WO2011083657A1

WO2011083657A1 - Avalanche photodiode and receiver using same

Info

Publication number: WO2011083657A1
Application number: PCT/JP2010/072087
Authority: WO
Inventors: 英根李; 斎藤　慎一; 杉井　信之; 康信松岡; 俊樹菅原
Original assignee: 株式会社日立製作所
Priority date: 2010-01-07
Filing date: 2010-12-09
Publication date: 2011-07-14
Also published as: JP2013080728A

Abstract

Disclosed is an avalanche photodiode for optical communication, which has a low dark current, a high speed, and a high gain. Also disclosed is a receiver using the avalanche photodiode. In the avalanche photodiode having a light absorbing layer (4) and a multiplying layer (7), the light absorbing layer (4) and the multiplying layer (7) are spatially and electrically separately disposed in the parallel direction (horizontal direction above a substrate (1)) to the crystal plane, and the light absorbing layer (4) and the multiplying layer (7) are electrically connected to each other with a conductive wiring line. Thus, since the multiplying layer (7) is thinned, and the light absorbing layer (4) and the multiplying layer (7) are formed of a high quality crystal, the low dark current, the high speed, and the high gain can be achieved in the avalanche photodiode.

Description

Avalanche photodiode and receiver using the same

The present invention relates to an avalanche photodiode for optical communication and a receiver using the same.

The transmission capacity of optical fiber communication is explodingly increasing at an annual rate of 1.5 times with the spread of the Internet as well as trunk line communication between large cities. The optical communication system has the following basic configuration. On the transmission side, electrical signals such as sound and images are converted into optical signals using a light source such as a semiconductor laser. After this optical signal is transmitted using an optical fiber as a transmission medium, the optical signal transmitted by the receiving element on the receiving side is converted back to an electric signal and returned to a desired signal by necessary signal processing. In this communication system, not only the light emitting element and the optical fiber, but also the performance of the light receiving element that converts an optical signal into an electrical signal is very important for the optical communication system.

The light receiving elements for optical communication are roughly classified into PIN photodiodes and avalanche photodiodes made of semiconductors. The PIN photodiode is composed of a p-type semiconductor, an undoped semiconductor, and an n-type semiconductor. When input light is incident, it is absorbed by an undoped semiconductor layer to which a bias electric field is applied, and then converted into electrons and holes and detected as an electric signal. The avalanche photodiode includes an avalanche amplification layer in addition to the PIN photodiode, has an optical amplification function, and is used as a light receiving element for a long-distance transmission system. The avalanche photodiode and the signal amplification function use a semiconductor avalanche breakdown phenomenon. The mechanism of signal amplification in the avalanche breakdown phenomenon is as follows.

Electrons or holes traveling in the semiconductor collide with the crystal lattice and are scattered. When a large electric field is applied to a semiconductor, electrons and holes (hereinafter, carriers) in the semiconductor are accelerated by the electric field. If the movement speed in the semiconductor increases and its kinetic energy exceeds the energy band gap, the probability of breaking bond bonds in the crystal lattice increases when carriers collide with the crystal lattice. Generate hole pairs.

This phenomenon is called impact ionization or impact ionization because the atoms that have been broken the bond bond have insufficient charge and appear to be ionized. The number of electron / hole pairs generated by impact ionization when an electron or hole travels a unit distance is called the ionization rate. Moreover, the ratio of the ionization rate by electrons and the ionization rate by holes is called the ionization rate ratio. The velocity of electrons and holes newly generated by the collision ionization is also accelerated by the applied electric field, and new electron / hole pairs are generated by further collision ionization. Thus, when impact ionization is repeated, a sudden increase in the number of carriers occurs and a large current flows (avalanche phenomenon). That is, even when a small signal (minority carrier) is input, the signal can be amplified by such an avalanche phenomenon.

As widely known, an ionization rate ratio is an important parameter in terms of the high speed and structure magnification of an avalanche photodiode. As the ionization rate ratio is larger than 1 or smaller than 1, that is, the larger the difference between the ionization rate due to electrons and the ionization rate due to holes, the higher the speed and the higher multiplication factor are possible. Become. Intuitively, when the ionization rate is close to 1, ionization caused by both electrons and holes continuously occurs in the multiplication layer for a long time, which makes it particularly difficult to increase the speed. Recognize.

The avalanche photodiodes used so far for optical communication have a wavelength of 1.3 μm band or 1.55 μm band (infrared region) for light used for optical communication, and therefore, an InP or InGaAs compound semiconductor is used as a material. Has been. However, the ionization ratio of InP is about 0.5, which is relatively close to 1. Even in InAlAs, it is 0.25 to 0.5 at most. For this reason, the band of an avalanche photodiode using an InP semiconductor is up to 10 GHz (assuming that the multiplication factor is about 10), and a high-speed avalanche photodiode of, for example, 25 GHz or 40 GHz has not been realized yet. is the current situation.

On the other hand, the ionization rate ratio of Si has an extremely small value of 0.1 to 0.01, and a high-speed and high-sensitivity avalanche photodiode can be realized. However, since Si cannot absorb the infrared light in the 1.3 μm band or 1.55 μm band used for optical communication, it cannot be used for optical communication.

In order to overcome the disadvantages of such avalanche photodiodes using Si, attempts have been made so far to combine Si with a compound semiconductor having sensitivity to light in the infrared region. That is, until now, attempts have been made to fabricate avalanche photodiodes in which the light absorption layer is a semiconductor capable of absorbing light in the infrared region and the multiplication layer is formed of Si. For example, attempts to epitaxially grow compound semiconductors on Si have been made for a long time, but high-quality crystals have not yet been obtained. As another method, an avalanche photodiode is manufactured by bonding an Si multiplication layer to an InGaAs layer epitaxially grown on an InP substrate by direct bonding using a wafer bonding technique (see Non-Patent Document 1). As the performance of the avalanche photodiode, the multiplication factor is 30 in the operation band of 10 GHz. The product of the band width and the gain (Gain), the so-called GB product, is 300, which is an improvement over the conventional GB products 150 to 200 when using an InP-based compound semiconductor. Furthermore, in recent years, a technique for crystal growth of high-quality Ge on Si has been developed, and an avalanche photodiode is manufactured using this technique (see Non-Patent Document 2). The performance of the avalanche photodiode in this case is also about the same as that of an element manufactured by the wafer bonding technique so far.

As described in “Background Art”, the performance of an avalanche photodiode manufactured using a wafer bonding technique has an operating band of 10 GHz and a multiplication factor of 30. When compared with a GB product, a conventional InP-based avalanche photodiode is used. It showed better properties. However, the bandwidth is 10 GHz, which is about the same as a conventional InP avalanche photodiode. This is because, during wafer bonding, internal diffusion of each material occurs at the interface between the InGaAs or InP layer of the light absorption layer and the Si layer, and the interface is not steep. When InGaAs or InP diffuses in the Si layer, the Si ionization rate ratio may be close to 1. In the case of a relatively low-speed avalanche photodiode, the Si amplification layer can be made thick, so that the influence of this internal diffusion is considered to be small. However, if the multiplication layer is made thinner (about 0.1 μm) for higher speed, the influence of this internal diffusion cannot be ignored. In Non-Patent Document 1, although the GB product has been improved to 300, the above is considered as the reason why the bandwidth is not improved.

Also in Non-Patent Document 2, as with Non-Patent Document 1, the GB product shows characteristics superior to those of conventional InP avalanche photodiodes (in this case, the GB product is about 300), but the bandwidth is 10 GHz. This is comparable to a conventional InP avalanche photodiode. In this case, when Ge is stacked on Si, the density of dislocation defects due to strain caused by the difference in lattice constant between Si and Ge is reduced by repeating high-temperature annealing. Internal diffusion occurs during this high temperature annealing, and Ge diffuses into the Si layer. Due to this internal diffusion, when the Si layer is thinned, the low ionization rate ratio peculiar to Si is not maintained, and the speed-up of the avalanche photodiode is not realized. Regarding this Si / Ge avalanche photodiode, it has also been reported that dark current increases due to dislocation defects in the Ge layer (Non-patent Document 2).

An object of the present invention is to provide an avalanche photodiode for optical communication with low dark current, high speed and high gain, and a receiver using the avalanche photodiode.

As an embodiment for achieving the above object, in an avalanche photodiode having a light absorption layer and a multiplication layer, the light absorption layer and the multiplication layer constitute each layer in a first region and a second region on the substrate. The avalanche is characterized in that the light absorption layer and the multiplication layer are electrically connected by a conductive wiring, and are arranged apart from each other in a direction parallel to the crystal plane of the crystal. A photodiode is used.

Further, the receiver includes the avalanche photodiode and an electronic circuit formed on the substrate on which the avalanche photodiode is formed and having a function of amplifying an electric signal.

With the above configuration, it is possible to provide a high-speed and high-gain optical avalanche photodiode for low-dark current and a receiver using the same.

1 is a schematic bird's-eye view of an avalanche photodiode having a Ge light absorption layer and a Si multiplication layer according to a first embodiment. It is a schematic sectional drawing of the avalanche photodiode which has Ge light absorption layer and Si multiplication layer based on a 1st Example. It is a figure which shows the result of having calculated the relationship between the multiplication factor with respect to the avalanche photodiode which concerns on a 1st Example, and 3 dB zone | band. It is a schematic sectional drawing of the avalanche photodiode which has an InGaAs light absorption layer and Si multiplication layer based on a 2nd Example. It is a schematic sectional drawing of the 2 terminal avalanche photodiode based on a 3rd Example. It is a schematic sectional drawing of the 3 terminal avalanche photodiode based on a 3rd Example. It is a schematic bird's-eye view of the avalanche photodiode which has the crystal plane of the upper surface of a mesa structure which has (100) based on a 4th Example. It is a schematic bird's-eye view of the other avalanche photodiode which has the crystal plane of the upper surface of a mesa structure which has (110) based on a 4th Example. It is a schematic sectional drawing of the back-illuminated avalanche photodiode which integrated the lens based on a 5th Example. It is a schematic sectional drawing of the waveguide type avalanche photodiode which injects light from the board | substrate end surface based on a 6th Example. It is a schematic sectional drawing of the avalanche photodiode by which the multiplication layer of Si based on the 7th Example was formed on Si substrate. It is a schematic sectional drawing of the receiver which integrated the avalanche photodiode and electronic circuit based on an 8th Example.

As described in the problem to be solved by the invention, in

Non-Patent Documents

1 and 2, internal multiplication of other materials into the Si amplifying layer may reduce the multiplication layer required for speeding up the avalanche photodiode. Have difficulty. Therefore, as a method for solving this problem, in this embodiment, in the avalanche photodiode having the light absorption layer and the multiplication layer, the light absorption layer and the multiplication layer are separated in a direction parallel to the crystal plane. An avalanche photodiode is proposed in which the light absorption layer and the multiplication layer are electrically connected by a conductive wiring. In this structure, since the light absorption layer (mesa portion) and the multiplication layer (mesa portion) are spatially separated, the multiplication layer can be easily thinned and the speed of the avalanche photodiode can be increased. .

A GeOI (Germanium on Insulator) substrate is used for dark current increase due to dislocation defects in the Ge layer in the Si / Ge avalanche photodiode. The GeOI substrate is manufactured by attaching a high-quality Ge layer to a SiO ₂ layer formed on a Si substrate, and it is considered that the dislocation defect density is lower than when Ge is epitaxially grown on Si. Further, since the Ge layer is laminated on the SiO _2, compared with a case where Ge on Si are stacked, is on SiO ₂ easy to move dislocation defects, when annealed, dislocation defects decreases (disappearance) It becomes easy to do. In order to further reduce dislocation defects, the avalanche photodiode has a mesa structure, and the top crystal plane of this mesa structure is the (100) plane and the side crystal plane is (110). As another mesa structure, the mesa structure is a mesa structure in which the crystal face on the top surface of the mesa structure is the (110) plane, the two faces facing the inside are the (110) faces, and the other two faces are the (110) faces. Similar to the effect of forming a mesa structure on Ge rather than on Si, dislocation density can be lowered by moving the dislocations and releasing them from the side surfaces of the film. Furthermore, by setting the top surface or side surface to (110), a free end perpendicular to the dislocation line in the <110> direction is formed, which is effective in reducing the dislocation density. In this way, dark current can be reduced by reducing dislocation defects.

Hereinafter, the embodiment will be described in detail.

The first embodiment will be described with reference to FIGS. 1 (a) and 1 (b). Note that matters described in the mode for carrying out the invention and not described in this embodiment can be applied to this embodiment.

FIG. 1A is a schematic bird's-eye view of a photodiode having a Ge light absorption layer and a Si multiplication layer, and FIG. 1B is a schematic cross-sectional view thereof. The avalanche photodiode according to this example includes an SiO ₂ layer 2, a p ⁺ -Ge contact layer 3, an undoped Ge light absorption layer 4, an n ⁺ -Ge contact layer 5, and an n ⁺ on a Si substrate 1. This is a light receiving element comprising a —Si contact layer 6, an n ⁻ —Si multiplication layer 7, an n ⁺ —Si contact layer 8, a dielectric layer 9, a protective film 10, and an electrode 11. In the present avalanche photodiode, the light absorption layer 4 and the multiplication layer 7 are spaced apart from each other in the direction parallel to the crystal plane (the horizontal direction above the substrate 1). Are electrically connected by a conductive wiring (electrode) 11. Reference numeral 12 denotes input light.

First, a method for manufacturing the avalanche photodiode will be described below.

In order to obtain a high-quality Ge absorption layer 4, the following two types of substrates are used. One is to use a SOI substrate (Silicon on Insulator: a substrate having a structure in which a SiO ₂ layer is sandwiched between a Si substrate and a surface Si thin film layer) to form a high-quality Ge thin film with a SiO ₂ layer 2 by an oxidation concentration method. Then, a Ge layer is formed thickly by epitaxial growth. The concentrate oxidation method, first, the SiGe layer is grown in a molecular beam epitaxy at a substrate temperature of about 500 ° C. on SOI, then is oxidized under heating for 1 h at 900 ℃ ~ 1100 ℃, Ge of the SiGe is deposited on SiO ₂ The Si originally on the SOI becomes SiO ₂ and is deposited on the Ge. In this state, when the uppermost SiO ₂ layer is removed by selective etching, a substrate having a high-quality Ge layer formed on the uppermost portion is obtained. The substrate structure is a Si substrate, a SiO ₂ layer, and a Ge layer from the bottom. The Ge layer may contain a trace amount of Si of less than about 1% due to the characteristics of the oxidation concentration method. In the present specification, the case where such a trace amount of Si is contained is also referred to as a Ge layer. .

Another substrate is a GeOI substrate (Germanium on Insulator: a substrate having a structure in which a SiO ₂ layer is sandwiched between a Si substrate and a surface Ge thin film layer). This substrate has a structure in which a high-quality Ge substrate is bonded onto a Si substrate / SiO ₂ by wafer bonding. When this Ge layer is used, a dark current value comparable to that of a Ge photodiode using a conventional Ge substrate can be expected. The dark current value of a commercially available Ge photodiode is, for example, 0.5 μA or less at a light receiving diameter of 0.25 mm ² . In the case of a high-speed PD of 10G or more, since the light receiving diameter is 20 μm, a low dark current of 1 nA or less can be expected considering that the dark current is proportional to the light receiving diameter. Incidentally, at present, the dark current of a light receiving diameter of 20 μm PD produced by stacking Ge on a Si substrate is 1 μA or more.

Using the above two types of substrates, a Ge layer having a thickness necessary for forming an avalanche photodiode is formed by epitaxial growth on a high-quality Ge thin film layer. Impurity doping of the Ge layer necessary for forming the contact layer may be performed during epitaxial growth, or may be performed by ion doping after the Ge layer is formed.

Next, after impurity doping of the Ge layer, a mesa structure is formed. Further, the Ge layer in the region forming the mesa structure including the amplification layer is removed by etching, and the Si layer is epitaxially grown. After the contact layer is doped with impurities, a mesa structure is formed. Further, after filling and planarizing with a dielectric such as polyimide between the Ge mesa structure portion and the Si mesa structure portion, a protective film 10 made of, for example, SiO ₂ and SiN film is formed as a protective film. Thereafter, the electrode 11 is formed using Au / Ti or Al material. Here, when the SiN film is a compressive strain film, tensile strain is applied to the Ge light absorption layer 4 and the energy band gap is reduced. That is, it is possible to absorb light having a long wavelength in the 1.55 μm band.

For surface incident type according to the present embodiment, by selecting the thickness of the SiO ₂ layer 2 suitably, it is possible to greatly reflecting mirror structure the reflection at the interface of the contact layer 3 and the SiO ₂ layer 2 , Quantum efficiency (light absorption efficiency) can be improved.

Based on the structure shown in FIG. 1, the performance of the avalanche photodiode was analyzed. The result (relation between multiplication factor and 3 dB band) is shown in FIG. The parameters used for the calculation are as follows. Light absorption layer i-Ge layer thickness: 0.5 μm, Si multiplication layer thickness: 0.1 μm, light receiving diameter: 15 μm, electrode surface line joining the light absorption layer and the multiplication layer: 5 × 50 μm ² , total capacitance ( (Sum of device capacitance 50 fF and parasitic capacitance 3.4 fF): 53.4 fF, Si ionization rate ratio of Si multiplication layer: 0.1, Ge electron saturation speed ⁶ × 10 ⁶ cm / s, Si electron saturation speed 1 × 10 ⁷ cm / s s. The element resistance Rs was calculated by changing from 25Ω to 100Ω. From the above results, it can be seen that when the element resistance Rs is 50Ω or less, a high-speed and high-amplification avalanche photodiode having a 3 dB band of 40 GHz or more and a multiplication factor of 10 or more can be realized.

According to the present embodiment, the above configuration can provide an avalanche photodiode for optical communication with low dark current and high speed and high gain. The avalanche photodiode can be used for a receiver.

The second embodiment will be described with reference to FIG. In addition, it describes in the form for inventing or Example 1, and the matter which is not described in a present Example is applicable also to a present Example.

FIG. 3 is a cross-sectional view of an avalanche photodiode having an InGaAs light absorption layer and a Si multiplication layer. The avalanche photodiode includes an SiO ₂ layer 2, a p ⁺ -InP contact layer 13, an undoped InGaAs light absorption layer 14, an n ⁺ -InP contact layer 15, and an n ⁺ -Si contact on an Si substrate 1. This is a light receiving element including a layer 6, an n ⁻ -Si multiplication layer 7, an n ⁺ -Si contact layer 8, a dielectric layer 9, a protective film 10, and an electrode 11. In the present embodiment, the light absorption layer 14 and the multiplication layer 7 are arranged in a direction parallel to the crystal plane (horizontal direction above the substrate 1), and the light absorption layer 14 and the multiplication layer 7 are separated from each other. They are electrically connected by a conductive wiring (electrode) 11.

Note that differences from the first embodiment will be described. Here, the p ⁺ -InP contact layer 13 may be p ⁺ -InGaAsP or p ⁺ -InGaAlAs. Further, the n ⁺ -InP contact layer 15 may be n ⁺ -InGaAsP or n ⁺ -InGaAlAs.

The substrate used in this example is a III-V OI substrate (III-V on Insulator: a substrate having a structure in which an SiO ₂ layer is sandwiched between a Si substrate and a surface III-V compound semiconductor thin film layer). This substrate has a structure in which a high-quality III-V crystal substrate is bonded onto a Si substrate / SiO ₂ by wafer bonding. Using this substrate, the avalanche photodiode in this example is manufactured by the method described in Example 1.

Also in the present embodiment, the same effect as in the first embodiment can be obtained. Further, since InP is used, a wavelength of 1.5 μm is possible, and it can be used for a long distance.

The third embodiment will be described with reference to FIGS. In addition, it describes in the form or Example 1 or 2 for inventing, and the matter which is not described in a present Example is applicable also to a present Example.

FIG. 4 is a sectional view of a two-terminal avalanche photodiode according to the present embodiment, and FIG. 5 is a sectional view of a three-terminal avalanche photodiode. In addition, the same code | symbol shows the same structure. In the present embodiment, the light absorption layer 17 and the multiplication layer 7 are arranged in a direction parallel to the crystal plane (horizontal direction above the substrate 1), and the light absorption layer 17 and the multiplication layer 7 are separated from each other. They are electrically connected by a conductive wiring (electrode) 11. Reference numeral 16 denotes a voltage power source. The element operation method will be described below.

There are two methods for applying an electric field necessary for device operation. One is a method of applying a voltage between two terminals (see FIG. 4). The second is a method of applying a voltage at three terminals, where the control of the electric field applied to the light absorption layer 17 and the control of the electric field applied to the amplification layer 7 can be controlled independently (see FIG. 5). In the case of two terminals, since there is one voltage power supply, the electronic circuit can be simplified. On the other hand, in the case of three terminals, since two voltage power supplies are required, there is a concern that the electronic circuit becomes complicated, but there is an advantage that the applied voltage applied to each layer can be accurately controlled. Since the applied voltage can be accurately controlled, the multiplication factor can be accurately controlled. Further, by applying a voltage only to the light absorption layer 17, it functions as a normal PIN photodiode having no amplification function. Reference numeral 18 denotes a voltage power supply for applying a light absorption layer electric field, and reference numeral 19 denotes a voltage power supply for applying a multiplication layer electric field.

Also in the present embodiment, the same effect as in the first embodiment can be obtained. Further, by using three terminals, it is possible to provide a light receiving element capable of accurately controlling the image magnification in the multiplication layer and capable of switching between an avalanche photodiode and a normal PIN photodiode.

The fourth embodiment will be described with reference to FIGS. It should be noted that items described in any of Embodiments 1 to 3 for carrying out the invention and not described in this embodiment can be applied to this embodiment.

FIG. 6 is a bird's-eye view of an avalanche photodiode having a (100) crystal plane on the top surface of the mesa structure, and FIG. 7 is a bird's-eye view of the avalanche photodiode having a (110) crystal plane. In addition, the same code | symbol shows the same structure. In the present embodiment, the light absorption layer 17 and the multiplication layer are spaced apart from each other in the direction parallel to the crystal plane (the horizontal direction above the substrate 1), and the light absorption layer and the multiplication layer are electrically conductive. Are electrically connected by a conductive wiring. The following will be described with respect to the crystal plane of the mesa structure.

In the mesa structure including the light absorption layer, in order to reduce the dislocation defect density of Ge, the crystal planes constituting the mesa structure may be as follows. First, as shown in FIG. 6, the crystal plane 20 on the top surface of the mesa structure is the (100) plane, and the crystal planes 21, 22, 23, and 24 on the side surfaces of the mesa structure are the (110) plane. As another structure, as shown in FIG. 7, the crystal face 25 on the top surface of the mesa structure is the (110) plane, the two crystal faces 26 and 27 facing the inside of the side face of the mesa structure are the (100) face, and the other faces. The crystal faces 28 and 29 on the two side faces are defined as (110) faces.

Also in the present embodiment, the same effect as in the first embodiment can be obtained. In addition, by setting the crystal plane of the upper surface of the mesa structure to the (100) plane or the (110) plane, the defect density can be reduced and a further reduction in dark current can be achieved.

The fifth embodiment will be described with reference to FIG. Note that items described in any one of Embodiments 1 to 4 for carrying out the invention and not described in this embodiment can also be applied to this embodiment.

FIG. 8 shows a cross-sectional view of a back-illuminated avalanche photodiode with an integrated lens. In the present embodiment, the light absorption layer 4 and the multiplication layer 7 are arranged apart from each other in the direction parallel to the crystal plane (horizontal direction above the substrate 1), and the space between the light absorption layer and the multiplication layer is They are electrically connected by conductive wiring (electrode) 11. A back-illuminated avalanche photodiode will be described below.

Avalanche photodiodes with the present embodiment, on the Si substrate 1, SiO ₂ layer ^2, p + -Ge contact layer 3, the light-absorbing layer of undoped Ge ^4, n + -Ge contact layer 5, ^{n +} - This is a light receiving element comprising a Si contact layer 6, an n ⁻ -Si multiplication layer 7, an n ⁺ -Si contact layer 8, a dielectric layer 9, a protective film 10, an electrode 11, and an integrated lens 30. Here, in the structure described in Example 2, the contact layer 3 is p ⁺ -InP, any one of p ⁺ -InGaAsP and p ⁺ -InGaAlAs, the light absorption layer 4 is undoped InGaAs, and the contact layer 5 is Any one of n ⁺ -InP, n ⁺ -InGaAsP, and n ⁺ -InGaAlAs may be used. Reference numeral 31 denotes input light.

The integrated lens 30 can reduce the beam spot size when incident on the light receiving portion, and can greatly improve the optical coupling tolerance. In this case, by selecting the thickness of the SiO ₂ layer 2 suitably, it is reduced and reflection on the interface of the Si substrate 1 and the SiO ₂ layer 2, a reflection at the interface of the contact layer 3 and the SiO ₂ layer 2 is necessary.

Also in the present embodiment, the same effect as in the first embodiment can be obtained. Moreover, the coupling tolerance can be improved by providing the integrated lens.

The sixth embodiment will be described with reference to FIG. Note that items described in any one of Examples 1 to 5 for carrying out the invention and not described in this example can be applied to this example.

FIG. 9 is a cross-sectional view of a waveguide type avalanche photodiode in which light is incident from the end face of the substrate. By adopting the waveguide type, the absorption layer can be made thin without impairing the photoelectric conversion efficiency, and high-speed operation becomes possible. In the present embodiment, the light absorption layer 17 and the multiplication layer 7 are arranged in a direction parallel to the crystal plane (horizontal direction above the substrate 1), and the light absorption layer 17 and the multiplication layer 7 are separated from each other. They are electrically connected by a conductive wiring (electrode) 11.

The avalanche photodiode according to the present embodiment has a SiO ₂ layer 2, a contact layer 3, a light absorption layer 17, a cladding layer 32, a contact layer 5, a contact layer 6, a multiplication layer 7, a contact layer 8, on a Si substrate 1. This is a light receiving element including a dielectric layer 9, a protective film 10 and an electrode 11. Light (input light) 33 incident from the end face of the substrate is confined in the vicinity of the light absorption layer 17 by the SiO ₂ layer 2 and the cladding layer 32 and propagates in the avalanche photodiode.

Also in the present embodiment, the same effect as in the first embodiment can be obtained.

The seventh embodiment will be described with reference to FIG. Note that items described in any one of Examples 1 to 6 for carrying out the invention and not described in this example can be applied to this example.

FIG. 10 is a cross-sectional view of an avalanche photodiode in which a Si multiplication layer is formed on a Si substrate. In the present embodiment, the light absorption layer 4 and the multiplication layer 7 are arranged in a direction parallel to the crystal plane (horizontal direction above the substrate 1), and the light absorption layer 4 and the multiplication layer 7 are separated from each other. They are electrically connected by a conductive wiring (electrode) 11.

Avalanche photodiodes with the present embodiment, on the Si substrate 1, SiO ₂ layer ^2, p + -Ge contact layer 3, the light-absorbing layer of undoped Ge ^4, n + -Ge contact layer 5, ^{n +} - This is a light receiving element comprising a Si contact layer 6, an n ⁻ -Si multiplication layer 7, an n ⁺ -Si contact layer 8, a dielectric layer 9, a protective film 10, and an electrode 11. The difference from Example 1 is that n ⁺ -Si contact layer 6, n ^-- Si multiplication layer 7 and n ⁺ -Si contact layer 8 are epitaxially grown on a Si substrate by high-quality Si. Is to form. Dark current can be reduced by high-quality Si.

Also in the present embodiment, the same effect as in the first embodiment can be obtained. Further, since the contact layer and the multiplication layer are epitaxial layers, the dark current is further reduced.

The eighth embodiment will be described with reference to FIG. Note that items described in any one of Examples 1 to 7 for carrying out the invention and not described in this example can be applied to this example.

FIG. 11 is a cross-sectional view of a receiver in which an avalanche photodiode and an electronic circuit having a function of amplifying an electric signal are integrated. In the present embodiment, the light absorption layer 4 and the multiplication layer 7 are arranged in parallel to the crystal plane (in the horizontal direction above the substrate 1), and the light absorption layer 4 and the multiplication layer 7 are separated from each other. They are electrically connected by a conductive wiring (electrode) 11.

Avalanche photodiodes with the present embodiment, on the Si substrate 1, SiO ₂ layer ^2, p + -Ge contact layer 3, the light-absorbing layer of undoped Ge ^4, n + -Ge contact layer 5, ^{n +} - This is a light receiving element comprising a Si contact layer 6, an n ⁻ -Si multiplication layer 7, an n ⁺ -Si contact layer 8, a dielectric layer 9, a protective film 10, and an electrode 11. Further, here, an electrical signal based on a CMOS circuit composed of the Si layer 34, the highly doped Si layer 35, the insulating film 36, the source electrode 37, the gate electrode 38, and the drain electrode 39 is passed through the dielectric layer 9. An electronic circuit having a function of amplifying is formed and constitutes a receiver. The high-temperature annealing necessary for manufacturing the electronic circuit is performed by laser annealing after masking the avalanche photodiode portion with a SiO ₂ layer and metal (Al, Cu, etc.).

According to this embodiment, it is possible to provide a receiver using an avalanche photodiode for optical communication with a low dark current and a high speed and a high gain.

An avalanche photodiode for optical communication exceeding a bandwidth of 10 GHz and a multiplication factor of 10 has not yet been developed, and a PIN photodiode and a semiconductor optical amplifier are used for long-distance transmission over a bandwidth of 10 GHz. However, the PIN photodiode and the semiconductor optical amplifier consume large power, and the operating wavelength band is limited by the band (about 50 nm) of the semiconductor optical amplifier. Therefore, if an avalanche photodiode for optical communication exceeding a bandwidth of 10 GHz and a multiplication factor of 10 can be realized, the technology can replace a PIN photodiode and a semiconductor optical amplifier as a receiver in high-speed long-distance transmission because of low power consumption and wide bandwidth. It is thought that it becomes.

1 ... Si substrate, 2 ... SiO ₂ layer, 3 ... contact layer, 4 ... Ge light absorbing layer, 5 ... contact layer, 6 ... contact layer, 7 ... multiplication layer, 8 ... contact layer, 9 ... dielectric layer, DESCRIPTION OF SYMBOLS 10 ... Protective film, 11 ... Electrode, 12 ... Input light, 13 ... Contact layer, 14 ... InGaAs light absorption layer, 15 ... Contact layer, 16 ... Voltage power supply, 17 ... Light absorption layer, 18 ... Light absorption layer For electric field application Voltage power supply, 19 ... multiplier layer electric field application voltage power supply, 20 ... (100) plane, 21 ... (110) plane, 22 ... (110) plane, 23 ... (110) plane, 24 ... (110) plane, 25 ... (110) plane, 26 ... (100) plane, 27 ... (100) plane, 28 ... (110) plane, 29 ... (110) plane, 30 ... integrated lens, 31 ... input light, 32 ... clad layer, 33 ... input light, 34 ... Si layer, 35 ... highly doped Si layer, 36 ... insulating film, 37 ... Source electrode, 38 ... Gate electrode, 39 ... Drain electrode.

Claims

In an avalanche photodiode having a light absorption layer and a multiplication layer,
The light absorption layer and the multiplication layer are disposed in the first region and the second region on the substrate, respectively, in a direction parallel to the crystal plane of the crystal constituting each layer,
An avalanche photodiode, wherein the light absorption layer and the multiplication layer are electrically connected by a conductive wiring.
The avalanche photodiode according to claim 1,
An avalanche photodiode, wherein the light absorption layer is made of Ge or InGaAs, and the multiplication layer is made of Si.
The avalanche photodiode according to claim 2,
The portion where the light absorption layer and the multiplication layer are formed has a mesa structure, the crystal plane of the top surface of the mesa structure is the (100) plane, and the crystal plane of the side surface of the mesa structure is the (110) plane. An avalanche photodiode.
The avalanche photodiode according to claim 2,
The portion that forms the light absorption layer and the multiplication layer has a mesa structure, the crystal plane of the upper surface of the mesa structure is the (110) plane, and the two faces facing the inner side of the mesa structure are the (110) plane, An avalanche photodiode characterized in that the other two facing surfaces are (100) surfaces.
The avalanche photodiode according to claim 2,
The avalanche photodiode is characterized in that the substrate is a GeOI substrate or a III-V OI substrate.
The avalanche photodiode according to claim 5,
The avalanche photodiode, wherein the control of the electric field applied to the light absorption layer and the control of the electric field applied to the amplification layer can be independently controlled.
The avalanche photodiode according to claim 6,
A back-illuminated avalanche photodiode having a lens formed on the back side of the substrate and receiving light from the back side of the substrate.
The avalanche photodiode according to claim 6,
A waveguide avalanche photodiode that receives light from the end face of the substrate.
An avalanche photodiode according to claim 6;
A receiver having an electronic circuit formed on the substrate on which the avalanche photodiode is formed and having a function of amplifying an electric signal.
A substrate,
A light absorption layer formed in a first region on the substrate;
A multiplication layer formed on the substrate in a second region different from the first region and spaced apart from the light absorption layer;
An avalanche photodiode comprising a conductive wiring that electrically connects the light absorption layer and the multiplication layer.
The avalanche photodiode according to claim 10,
An avalanche photodiode according to claim 1, wherein the multiplication layer is a Si layer.
The avalanche photodiode according to claim 10,
The avalanche photodiode is characterized in that the input light is a back-illuminated type that enters the light absorption layer from the substrate side.
The avalanche photodiode according to claim 10,
The avalanche photodiode is characterized in that the input light is of a waveguide type that enters the light absorption layer from the end face of the substrate.
The avalanche photodiode according to claim 10,
An avalanche photodiode, wherein the conductive wiring can be applied with a voltage from the outside.
An avalanche photodiode according to claim 10;
A receiver having an electronic circuit formed on the substrate on which the avalanche photodiode is formed and having a function of amplifying an electric signal.