JPH08316522A - Photodetector with hemt type photo-detecting part - Google Patents

Abstract

PURPOSE: To obtain a photodetector excellent in photofrequency response characteristics, photoelectric current characteristics, time response characteristics and noise characteristics. CONSTITUTION: Within the title photodetector with HEMT type photodetector detecting light by the current running between source/drain electrodes 11, 12 using ϕ-GaAs layer 5 including the secondary element electron gas layer as a light detecting layer, a photo-detecting part 10, a discharge electrode 14 of the hole made in the region excluding the photo-detecting layer 5 of the part 10 and a signal amplifying HEMT 20 in the same layer composition and electrode material as those of the part 10 are monolighically integrated on the same substrate 1. Besides, the hole discharge electrode 14 and the amplifying HEMT 20 are electrically isolated while the gate electrode 13 of one amplifying HEMT 20 is impressed with the photocurrent of part 10. Finally, the amplifying part 20 in the same layer composition is electrically isolated from the hole discharge electrode 14 not to be affected thereby so that the channel strangulation of the amplifying part 20 may be avoided to improve the amplifying efficiency as well as power consumption to be cut down.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal detector in optical communication and the like, and more specifically to a HEMT.
The present invention relates to integration of a photodetection unit that detects light using a structure and an amplifier of a photodetection signal.

[0002]

2. Description of the Related Art Conventionally, PIN photodiodes and avalanche photodiodes are known as high-speed photodetectors. In addition, HEMT (High Electron Mobility)
A photodetector using a Transistor (high electron mobility transistor) structure is also expected to operate at high speed, and there are some reports (eg, CYChen et.al., Appl Phys Lett. 4
1, p1040 (1983), Baba et al. SIQ OQE92-43
p81 (1992)).

7 and 8 show a conventional example of a photodetector having a HEMT structure. Each of them will be referred to as an element A and an element B. Element A is semi-insulating (hereinafter referred to as SI)
On a -GaAs substrate 1001, a φ-GaAs buffer layer 1002 having a thickness of 1.0 μm and n-Al _0.3 Ga _0.7 As.
A layer 1003 having a thickness of 0.1 μm and an n ⁺ -GaAs contact layer 1004 having a thickness of 0.05 μm are sequentially stacked, and a source electrode 1011 and a drain electrode 1012 are provided thereon, and then an n ⁺ -GaAs contact layer is formed. It is manufactured by etching 1004 and providing a recess type gate 1013. In the element A, a two-dimensional electron gas (hereinafter referred to as 2DEG
Layer) is the φ-GaAs buffer layer 1002 and φ-A.
It is formed at the interface with the _0.3 Ga _0.7 As layer 1003. On the other hand, the device B has a structure in which p-G is formed on the p-GaAs substrate 1021.
The aAs buffer layer 1022 has a thickness of 1.0 μm and 2DE
The φ-GaAs layer 1023 including the G layer has a thickness of 0.05 μm.
Then, the thickness of the n-Al _0.3 Ga _0.7 As layer 1024 is set to 0.1 μm.
m, the n ⁺ -GaAs contact layer 1025 has a thickness of 0.
The source electrode 1031 is stacked on top of this with a thickness of 05 μm.
And the drain electrode 1032 are provided, the n ⁺ -GaAs contact layer 1025 is etched to form the recess type gate 1
033 is provided, and further, a hole discharge electrode 1034 is provided on the back surface of the substrate 1021, which is a manufacturing process.

The operation of each element will be described below.

With element A in a biased state, φ-GaAs
The buffer layer 1002 and the φ-Al _0.3 Ga _0.7 As layer 100
The gate voltage is set so that electrons do not exist in the 2DEG layer formed at the interface with 3 (pinch off). In this state, when light is incident from the upper surface, φ-GaA
Carriers are generated by the light absorbed in the s layer 1002. The carriers generated here are electrons and holes, and the amount thereof depends on the light intensity. The electrons immediately reach the drain electrode 1012 and are detected by the electric field using the 2DEG layer as a channel through which the electrons flow. On the other hand, the holes generated just below the 2DEG layer widen the width of the channel in which electrons travel, and as a result, the current I _D corresponding to the light intensity flows.

The element B has a p-type on the substrate 1021 side, and a bias is applied to the p-type to expel holes to improve the response speed.

[0007]

Holes have a much slower moving speed than electrons. Therefore, in the element A of the above-mentioned conventional example, an electric field is hardly applied to the substrate 1001 side from the 2DEG layer. Therefore, when the hole generated in this region receives the optical signal subjected to the high speed modulation, The signal is accumulated until the moment the signal is received, which causes deterioration in response speed. In addition, since the accumulation of such charges changes the potential on the substrate 1001 side, it becomes a factor that makes the photocurrent characteristics unstable.

On the other hand, in the element B, the response speed and the photocurrent characteristic are improved by making the substrate 1021 side p-type and providing the mechanism 1034 for discharging holes. However, among the holes accumulated in the element A, the holes directly under the 2DEG layer have a function of expanding the 2DEG channel toward the substrate as described above, which is directly related to the amplification effect of the photocurrent. There is. Therefore, in the device B, the holes generated in the p-type region do not participate in the photocurrent characteristics at all, and the photocurrent becomes extremely small. As a result, an amplifier circuit is required to use the element B, but if an external one is used, the capacitance and resistance as a whole increase, and the response characteristics eventually deteriorate. When the HEMT having this structure is integrated with the HEMT for detecting light and used for amplification, in order to prevent the substrate side level of the amplification HEMT from varying and becoming unstable in accordance with an optical signal, A large bias is required for the hole discharge electrode. However, as a result, the channel becomes narrow, and sufficient amplification cannot be obtained unless a large voltage is applied to the drain. Therefore, not only the power consumption increases, but also the noise characteristics of the entire element deteriorate.

Accordingly, it is an object of the present invention to provide a photodetector having the features of both the above-mentioned elements which solves these problems.

[0010]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
A photodetector comprising a HEMT type photodetector for detecting light by a current flowing between a source electrode and a drain electrode using a φ-GaAs layer including a three-dimensional electron gas layer as a photodetection layer, the photodetector comprising: Means for ejecting holes generated in a region outside the photodetection layer of the photodetection unit and at least 1 for amplifying a signal having the same layer structure and the same electrode material as the photodetection unit
The two amplifying HEMTs are monolithically integrated on the same substrate, and means for discharging holes and the amplifying HEMTs.
Are electrically isolated from each other, and are achieved by a photodetector characterized by applying a photocurrent of the photodetection section to the gate electrode of one amplification HEMT. With this configuration, the photoresponse characteristics and photocurrent characteristics of the photodetector unit can be improved and the stray capacitance / input capacitance generated between the detector and amplifier can be reduced without changing the fabrication process substantially. By doing so, it is possible to improve the noise / response characteristics and to amplify the photocurrent output without substantially degrading the characteristics of the photodetector unit. Further, by improving the photodetection characteristics and electrically isolating the amplification section having the same layer structure so as not to be affected by the hole discharge electrode, the channel narrowing of the amplification section is prevented and the amplification efficiency is increased. Along with this, power consumption is reduced.

[0011]

First Embodiment FIG. 1 shows a first embodiment of the present invention. In this embodiment, Al is a III-V compound semiconductor.
_The description will be made using the xGa1 _- xAs / GaAs system. Since the light detection portion and the light amplification portion of this element have the HEMT structure, the source electrodes 11 and 21 and the drain electrodes 12 and 22 are made of Au.
/ Ni / Au-Ge is used in ohmic contact, Ti / Pt / Au is used in Schottky contact as the gate electrodes 13 and 23, and Cr / Au is used in ohmic contact for the hole discharge electrode 14. HE for light detection
The MT element size is a gate length of 1 μm, a gate width of 5 μm, a source-gate interval of 2 μm, and a gate-drain interval of 2 μm. On the other hand, the amplification HEMT has a gate width of 150 μm, and the others are of a photodetection HEMT element size. Same size as the HEMT10 for photodetection and H for amplification
The distance between the EMTs 20 is 150 μm. The photodetection HEMT 10 and the signal amplification HEMT 20 have exactly the same layer structure and electrode material except for the hole discharge electrode 14.

Here, the creation process will be described.
Φ-GaAs buffer layer 2 on SI-GaAs substrate 1
Is 1.0 μm thick, the p ⁺ -GaAs contact layer 3 is 0.5 μm thick, and the p-GaAs layer 4 is 0.5 μm thick.
Then, the φ-GaAs photodetection layer 5 including the two-dimensional electron gas layer has a thickness of 0.05 μm, the φ-Al _0.3 Ga _0.7 As spacer layer 6 has a thickness of 0.008 μm, and n-Al _0.3 Ga _0.7 As.
The layer 7 has a thickness of 0.05 μm, and the n ⁺ -GaAs contact layer 8 has a thickness of 0.03 μm, which are sequentially laminated using the MBE method. First, the source electrode 1 is formed by photolithography.
The portions other than the formation portions 1 and 21 and the formation portions of the drain electrodes 12 and 22 are covered with a resist, and the n ⁺ -GaAs contact layer 8 is removed by etching. Similarly, a portion other than the portion where the hole discharge electrode 14 is formed is covered with a resist by photolithography, and the p ⁺ -GaAs contact layer 3 is etched. Here, after heating the sample and depositing silicon oxide 9 with a thickness of 0.05 μm on the entire surface by a sputtering method, in order to form the electrical separation section 30 between the HEMT 10 for photodetection and the HEMT 20 for signal amplification, A portion other than the electrical isolation portion 30 is covered with a resist by a photolithography method, the silicon oxide 9 is etched with buffer hydrofluoric acid, the semiconductor wafer is etched with a sulfuric acid-based etching solution until the φ-GaAs buffer layer 2 is reached, and the MOCVD method is used. A φ-As _0.3 Ga _0.7 As high resistance buried layer 31 is formed.

Next, the portions other than the portion where the hole discharge electrode 14 is formed are covered with a resist, the silicon oxide 9 is etched using buffer hydrofluoric acid, and Cr / Au is continuously vapor-deposited.
By removing the resist with a release agent, the hole discharge electrode 14 is lifted off. Similarly, the source electrode 1
1, 12 and the portions other than the drain electrodes 21 and 22 and the cathode electrode 41 are covered with a resist to etch the silicon oxide 9, and Au-Ge / Ni / Au is continuously vapor-deposited. Then, the source electrodes 11 and 21 and the drain electrode are formed. 12, 22,
The doughnut-shaped cathode electrode 41 is lifted off.
Here, alloying is performed to make ohmic contact with the electrodes formed so far. Next, after forming a resist pattern, Ti / Au is continuously vapor-deposited to lift-off the extraction electrode (interconnection metal) 15.

Finally, the portions other than the gate electrodes 13 and 23 and the anode electrode 42 are covered with a resist mask, the silicon oxide 9 is selected with buffer hydrofluoric acid, and the n ⁺ -GaAs contact layer 6 is selected with an ammonia-based etching solution. Etching and continuously depositing Ti / Pt / Au,
The gate electrodes 13 and 23 and the circular anode electrode 42 are formed by lift-off.

The operation of the photodetector easily integrated by the above process will be described. A positive electric field V _D is applied to the source electrode 11 to the drain electrode 12 of the HEMT 10 for light detection, and a negative electric field V _G is applied to the gate electrode 13 to the source electrode 11 to set the bias state. Figure 2
Shows an energy band diagram of the semiconductor layer under the gate electrode 13 of the HEMT 10 for light detection of the present element, in which the broken line shows the case where no voltage is applied to the gate 13, and the solid line shows the pinch-off described later. It shows the state. In this device, the gate electrode 13 is n-Al.
_0.3 Ga _0.7 As layer 7 is in Schottky contact,
A depletion layer extends from here to the substrate 1 side. When a negative gate voltage V _G is applied, the energy band changes from the broken line to the solid line, and the channel width becomes narrow. As a result, the current I _D flowing between the drain electrode 12 and the source 11 electrode decreases. Now, when V _G is changed so that electrons do not exist (pinch off) in the two-dimensional electron gas layer as shown by the solid line, the channel is closed and the current I
The value of _D becomes 0. In this state, when the light 50 is incident from the upper surface, the light absorbed by the photodetection layer 5 generates electrons and holes (holes) which are current carriers in an amount according to the light intensity. The electrons flow into the portion forming the two-dimensional electron gas layer in the equilibrium state and immediately reach the drain electrode 12 by the electric field and are detected. As a result, the current I _D according to the light intensity starts to flow. In this element, n−
By placing the spacer layer 6 immediately below the Al _0.3 Ga _0.7 As layer 7, the mobility of electrons leached from the two-dimensional electron gas layer and traveling is increased.

On the other hand, the hole discharge electrode 14 is the source 1
Since a negative electric field is applied to 1 and it is in a reverse bias state, holes are discharged from the electrode 14 and do not participate in light detection, and response characteristics are improved, but on the other hand, the current I _D
The value of is small. Therefore, in order to amplify this _ID , a transimpedance type amplifier circuit as shown in FIG. 3 is constructed in this embodiment.

In FIG. 3, reference numeral 10a denotes a HEMT photodetection section, 2
0a, 20b, 20c are HEMTs for amplification, 40a, 4
0b is a Schottky diode, and R _F is a feedback resistor. In this device, these three HEMTs for amplification and 1
One HEMT for light detection and two diodes are monolithically integrated. HEMT for light detection
The drain current I _{D of} 10a is connected to the gate of the HEMT 20a for amplification to input a signal to the amplifier circuit. Here, since the amplification HEMTs 20a, 20b, 20c are electrically separated from the hole discharge electrode 14, they can operate as a normal HEMT. Since the transimpedance type amplifier operates in a wide dynamic range, almost all the bias voltage appears at the diode end even when the input power is large and a considerably large photoelectric current is generated. The feedback resistor R _F determines the thermal noise. The feedback resistor R _F must be large in order to minimize noise and maximize the output voltage.

In this embodiment, the diode 40a,
40b is connected in two stages to match the voltages, but it is easy to increase the number by adjusting the voltages. When constructing such a circuit, the wiring capacitance for connecting the electrodes becomes a problem, but in the present embodiment, the photodetection element 10a and the amplification electric elements 20a, 2
Since 0b and 20c have exactly the same layer structure, it is not necessary to stack an extra layer structure and there is almost no step between elements. Therefore, the width of the interconnect metal 15 can be suppressed to about 2 μm, and the capacitance can be reduced.

[0019]

Second Embodiment FIG. 3 shows a second embodiment of the present invention. Also in this embodiment, Al _x which is a III-V group compound semiconductor is used.
The description will be given using the Ga _1-x As / GaAs system. The photodetection part of this element has a HEMT structure having a pn heterojunction gate using a two-dimensional electron gas layer by modulation doping as a channel.

On the SI-GaAs substrate 1, φ-GaAs
The buffer layer 2 has a thickness of 1.0 μm, the p ⁺ -GaAs contact layer 3 has a thickness of 0.5 μm, and p ⁺ -Al _0.5 Ga _0.5
The As lower clad layer 61 has a thickness of 0.8 μm and is φ-Al.
_0.2 Ga _0.8 As Lower optical guide layer 62 with a thickness of 0.2 μm
Then, the φ-GaAs quantum well layer 63, which is an electron transit layer, has a thickness of 150Å, and the φ-Al _0.2 Ga _0.8 As spacer layer 64 is formed.
N-Al with a thickness of 30 Å and doped with 1 × 10 ¹⁸ Si
_0.2 Ga _0.8 As electron supply layer 65 with a thickness of 500 Å, n-
The GaAs etch stop layer 66 has a thickness of 100 Å and p-
Al _0.2 Ga _0.8 As Upper optical guide layer 67 has a thickness of 0.2 μm.
Then, the p-Al _0.5 Ga _0.5 As upper cladding layer 68 having a thickness of 0.8 μm and the p ⁺ -GaAs gate electrode contact layer 69 having a thickness of 0.5 μm are sequentially laminated by the MBE method. The layers 62, 63, 64, 65, 66, 67 form the light guide layer. The gate electrodes 73 and 83 are covered with a resist by photolithography to etch the n-GaAs active layer 66 to form a stripe-shaped gate / ridge having a width of 2.3 μm. Cover parts other than the part to be formed with resist p
Etching is performed up to the ⁺ -GaAs contact layer 3, and then the portions other than the electrical isolation portion 90 are covered with a resist, and φ-Ga
The electrical isolation portion 80 is formed by etching the As buffer layer 2. Here, the SiO ₂ protective film 91 was formed by sputtering on the entire surface by self-alignment process using the dry etching of the spin-coated and CF ₄ gas of the resist portion of the gate electrode 73, 83 of SiO ₂ film 91 After removal by etching and continuous vapor deposition of Cr / Au, the gate electrodes 73 and 83 are formed by lift-off. Next, the area around the discharge electrode 74 and the electrical isolation portion 90 are covered with a resist, the SiO ₂ film 91 is removed by etching using the resist and the gate electrodes 73 and 83 as a mask, and Au—Ge / Au is continuously vapor-deposited. The source electrodes 71, 8 are lifted off by the peeling liquid.
1 and the drain electrodes 72 and 82 are formed. Then, the portion other than the discharge electrode 74 is masked with a resist, the SiO ₂ film 91 is removed by etching with buffer hydrofluoric acid to continuously deposit Cr / Au, and then the discharge electrode 74 is formed by lift-off. Alloy to make ohmic contact with all electrodes.

The operation of the photodetector integrated by the above process will be described. A positive electric field V _D is applied to the drain electrode 72 of the photodetection HEMT 70 with respect to the source electrode 71, and a negative electric field V _G is applied to the gate electrode 73 with respect to the source electrode 71 to bring the gate electrode 73 into a biased state. FIG. 5 is an energy band diagram in the vicinity of the electron transit layer 63 below the gate electrode 73 of the HEMT 70 for light detection of this element. In the φ-GaAs quantum well layer 63, which is an electron transit layer, as shown in FIG. 5, electrons are transferred from the n-Al _0.2 Ga _0.8 As electron supply layer 65 to form a two-dimensional electron gas. In this device, p-Al _0.2 Ga below the gate electrode 73 is used.
_The interface between _0.8 As67 and the n-GaAs layer 66 is n-Al _0.3 Ga _0.7 with the gate electrodes 13 and 23 in the first embodiment.
It corresponds to the interface of the As layer 7. Therefore, by changing the voltage V _G applied to this interface, the concentration of the two-dimensional electron gas changes, and as a result, the current I _D between the drain electrode and the source electrode changes, and a pinch-off state can be formed. In this element, φ-Al _0.2 Ga _0.8 under the gate electrode 73
The As lower optical guide layer 62 has a three-dimensional waveguide structure in which the p-Al _0.2 Ga _0.8 As upper optical guide layer 67 is used as an optical guide layer, and the φ-GaAs quantum well layer 63 efficiently uses electron-hole pairs. Are generated and converted into photocurrent. This time,
The electrons immediately flow into the drain electrode through the electron transit layer 63. In this element, holes generated in the light penetration region on the substrate side from the vicinity of the electron transit layer 63 are discharged through the electrode 14, and holes are sucked by the gate electrode 73 in the light penetration region on the gate electrode 73 side. Therefore, the holes do not participate in light detection and the response speed is high, but the value of the photocurrent I _D is small. Therefore, in order to amplify this _ID , a high impedance type amplifier circuit as shown in FIG. 6 is constructed in this embodiment.

In FIG. 6, reference numeral 70a denotes a photodetection HEMT having a hole discharge electrode, and 80a, 80b and 80c.
Is a HEMT for amplification, and R _F is a load resistance.
This device consists of these three HEMTs for amplification and HEMs for photodetection.
T1 is integrated. In the high impedance type amplifier circuit, the load resistance R _F is large, the input impedance of the amplifier is large, and the thermal noise is minimized. However, since the bandwidth is narrow, it is preferably used when high sensitivity (low noise) detection and a narrow dynamic range are sufficient.

Also in this embodiment, the light detecting element 70a is used.
Since the electric elements 80a, 80b, 80c for amplification have exactly the same layer structure, it is not necessary to stack an extra layer structure, the capacity can be reduced, and a process added for integration is also required. The number of steps is small and easy. In particular, when light is guided in the semiconductor as in the present device, when the part to be irradiated with light is large except the light absorption layer and the part on the substrate side is semi-insulating and is not biased, The Fermi level becomes unstable due to activation of defects, impurities, etc. by light irradiation, and as a result, the photocurrent characteristic and the frequency response characteristic are also adversely affected. Therefore, as in this embodiment, it is extremely effective to bias the regions other than the light absorption layer to which light is irradiated so that the carriers flow. Further, in this element, since the hole discharge mechanism is provided only in the light detection unit, the power consumption during operation is lower than that in the case where the hole discharge mechanism is provided for both elements without electrically separating them. Overwhelmingly few.

[0024]

As described above, the present invention has the following effects. 1. By discharging holes, the optical frequency response characteristic is improved. 2. Since the electric field due to the accumulation of holes is not generated, the potential is stabilized and the photocurrent characteristic is improved over the entire photodetector. 3. Since the photo detector and the amplifier have the same layer structure,
The capacity due to the layer structure can be reduced, and the time response characteristic and the noise characteristic are improved. 4. The photocurrent which becomes weak by spitting out the holes,
Since the amplification can be performed without substantially deteriorating the characteristics, the detection sensitivity is improved. 5. There are few additional processes to integrate,
It's also easy to find.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is an energy band diagram showing the movement of carriers according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram of a first embodiment of the present invention.

FIG. 4 is a sectional view of a second embodiment of the present invention.

FIG. 5 is an energy band diagram showing the movement of carriers according to the second embodiment of the present invention.

FIG. 6 is a circuit diagram of a second embodiment of the present invention.

FIG. 7 is a diagram showing a first conventional example (element A) of the present invention.

FIG. 8 is a diagram showing a second conventional example (element B) of the present invention.

[Explanation of symbols]

 1, 1001 Semi-insulating GaAs substrate 2, 1002 φ-GaAs buffer layer 3 p⁺-GaAs contact layer 4 p^--GaAs layer 5 φ-GaAs photodetection layer 6 φ-Al_0.3Ga_0.7As spacer layer 7,1003 n-Al_0.3Ga_0.7As layer 8,1004 n⁺-GaAs contact layer 9,91 Silicon oxide 10, 10a HEMT for light detection 11, 21, 71, 81, 1011, 1031 Saw
Electrode 12, 22, 72, 82, 1012, 1032
In electrodes 13, 23, 73, 83, 1013, 1033 games
Electrode 14, 74, 1034 Hole discharge electrode 15 Extraction electrode 20, 20a, 20b, 20c, 80, 80a, 80
b, 80c HEMT for signal amplification 30, 90 Electrical separation part 31 φ-Al_0.3Ga_0.7As high-resistance embedded layer 40, 40a, 40b diode 41 cathode electrode 42 anode electrode 50 incident light 61 p⁺-Al_0.5Ga_0.5As lower clad layer 62 φ-Al_0.2Ga_0.8As lower optical guide layer 63 φ-GaAs quantum well layer 64 φ-Al_0.2Ga_0.8As spacer layer 65 n-Al_0.2Ga_0.8As electron supply layer 66 n-GaAs etch stop layer 67 p-Al_0.2Ga_0.8As upper light guide layer 68 p -Al_0.5Ga_0.5As upper clad layer 69 p⁺-GaAs gate electrode contact layer 70, 70a HEMT for light detection 1021 p-GaAs substrate 1022 p-GaAs buffer layer 1023 φ-Ga As layer 1024 n-Al_0.3Ga_0.7As layer 1025 n⁺-GaAs contact layer

Claims (4)

[Claims] 1. A photodetector comprising a layer containing a two-dimensional electron gas as a photodetection layer, and a HEMT type photodetection unit for detecting light input to the photodetection layer by a current flowing between a source electrode and a drain electrode. The photodetector, means for ejecting holes generated in a region outside the photodetection layer of the photodetector, and means for amplifying a signal having the same layer material and the same electrode material configuration as the photodetector At least one amplifying HEMT is monolithically integrated on the same substrate, the amplifying HEMT is electrically isolated from the means for ejecting the hole, and the photocurrent of the photodetector is one. A photodetector characterized by being applied to the gate of an amplifying HEMT. 2. An amplifier circuit composed of the HEMT for amplification is a transimpedance type including a diode, and the diode has the same layer structure as the HEMT.
The photodetector according to claim 1, wherein the photodetector is a Schottky diode made of the same electrode material. 3. The photodetector according to claim 1, wherein the amplifier circuit composed of the HEMT for amplification is of a high impedance type. 4. The photodetector according to claim 1, wherein the light input to the photodetection layer is configured to be guided light.