JPH10190042A - Semiconductor photodetector and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor photodetector which has high reliability although the photodetector is constituted to directly combine light rays made incident to the photodetector from the lateral direction at a high efficiency. SOLUTION: A semiconductor photodetector is constituted by providing grown layers composed of a first semiconductor layer 12 having a first conductivity, a second semiconductor layer 14 having a second conductivity, and a photodetector layer 13 held between the semiconductor layers 12 and 14 on a substrate 15. On the end faces of the layers 12, 13, and 14 and substrate 15, a light incident end face 11 tilted inward as becoming farther from the surface is provided so that incident light can be refracted on the end face 11 and can press through the photodetecting layer 13 obliquely to the thickness direction of the layer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor light receiving device and a method for manufacturing the same.

[0002]

2. Description of the Related Art A conventional semiconductor light receiving element is shown in FIG.
As shown in (b), the structure differs depending on the incident direction of light.

That is, in the surface type semiconductor light receiving element shown in FIG. 2A, the incident direction of light is limited to the upper surface or the lower surface, and it is not possible to perform direct optical coupling with an optical fiber, an optical waveguide, or the like from the lateral direction. There is. Incidentally, in FIG.
1a is a light incident surface, 22a is a p-InP layer, 23a is InG
aAs light absorbing layer, 24a is n-InP layer, 25a is n-In
A P substrate, 26a is a p electrode, and 27a is an n electrode.

On the other hand, in the optical waveguide type semiconductor light receiving device shown in FIG. 2 (b), 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, reference numeral 21b denotes a light incident end face,
b is a p-InP layer, 222b is a p-InGaAsP light guide layer, 23b is an InGaAs light absorption layer, and 24b is n-InGa.
AsP light guide layer, 25b is n-InP substrate, 26b is p
The electrode 27b is an n-electrode.

[0005]

However, quartz optical fibers and optical waveguides have a light spot diameter of about 10 μm, and in order to perform direct optical coupling with these optical fibers with high efficiency, it is necessary to use a semiconductor growth layer of a semiconductor light receiving element. A thickness of about 10 μm is required.

It is not easy to grow such a semiconductor layer having a thick mixed crystal composition, and there is a problem that the dark current increases and the reliability is deteriorated due to a composition shift, a lattice defect, a transition, or the like.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor light receiving element which is highly efficient by direct optical coupling with respect to light incident from the lateral direction and has high reliability, and a method of manufacturing the same.

[0008]

According to a first aspect of the present invention, there is provided a semiconductor light receiving device having a first semiconductor layer having a first conductivity type and a second semiconductor layer having a second conductivity type. A semiconductor light-receiving element in which a growth layer comprising a semiconductor layer and a light-receiving layer sandwiched between the first semiconductor layer and the second semiconductor layer is provided on a substrate; By providing a light incident end face that is inclined inward as away from the surface side, the incident light is refracted at the light incident end face so that the incident light passes through the light receiving layer obliquely to the layer thickness direction, The incident light is absorbed by the light absorbing layer and can be detected as a current with high efficiency.

As described above, the incident light is refracted at the light incident end face, and the light obliquely passes through the light absorbing layer, thereby effectively increasing the light absorption length. The thickness of the absorbing layer can be smaller than that of the device. In addition, compared with a lateral incidence type waveguide type semiconductor light receiving element, it is か ら to 1
A semiconductor growth layer thickness of about / 3 is sufficient. As described above, the present embodiment is different from the prior art in that light can be received in a highly efficient manner with a thin semiconductor growth layer with respect to direct optical coupling with an optical fiber or an optical waveguide, while allowing lateral light incidence.

Further, the method of manufacturing a semiconductor light receiving device according to claim 2 or 3 of the present invention, which achieves the above object, comprises: a first semiconductor layer having an intrinsic or first conductivity type; A second semiconductor layer having the same first conductivity type and a growth layer comprising a light receiving layer sandwiched between the first semiconductor layer and the second semiconductor layer are provided on the substrate, The main inner part of the semiconductor layer or the main inner part of the semiconductor layer on the surface side including the part of the light receiving layer is selectively made to have a second conductive property by diffusion of impurities or by ion implantation and subsequent annealing. Convert to shape,
Further, by providing a light incident end face which is inclined inward as the distance from the front side is increased, the incident light is refracted at the light incident end face, so that the incident light passes through the light receiving layer. It is characterized by passing obliquely to the layer thickness direction.

As described above, the main inner portion of the first semiconductor layer or the main inner portion of the semiconductor layer including the part of the light receiving layer on the front surface side is converted into the second conductivity type, and the first semiconductor layer is formed. By setting the end face portion of the first conductivity type, a dark current that easily flows on the surface or the end face of the semiconductor does not easily flow, and the value can be reduced by about two digits.

According to a fourth aspect of the present invention, there is provided a semiconductor light-receiving element having a first conductivity type, a semiconductor layer of an intrinsic or first conductivity type, and a superlattice semiconductor layer. Or, between the Schottky electrode and the light absorption layer made of a multiple quantum well semiconductor layer, a Schottky barrier higher than the Schottky barrier between the light absorption layer and the Schottky electrode with respect to the Schottky electrode In a semiconductor light receiving element having a multi-layer structure having a semiconductor layer having a high Schottky barrier height on a substrate, a light incident end surface inclined inward as the distance from the front surface increases is increased at an end surface of the multi-layer structure and the substrate. By 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 absorbing layer obliquely with respect to the thickness direction.

As described above, since the so-called semiconductor layer having a high Schottky barrier height is interposed between the light absorbing layer and the Schottky electrode, the entire light receiving element can be formed without the pn junction semiconductor layer, and the light receiving element is formed by impurity diffusion or the like. Since the pn junction is not required and the pn junction is not exposed to the end face via the light absorbing layer, there is an advantage that the dark current is small, and the incident light passes obliquely to the light absorbing layer. The same effect as the semiconductor light receiving element according to the first aspect is obtained, for example, the light absorption length is effectively increased and the absorption layer thickness is reduced as compared with the conventional surface type semiconductor light receiving element.

According to a fifth or sixth aspect of the present invention, there is provided a semiconductor light receiving device according to the fourth aspect of the present invention, wherein the semiconductor layer having a high Schottky barrier height is made of In _1-xy G.
a _x Al _y As (0 ≦ x ≦ 1, 0 ≦ y ≦ 1)
_{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 (0 ≦ u ≦ 1,0 ≦ v
.Ltoreq.1), wherein the semiconductor light receiving element according to claim 7 of the present invention which achieves the above object is provided as claims 4-6.
Wherein between the light absorbing layer and the semiconductor layer having a high Schottky barrier height, a continuous or stepwise transition from the same composition as the light absorbing layer to the same composition as the semiconductor layer having a high Schottky barrier height A gradient composition layer having a composition gradient that changes to

According to another aspect of the present invention, there is provided a semiconductor light receiving device, comprising: a lower surface on a substrate side in a thickness direction of the light absorbing layer; and a light incident end face of the semiconductor light receiving device which is parallel to the semiconductor surface. The height difference at the center of the optical axis of the optical waveguide provided so as to be optically coupled through the optical waveguide is smaller than the value given by Zh _{+ 30% in} the following equation. Zh _{+ 30%} = nπω ₀ 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 circular constant, and ω ₀ is 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 between the optical axis center of the refracted light and the light absorbing layer.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, since the incident light passes through the light absorbing layer obliquely due to refraction on the incident surface, the effective light absorption length becomes longer. In comparison, the thickness of the absorbing layer can be reduced.

For this reason, in the growth of the wafer, the occurrence of a shift in the growth composition, lattice defects, dislocation, and the like are reduced, and a highly reliable device having a small dark current can be manufactured. In addition, since the absorption layer can be made thin, the absorption layer is completely depleted at a low voltage, and an extremely high light receiving sensitivity can be obtained at a low applied voltage.

Further, since a light receiving element of a type in which light is incident from the lower surface usually has an optical path length of about 100 μm which is the substrate thickness, it is necessary to increase the element size in consideration of the spread of light therebetween. However, in the case of the present invention, since the optical path length can be at most about several tens of μm, the element size can be reduced and the element capacitance can be reduced.

Similarly, in order to obtain a sufficient light-receiving sensitivity, a waveguide-type semiconductor light-receiving element also needs an element length of about 100 μm or more. However, in the present invention, the element length is about several tens μm. In addition, the element capacitance can be reduced.

Further, when a semiconductor layer having a so-called high Schottky barrier height is interposed between the light absorbing layer and the Schottky electrode, the entire light receiving element can be constructed without a pn junction semiconductor layer, and the pn junction due to impurity diffusion or the like can be formed. Since the junction is not required and the pn junction is not exposed to the end face via the light absorbing layer, there is an advantage that the dark current can be reduced.

[0021]

【Example】

Embodiment 1 FIG. 1 shows a first embodiment of the present invention. In the figure, 11 is a light incident end face, and 12 is a 1 μm thick pI
nP 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
It is 30 μm × 50 μm.

The light incident end face 11 is formed on the growth layers 12, 13, 1
4 and the end face of the substrate 15 have a shape that is inclined inward as the distance from the front side increases. That is, the light incident end face 11 is
It is formed as a so-called inverted mesa structure.

Accordingly, the refraction of the incident light at the light incident end face 11 allows the incident light to pass obliquely to the light absorbing layer 13, thereby increasing the effective light absorption length and increasing the absorption layer thickness to 1.5.
By forming a non-reflective film on the light incident end face 11 at a light incidence
At V, a large value of light receiving sensitivity of 0.95 A / W or more was obtained.

The overall thickness of the grown layer was as small as 3.5 μm, and a light receiving sensitivity equal to or higher than that of a laterally incident light waveguide type semiconductor photodetector was obtained with a thickness of less than half. Also, the element area can be small, and the element capacitance is also 0.4 pF.
Or less.

In this embodiment, the light incident end face 11 is
The wafer on the (001) surface was subjected to wet etching using bromomethanol to form the (111) A surface, which was used. For this reason, the mesa angle (5
5 °), and a uniform element was produced.

Of course, the inverted mesa structure may be formed by using another wet etching solution or a dry etching method.
Another crystal plane may be used, or the angle may be controlled by using the adhesion of the etching mask.

In this embodiment, an n-InP substrate is used. However, even if a p-InP substrate is used, the above-mentioned p and n can be reversed and the same can be produced. It can be manufactured similarly using a non-conductive substrate.

Although a bulk having a uniform composition is used as the absorption layer, it goes without saying that a semiconductor layer having an avalanche photodiode structure or a superlattice structure may be used. Further, InGaAlAs / InGaAs /
It goes without saying that a material system such as InGaAsP or AlGaAs / GaAs or a material system having intrinsic strain may be used.

Embodiment 2 FIG. 3 shows a second embodiment of the present invention.
Shown in In the figure, 31 is a light incident end face, 32 is 1 μm.
m-th InP layer 322 is a p-I layer formed by Zn diffusion.
nP layer, 33 is a 1.5 μm thick InGaAs light absorbing layer, 34
Is a 1 μm thick n-InP 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
It is 30 μm × 50 μm.

The light incident end face 31 is formed on the growth layers 32, 33, 3
4 and the end surface of the substrate 35 have a shape that is inclined inward as the distance from the front side increases. That is, the light incident end face 31 is
It is formed as a so-called inverted mesa structure.

Accordingly, the incident light passes obliquely to the light absorbing layer 33 due to the refraction of the light at the light incident end face 31, so that the effective light absorption length becomes longer and the light absorbing layer thickness becomes 1.5 μm.
m, a non-reflective film is formed on the light incident end face 31 so that a reverse bias of 1.5 μm is applied to light having a wavelength of 1.3 μm.
At V, a large value of light receiving sensitivity of 0.95 A / W or more was obtained.

The overall thickness of the grown layer was as thin as 3.5 μm, and equivalent or better light receiving sensitivity was obtained with a grown layer thickness of less than half that of the lateral light incident waveguide type semiconductor light receiving element.

Even after the formation of the anti-reflection film, the dark current remains at 1
A sufficiently small value of about 0 pA was obtained. In addition, the element area was small, and the element capacitance was about 0.4 pF or less.

In this embodiment, the light incident end face is (00
1) The wafer on the surface was subjected to wet etching using bromomethanol to form the (111) A surface, which was used. Therefore, the mesa angle (55 degrees with respect to the upper surface)
Thus, a uniform element having uniformity was produced.

Of course, the reverse mesa may be formed by using another wet etching solution or a dry etching method, may be formed by using another crystal plane, or by controlling the angle using the adhesion of an etching mask. You may.

In this embodiment, the main inner portion of the InP layer 32 on the surface side is formed of the p-InP layer 322 by the diffusion of Zn, so that there is an advantage that the dark current can be remarkably reduced.
That is, the dark current easily flows on the surface or the end face of the semiconductor. However, as shown in the present embodiment, by making the conductivity type of the main inner portion of the InP layer 32 on the front side different from that of the end face portion, the dark current is reduced. Becomes difficult to flow, and the value can be reduced by about two digits.

The determination of the conductivity type of the main inner portion of the semiconductor on the surface side is not limited to the determination by the diffusion of Zn, but may be performed by ion implantation and subsequent annealing. In this embodiment, an n-InP substrate is used. However, even when a p-InP substrate is used, the above-described p and n can be reversed and the same can be obtained. It can be manufactured in the same manner using the above substrate.

Although a bulk having a uniform composition is used as the absorption layer, it goes without saying that a semiconductor layer having an avalanche photodiode structure or a superlattice structure may be used. Further, InGaAlAs / InGaAs /
It goes without saying that a material system such as InGaAsP or AlGaAs / GaAs or a material system having intrinsic strain may be used. Further, the light receiving layer may have a multilayer structure including an intrinsic semiconductor layer or a superlattice semiconductor layer.

[Embodiment 3] FIG. 4 shows a third embodiment of the present invention.
Shown in In the figure, reference numeral 41 denotes a light incident end face;
2 μm thick undoped or n ⁻ -InAlAs layer, 43
0.1μm was smoothly changing the composition from nAlAs to InGaAs thickness undoped or _{^{n - -In 1- xy Ga x Al}} y
As (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) layer, 44 is 1.5 μm
Thick undoped or n ^-- InGaAs light absorbing layer, 45 is 1
μm thick n-InP layer, 46 is an n-InP substrate, 47 is Pt
A / Ti / Au Schottky electrode 48 is an ohmic n-electrode. The absorption layer area of the device is 30 μm × 50 μm.

The light incident end face 41 has a shape which is inclined inward toward the end face of the substrate 46 as the distance from the front side increases. That is, the light incident end face 41 is so-called
This is formed as an inverted mesa structure. Therefore, the incident light passes obliquely to the light absorbing layer 44 due to the refraction of the light at the light incident end face 41, so that the effective light absorption length increases.
In addition, since the Schottky electrode 47 acts as a reflection mirror with respect to the refracted incident light, the absorption length is further equivalently doubled, and the thickness of the absorption layer is 1.5 μm and a non-reflection film is formed on the light incident end face. With light having a wavelength of 1.3 μm, a light receiving sensitivity of 0.95 A /
A large value of W or more was obtained.

The overall thickness of the grown layer was as thin as 2.8 μm, and a light receiving sensitivity equal to or higher than that of a laterally incident light waveguide type semiconductor light receiving element was obtained with a thickness of less than half. The dark current is
Even after the formation of the antireflection film, a sufficiently small value of about 1 nA was obtained. In addition, the element area can be small, and the element capacitance is about 0.4 pF or less.

In this embodiment, the InAlAs layer 42
Is a so-called semiconductor layer having a high Schottky barrier height, and has 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. Therefore, the entire light receiving element can be configured without the pn junction semiconductor layer, and the pn junction due to impurity diffusion or the like becomes unnecessary, 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.

In this embodiment, the light incident end face is (0
01) The wafer on the surface was wet-etched using bromomethanol to form the (111) A surface, which was used. An element having a mesa angle of about 55 degrees with respect to the upper surface could be manufactured. Of course, the reverse mesa may be formed by using another wet etching solution or a dry etching method, may be formed by using another crystal plane, or by controlling the angle using the adhesion of an etching mask. Good.

In this embodiment, the In _1-xy G _ax Al _y As layer 4
As No. 3, a smooth connection of the conduction band and the valence band is achieved by using a gradient composition layer whose composition is smoothly changed from InAlAs to InGaAs, and this layer is a step formed of one or more multilayer semiconductor thin films. A pseudo gradient composition layer composed of a composition layer having a shape of a circle may be used. Further, also between the InGaAs light absorbing layer 44 and the n-InP layer 45 was changed composition of InGaAs to _{InP In 1-u Ga u As} 1-v P v (0 ≦ u ≦
1,0 ≦ v ≦ 1) A smooth connection between the conduction band and the valence band may be achieved by using a gradient composition layer or a pseudo gradient composition layer.

Although the present embodiment is an example using the n-InP substrate 46, it can be similarly manufactured by reversing the above n and p even if a p-InP substrate is used. It can be manufactured in the same manner using the above substrate. Further, the present invention can be similarly applied to other substrates such as GaAs. In addition, here, a bulk having a uniform composition is used as the light absorbing layer 44, but it goes without saying that a semiconductor layer having an avalanche photodiode structure, a superlattice structure, a multiple quantum well semiconductor layer, or the like may be used.

Further, InGaAs other than InGaAlAs type
P, AlGaAs, AlInPAs, InGaPSb, AlGaP
Needless to say, a material system such as Sb, AlGaAsSb, AlInAsSb, and AlInPSb or a material system having a strain therein may be used.

[Embodiment 4] FIG. 5 shows a fourth embodiment of the present invention.
Shown in In the figure, 51 is a light incident end face, 59 is 5n
m-thick undoped or n ^-- InP layer, 52 is 0.2 μm
Thick undoped or n ^-- InAlAs layer, 53 is InAlA
0.1 whose composition was smoothly changed from s to InGaAs.
μm thick undoped or _{^{n - -In 1-xy Ga x}} Al y As (0
≦ x ≦ 1,0 ≦ y ≦ 1 ) layer, 54 is 1.5μm thick undoped or ⁿ - -InGaAs light-absorbing layer, 55 is 1μm thick n
-InP layer, 56 is an n-InP substrate, 57 is Pt / Ti / A
The u-Schottky electrode 58 is an ohmic n-electrode.
The absorption layer area of the device is 30 μm × 50 μm.

The light incident end face 51 has a shape which is inclined inward toward the end face of the substrate 56 as the distance from the front side increases. That is, the light incident end face 51 is so-called
This is formed as an inverted mesa structure. Accordingly, since the incident light passes obliquely to the light absorbing layer 54 due to the refraction of the light at the light incident end face 51, the effective light absorption length becomes longer.
In addition, since the Schottky electrode 57 acts as a reflecting mirror with respect to the refracted incident light, the absorption length is further equivalently doubled, and the thickness of the absorbing layer is 1.5 μm and a non-reflective film is formed on the light incident end face. As a result, a large value of light receiving sensitivity of 0.95 A / W or more was obtained at an applied reverse bias of 1.5 V at a wavelength of 1.3 μm. The overall thickness of the grown layer was as thin as about 2.8 μm, and a light receiving sensitivity equal to or higher than that of a laterally light incident waveguide type semiconductor light receiving element was obtained with a grown layer thickness of half or less.

Further, in this embodiment, the extremely thin In
Since the P layer 59 is used, 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 of this, the general formula In is used.
It is also possible to use a layer represented by _{1-u Ga u As 1-} v P v (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 immersion was small, and the element capacitance was about 0.4 pF or less.

In this embodiment, the InAlAs layer 52
Is a so-called semiconductor layer having a high Schottky barrier height, and has a higher Schottky barrier than the Schottky barrier when the light absorbing layer 54 and the Schottky electrode 57 are in direct contact with each other. Therefore, the entire light receiving element can be configured without the pn junction semiconductor layer, and the pn junction due to impurity diffusion or the like becomes unnecessary, 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.

In this embodiment, the light incident end face is (0
01) The wafer on the surface was wet-etched using bromomethanol to form the (111) A surface, which was used. An element having a mesa angle of about 55 degrees with respect to the upper surface could be manufactured. Of course, the reverse mesa may be formed by using another wet etching solution or a dry etching method, may be formed by using another crystal plane, or by controlling the angle using the adhesion of an etching mask. Good.

In this embodiment, the In _1-xy G _ax Al _y As layer 5
As No. 3, a smooth connection of the conduction band and the valence band is achieved by using a gradient composition layer whose composition is smoothly changed from InAlAs to InGaAs, and this layer is a step formed of one or more multilayer semiconductor thin films. A pseudo gradient composition layer composed of a composition layer having a shape of a circle may be used. Further, between the InGaAs light absorbing layer 54 and the n-InP layer 55, In ₁ -u _Gau As _{1 -v Pv} (0 ≦ u ≦) whose composition is changed from InGaAs to InP.
1,0 ≦ v ≦ 1) A smooth connection between the conduction band and the valence band may be achieved by using a gradient composition layer or a pseudo gradient composition layer.

Although the present embodiment is an example using the n-InP substrate 56, the above-mentioned p-InP substrate may be used even if a p-InP substrate is used.
And n can be made in the same way, and can be made in the same manner using a semi-insulating substrate. Also, GaAs
Etc. can be similarly applied to other substrates. In this embodiment,
Although a bulk having a uniform composition is used as the light absorbing layer 54,
Needless to say, a semiconductor layer having an avalanche photodiode structure or a superlattice structure, a multiple quantum well semiconductor layer, or the like may be used.

Further, InGaAsP other than InGaAlAs type
And AlGaAs, AlInPAs, InGaPSb, AlGaPS
It goes without saying that a material system such as b, AlGaAsSb, AlInAsSb, and AlInPSb or a material system having an intrinsic strain may be used.

[Embodiment 5] FIG. 6 shows a fifth embodiment of the present invention.
Shown in In the figure, the semiconductor light receiving element 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 absorbing layer, and 64 is a 1 μm thick n
-InP layer, 65 is an n-InP substrate, 66 is a p-electrode, 67
Is an n-electrode.

Since the light passes obliquely to the light absorbing layer due to the refraction of the light on the incident surface, the effective light absorption length increases, and the absorption layer has a thickness of 1.5 μm. With this arrangement, a sufficiently large light receiving sensitivity can be obtained at a wavelength of 1.3 μm with an applied reverse bias of 1.5 V. In addition, the total thickness of the grown layer is as thin as 3.5 μm, and a light receiving sensitivity equal to or higher than that of a laterally incident light waveguide type semiconductor light receiving element can be obtained with a grown layer thickness of half or less. As for the dark current, a sufficiently small value of about 10 pA was obtained even after the formation of the antireflection film.

In this embodiment, the light incident surface is (00
1) The wafer on the surface was subjected to wet etching using bromomethanol to form the (111) A surface, which was used. 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 inverted mesa may be formed by using another wet etching solution or dry etching method, or may be formed by using another crystal plane or controlling the angle by 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, the above-described p and n can be reversed and the same can be manufactured. It can also be manufactured similarly.

In addition, here, a bulk having a uniform composition is used as the absorption layer, but it goes without saying that a semiconductor layer having an avalanche photodiode structure or a superlattice structure may be used. In addition, In InAs other than InGaAsP / InP type
It goes without saying that a material system such as a GaAlAs / InGaAsP or AlGaAs / GaAs system or a material system having intrinsic strain may be used.

The semiconductor light receiving element is mounted so as to be coupled to an optical waveguide 69 (spot size ω ₀ = 5 μm) made of SiO ₂ formed on a silicon substrate 68 as shown in FIG. At this time, the lower surface 63a of the light absorbing layer on the side of the InP substrate.
And the height difference (Zh) at the optical axis center of the optical waveguide was 10 μm.

Generally, the Gaussian beam emitted from the optical waveguide spreads as it travels. When Zh is increased, the optical path length for receiving the refracted light in the light receiving layer becomes longer, and in order to maintain the same light receiving sensitivity, it is necessary to increase the light receiving area in accordance with the spread of the beam. Since the increase in the area is proportional to the junction capacitance of the element, the response speed of the element is also greatly deteriorated. The graph shows the square of the spot size at the point where the center of the light beam reaches the light-receiving layer (almost proportional to the required light-receiving area), with Zh being the horizontal axis, the light-receiving element and the optical waveguide being arranged in the immediate vicinity. 7 (solid line).

As shown in FIG. 7, when Zh is increased, the required light receiving area suddenly increases, and the response band of the element sharply decreases in proportion thereto. Therefore, in this embodiment, Zh is set to 10 μm where the spread of the beam can be almost ignored. As a result, the element area can be small, and the absorption layer area can be reduced to 15
When μm × 50 μm, the light receiving sensitivity was 0.9 A / W or more, and the element capacitance was a small value of about 0.2 pF or less.

The broken line in FIG. 7 also shows the relationship when the spot size of the optical waveguide is 2 μm. As described above, when ω ₀ is reduced, the beam spread becomes more rapid. Therefore, it is important to reduce Zh to as much as ω _{0 as} much as possible. For example, when Zh is set to 50 μm, the light receiving area becomes approximately equal to that when Zh = 4 μm. This is required as much as 15 times, and the element capacity increases drastically.

This relationship is naturally related to the inverse mesa angle θ of the light receiving element.
Also depends. Beam area is 30% of initial beam area
Assuming that the increasing point is Zh _{+ 30%} , Zh _{+ 30%} = nπω
It is given by ₀ ² (0.3) ^1/2 / λsin (φ). Where n
Is the refractive index of the semiconductor for light of wavelength λ, π is the circular constant, ω
₀ is the spot size of the optical waveguide (in the case of a rectangular waveguide or the like, the equivalent spot size characterizing the waveguide);
φ is the angle between the optical axis center of the refracted light and the light absorbing layer.

For light having a wavelength of 1.3 μm, θ = 55
Assuming that the refractive index of the InP substrate is n = 3.209, ω₀=
Zh at 5μm_{+ 30%}= 44.4 μm, ω₀= 2 μm
And Zh _{+ 30%}= 7.1 μm, small spot size
Especially when using an optical waveguide that is close to the light-receiving layer side surface
It is important to bring the center of the optical waveguide optical axis to
I understand.

Although the present embodiment uses an optical waveguide formed on a silicon substrate as an optical waveguide, other optical waveguides such as an optical fiber and a polymer optical waveguide may be hybrid-integrated on an appropriate substrate. It goes without saying that it is good. Also, the light receiving layer surface and the optical axis direction of the optical waveguide need not be completely parallel, and it is sufficient that the light receiving layer refracts light at the incident end face and receives light at the light receiving layer, and the angle slightly deviates from the parallel direction. There is no problem even if you do. The p-InP layer 62
Although 2 was formed by Zn diffusion, it may be alternatively switched to the second conductivity type by ion implantation and subsequent annealing.

Embodiment 6 FIG. 8 shows a sixth embodiment of the present invention.
Shown in In the drawing, reference numeral 81 denotes a light incident surface, and 82 denotes a 1 μm thick p-I.
nP 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 p
The electrode 87 is an n-electrode. In this embodiment, (001)
Since the above-described layer structure is grown on a substrate having a polished surface inclined at 20 degrees with respect to the surface, the mesa angle is 70 degrees with respect to the surface as shown in FIG. Is formed.

The area of the absorption layer of the device is 20 μm × 80 μm. Since light passes obliquely to the light absorption layer due to refraction of light on the incident surface, the effective light absorption length becomes longer, and a 1.5 μm thick absorbing layer and a non-reflective film are formed on the incident surface. As a result, a large value of light receiving sensitivity of 0.9 A / W or more was obtained at an applied reverse bias of 1.5 V with light having a wavelength of 1.3 μm. Also, the overall growth layer thickness was as thin as 3.5 μm, and a light receiving sensitivity equal to or higher than that of a growth layer thickness of half or less of the lateral light incident waveguide type semiconductor light receiving element was obtained.

In the present embodiment, a substrate having a polished surface inclined by 20 degrees with respect to the (001) plane is used. However, by selecting this angle appropriately, the mesa angle can be adjusted accordingly. Needless to say, you can choose.
Needless to say, the present invention can be similarly applied to a semiconductor layer configuration as in the second to fourth embodiments. In this embodiment, n
Although this is an example using an InP substrate, it can be manufactured in the same manner by using a p-InP substrate by reversing the above p and n, and can be manufactured similarly using a semi-insulating substrate. It is.
Further, here, a bulk having a uniform composition is used as the absorption layer, but it goes without saying that a semiconductor layer having an avalanche photodiode structure or a superlattice structure may be used.

In addition, InGaP other than the InGaAsP / InP type
It goes without saying that a material system such as AlAs / InGaAsP or AlGaAs / GaAs system or a material system having intrinsic strain may be used.

[0070]

As described above in detail with reference to the embodiments, the semiconductor light receiving element has a light receiving surface having an inverted mesa structure on the front surface side.
Based on the mesa angle of the inverted mesa, the incident light is refracted toward the upper surface at the incident end face and obliquely passes through the light absorbing layer, effectively increasing the light absorption length. The thickness of the absorption layer can be smaller than that of the semiconductor light receiving device. Also,
Compared with the lateral incidence type waveguide type semiconductor light receiving element, it is 1 /
A semiconductor growth layer thickness of about 2/3 is sufficient.

As described above, while light can enter in the lateral direction, light can be received efficiently with a small semiconductor growth layer thickness for direct optical coupling with an optical fiber or an optical waveguide. Furthermore, 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.

Further, when a so-called semiconductor layer having a high Schottky barrier height is interposed between the light absorbing layer and the Schottky electrode, the entire light receiving element can be formed without a pn junction semiconductor layer, and the pn junction is formed by impurity diffusion or the like. Since the junction is not required and the pn junction is not exposed to the end face via the light absorbing layer, there is an advantage that the dark current can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic structural view 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 schematic structural view of a semiconductor light receiving element according to a second embodiment of the present invention.

FIG. 4 is a schematic structural view of a semiconductor light receiving element according to a third embodiment of the present invention.

FIG. 5 is a schematic structural view of a semiconductor light receiving element according to a fourth embodiment of the present invention.

FIG. 6 is a schematic structural diagram of a semiconductor light receiving element according to a fifth embodiment of the present invention.

FIG. 7 shows the height difference (Zh) between the lower surface 63a of the light absorbing layer on the InP substrate side and the optical axis center of the optical waveguide and the square of the spot size at the point where the light beam center reaches the light receiving layer (substantially less than the required light receiving area). 6 is a graph showing a relationship of (proportional).

FIG. 8 is a schematic structural view of a semiconductor light receiving element according to a sixth embodiment of the present invention.

[Explanation of symbols]

11, 31 Light incidence end face 12 p-InP layer 13, 33 InGaAs light absorbing layer 14, 34 n-InP layer 15, 35 n-InP substrate 16, 36 p electrode 17, 37 n electrode 32 InP layer 322 Zn formed by diffusion p-InP layer 41 light incident end face 42 InAlAs layer 43 which is _{In 1-xy Ga x Al y} As layer 44 InGaAs light absorbing 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-xy Ga x Al} y As layer 54 InGaAs light absorbing 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 1.5 μm thick InGaAs light absorption layer 63a 1.5 μm thick In Lower surface of the aAs light absorbing layer on the side of the InP substrate 64 1 μm thick n-InP layer 65 n-InP substrate 66 p electrode 67 n electrode 68 silicon substrate 69 optical waveguide formed on the silicon substrate 81 light incident surface 82 1 μm thick p-InP Layer 83 1.5 μm thick InGaAs light absorbing layer 84 1 μm thick n-InP layer 85 n-InP substrate 86 p electrode 87 n electrode

Claims (8)

[Claims] A first semiconductor layer having a first conductivity type;
In a semiconductor light receiving element, a second semiconductor layer having a second conductivity type and a growth layer comprising a light receiving layer sandwiched between the first semiconductor layer and the second semiconductor layer are provided on a substrate.
By providing a light incident end face that is inclined inward as the end face of the growth layer and the substrate is separated from the front side,
A semiconductor light receiving element, wherein 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. 2. 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 a first semiconductor layer having a first conductivity type. A growth layer comprising a light receiving layer sandwiched between two semiconductor layers is provided on the substrate, and the semiconductor on the front side including a main inner portion of the first semiconductor layer on the front side or a part of the light receiving layer is provided. A main inner portion of the layer is selectively converted to the second conductivity type by diffusion of impurities, and further, a light incident end face inclined inward away from the surface side is provided on an end face of the growth layer and the substrate. The method for manufacturing a semiconductor light receiving element, wherein 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. 3. 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 a first semiconductor layer having a first conductivity type. A growth layer comprising a light receiving layer sandwiched between two semiconductor layers is provided on the substrate, and the semiconductor on the front side including a main inner portion of the first semiconductor layer on the front side or a part of the light receiving layer is provided. The main inner part of the layer is selectively converted to the second conductivity type by ion implantation and subsequent annealing, and furthermore, the growth layer and the end face of the substrate have light inclining inward as they move away from the surface side. A method for manufacturing a semiconductor light receiving element, wherein an incident end face is provided to refract incident light at the light incident end face so that the incident light passes through the light receiving layer obliquely to a layer thickness direction. . 4. A light-absorbing layer on a semiconductor layer having a first conductivity type, comprising an intrinsic or first conductivity-type semiconductor layer, a superlattice semiconductor layer or a multiple quantum well semiconductor layer, and a Schottky electrode. A multi-layer structure having 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 with respect to the Schottky electrode. In the semiconductor light-receiving element configured above, the multilayer structure and the end face of the substrate, by providing a light incident end face inclined inward as away from the front side, to refract incident light at the light incident end face, A semiconductor light receiving element, wherein incident light passes through the light absorbing layer obliquely to a layer thickness direction. 5. The semiconductor layer having a high Schottky barrier height is made of In _1-xy G _ax Al _y As (0 ≦ x ≦ 1, 0 ≦ y).
The semiconductor light receiving device according to claim 4, wherein ≤ 1). 6. The semiconductor layer having a high Schottky barrier height is made of In _1-xy G _ax Al _y As (0 ≦ x ≦ 1, 0 ≦ y).
≦ 1) and their thin upper _{In 1-u Ga u As 1} -v P v (0 ≦ u ≦
5. The semiconductor light receiving device according to claim 4, wherein 1, 0 ≦ v ≦ 1). 7. A continuous arrangement between the light absorbing layer and the semiconductor layer having a high Schottky barrier height from the same composition as the light absorbing layer to the same composition as the semiconductor layer having a high Schottky barrier height. 7. The semiconductor light receiving device according to claim 4, wherein a graded composition layer having a composition gradient that changes stepwise is interposed. 8. An optical axis of an optical waveguide provided so as to be optically coupled via a light incident end face of the semiconductor light receiving element in a direction parallel to a semiconductor surface and a lower surface on a substrate side in a thickness direction of the light absorbing layer. 8. The semiconductor light receiving device according to claim 1, wherein the height difference at the center is smaller than a value given by Zh _{+ 30%} of the following equation. Zh _{+ 30%} = nπω ₀ 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 circular constant, and ω ₀ is 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 between the optical axis center of the refracted light and the light absorbing layer.