JP3620761B2 - Semiconductor light receiving element and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light receiving element and a method for manufacturing the same.
[0002]
[Prior art]
As shown in FIGS. 2A and 2B, the conventional semiconductor light-receiving element has a structure that differs depending on the incident direction of light.
[0003]
That is, the planar semiconductor light receiving element shown in FIG. 2A has a drawback that the light incident direction is limited to the upper surface or the lower surface, and direct optical coupling cannot be performed from the lateral direction with an optical fiber or an optical waveguide. 2A, 21a is a light incident surface, 22a is a p-InP layer, 23a is an InGaAs light absorption layer, 24a is an n-InP layer, 25a is an n-InP substrate, 26a is a p-electrode, and 27a is n electrode.
[0004]
On the other hand, in the optical waveguide type semiconductor light receiving element shown in FIG. 2B, light can be incident from the lateral direction and can be directly optically coupled to the optical fiber or the optical waveguide from the lateral direction. In FIG. 2B, 21b is a light incident end face, 221b is a p-InP layer, 222b is a p-InGaAsP light guide layer, 23b is an InGaAs light absorption layer, 24b is an n-InGaAsP light guide layer, and 25b is n. -InP substrate, 26b is a p-electrode, and 27b is an n-electrode.
[0005]
[Problems to be solved by the invention]
However, silica-based optical fibers and optical waveguides have a light spot diameter of about 10 μm, and in order to perform direct optical coupling with these with high efficiency, a semiconductor growth layer thickness of the semiconductor light receiving element is required to be about 10 μm.
[0006]
Growth of such a semiconductor layer having a thick mixed crystal composition is not easy, and there are problems such as increase in dark current and deterioration in reliability due to compositional shift, lattice defect, transition, and the like.
[0007]
An object of the present invention is to provide a highly reliable semiconductor light-receiving element and a method for manufacturing the same, which is highly efficient by direct optical coupling with respect to light incident from the lateral direction.
[0008]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a first semiconductor layer having a first conductivity type, a second semiconductor layer having a second conductivity type, and the first semiconductor layer. In a semiconductor light-receiving element comprising a growth layer comprising a layer and a light-receiving layer sandwiched between second semiconductor layers on a substrate, the growth layer and the end face of the substrateWith the light receiving layerSurface side partonlyInclined inward as you move away from the surface sideReverse mesa structureBy providing the light incident end face, the incident light is refracted at the light incident end face so that the incident light passes through the light receiving layer obliquely with respect to the layer thickness direction. It can be detected as current with efficiency.
[0009]
In this way, incident light is refracted at the light incident end face, and light passes obliquely with respect to the light absorption layer, so that the light absorption length is effectively increased. The absorption layer thickness can be thin. Further, the thickness of the semiconductor growth layer is about 1/2 to 1/3 as compared with the lateral incidence type waveguide type semiconductor light receiving element. As described above, the conventional technique is different from the conventional technique in that light can be incident in a lateral direction and light can be received efficiently with a thin semiconductor growth layer thickness for direct optical coupling with an optical fiber or an optical waveguide.
[0010]
Furthermore, the method for manufacturing a semiconductor light receiving element according to claim 2 or 3 of the present invention that achieves the above object includes a first semiconductor layer having an intrinsic or first conductivity type and the same method as the first semiconductor layer. A growth layer comprising a second semiconductor layer having one conductivity type and a light-receiving layer sandwiched between the first semiconductor layer and the second semiconductor layer is provided on the substrate; The main inner portion or the main inner portion of the semiconductor layer on the surface side including a part of the light receiving layer is selectively converted to the second conductivity type by impurity diffusion or by ion implantation and subsequent annealing. Furthermore, the growth layer and the end face of the substrateWith the light receiving layerSurface side partonlyInclined inward as you move away from the surface sideReverse mesa structureBy providing the light incident end face, the incident light is refracted by the light incident end face so that the incident light passes through the light receiving layer obliquely with respect to the layer thickness direction.
[0011]
Thus, the main inner portion of the first semiconductor layer or the main inner portion of the semiconductor layer on the surface side including a part of the light receiving layer is converted to the second conductivity type, and the end surface portion of the first semiconductor layer Is made the first conductivity type, it becomes difficult for a dark current that easily flows on the surface or end face of the semiconductor to flow, and the value can be reduced by about two orders of magnitude.
[0012]
A semiconductor light receiving element according to a fourth aspect of the present invention that achieves the above object is provided on a semiconductor layer having a first conductivity type, and is an intrinsic or first conductivity type semiconductor layer, a superlattice semiconductor layer, or a multiple quantum semiconductor. A Schottky having a Schottky barrier higher than the Schottky barrier between the light absorption layer and the Schottky electrode between the light absorption layer made of a well semiconductor layer and the Schottky electrode. In a semiconductor light receiving element comprising a multilayer structure on a substrate with a semiconductor layer having a high barrier height, the multilayer structure and end surfaces of the substrate are formed.With the light receiving layerSurface side partonlyInclined inward as you move away from the surface sideReverse mesa structureBy providing the light incident end face, the incident light is refracted by the light incident end face so that the incident light passes through the light absorption layer obliquely with respect to the layer thickness direction.
[0013]
Thus, since the so-called semiconductor layer having a high Schottky barrier height is interposed between the light absorption layer and the Schottky electrode, the entire light receiving element can be configured without a pn junction semiconductor layer, and a pn junction due to impurity diffusion or the like can be formed. It becomes unnecessary, and the pn junction portion is not exposed to the end face through the light absorption layer, so that there is an advantage that the dark current can be reduced. In addition, since incident light passes through the light absorption layer obliquely, it is effective. The light absorption length is longer and the absorption layer thickness is smaller than that of the conventional surface type semiconductor light receiving element.
[0014]
The semiconductor light receiving element according to claim 5 or 6 of the present invention that achieves the above object is characterized in that, in claim 4, the semiconductor layer having a high Schottky barrier height is In_1-xyGa_xAl_yAs (0 ≦ x ≦ 1, 0 ≦ y ≦ 1), In_1-xyGa_xAl_yAs (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) and thin In on it_1-uGa_uAs_1-vP_v(0 ≦ u ≦ 1, 0 ≦ v ≦ 1), and the semiconductor light-receiving element according to claim 7 of the present invention, which achieves the above object, comprises: Between the semiconductor layer with a high Schottky barrier height, a composition gradient that changes continuously or stepwise from the same composition as the light absorption layer to the same composition as the semiconductor layer with a high Schottky barrier height A gradient composition layer is interposed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, since the incident light passes through the light absorption layer obliquely due to refraction at the incident surface, the effective light absorption length becomes longer, so that the absorption layer thickness is thinner than that of the conventional surface type semiconductor light receiving element. I'll do it.
[0017]
For this reason, deviation of growth composition, lattice defects, occurrence of dislocation, etc. are reduced during wafer growth, and it becomes possible to manufacture a highly reliable device with a small dark current.
Further, since the absorption layer can be thin, the absorption layer is completely depleted at a low voltage, and extremely high light receiving sensitivity can be obtained at a low applied voltage.
[0018]
Furthermore, in general, a light receiving element of a type in which light is incident from the lower surface has an optical path length of about 100 μm, which is the substrate thickness. Therefore, it is necessary to increase the element size in consideration of the spread of light between them, In the case of the present invention, since the optical path length may be about several tens of μm at most, the element size can be reduced and the element capacitance can be reduced.
[0019]
Similarly, in order to obtain sufficient light receiving sensitivity even in the waveguide type semiconductor light receiving element, an element length of about 100 μm or more is required. However, in the present invention, the element length is only about several tens of μm, so that the element capacitance Can be reduced.
[0020]
Furthermore, when a so-called semiconductor layer having a high Schottky barrier height is interposed between the light absorption layer and the Schottky electrode, the entire light receiving element can be configured without a pn junction semiconductor layer, and no pn junction due to impurity diffusion or the like is required. Thus, the pn junction portion is not exposed to the end face through the light absorption layer, and there is an advantage that the dark current can be reduced.
[0021]
【Example】
[Example 1]
A first embodiment of the present invention is shown in FIG. In the figure, 11 is a light incident end face, 12 is a 1 μm thick p-InP layer, 13 is a 1.5 μm thick InGaAs light absorbing layer, 14 is a 1 μm thick n-InP layer, 15 is an n-InP substrate, 16 Is a p-electrode, and 17 is an n-electrode. The absorption layer area of the element is 30 μm × 50 μm.
[0022]
The light incident end face 11 has a shape that is inclined inward toward the end faces of the growth layers 12, 13, and 14 and the substrate 15 as the distance from the surface side increases. That is, the light incident end face 11 is formed as a so-called inverted mesa structure.
[0023]
Therefore, the incident light passes through the light absorption layer 13 obliquely due to the refraction of the incident light at the light incident end face 11, so that the effective light absorption length becomes long, and the absorption layer thickness is 1.5 μm. By forming the non-reflective film on the incident end face 11, a large value of 0.95 A / W or more in light receiving sensitivity was obtained with an applied reverse bias of 1.5 V in light having a wavelength of 1.3 μm.
[0024]
Further, the overall growth layer thickness was as thin as 3.5 μm, and a light receiving sensitivity equal to or higher than that was obtained with a growth layer thickness less than half that of the lateral light incident waveguide type semiconductor light receiving element. Further, the element area is small, and the element capacitance is about 0.4 pF or less.
[0025]
In the present embodiment, the light incident end face 11 is formed by using the (111) A plane that is obtained by performing wet etching on a (001) surface wafer using bromomethanol. For this reason, a uniform element with a uniform mesa angle (55 degrees with respect to the upper surface) could be produced.
[0026]
Of course, the reverse mesa structure may be formed by using other wet etching solutions or dry etching methods, or by using other crystal planes or by controlling the angle using the adhesion of the etching mask. Also good.
[0027]
In this embodiment, an n-InP substrate is used. However, even if a p-InP substrate is used, it can be similarly manufactured by reversing the above-mentioned p and n, and a semi-insulating substrate. It is possible to produce the same in the same way.
[0028]
Further, although a bulk having a uniform composition is used as the absorption layer, it goes without saying that an avalanche photodiode structure, a semiconductor layer having a superlattice structure, or the like may be used. Furthermore, it goes without saying that a material system such as InGaAlAs / InGaAsP or AlGaAs / GaAs other than the InGaAs / InP system, or a material system with inherent strain may be used.
[0029]
[Example 2]
A second embodiment of the present invention is shown in FIG. In the figure, 31 is a light incident end face, 32 is a 1 μm thick InP layer, 322 is a p-InP layer formed by Zn diffusion, 33 is a 1.5 μm thick InGaAs light absorption layer, and 34 is a 1 μm thick n-InP layer. The layer, 35 is an n-InP substrate, 36 is a p-electrode, and 37 is an n-electrode. The absorption layer area of the element is 30 μm × 50 μm.
[0030]
The light incident end face 31 has a shape that is inclined inward toward the end faces of the growth layers 32, 33, and 34 and the substrate 35 as the distance from the surface side increases. That is, the light incident end face 31 is formed as a so-called inverted mesa structure.
[0031]
Therefore, the incident light passes obliquely with respect to the light absorption layer 33 due to the refraction of the light at the light incident end face 31, so that the effective light absorption length is increased, and the light absorption layer thickness is 1.5 μm. By forming the non-reflective film on the incident end face 31, a light receiving sensitivity of 0.95 A / W or higher was obtained at an applied reverse bias of 1.5 V in light having a wavelength of 1.3 μm.
[0032]
Further, the overall growth layer thickness was as thin as 3.5 μm, and a light receiving sensitivity equal to or higher than that was obtained with a growth layer thickness less than half that of the lateral light incident waveguide type semiconductor light receiving element.
[0033]
As for the dark current, a sufficiently small value of about 10 pA was obtained even after the formation of the antireflection film. Further, the element area is small, and the element capacitance is about 0.4 pF or less.
[0034]
In this example, the light incident end face was formed by using the (111) A face that was obtained by performing wet etching on a (001) surface wafer using bromomethanol. For this reason, a uniform element with a uniform mesa angle (55 degrees with respect to the upper surface) could be produced.
[0035]
Of course, the reverse mesa may be formed using another wet etching solution or a dry etching method, or may be formed using another crystal plane or controlling the angle using the adhesion of the etching mask. good.
[0036]
The present embodiment has an advantage that the dark current can be remarkably reduced because the main inner portion of the InP layer 32 on the surface side is the p-InP layer 322 layer by diffusion of Zn.
That is, the dark current easily flows on the surface or end face of the semiconductor. However, by making the conductivity type of the main inner portion of the InP layer 32 on the surface side different from that of the end face portion as in this embodiment, the dark current is changed. Becomes difficult to flow, and the value can be reduced by about two orders of magnitude.
[0037]
The determination of the conductivity type of the main inner portion of the semiconductor on the surface side is not limited to that performed by Zn diffusion, but may be performed by ion implantation and subsequent annealing.
In this embodiment, an n-InP substrate is used. However, even if a p-InP substrate is used, it can be similarly manufactured by reversing the above-mentioned p and n, and semi-insulating. The same substrate can be manufactured using this substrate.
[0038]
In addition, although a bulk having a uniform composition is used as the absorption layer, it goes without saying that an avalanche photodiode structure or a semiconductor layer having a superlattice structure may be used. Furthermore, it goes without saying that a material system such as InGaAlAs / InGaAsP or AlGaAs / GaAs other than the InGaAs / InP system, or a material system with inherent strain may be used.
Furthermore, the light receiving layer may have a multilayer structure including an intrinsic semiconductor layer or a superlattice semiconductor layer.
[0039]
[referenceExample1]
Of the present inventionreferenceExample1Is shown in FIG. In the figure, 41 is a light incident end face, 42 is 0.2 μm thick undoped or^--InAlAs layer, 43 is a 0.1 .mu.m thick undoped or n layer whose composition is smoothly changed from InAlAs to InGaAs.^--In_1-xyGa_xAl_yAs (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) layer, 44 is 1.5 μm thick undoped or n^--InGaAs light absorption layer, 45 is a 1 .mu.m thick n-InP layer, 46 is an n-InP substrate, 47 is a Pt / Ti / Au Schottky electrode, and 48 is an ohmic n electrode. The absorption layer area of the element is 30 μm × 50 μm.
[0040]
The light incident end surface 41 has a shape that is inclined inwardly toward the end surface of the substrate 46 as the distance from the surface side increases. That is, the light incident end face 41 is formed on the end face of the substrate 46 as a so-called reverse mesa structure.
Therefore, incident light passes through the light absorption layer 44 obliquely due to light refraction at the light incident end face 41, and the effective light absorption length becomes long.
In addition, the incident light refracted by the Schottky electrode 47 acts as a reflection mirror, so that the absorption length is equivalently doubled, the absorption layer thickness is 1.5 μm, and a non-reflective film is formed on the light incident end face. As a result, a large light receiving sensitivity of 0.95 A / W or higher was obtained at an applied reverse bias of 1.5 V in light having a wavelength of 1.3 μm.
[0041]
Further, the total growth layer thickness was as thin as 2.8 μm, and a light receiving sensitivity equal to or higher than that was obtained with a growth layer thickness less than half that of the lateral light incident waveguide type semiconductor light receiving element.
As for the dark current, a sufficiently small value of about 1 nA was obtained even after the formation of the antireflection film. Also, the element area is small, and the element capacitance is about 0.4 pF or less.
[0042]
BookreferenceIn the example, the InAlAs layer 42 is a so-called semiconductor layer having a high Schottky barrier height, and a Schottky barrier higher than the Schottky barrier when the light absorption layer 44 and the Schottky electrode 47 are in direct contact with each other is Schottky. It has with respect to the electrode 47. FIG.
Therefore, the entire light receiving element can be configured without a pn junction semiconductor layer, a pn junction by impurity diffusion or the like is not necessary, and the pn junction portion is not exposed to the end face via the light absorption layer, so that the dark current can be reduced. There are advantages.
[0043]
BookreferenceIn the example, the light incident end face was formed by taking advantage of the (111) A face that was obtained by performing wet etching on a (001) surface wafer using bromomethanol.
A mesa angle of about 55 degrees with respect to the upper surface could be fabricated. Of course, the reverse mesa may be formed by using another wet etching solution or a dry etching method, or may be formed by using another crystal plane or by controlling the angle using the adhesion of the etching mask. Good.
[0044]
BookreferenceIn the example, In_1-xyGa_xAl_yThe As layer 43 uses a graded composition layer whose composition is smoothly changed from InAlAs to InGaAs to achieve smooth connection of conduction band and valence band. This layer is composed of one or more multilayer semiconductor thin films. It may be a pseudo gradient composition layer composed of stepwise composition layers.
Further, the In changed the composition from InGaAs to InP between the InGaAs light absorption layer 44 and the n-InP layer 45._1-uGa_uAs_1-vP_v(0 ≦ u ≦ 1, 0 ≦ v ≦ 1) The conduction band and the valence band may be smoothly connected using a gradient composition layer or a pseudo gradient composition layer.
[0045]
BookreferenceThe example is an example using the n-InP substrate 46. However, even if a p-InP substrate is used, it can be similarly manufactured by reversing the above n and p, and using a semi-insulating substrate. Can be produced in the same way. Further, it can be similarly applied to other substrates such as GaAs.
In addition, here, a bulk having a uniform composition is used as the light absorption layer 44, but it goes without saying that an avalanche photodiode structure, a semiconductor layer having a superlattice structure, a multiple quantum well semiconductor layer, or the like may be used.
[0046]
Furthermore, it goes without saying that a material system such as InGaAsP, AlGaAs, AlInPAs, InGaPSb, AlGaPSb, AlGaAsSb, AlInAsSb, and AlInPSb system other than the InGaAlAs system and a material system with inherent strain may be used.
[0047]
[referenceExample2]
Of the present inventionreferenceExample2Is shown in FIG. In the figure, 51 is a light incident end face, 59 is 5 nm thick undoped or n^--InP layer, 52 is 0.2 μm thick undoped or n^--InAlAs layer, 53 is a 0.1 .mu.m thick undoped or n layer whose composition is smoothly changed from InAlAs to InGaAs.^--In_1-xyGa_xAl_yAs (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) layer, 54 is 1.5 μm thick undoped or n^--InGaAs light absorption layer, 55 is a 1 .mu.m thick n-InP layer, 56 is an n-InP substrate, 57 is a Pt / Ti / Au Schottky electrode, and 58 is an ohmic n electrode. The absorption layer area of the element is 30 μm × 50 μm.
[0048]
The light incident end face 51 has a shape that is inclined inward toward the end face of the substrate 56 as the distance from the surface side increases. That is, the light incident end face 51 is formed on the end face of the substrate 56 as a so-called reverse mesa structure.
Accordingly, since the incident light passes through the light absorption layer 54 obliquely due to the refraction of light at the light incident end face 51, the effective light absorption length becomes long.
In addition, the incident light refracted by the Schottky electrode 57 acts as a reflection mirror, so that the absorption length is equivalently doubled, the absorption layer thickness is 1.5 μm, and a non-reflective film is formed on the light incident end face. As a result, a large value of 0.95 A / W or higher in light receiving sensitivity was obtained at an applied reverse bias of 1.5 V at a wavelength of 1.3 μm. Further, the total growth layer thickness was as thin as about 2.8 μm, and a light receiving sensitivity equal to or higher than that was obtained with a growth layer thickness less than half that of the lateral light incident waveguide type semiconductor light receiving element.
[0049]
In addition, bookreferenceIn the example, since an extremely thin InP layer 59 is used on the outermost surface, there is an advantage that the surface oxidation resistance is higher than that of InAlAs.
Here, the InP layer 59 is used as an example, but instead, the general formula In is used._1-uGa_uAs_1-vP_vIt is also possible to use a layer represented by (0 ≦ u ≦ 1, 0 ≦ v ≦ 1).
As for the dark current, a sufficiently small value of about 1 nA was obtained even after the formation of the antireflection film. In addition, the element surface dipping is small, and the element capacitance is about 0.4 pF or less.
[0050]
BookreferenceIn the example, the InAlAs layer 52 is a so-called semiconductor layer having a high Schottky barrier height, and a Schottky barrier higher than the Schottky barrier when the light absorption layer 54 and the Schottky electrode 57 are in direct contact with each other is Schottky. It has with respect to the electrode 57. FIG.
Therefore, the entire light receiving element can be configured without a pn junction semiconductor layer, a pn junction by impurity diffusion or the like is not necessary, and the pn junction portion is not exposed to the end face via the light absorption layer, so that the dark current can be reduced. There are advantages.
[0051]
BookreferenceIn the example, the light incident end face was formed by taking advantage of the (111) A face that was obtained by performing wet etching on a (001) surface wafer using bromomethanol. A mesa angle of about 55 degrees with respect to the upper surface could be fabricated.
Of course, the reverse mesa may be formed by using another wet etching solution or a dry etching method, or may be formed by using another crystal plane or by controlling the angle using the adhesion of the etching mask. Good.
[0052]
BookreferenceIn the example, In_1-xyGa_xAl_yThe As layer 53 uses a graded composition layer whose composition is smoothly changed from InAlAs to InGaAs to achieve smooth connection of the conduction band and valence band. This layer is composed of one or more multilayer semiconductor thin films. It may be a pseudo gradient composition layer composed of stepwise composition layers.
Also, the In changed the composition from InGaAs to InP between the InGaAs light absorption layer 54 and the n-InP layer 55._1-uGa_uAs_1-vP_v(0 ≦ u ≦ 1, 0 ≦ v ≦ 1) The conduction band and the valence band may be smoothly connected using a gradient composition layer or a pseudo gradient composition layer.
[0053]
Also bookreferenceThe example is an example using the n-InP substrate 56. However, even if a p-InP substrate is used, it can be similarly manufactured by reversing the above-described p and n, and using a semi-insulating substrate. Can be produced in the same way. Further, it can be similarly applied to other substrates such as GaAs.
BookreferenceIn the example, a bulk of uniform composition is used as the light absorption layer 54, but it goes without saying that an avalanche photodiode structure, a superlattice semiconductor layer, a multiple quantum well semiconductor layer, or the like may be used.
[0054]
Furthermore, it goes without saying that a material system such as InGaAsP, AlGaAs, AlInPAs, InGaPSb, AlGaPSb, AlGaAsSb, AlInAsSb, or AlInPSb system other than the InGaAlAs system, or a material system with inherent strain may be used.
[0055]
Example 5
First of the present invention3An example of this is shown in FIG.
In the figure, the semiconductor light receiving element portion is as follows. 61 is a light incident surface, 62 is a 1 μm thick InP layer, 622 is a p-InP layer formed by Zn diffusion, 63 is a 1.5 μm thick InGaAs light absorption layer, 64 is a 1 μm thick InP layer, 65 is an n-InP substrate, 66 is a p-electrode and 67 is an n-electrode.
[0056]
Since light passes through the light absorbing layer obliquely due to light refraction at the incident surface, the effective light absorption length is increased, and an antireflective film is formed on the incident surface with an absorption layer thickness of 1.5 μm. Thus, a sufficiently large light receiving sensitivity can be obtained with an applied reverse bias of 1.5 V at a wavelength of 1.3 μm.
Further, the overall growth layer thickness is as thin as 3.5 μm, and a light receiving sensitivity equal to or higher than that can be obtained with a growth layer thickness less than half that of the lateral light incident waveguide type semiconductor light receiving element. As for the dark current, a sufficiently small value of about 10 pA was obtained even after the formation of the antireflection film.
[0057]
In this example, the light incident surface was formed by utilizing the (111) A surface that was obtained by performing wet etching on a (001) surface wafer using bromomethanol. For this reason, a uniform element having a uniform mesa angle (an angle of 55 degrees with respect to the upper surface) can be manufactured.
Of course, the reverse mesa may be formed using another wet etching solution or a dry etching method, or may be formed using another crystal plane or controlling the angle using the adhesion of the etching mask. Good. In this embodiment, an n-InP substrate is used. However, even if a p-InP substrate is used, it can be similarly manufactured by reversing the above p and n, and a semi-insulating substrate is used. But it can be produced in the same way.
[0058]
Further, here, a bulk of a uniform composition is used as the absorption layer, but it goes without saying that an avalanche photodiode structure, a semiconductor layer having a superlattice structure, or the like may be used.
Needless to say, a material system other than the InGaAsP / InP system, such as InGaAlAs / InGaAsP or AlGaAs / GaAs system, or a material system with inherent strain may be used.
[0059]
This semiconductor light receiving element is formed on a silicon substrate 68 with SiO.₂An optical waveguide 69 (spot size ω₀= 5 μm) and are mounted so as to be coupled as shown in the figure. At this time, the height difference (Zh) between the InP substrate side lower surface 63a of the light absorption layer and the optical waveguide center is set to 10 μm.
[0060]
In general, the Gaussian beam emitted from the optical waveguide spreads as it progresses. When Zh is increased, the optical path length for receiving the refracted light in the light receiving layer becomes longer, and in order to keep the light receiving sensitivity at the same value, it is necessary to increase the light receiving area corresponding to the spread of the beam. Since the increase in area is proportional to the junction capacitance of the element, the response speed of the element is greatly degraded. A graph showing the square of the spot size (approximately proportional to the required light receiving area) at the point where Zh is on the horizontal axis and the light receiving element and the optical waveguide are arranged closest to each other and the center of the light beam reaches the light receiving layer. 7 (solid line).
[0061]
When Zh is increased as shown in FIG. 7, the required light receiving area increases rapidly, and the response band of the element also decreases rapidly in proportion to this. Therefore, in this embodiment, Zh = 10 μm where the beam spread can be almost ignored. Thus, the element area can be reduced, and when the absorption layer area is 15 μm × 50 μm, the light receiving sensitivity is a large value of 0.9 A / W or more and the element capacitance is a small value of about 0.2 pF or less.
[0062]
Moreover, the broken line in FIG. 7 also shows the relationship when the spot size of the optical waveguide is 2 μm. Ω like this₀As the beam becomes smaller, the beam divergence becomes more rapid.₀For example, if Zh is set to 50 μm, the light receiving area is required to be about 15 times as large as Zh = 4 μm, and the element capacitance is drastically increased.
[0063]
This relationship naturally depends on the reverse mesa angle θ of the light receiving element. The point where the beam area increases by 30% of the initial beam area is Zh_{+ 30%}Zh_{+ 30%}= Nπω₀ ²(0.3)^1/2/ Λsin (φ). Where n is the refractive index of the semiconductor with respect to light of wavelength λ, π is the circumference, ω₀Is the spot size of the optical waveguide (in the case of a rectangular waveguide or the like, an equivalent spot size characterizing the waveguide), and φ is the angle formed by the center of the optical axis of the refracted light and the light absorption layer.
[0064]
For light with a wavelength of 1.3 μm, if θ = 55 degrees and the refractive index n of the InP substrate is 3.209, then ω₀= Zh at 5μm_{+ 30%}= 44.4 μm, ω₀Zh when = 2μm_{+ 30%}= 7.1 μm, and when using an optical waveguide with a small spot size, it can be seen that it is important to bring the optical axis center of the optical waveguide particularly close to the surface of the light receiving layer.
[0065]
In this embodiment, an optical waveguide formed on a silicon substrate is used. However, it is also possible to hybridly integrate other various optical waveguides such as an optical fiber and a polymer optical waveguide on an appropriate substrate. Needless to say. Further, the optical axis direction of the light receiving layer surface and the optical waveguide need not be completely parallel. It is sufficient that the light receiving layer is refracted at the incident end surface and can be received by the light receiving layer, and is slightly deviated from the parallel direction. No problem.
Note that the p-InP layer 622 is formed by Zn diffusion, but instead, the p-InP layer 622 may be selectively converted to the second conductivity type by ion implantation and subsequent annealing.
[0066]
[referenceExample3]
Of the present inventionreferenceExample3Is shown in FIG.
In the figure, 81 is a light incident surface, 82 is a 1 μm thick p-InP layer, 83 is a 1.5 μm thick InGaAs light absorbing layer, 84 is a 1 μm thick n-InP layer, 85 is an n-InP substrate, 86 is a p electrode, Reference numeral 87 denotes an n electrode.
In this example, a substrate having a polished surface inclined by 20 degrees with respect to the (001) plane is used, and the layer structure is grown thereon. Therefore, when cleavage is performed, as shown in FIG. A cleavage end face having a mesa angle of 70 degrees with respect to the surface is formed.
[0067]
The absorption layer area of the element is 20 μm × 80 μm. Since light passes through the light absorbing layer obliquely due to light refraction at the incident surface, the effective light absorption length is increased, and an antireflective film is formed on the incident surface with an absorption layer thickness of 1.5 μm. As a result, a large light receiving sensitivity of 0.9 A / W or more was obtained at an applied reverse bias of 1.5 V in light having a wavelength of 1.3 μm. Further, the overall growth layer thickness was as thin as 3.5 μm, and a light receiving sensitivity equal to or higher than that was obtained with a growth layer thickness less than half that of the lateral light incident waveguide type semiconductor light receiving element.
[0068]
BookreferenceIn the example, a substrate having a polished surface inclined by 20 degrees with respect to the (001) plane is used, but it goes without saying that the mesa angle can be appropriately selected according to this angle. Yes. Examples2Needless to say, the present invention can be similarly applied to such a semiconductor layer configuration.
thisreferenceIn the example, an n-InP substrate is used. However, even if a p-InP substrate is used, the above-described p and n can be reversed in the same manner, and a semi-insulating substrate can be used. It can be produced in the same way. In addition, here, a bulk having a uniform composition is used as the absorption layer, but it goes without saying that an avalanche photodiode structure, a semiconductor layer having a superlattice structure, or the like may be used.
[0069]
Needless to say, a material system other than the InGaAsP / InP system, such as InGaAlAs / InGaAsP or AlGaAs / GaAs system, or a material system with inherent strain may be used.
[0070]
【The invention's effect】
As described above in detail based on the embodiment, in the semiconductor light-receiving element, the light receiving surface having the reverse mesa structure is provided on the surface side, and the light incident from the side is based on the mesa angle of the reverse mesa. The incident light is refracted toward the upper surface at the incident end face and passes obliquely with respect to the light absorption layer, effectively increasing the light absorption length. The thickness is thin. Further, a semiconductor growth layer thickness of about 1/2 to 1/3 is sufficient as compared with a lateral incidence type waveguide type semiconductor light receiving element.
[0071]
As described above, it is possible to receive light efficiently with a thin semiconductor growth layer thickness for direct optical coupling with an optical fiber or an optical waveguide while allowing lateral light incidence. Further, there is an advantage that the element length for obtaining sufficient light receiving sensitivity is about half or less as compared with the lateral light incident waveguide type semiconductor light receiving element.
[0072]
Furthermore, when a so-called semiconductor layer having a high Schottky barrier height is interposed between the light absorption layer and the Schottky electrode, the entire light receiving element can be configured without a pn junction semiconductor layer, and no pn junction due to impurity diffusion or the like is required. Thus, the pn junction portion is not exposed to the end face through the light absorption layer, and there is an advantage that the dark current can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic view of the structure of a semiconductor light receiving element according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram of a conventional semiconductor light receiving element.
FIG. 3 is a structural schematic view of a semiconductor light receiving element according to a second embodiment of the present invention.
FIG. 4 of the present inventionreferenceExample1It is a structure schematic diagram of the semiconductor light receiving element concerning.
FIG. 5 shows the present invention.referenceExample2It is a structure schematic diagram of the semiconductor light receiving element concerning.
FIG. 6 shows the first of the present invention.3It is a structure schematic diagram of the semiconductor light receiving element according to the example.
FIG. 7 shows the difference in height (Zh) between the InP substrate side lower surface 63a of the light absorption layer and the optical waveguide optical axis center, and the square of the spot size at the point where the light beam center reaches the light receiving layer. It is a graph which shows the relationship of (proportional).
FIG. 8 shows the present invention.referenceExample3It is a structure schematic diagram of the semiconductor light receiving element concerning.
[Explanation of symbols]
11, 31 Light incident end face
12 p-InP layer
13,33 InGaAs light absorption layer
14,34 n-InP layer
15,35 n-InP substrate
16, 36 p-electrode
17, 37 n-electrode
32 InP layer
322 p-InP layer formed by Zn diffusion
41 Light incident end face
42 InAlAs layer
43 In_1-xyGa_xAl_yAs layer
44 InGaAs light absorption layer
45 n-InP layer
46 n-InP substrate
47 Pt / Ti / Au Schottky electrode
48 Ohmic n electrode
51 Light incident end face
59 InP layer
52 InAlAs layer
53 In_1-xyGa_xAl_yAs layer
54 InGaAs light absorption layer
55 n-InP layer
56 n-InP substrate
57 Pt / Ti / Au Schottky electrode
58 Ohmic n electrode
61 Light incident surface
62 1 μm thick InP layer
622 p-InP layer formed by Zn diffusion
63 1.5μm thick InGaAs light absorption layer
63 InP substrate side underside of 1.5μm thick InGaAs light absorption layer
64 1 μm thick n-InP layer
65 n-InP substrate
66 p-electrode
67 n-electrode
68 Silicon substrate
69 Optical waveguides formed on silicon substrates
81 Light incident surface
82 1μm thick p-InP layer
83 1.5μm thick InGaAs light absorption layer
84 1μm thick n-InP layer
85 n-InP substrate
86 p-electrode

Claims (7)

A growth layer comprising a first semiconductor layer having a first conductivity type, a second semiconductor layer having a second conductivity type, and a light-receiving layer sandwiched between the first semiconductor layer and the second semiconductor layer In the semiconductor light-receiving element provided on the substrate, only the surface side portion of the growth layer and the end surface of the substrate where the light-receiving layer is provided is a light incident end surface having an inverted mesa structure that is inclined inward as the distance from the surface side increases. The semiconductor light receiving element is characterized in that incident light is refracted by the light incident end face so that incident light passes through the light receiving layer obliquely with respect to the layer thickness direction. A first semiconductor layer having an intrinsic or first conductivity type; a second semiconductor layer having the same first conductivity type as the first semiconductor layer; and the first semiconductor layer and the second semiconductor layer. A growth layer comprising a sandwiched light-receiving layer is provided on the substrate, while a main inner portion of the first semiconductor layer on the surface side or a main inner portion of the semiconductor layer on the surface side including a part of the light-receiving layer Is selectively converted to the second conductivity type by diffusion of impurities, and only the surface side portion of the growth layer and the end surface of the substrate where the light-receiving layer is provided is inclined inward as the distance from the surface side increases. By providing the light incident end face having the inverted mesa structure, the incident light is refracted by the light incident end face so that the incident light passes through the light receiving layer obliquely with respect to the layer thickness direction. Manufacturing method of semiconductor light receiving element. A first semiconductor layer having an intrinsic or first conductivity type; a second semiconductor layer having the same first conductivity type as the first semiconductor layer; and the first semiconductor layer and the second semiconductor layer. A growth layer comprising a sandwiched light-receiving layer is provided on the substrate, while a main inner portion of the first semiconductor layer on the surface side or a main inner portion of the semiconductor layer on the surface side including a part of the light-receiving layer Is selectively converted to the second conductivity type by ion implantation and subsequent annealing, and only the surface side portion of the growth layer and the end face of the substrate where the light receiving layer is located is separated from the surface side. By providing a light incident end surface with an inverted mesa structure inclined inward according to the above, the incident light is refracted at the light incident end surface so that the incident light passes through the light receiving layer obliquely with respect to the layer thickness direction. For manufacturing semiconductor light-receiving elements characterized by . On the semiconductor layer having the first conductivity type, between the light absorption layer made of an intrinsic or first conductivity type semiconductor layer, a superlattice semiconductor layer, or a multiple quantum well semiconductor layer, and the Schottky electrode, A multilayer structure including a semiconductor layer having a high Schottky barrier height having a Schottky barrier higher than the Schottky barrier between the light absorption layer and the Schottky electrode is formed on the substrate. In the semiconductor light-receiving element, the light incident end surface having an inverted mesa structure inclined inwardly with increasing distance from the surface side is provided only on the surface side portion of the multilayer structure and the end surface of the substrate where the light-receiving layer exists. A semiconductor light receiving element, wherein incident light is refracted at an incident end face so that incident light passes through the light absorption layer obliquely with respect to a layer thickness direction. 5. The semiconductor light receiving element according to claim 4, wherein the semiconductor layer having a high Schottky barrier height is made of In _1-xy Ga _x Al _y As (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). The Schottky barrier height with high semiconductor _{layer, In 1-xy Ga x Al} y As (0 ≦ x ≦ 1,0 ≦ y ≦ 1) thin on the Part _{In 1-u Ga u As 1} -v P v 5. The semiconductor light receiving element according to claim 4, wherein the light receiving element comprises (0 ≦ u ≦ 1, 0 ≦ v ≦ 1). Between the light absorbing layer and the semiconductor layer having a high Schottky barrier height, the composition changes from the same composition as the light absorbing layer to the same composition as the semiconductor layer having a high Schottky barrier height. 7. A semiconductor light receiving element according to claim 4, wherein a graded composition layer having a composition grade is interposed.

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