific element from the buffer layer. Can be prevented. And with respect to mixing of the above excited nitrogen into the buffer layer, it is preferable to use In _x Ga _1-x As that is highly stable to nitrogen (low in foreign matter formation reactivity) for the buffer layer. Crystallinity can be ensured. The buffer layer and the light receiving layer are assumed to be continuously performed in the same film forming apparatus (furnace), but as described above, what kind of film forming method and film forming apparatus are used. May be.

  According to the present invention, it is possible to provide a semiconductor light receiving element capable of forming a light receiving layer having good crystallinity with a high yield, and in particular, a dark current is small while containing nitrogen for receiving light in a long wavelength region. A semiconductor light receiving element having a light receiving layer can be provided.

  Next, embodiments and examples of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an epitaxial multilayer structure for explaining a semiconductor light receiving element in an embodiment of the present invention. An InGaAs buffer layer 12 is used on the InP substrate 11, a light receiving layer 13 is formed thereon, and a window layer 14 is provided on the light receiving layer 13. When the InGaAs layer 12 is used for the buffer layer, it is not necessary to use P (in the case where InP or the like is used for the buffer layer) which is liable to adhere to the furnace wall, and a compound semiconductor light-receiving layer containing N is formed. In this case, it is not necessary to use Al (when AlInAs or the like is used for the buffer layer), which is likely to cause crystal defects. For this reason, in order to provide a high-quality semiconductor light-receiving element with a high yield, the degree of freedom in selecting a material for the buffer layer can be expanded. In this case, the epitaxial growth method can be any method such as MBE method or MOVPE method.

  FIG. 2 is a diagram showing an epitaxial multilayer structure for explaining a semiconductor light receiving element according to another embodiment of the present invention. Compared to FIG. 1, the buffer layer 12 is different in that there is a layer 12 a containing nitrogen. As described above, the InGaAs layer has a relatively low foreign matter formation reactivity with nitrogen. That is, nitrogen has a low tendency to form a different crystal in the InGaAs crystal by reacting by selecting a specific element from InGaAs having a crystal structure. Therefore, in the case of the MBE method, when the InGaAs buffer layer is formed, N excitation can be started in the N cell without worrying about leakage from the N excitation cell. Even if N in an excited state leaking from the N cell is mixed in the InGaAs buffer layer, the lattice constant of the InGaAs buffer layer is only reduced (a measure for making the lattice constant of the buffer layer constant will be described later). ). Further, in the case of the MOVPE method, at the stage where the InGaAs buffer layer is formed, the material supply valve is switched and the N material starts to flow. As a result, even if nitrogen is mixed into the InGaAs buffer layer, the same as the MBE method Only the phenomenon occurs.

  As shown in FIG. 2, having an N-containing InGaAs buffer layer 12a includes N after the buffer layer is formed on the buffer layer 12 without leaving any time (without the specific element evaporating from the surface). It means that the light receiving layer 13 is formed. This means that the light-receiving layer 13 containing N is formed on the buffer layer 12 with excellent surface flatness, and that the light-receiving layer 13 having excellent flatness and crystallinity is obtained. As a result, the detection limit on the long wavelength side of infrared light can be expanded and dark current can be suppressed. Next, examples of the present invention will be described.

(Example 1)
FIG. 3 is a diagram showing an epitaxial multilayer structure for explaining the semiconductor light receiving element of the example of the present invention in Example 1. In FIG. An epitaxial laminated crystal for a photodiode as shown in FIG. 3 was formed by MBE growth. As the substrate, a 2-inch S-doped InP substrate 11 having a (001) plane was used. Solid Ga, In, Al, As, Si, and ECR nitrogen radicals were used as raw materials for epitaxial growth. The growth temperature of each layer was 470 ° C., and the growth rate was 1.4 μm / hour. As described above, the InGaAs layer 12 was used for the buffer layer. The film thickness of the InGaAs layer 12 was 1.5 μm, and Si was supplied during growth to be n-conductive type. The carrier concentration was 5 × 10 ¹⁶ cm ⁻³ . The composition will be described later.

Were then grown absorption layer 13 made of _{GaInNAs (Ga y In 1-y} N z As w). The film thickness of the light receiving layer 13 was 2.5 μm. Ga composition is 17% (y = 0.17), In composition is 83% (1-y = 0.83), N composition is 10% (z = 0.1), As composition is 90% (w = 0) 9) and lattice-matched to the InP substrate. Doping is not performed. Next, the window layer 14 made of (Al _x In _1-x As) was grown. The film thickness is 0.6 μm, the In composition is 52% (1−x = 0.52), and lattice matching is performed on the InP substrate. In the InGaAs buffer layer 12, an N-containing InGaAs layer 12a is formed on the surface side.

Next, the reason why the N-containing InGaAs layer 12a is formed on the surface side (light receiving layer side) in the InGaAs buffer layer 12 will be described. The InGaAs buffer layer 12 and the GaInNAs light-receiving layer 13 are continuously grown without interruption when the growth is switched from the buffer layer 12 to the light-receiving layer 13 in order to prevent the surface of the epitaxial layer of the InGaAs buffer layer 12 from being rough. For this reason, it is necessary to generate ECR nitrogen radicals used during the growth of the GaInNAs layer 13 during the growth of the InGaAs buffer layer 12. At this time, since nitrogen gas flows into the MBE device, a region of the InGaAs buffer layer 12 that is in contact with the GaInNAs light-receiving layer 13 is grown in a nitrogen atmosphere. Nitrogen is mixed into the crystal, and the N-containing InGaAs layer 12a. Occurs. In this example, as shown in FIG. 4, in the InGaAs buffer layer, N is mixed in a region within 0.2 μm from the interface with the light receiving layer 13. The mixing density of N is about 1.8 × 10 ²⁰ cm ⁻³ , which corresponds to about 0.92% in composition. The unit of N mixing density is the number / cm ³ .

When 0.92% of nitrogen is mixed in InGaAs (In _x Ga _1-x As), the difference in lattice constant from the InP substrate is reduced by about 0.21%. In order to cancel this, the composition of In and Ga in the InGaAs (In _x Ga _1-x As) buffer layer 12 was changed in the thickness direction as shown in FIG. In the InGaAs buffer layer 12a, the In composition is 53% (x = 0.53) and the Ga composition is 47% (1-x = 0.47) in the region not containing nitrogen, and In is contained in the region containing nitrogen. The composition was 55.5% (x = 0.555), and the Ga composition was 44.5% (1-x = 0.445).

  The lattice constant difference Δa / a between the InGaAs buffer layer 12 and the InP substrate 11 was calculated. The outline of the calculation method of Δa / a is as follows. (1) The lattice constant is calculated from the composition of each layer according to Vegard's law. (2) The lattice constant difference Δa / a is calculated from the lattice constant of the buffer layer and the lattice constant of the InP substrate. Δa / a of the InGaAs buffer layer in this example was within ± 0.1% as shown in FIG.

  In addition to the above-described manufacturing flow, the growth was interrupted when the InGaAs buffer layer 12 (including the N-containing InGaAs layer 12a) and the GaInNAs light-receiving layer 13 were grown on the InP substrate 11. Produced. And the photoluminescence was investigated about the epitaxial laminated structure. The photoluminescence spectrum had a peak at a wavelength of 3.0 μm. Accordingly, it was confirmed that the light receiving layer had detection sensitivity up to 3.0 μm.

(Comparative example)
As in the above-described example of the present invention, a photodiode crystal having the epitaxial structure shown in FIG. 6 was grown by MBE growth. The growth conditions are the same as in the example of the present invention except that the InGaAs buffer layer 12 is replaced with the AlInAs buffer layer 112 (as a result, the buffer layer 112 includes the N-containing AlInAs 112a). An InP substrate 111 was used as the substrate, and Al _x In _1-x As was used for the buffer layer 112 as described above. The In composition was 52% (1-x = 0.52). The film thickness is 1.5 μm, and Si is supplied at the time of growth to be of n conductivity type. The carrier concentration was 5 × 10 ¹⁶ cm ⁻³ . Similarly to the example of the present invention, in the AlInAs buffer layer 112, as shown in FIGS. 6 and 7, nitrogen atoms are mixed in a region within 0.3 μm from the interface with the light receiving layer 113. The density of N contamination is about 3.0 × 10 ²⁰ cm ⁻³ and corresponds to about 1.5% in terms of composition. The lattice constant difference Δa / a between the N-containing AlInAs layer 112a and the InP substrate 111 is −0.34% according to the above calculation. Conditions of the light receiving layer 113 and the window layer 114 formed on the light receiving layer 113 were the same as those of the present invention example.

(Measurement of dark current)
A PIN photodiode 10 as shown in FIG. 8 was fabricated using the epitaxial multilayer crystals of the present invention and the comparative example. A method for manufacturing the PIN photodiode 10 will be briefly described. After producing the epitaxial laminated structure of FIG. 3 (invention example) and FIG. 6 (comparative example), a SiN film 18 is formed on the window layer by plasma CVD (PCVD) method, and by ordinary photolithography and etching techniques, A diffusion window or a light receiving portion region for introducing a p-type impurity is opened. Next, using the pattern of this SiN film 18 as a mask, p-type impurity Zn is introduced from the light-receiving portion through the window layer 14 to the GaInNAs light-receiving layer 13, thereby forming the p-type region 15. By forming the p-type region 15, a pn junction is formed in the GaInNAs light receiving layer 13.

  Next, an AR (Anti-Reflection) coat film 17 such as SiON is formed so as to cover the light receiving region of the SiN film 18 and the SiN film 18. Then, using a resist film pattern (not shown), the window layer 14 in the p-type region is etched to form a contact hole (not shown) leading to the GaInNAs light receiving layer 13. Next, an electrode film made of Ti / Pt / Au is formed on the resist film pattern including the contact hole by vapor deposition. Subsequently, the p-part electrode 32 can be obtained by removing the resist film pattern and the electrode film deposited thereon (lift-off). After the epitaxial film is stacked on the first main surface of the InP substrate as described above, the n-part electrode 31 is formed of AuGeNi on the second main surface opposite to the first main surface. The PIN photodiode 10 shown in FIG. 8 can be formed by the above method. The light receiving diameter of the light receiving part was 30 μm.

  The dark current was measured for the photodiode 10 manufactured for the inventive example and the comparative example. The measurement results are shown in FIG. According to FIG. 9, in the photodiode of the present invention, the dark current is reduced by about two orders of magnitude compared to the photodiode of the comparative example. In summary, it is confirmed that the semiconductor light-receiving element of the present invention example in this example can greatly expand the detection sensitivity range to a long wavelength region of 3.0 μm and further suppress dark current. It was.

(Example 2-GaInNAsSb light-receiving layer)
Example 2 is characterized in that the GaInNAs light-receiving layer of Example 1 of the present invention in Example 1 is replaced with a GaInNAsSb light-receiving layer. First, a photodiode crystal having an epitaxial structure as shown in FIG. 10 was grown by MBE growth. The present embodiment is the same as the first embodiment of the present invention in that the InGaAs buffer layer 12 is disposed on the InP substrate 11. The film thickness and doping concentration are the same as in the first embodiment. As shown in FIG. 11, in the InGaAs buffer layer 12, the N-containing InGaAs layer 12 a is formed in the region of 0.35 μm from the interface with the light-receiving layer 13 by mixing N as in the present invention example of Example 1. Yes. The composition of the InGaAs layer not containing N is In 53% (x = 0.53) and Ga 47% (1-x = 0.47). In the N-containing InGaAs layer 12a, In 55.9% (x = 0.559) Ga44.1% (1-x = 0.441). The calculated value of Δa / a with the InP substrate was within ± 0.1% as shown in FIG.

Then, it was grown GaInNAsSb absorption layer _{(Ga y In 1-y N} z As w Sb 1-z-w) 13. For Sb, solid Sb was used as a raw material, the composition was 3% (1-zw = 0.03), and the group III composition was adjusted so as to lattice match with the InP substrate. The film thickness was 2.5 μm. Doping is not performed. Next, an AlInAs window layer 14 was grown. The composition and film thickness are the same as those of the inventive example of Example 1. The RMS roughness of 1 μm square on the surface was improved to 2.0 angstroms as compared with 4.5 angstroms of the epitaxial laminated film for photodiodes of the example of the present invention (GaInNAs light receiving layer) in Example 1, and the flatness was improved. This means that since the GaInNAsSb light-receiving layer 13 is used, the surface properties of the light-receiving layer are improved, and the roughness of the window layer having the light-receiving layer as a base is improved.

  Using this crystal, a PIN photodiode as shown in FIG. 8 was produced. Since the structure is the same as that of the example and comparative example, the description is omitted. When comparing the dark current of the PIN type photodiode, it was found that the dark current was reduced to about 1/5 of the inventive example of Example 1 as shown in FIG. As described above, the surface flatness is improved by adding Sb, and this is an effect of reducing dark current.

  In parallel with the above, an epitaxial multilayer structure was fabricated in which the growth was interrupted when the InGaAs buffer layer 12 (including the N-containing InGaAs layer 12a) and the GaInNAsSb light-receiving layer 13 were grown on the InP substrate 11 separately. When photoluminescence was examined for this epitaxial multilayer structure, the photoluminescence spectrum had a peak at a wavelength of 3.0 μm. As a result, it was confirmed that a light receiving element having detection sensitivity up to a wavelength of 3.0 μm and sufficiently small dark current was realized.

(Example 3-GaInNAsP light-receiving layer)
Example 3 is characterized in that the GaInNAs light-receiving layer of Example 1 of the present invention in Example 1 is replaced with a GaInNAsP light-receiving layer. First, a photodiode crystal having an epitaxial structure as shown in FIG. 13 was grown by MBE growth. Trimethylindium (TMIn), triethylgallium (TEGa), tertiarybutylarsine (TBAs), tertiarybutylphosphine (TBP), dimethylhydrazine (DMHy), and tetraethylsilane (TESi) were used as raw materials.

An InGaAs buffer layer 12 slightly doped with Si is formed on a 2-inch square S-doped n-conducting InP substrate 11, and then a GaInNAsP light-receiving layer 13 (carrier concentration 1 × 10 ¹⁶ cm ⁻³ , 2 μm thickness) slightly doped with Si ), A non-doped InP window layer 14 (1.5 μm thickness) was epitaxially grown by the MOVPE method. The epitaxial growth temperature is 520 ° C.

  As the InP substrate 11, an off-angle substrate inclined by 13 ° in the (100) to (111) direction was used. Further, an N-containing InGaAs layer 12a in which N gradually increases is provided on the light-receiving layer side of the INGaAs buffer layer 12, as shown in FIG. At this time, the In composition in the N-containing InGaAs layer 12a was also gradually increased in accordance with the increasing tendency of the N content so as to lattice match with the InP substrate 11 and the InGaAs buffer layer 12. That is, x was increased linearly with a constant gradient in the N-containing buffer layer 12a along the thickness direction. This is in line with the increase in N content along the same direction. According to the above calculation, the lattice constant difference Δa / a between the InGaAs buffer layer 12 including the N-containing InGaAs layer 12a and the InP substrate 11 is within ± 0.1%. That is, the lattice constant of the InGaAs buffer layer 12 including the N-containing InGaAs layer 12a was 99.9% or less and 100.1% or less of the lattice constant of the InP substrate.

The GaInNAsP receiving layer _{(Ga y In 1-y N} z As w P 1-z-w layer) N composition 5% (z = 0.05), P composition 4% (1-z-w = 0 .04), the group III composition was adjusted so as to lattice match with the InP substrate 11. The RMS roughness of 1 μm square on the surface was 3.7 angstroms, which was improved in flatness compared with 4.5 angstroms of the epitaxial laminated film for photodiodes of the inventive example (GaInNAs light receiving layer) of Example 1.

  A PIN type photodiode as shown in FIG. 8 was fabricated using the above epitaxial laminated film. The light receiving diameter was 30 μm. The structure of the PIN photodiode is the same as that of the first embodiment of the present invention. Comparing the dark current, as shown in FIG. 15, it was found that the dark current was reduced as compared with Example 1 although it did not reach Example 2. This is an effect of improving the surface flatness by adding P.

  Separately, the growth was interrupted when the InGaAs buffer layer 12 (including the N-containing InGaAs layer 12a) and the GaInNAsP light-receiving layer 13 were grown on the InP substrate, and the photoluminescence was examined. The photoluminescence spectrum had a peak at a wavelength of 2.5 μm. This confirmed that there was detection sensitivity up to a wavelength of 2.5 μm. In summary, in Example 3, it was confirmed that a light receiving element in which the detection sensitivity was extended to the long wavelength side and the dark current was sufficiently small could be realized.

  Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is the implementation of these inventions. It is not limited to the form. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  By using the semiconductor light receiving element and the manufacturing method thereof according to the present invention, the use of P in InP or the like can be avoided by using the InGaAs buffer layer, and the crystallinity of the light receiving layer with the buffer layer as a base in certain cases. Can be improved. For this reason, the range of material selection for the buffer layer can be expanded. In particular, when a compound semiconductor containing N is used for the light-receiving layer, the light-receiving layer having excellent crystallinity can be easily formed because of the low foreign matter formation reactivity with N. For this reason, significant contributions are expected in the future, mainly in the communications field.

It is a figure for demonstrating the semiconductor light receiving element in embodiment of this invention. It is a figure for demonstrating the semiconductor light receiving element in another embodiment of this invention. 1 is a diagram showing an epitaxial laminated structure of an example of the present invention in Example 1. FIG. It is a figure which shows the N mixing density of the depth direction of the buffer layer and light receiving layer of FIG. It is a figure which shows the element composition and lattice constant of the depth direction of the buffer layer and light receiving layer of FIG. It is a figure which shows the epitaxial laminated structure of the comparative example in Example 1 of this invention. It is a figure which shows the N mixing density of the depth direction of the buffer layer and light receiving layer of FIG. It is a figure which shows the PIN type photodiode used in order to measure dark current. It is a figure which shows the dark current measurement result in Example 1. FIG. 6 is a diagram showing an epitaxial laminated structure of an example of the present invention in Example 2. FIG. It is a figure which shows the element composition and lattice constant of the depth direction of the buffer layer and light receiving layer of FIG. It is a figure which shows the dark current measurement result in Example 2. FIG. 6 is a diagram showing an epitaxial multilayer structure of an example of the present invention in Example 3. FIG. It is a figure which shows the element composition and lattice constant of the depth direction of the buffer layer and light receiving layer of FIG. It is a figure which shows the dark current measurement result in Example 3.

Explanation of symbols

10 photodiode, 11 InP substrate, 12 InGaAs buffer layer, 12a N-containing InGaAs buffer layer, 13 light receiving layer, 14 window layer, 15 p-type region, 17 AR film or protective film, 18 SiN film, 31 n-part electrode, 32 p part electrode, 111 InP substrate, 112 AlInAs buffer layer, 112a N-containing AlInAs buffer layer, 113 light receiving layer, 114 window layer.

Claims (7)

An InP substrate;
An In _x Ga _1-x As buffer layer (0 ≦ x ≦ 1) located on the InP substrate;
A semiconductor light-receiving element comprising: a compound semiconductor light-receiving layer containing nitrogen located on the In _x Ga _1-x As buffer layer. The light-receiving layer containing nitrogen is Ga _y In _1-y N _z As _w Sb _1-zw (0 <z ≦ 1, 0 ≦ y ≦ 1, 0 ≦ w <1) or Ga _y In _1-y. 2. The semiconductor light receiving element according to claim 1, comprising N _z As _w P _1-zw (0 <z ≦ 1, 0 ≦ y ≦ 1, 0 ≦ w <1). 3. The semiconductor light receiving element according to claim 1, wherein the light receiving layer side of the In _x Ga _1-x As buffer layer contains nitrogen. 4. 4. The semiconductor light receiving element according to claim 1, wherein the composition ratio x in the In _x Ga _1-x As buffer layer changes in the thickness direction. 5. The lattice constant of the In _x Ga _1-x As buffer layer is adjusted to be 99.9% or more and 100.1% or less of the lattice constant of the InP substrate, Item 5. The semiconductor light receiving device according to Item 4. Forming an In _x Ga _1-x As buffer layer (0 ≦ x ≦ 1) on the InP substrate;
And a step of forming a light-receiving layer of a compound semiconductor on the In _x Ga _1-x As buffer layer. The light-receiving layer is a compound semiconductor layer containing nitrogen, and the buffer layer is exposed to nitrogen prepared for forming the light-receiving layer containing nitrogen during the step of forming the In _x Ga _1-x As buffer layer. The method for manufacturing a semiconductor light receiving element according to claim 6, wherein:

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