JP3612638B2 - Semiconductor optical device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor optical device and a manufacturing method thereof.
[0002]
[Prior art]
As an example of a general semiconductor waveguide optical device, a waveguide photodetector shown in FIG. 2 is known (K. Kato et al., “High-efficiency waveguide InGaAs pin photodiode with bandwidth 40 GHz”, IEEE Photonics Technology Letters, 3, 473, 1991).
[0003]
As shown in the figure, this waveguide type photodetector is made of an InP-based material that does not absorb signal light above and below a core layer (InGaAs in the case of FIG. 2) 203 made of an InP-based material that absorbs signal light. Upper and lower cladding layers (InP in the case of FIG. 2) 202 and 204 are laminated on the substrate 201.
Here, the upper clad layer 204 is p-type, the lower clad layer 202 is n-type, and the core layer 203 is non-doped and is actually a low-concentration n-type.
[0004]
Further, as shown in the figure, the lower clad layer 202 has a larger area than the upper clad layer 204 and the core layer 203 and protrudes to the left in the figure on the substrate 201, and a p-type ohmic electrode 205 is formed thereon. On the other hand, an n-type ohmic electrode 206 is formed on the upper cladding layer 204.
In this semiconductor waveguide type photodetector, a reverse bias voltage is applied between the upper cladding layer 204 and the lower cladding layer 202, which are conductive layers, to form a depletion layer in the non-doped core layer 203. Using the high electric field applied to the depletion layer, the signal light propagating along the core layer 203 in the semiconductor waveguide type photodetector is photoelectrically converted.
[0005]
By the way, since the electrostatic capacity of this conventional semiconductor waveguide type photodetector is proportional to the area of the optical waveguide, the response speed is inversely proportional to the area of the optical waveguide. On the other hand, in order to increase the photoelectric conversion efficiency of the semiconductor waveguide type photodetector, it is necessary to sufficiently lengthen the optical waveguide, so it is not possible to satisfy both high speed response and high efficiency at the same time. It was possible.
[0006]
Therefore, a traveling wave waveguide type photodetector without speed limitation due to the presence of capacitance has been devised (KS Giboney et al., “Traveling-wave photodetectors with 172-GHz bandwidth and 76-GHz bandwidth”). efficiency product ", IEEE Photonics Technology Letters, Vol. 7, p. 412, 1995).
[0007]
That is, as shown in FIG. 3, upper and lower cladding layers (AlGaAs in the case of FIG. 3) 302, 304 that do not absorb the signal light are provided above and below the core layer (GaAs in the case of FIG. 3) 303 that absorbs the signal light. A waveguide type photodetector is formed by laminating the substrate 301, and a lower clad layer 302 is projected from the upper clad layer 304 and the core layer 303 to the left and right sides in the drawing, and an n-type ohmic electrode is formed thereon. On the other hand, a p-type ohmic electrode 305 is formed on the upper clad layer 304.
[0008]
As a result, a coplanar line type electrode designed so that the capacitance of the photodetector and the inductance of the coplanar line have a characteristic impedance of 50Ω could be obtained.
[0009]
[Problems to be solved by the invention]
Now, since the electromagnetic field distribution of the optical signal propagating in the traveling wave type waveguide photodetector is confined in the semiconductor, the effective guide wavelength is equal to the guide wavelength in the semiconductor.
On the other hand, since the upper half of the electromagnetic field distribution of the electric signal propagating through the coplanar line leaks into the air, the effective guide wavelength is an average value of the guide wavelength in the semiconductor and the wavelength in the air.
[0010]
Since the speed of the electromagnetic wave is inversely proportional to the effective guide wavelength, the speed of the light in the optical waveguide and the speed of the electric signal guided through the coplanar line in the conventional traveling wave type waveguide photodetector is conventional. There is a problem that the photodetector does not respond at high speed due to mismatching.
[0011]
This is because both the optical signal and the electric signal propagating through the coplanar line are electromagnetic waves, but the frequency is significantly different, so that the refractive index may be greatly different between the optical signal and the electric signal depending on the material forming the optical waveguide. This is because the refractive indexes of semiconductors are equal.
An object of the present invention is to provide a semiconductor traveling wave photodetector capable of solving the above-described problems of the prior art and capable of high-efficiency and high-speed response.
[0012]
[Means for Solving the Problems]
In order to achieve such an object, the present invention is characterized in that a semiconductor layer is disposed above a traveling wave waveguide type photodetector having a coplanar line. Further, a traveling wave type waveguide type photodetector having a slot line instead of the coplanar line can be configured in the same manner. The present invention differs from the prior art in that most of the electromagnetic field of the electric signal propagating through the coplanar line or the slot line is distributed in the semiconductor.
[0013]
[Action]
Since the semiconductor layer is disposed above the traveling wave type waveguide photodetector provided with the coplanar line, most of the electromagnetic field of the electric signal propagating through the coplanar line is confined in the semiconductor. Similar to the effective guide wavelength of the optical signal, the effective guide wavelength of the electrical signal becomes equal to the guide wavelength of the semiconductor.
[0014]
Therefore, the speed of light in the optical waveguide is almost equal to the speed of the electrical signal guided through the coplanar line, and the response speed drop due to speed mismatch is eliminated. A waveguide type photodetector can be realized.
Further, the traveling wave type waveguide photodetector having a slot line instead of the coplanar line has the same effect.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
[Example 1]
FIG. 1A shows a cross-sectional structure diagram of a semiconductor traveling wave waveguide type photodetector according to a first embodiment of the present invention.
In this embodiment, in a semiconductor waveguide type optical device having a coplanar line arranged in parallel with a semiconductor optical waveguide as an electrode, a semiconductor layer is arranged on the upper part of the coplanar line, and the speed of the electric signal and the optical signal in the semiconductor optical waveguide are This is a semiconductor waveguide type optical device capable of high-speed response, characterized by a structure that can be matched with the speed of.
In the figure, 101 is a semi-insulating InP substrate, 102 is an n-type InP lower cladding layer having a thickness of 0.5 μm, 103 is a non-doped InGaAs layer having a thickness of 0.2 μm, and 104 is a p-type InP having a thickness of 0.5 μm. The upper cladding layer, 105 is a 4 μm wide p-type ohmic electrode, 106 is an n-type ohmic electrode, and 107 is another semi-insulating InP substrate.
[0016]
As shown in the figure, in this embodiment, three mesas including an n-type InP lower cladding layer 102, an InGaAs layer 103, and an upper cladding layer 104 are formed on a semi-insulating InP substrate 101 having a high resistance. A wafer-like semi-insulating InP substrate 107 is placed thereon. Three electrodes 105 and 106 were formed on three mesas.
[0017]
Here, of the three mesas on the substrate 101, the central mesa is an optical waveguide, and the right and left mesas are pedestals for fixing the substrate 107. After forming the p and n electrodes on these mesas, the electrodes A semi-insulating InP substrate 107 is disposed so as to be in contact with 105 and 106. The semi-insulating InP substrate 107 can be fixed by heat fusion or the like.
The substrate 107 is not necessarily the same type as the substrate 101, and a substrate having a refractive index that is equal to or close to the refractive index of the substrate 101 is used.
[0018]
The central mesa has a width of 5 μm and is viewed as a waveguide. The p-type InP layer 104 is an upper cladding layer, the non-doped InGaAs layer 103 is a core layer, the n-type InP layer 102 is a lower cladding layer, and is also a photodetector. This is a pin photodiode configuration in which the non-doped InGaAs layer 103 is a photoelectric conversion layer.
Further, as shown in the figure, the electrode on the center mesa is the center electrode 105 serving as a signal line, and the electrodes 106 on the left and right mesas are coplanar lines having a ground electrode configuration, and its characteristic impedance The distance between the center electrode 105 and the ground electrode 106 is set to 5 μm so as to be 50Ω.
[0019]
In the semiconductor traveling wave type waveguide photodetector according to the present embodiment, an optical signal is gradually absorbed in the optical waveguide and converted into an electromagnetic wave (electric signal) guided through a coplanar line.
Here, since the semi-insulating substrates 101 and 107 which are semiconductor layers exist above and below the coplanar line, most of the electromagnetic field distribution exists in a semiconductor having a large dielectric constant. The target guide wavelength is approximately equal to the guide wavelength in the semiconductor.
[0020]
As a result, the electric signal speed is almost equal to the optical signal speed, the response speed reduction due to the speed mismatch is eliminated, and a high-speed optical signal of 150 GHz can be converted into an electric signal.
In this embodiment, an example in which a wafer-like semiconductor substrate 107 is disposed on a coplanar line is shown. However, as shown in FIG. 1B, a method such as semiconductor vapor deposition, semiconductor particle coating, or low-temperature crystal growth is used. Thus, even if the semi-insulating InP layer 108 which is a semiconductor layer is formed on the coplanar line, the same effect can be obtained.
[0021]
In the present embodiment, an example in which a material that lattice-matches with the InP substrate is used as the semiconductor material, but the same effect can be expected even if a part or all of these materials do not lattice-match with InP.
In addition, although an example in the case where the signal light wavelength is 1.55 μm has been shown, the semiconductor traveling wave type having the same effect as the present embodiment with respect to signal light other than the wavelength 1.55 μm by appropriately selecting the material. A waveguide type photodetector can be realized. Furthermore, this structure can be applied to other optical elements such as a semiconductor laser or a semiconductor optical modulator.
[0022]
Furthermore, in this embodiment, the ohmic electrodes 105 and 106 are given as an example. However, the present invention is not limited to this, and microwave electrodes can be widely used. An example is shown in FIG.
[0023]
[Example 2]
FIG. 4 shows a sectional structural view of a semiconductor traveling wave waveguide type photodetector according to the second embodiment of the present invention.
This embodiment adopts a configuration of a ground electrode only on one side called a slot line, and the other configuration is the same as that of the above-described embodiment.
That is, two mesas including an n-type InP lower cladding layer 402, a non-doped InGaAs layer 403, and a p-type InP upper cladding layer 404 are formed on a semi-insulating InP substrate 401, and a wafer-like semi-insulating InP substrate is formed thereon. 407. A p-type ohmic electrode 405 and an n-type ohmic electrode 406 were formed on the two mesas.
[0024]
Here, the mesa on the left side of the drawing on the substrate 401 is an optical waveguide, and an electrode 405 serving as a signal line is formed, and a pedestal on which the mesa on the right side of the drawing on the substrate 401 fixes another substrate 407. And constitutes a slot line in which an electrode 406 is formed as a ground electrode.
In this embodiment, since a slot line is used instead of the coplanar, the ground electrode only needs to be provided on one side as compared with the above-described embodiment, and there is an advantage that the manufacturing cost and the process can be reduced, and the size and weight can be reduced. is there.
[0025]
【The invention's effect】
As described above in detail based on the embodiments, the speed of light in the optical waveguide, the coplanarity can be obtained by arranging the semiconductor layer above the traveling wave type waveguide type photodetector provided with the coplanar line. The speed of the electric signal guided through the line is almost equal, and there is an advantage that a semiconductor traveling wave waveguide type photodetector capable of high-speed response can be realized. Further, if a slot line is used instead of the coplanar line, there are advantages that the manufacturing cost and the process can be reduced, and that a reduction in size and weight can be achieved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a semiconductor traveling wave waveguide type photodetector according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram of a conventional semiconductor waveguide type photodetector.
FIG. 3 is a schematic diagram of a conventional semiconductor traveling wave waveguide type photodetector.
FIG. 4 is a cross-sectional view showing a semiconductor traveling wave waveguide photodetector according to a second embodiment of the present invention.
[Explanation of symbols]
101, 401 Semi-insulating InP substrate 102, 402 n-type InP lower cladding layer 103, 403 Non-doped InGaAs layer 104, 404 p-type InP upper cladding layer 105, 405 p-type ohmic electrode 106, 406 n-type ohmic electrode 107, 407 half Insulating InP substrate 108, 408 Insulating InP layer 201 Semi-insulating InP substrate 202 N-type InP lower cladding layer 203 Non-doped InGaAs layer 204 p-type InP upper cladding layer 205 p-type ohmic electrode 206 n-type ohmic electrode 301 Semi-insulating GaAs Substrate 302 N-type AlGaAs lower cladding layer 303 Non-doped GaAs layer 304 p-type GaAs upper cladding layer 305 p-type ohmic electrode 306 n-type ohmic electrode

Claims (8)

A semiconductor optical waveguide formed on a semiconductor substrate having a high resistance, a signal line is formed on the semiconductor waveguide, and a ground conductor arranged in parallel with the semiconductor optical waveguide is formed on the semiconductor substrate. In a semiconductor optical device having a wave electrode, a semiconductor having a refractive index equal to or close to a refractive index of the semiconductor substrate is disposed at least in a region extending from above the signal line to the ground conductor. A semiconductor optical device. Three mesas consisting of a lower clad layer, a core layer, and an upper clad layer are arranged in parallel on a semiconductor substrate having a high resistance, and the central mesa is a semiconductor optical waveguide on which an electrode serving as a signal line is formed. In a semiconductor optical device in which a coplanar line having a ground electrode configuration is formed on the right and left mesas, respectively, at least in the region extending from the signal line to the coplanar line, the refractive index of the semiconductor substrate A semiconductor optical device, wherein a semiconductor having a refractive index equal to or close to is disposed . Two mesas consisting of a lower clad layer, a core layer and an upper clad layer are arranged in parallel on a semiconductor substrate having high resistance, and one mesa is a semiconductor optical waveguide on which an electrode serving as a signal line is formed. In the semiconductor optical device in which a slot line having a ground electrode configuration is formed on the other mesa, the refractive index of the semiconductor substrate is adjusted to at least a region extending from the signal line to the slot line. A semiconductor optical device comprising a semiconductor having a refractive index which is equal to or close to the refractive index . 4. The semiconductor optical device according to claim 1, wherein the semiconductor is a semiconductor in which a wafer-like semiconductor is arranged by heat fusion . 4. The semiconductor optical device according to claim 1, wherein the semiconductor is a semiconductor in which a particulate semiconductor is disposed by coating . 4. The semiconductor optical device according to claim 1, wherein the semiconductor is a semiconductor disposed by vapor deposition . 4. The semiconductor optical device according to claim 1, wherein the semiconductor is a semiconductor arranged by low-temperature crystal growth. 8. The semiconductor optical device according to claim 1, wherein the semiconductor optical waveguide is a waveguide type semiconductor photodetector.

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