JP6030416B2 - Avalanche photodiode and manufacturing method thereof - Google Patents

Description

  The present invention relates to an avalanche photodiode using an avalanche phenomenon and a manufacturing method thereof.

  An avalanche photodiode (APD), which is one of the photodiodes, accelerates the carriers generated in the semiconductor light absorption layer with a high electric field to collide with lattice position atoms to generate secondary electrons and holes. This is a photodiode using avalanche multiplication in which generated electrons and holes are accelerated by an electric field and repeatedly collide. In other words, the efficiency of converting light into electricity is limited to 100% in a general photodiode, whereas an avalanche photodiode has a multiplication function in the element itself, so that the efficiency is much higher than 100%. Is possible.

  Avalanche photodiodes used for optical communication generally use InGaAs as a light absorption layer in order to efficiently convert optical signals in the 1.55 μm band and 1.3 μm band, which are communication wavelength bands, into electrical signals. It is done. However, since InGaAs increases the leakage current in a high electric field state that causes avalanche multiplication, InP and InAlAs, which are materials having a larger band gap, are used as a multiplication layer, and the electric field of the light absorption layer is low during device operation. A SAM structure (Non-Patent Document 1) in which only the multiplication layer has a high electric field is used.

  In addition, since the ionization rates that cause collisional ionization of electrons and holes are different from each other and the ratio varies depending on the material, carriers having a large ionization rate are injected from the light absorption layer to the multiplication layer. Since the ionization rate is large, the hole injection type is common, and in InAlAs, the electron ionization rate is large and the electron injection type is common.

  In a receiver using an avalanche photodiode, in order to obtain higher sensitivity, it is necessary to increase the multiplication factor of the avalanche photodiode. However, in general, avalanche photodiodes have a trade-off relationship that the band decreases at a high multiplication factor, and this relationship is defined as a gain-bandwidth product (GBP) (see FIG. 9). ).

  For example, when the multiplication layer is composed of InP, GBP is reported to be about 100 GHz (see Non-Patent Document 2), and when the multiplication layer is composed of InAlAs, GBP is reported to be about 220 GHz (see Non-Patent Document 3). . These values mean, for example, that when the operating frequency is 20 GHz, the multiplication factor = 5 in the InP multiplication layer and the multiplication factor = 11 in the InAlAs multiplication layer are material limits.

  As described above, in order to operate the avalanche photodiode with higher gain and wider bandwidth, it is necessary to increase the GBP. However, the GBP is greatly influenced by the ratio of the ionization rate of the electron and the hole of the material, and is ionized. The smaller the ratio, the higher the GBP.

  InP and InAlAs are materials that lattice match with InGaAs used as a light absorption layer, and the ionization rate ratio of InP is reported to be approximately 1.0, and the ionization rate of InAlAs is reported to be approximately 0.2 (non-patent document). 4, see Non-Patent Document 5). In recent years, multiplication layer materials capable of realizing higher GBP such as GaN, Si, SiC, InAs, and HgCdTe have been reported when the lattice matching condition with InGaAs is eliminated.

  Since these materials do not lattice match with the light absorption layer, it is difficult to produce an avalanche photodiode for optical communication by crystal growth. In view of this, a method for manufacturing an avalanche photodiode, which is an avalanche photodiode for use in optical communication, has been proposed (see Non-Patent Document 6) in which the restriction of lattice matching between the light absorption layer and the multiplication layer is eliminated. In this technique, Si is used as a multiplication layer, InGaAs, which is a material having a smaller band gap than the multiplication layer, is used as a light absorption layer, and an avalanche photodiode is manufactured even when lattice matching with the light absorption layer is not achieved.

On the other hand, it has been reported that there are multiplication layer materials having a very small ionization rate ratio, such as InAs and HgCdTe, in which ionization by hole collision does not occur in principle (see Non-Patent Document 7). According to Non-Patent Document 7, it is said that operation of GBP of 500 GHz or more is possible by using InAs as a multiplication layer.

N. Susa et al., "Characteristics in InGaAs / InP Avalanche Photodiodes with Separated Absorption and Multiplication Regions", IEEE Journal of Quantum Electronics, vol.QE-17, no.2, pp.243-250, 1981. Y. Hirota et al., "Reliable non-Zn-diffused InP / InGaAs avalanche photodiode with buried n-InP layer operated by electron injection mode", ELECTRONICS LETTERS, vol.40, no.21, 1378, 2004. M. Nada et al., "Inverted InAlAs / InGaAs Avalanche Photodiode with Low.High.Low Electric Field Profile", Japanese Journal of Applied Physics, vol.51,02BG03, 2012. L. W. Cook et al., "Electron and hole impact ionization coefficients in InP determined by photomultiplication measurements", Appl. Phys. Lett., Vol.40, no.7, pp.589-591, 1982. Y. L. Goh et al., "Avalanche Multiplication in InAlAs", IEEE Trans. Electron. Devices, vol.54, no.1, pp.11-16, 2007. Aaron R. Hawkins et al., "High gain-bandwidth-product silicon heterointerface features", Appl. Phys. Lett., Vol.70, no.3, pp303-305, 1997. Andrew R. J. Marshall et al., "High speed InAs electron avalanche photodiodes overcome the conventional gain-bandwidth product limit", OPTICS EXPRESS, vol.19, no.23, pp.23341-23349, 2011. T. Shimatsu et al., "Atomic diffusion bonding of wafers with thin nanocrystalline metal films", J. Vac. Sci. Technol B, vo.28, no.4, pp.706-715, 2010. C. R. Crowell et al., "BALLISTIC MEAN FREE PATH MEASUREMENTS OF HOT ELECTRONS IN Au FILMS", Phys. Rev. Lett., Vol.15, no.16, pp.659-661, 1965. A. R. J. Marshall et al., "Electron dominated impact ionization and avalanche gain characteristics in InAs photodiodes", APPLIED PHYSICS LETTERS, vol.93, 111107, 2008. Y. Muramoto et al., "InP / InGaAs pin photodiode structure maximizing bandwidth and efficiency", ELECTRONICS LETTERS, vol.39, no.24, 1749, 2003. T. Ishibashi et al., "Uni-Traveling-Carrier Photodiodes", Ultrafast Electronics and Optoelectronics, vol.13, pp83-87, 1997. M. Nada, Y. Muramoto, H. Yokoyama, T. Ishibashi and S. Kodama, "InAlAs APD with high multiplied responsivity-bandwidth product (MR-bandwidth product) of 168 A / W.GHz for 25 Gbit / s high- speed operations ", ELECTRONICS LETTERS, vol.48, no.7, 2012.

However, for example, InAs has a smaller band gap than InGaAs. Therefore, when an optical communication wavelength of 1.55 μm to 1.3 μm is incident, light absorption occurs in the multiplication layer in addition to the light absorption layer. Holes are generated in the double layer. In this case, since InAs and HgCdTe do not cause ionization due to hole collision in principle, holes are induced in the multiplication layer even though they are materials that enable high GBP and effective. However, there was a problem that GBP decreased.

  Furthermore, when the band gap of the multiplication layer material is smaller than the band gap of the light absorption layer, the multiplication layer is formed before the electric field strength in the light absorption layer reaches the electron saturation speed when a voltage is applied to the avalanche photodiode. Breakdown will occur. For this reason, electrons cannot be sufficiently accelerated before the breakdown of the avalanche photodiode, resulting in a problem that a high-speed avalanche photodiode cannot be realized.

The present invention has been made in order to solve the above-described problems, and is intended to enable a multiplication layer of an avalanche photodiode to be composed of a semiconductor that does not cause ionization due to hole collision when a voltage is applied. Objective.

The avalanche photodiode according to the present invention includes a first contact layer made of a p-type compound semiconductor formed on a substrate, a second contact layer made of an n-type compound semiconductor formed on the substrate, A light absorption layer made of a III-V group compound semiconductor formed between the first contact layer and the second contact layer, and an increase made of an undoped compound semiconductor formed between the light absorption layer and the second contact layer. A double layer, an electric field control layer made of an n-type compound semiconductor formed between the light absorption layer and the multiplication layer, and a reflection made of a semiconductor multilayer structure formed between the light absorption layer and the multiplication layer The structure layer includes at least a first electrode formed in connection with the first contact layer, and a second electrode formed in connection with the second contact layer, and the multiplication layer collides with holes when a voltage is applied. Do not cause ionization due to And a compound semiconductor.

  The avalanche photodiode includes a junction metal layer formed between the multiplication layer and the light absorption layer, and the junction metal layer has a thickness equal to or less than the length of the mean free path of electrons. Good. In this case, the electric field control layer is composed of an n-type compound semiconductor in which impurities are introduced in a state in which the band offset from the light absorption layer to the multiplication layer does not inhibit carrier travel, and the light absorption layer side of the junction metal layer And it is good to be formed on at least one side of the multiplication layer side. The electric field control layer is formed on the light absorption layer side and the multiplication layer side of the bonding metal layer, and the bonding metal layer is formed on the electric field control layer and multiplication layer side formed on the light absorption layer side. It may be formed so as to be sandwiched between the formed electric field control layers.

  In the avalanche photodiode, an electron transit layer made of an undoped compound semiconductor formed between the second contact layer and the multiplication layer, and an n-type compound formed between the electron transit layer and the multiplication layer You may make it provide the other electric field control layer which consists of semiconductors.

The method for manufacturing an avalanche photodiode according to the present invention includes a step of forming a p-type first contact layer made of a compound semiconductor on a first substrate, and a group III-V compound semiconductor on the first contact layer. A step of forming a light absorption layer comprising: a step of forming a second contact layer comprising an n-type compound semiconductor on the second substrate; and a multiplication layer comprising an undoped compound semiconductor on the second contact layer. Forming a reflective structure layer having a semiconductor multilayer structure disposed between the light absorption layer and the multiplication layer, and an n-type disposed between the reflection structure layer and the multiplication layer The step of forming an electric field control layer made of the compound semiconductor and the light absorption layer formation side of the first substrate and the multiplication layer formation side of the second substrate are bonded to each other on the first substrate. 1 contact layer, light absorption layer, reflection structure A step of laminating a layer, an electric field control layer, a multiplication layer, and a second contact layer in that order, a step of removing a selected one of the first substrate and the second substrate, and a first contact layer A first electrode connected to the second contact layer and a second contact layer formed to connect the second electrode, and the multiplication layer is a semiconductor in which ionization due to hole collision does not occur when a voltage is applied Consists of.

  In the manufacturing method of the avalanche photodiode, the light absorption layer forming side of the first substrate and the multiplication layer forming side of the second substrate may be bonded to each other through a bonding metal layer. In this case, the bonding metal layer has a thickness equal to or less than the length of the mean free path of electrons in the bonded state. In the case where a connection alloy layer is used, the electric field control layer is composed of an n-type compound semiconductor in which impurities are introduced in a state where the band offset from the light absorption layer to the multiplication layer does not hinder carrier travel in a bonded state. And it is good to form in the at least one side of a 1st board | substrate and a 2nd board | substrate. The electric field control layer is formed on each of the first substrate side and the second substrate side, and the bonding via the bonding metal layer is performed on the electric field control layer formed on the first substrate side and the second substrate side. The electric field control layer formed in the above may be bonded through a bonding metal layer.

  In the manufacturing method of the avalanche photodiode, a step of forming an electron transit layer made of an undoped compound semiconductor between the second contact layer and the multiplication layer on the second substrate, and an electron transit on the second substrate And a step of forming another electric field control layer made of an n-type compound semiconductor between the layer and the multiplication layer.

As described above, according to the present invention, the multiplication layer of the avalanche photodiode can be formed of a semiconductor that does not cause ionization due to hole collision when a voltage is applied, and has an avalanche having high gain and broadband device characteristics. An excellent effect is obtained that a photodiode can be obtained.

FIG. 1 is a cross-sectional view schematically showing a configuration of an avalanche photodiode according to Embodiment 1 of the present invention. FIG. 2 is a band diagram showing a change in the band gap in the stacking direction of the avalanche photodiode in the first embodiment of the present invention. FIG. 3 is an explanatory diagram for explaining the manufacturing method of the avalanche photodiode according to the first embodiment of the present invention. FIG. 4 is a band diagram showing an electric field profile when a voltage is applied to the avalanche photodiode according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view schematically showing the configuration of the avalanche photodiode in the second embodiment of the present invention. FIG. 6 is a band diagram showing a change in the band gap in the stacking direction of the avalanche photodiode in the second embodiment of the present invention. FIG. 7 is an explanatory diagram for explaining the manufacturing method of the avalanche photodiode according to the second embodiment of the present invention. FIG. 8 is a band diagram showing an electric field profile when a voltage is applied to the avalanche photodiode according to the second embodiment of the present invention. FIG. 9 is an explanatory diagram for explaining a trade-off relationship that the band decreases at a high multiplication factor in the avalanche photodiode.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
First, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view schematically showing a configuration of an avalanche photodiode according to Embodiment 1 of the present invention. FIG. 2 is a band diagram showing a change in the band gap in the stacking direction of the avalanche photodiode according to the first embodiment of the present invention.

  In the avalanche photodiode, first, a first contact layer 102 made of a p-type compound semiconductor formed on a substrate 101 and a second contact layer 103 made of an n-type compound semiconductor formed on the substrate 101 are used. And a light absorption layer 104 made of a III-V group compound semiconductor formed between the first contact layer 102 and the second contact layer 103.

  The avalanche photodiode includes a multiplication layer 105 made of an undoped compound semiconductor formed between the light absorption layer 104 and the second contact layer 103, and between the light absorption layer 104 and the multiplication layer 105. The formed electric field control layer 106 made of an n-type compound semiconductor, the reflective structure layer 107 made of a semiconductor multilayer structure formed between the light absorption layer 104 and the multiplication layer 105, the multiplication layer 105, and the light absorption. A bonding metal layer formed between the layer 104 and the layer 104.

Here, in the avalanche photodiode, first, the junction metal layer 108 has a thickness equal to or less than the length of the electron mean free path. In addition, the multiplication layer 105 is made of a compound semiconductor that does not cause ionization due to hole collision when a voltage is applied. The first electrode 109 formed to be connected to the first contact layer 102 and the second electrode 110 formed to be connected to the second contact layer 103 are provided. An antireflection layer 111 is formed on the back surface of the substrate 101 opposite to the first contact layer 102.

  In the first embodiment, the first contact layer 102 is formed in contact with the substrate 101, the light absorption layer 104 is formed in contact with the first contact layer 102, and is reflected on the light absorption layer 104. The structural layer 107 is formed in contact, the electric field control layer 106 is formed in contact with the reflective structure layer 107, the bonding metal layer 108 is formed in contact with the electric field control layer 106, and the bonding metal layer 108 is formed on the bonding metal layer 108. The case where the multiplication layer 105 is formed in contact with the second contact layer 103 on the multiplication layer 105 is described. In this configuration, light is incident from the substrate 101 side. Further, the case where the light absorption layer 104 is undoped is described.

  For example, the substrate 101 is made of semi-insulating InP, the first contact layer 102 is made of p-type InGaAsP, and the light absorption layer 104 is made of InGaAs. The second contact layer 103 is made of n-type InAs, the multiplication layer 105 is made of undoped InAs, and the electric field control layer 106 is made of n-type InAlGaAs.

  The reflective structure layer 107 may be a Bragg distributed reflector (DBR) structure made of InAlGaAs whose composition is periodically changed. The first electrode 109 only needs to be composed of a three-layer laminated film of titanium layer / platinum layer / gold layer. Moreover, the 2nd electrode 110 should just be comprised from Al, for example. The antireflection layer 111 may be composed of a dielectric multilayer film.

  Next, a method for manufacturing the avalanche photodiode in the first embodiment will be described. First, as shown in FIG. 3A, a first contact layer 102 made of p-type InGaAsP, which is a group III-V compound semiconductor, is formed on a semi-insulating substrate (first substrate) 101 made of InP. Then, a light absorption layer 104 made of InGaAs, which is a group III-V compound semiconductor, is formed on the first contact layer 102. In addition, a reflective structure layer 107 composed of a plurality of InAlGaAs layers whose composition is periodically changed is formed on the light absorption layer 104. In addition, a III-V group compound semiconductor is formed on the reflective structure layer 107. An electric field control layer 106 made of some n-type InAlGaAs is formed. These may be formed by epitaxial growth using a well-known metal organic chemical vapor deposition method.

Further, as shown in FIG. 3B, an n-type second contact layer 103 made of InAs is formed on a substrate (second substrate) 130 made of InAs, and on the second contact layer 103. A multiplication layer 105 made of undoped InAs is formed. For example, n-type InAs may be epitaxially grown on the substrate 130 and then undoped InAs may be epitaxially grown by a well-known metal organic chemical vapor deposition method. InAs is a semiconductor that does not cause ionization by holes collide when a voltage is applied.

  Next, the formation side of the light absorption layer 104 of the substrate 101 and the formation side of the multiplication layer 105 of the substrate 130 are directly bonded to each other via a metal layer (bonding metal layer). to paste together. For example, on the surface 161 of the electric field control layer 106 and the surface 151 of the multiplication layer 105, a metal layer (bonding metal layer) made of Au and having a layer thickness of several nm is formed by electron beam evaporation or sputtering. Next, the formed metal layers are directly joined (see Non-Patent Document 8). For example, in a processing apparatus in which a metal layer is formed, the surfaces of the metal layers may be brought into contact with each other and bonded by applying a predetermined pressure. This joining can be performed at about room temperature (about 23 ° C.).

  By this bonding, the formation side of the light absorption layer 104 (electric field control layer 106) of the substrate 101 and the multiplication layer 105 formation side (multiplication layer 105) of the substrate 130 are bonded metal layers as shown in FIG. It is in a state of being bonded via 108. Note that the metal layer may be bonded in a state where the metal layer is formed on one surface of the multiplication layer 105 or the electric field control layer 106.

  Next, the substrate 130 is removed (peeled) from the second contact layer 103. For example, the substrate 130 is removed by polishing, etching, or the like. Next, the second electrode 110 is formed on the second contact layer 103 exposed by removing the substrate 130. For example, a resist mask pattern having an opening in a region to be the second electrode 110 is formed, and a three-layer laminated film of platinum layer / titanium layer / gold layer is formed thereon by electron beam evaporation. Thereafter, if the resist mask pattern is removed, the second electrode 110 that is in ohmic contact with the second contact layer 103 can be formed. This is a manufacturing method called a so-called lift-off method.

  Next, the light absorption layer 104, the reflective structure layer 107, the electric field control layer 106, the bonding metal layer 108, the multiplication layer 105, and the second contact layer 103 are patterned by a known lithography technique and etching technique (wet etching or the like). Then, it is processed into a desired mesa shape (for example, a cylindrical shape). Next, a first electrode 109 is formed on the first contact layer 102 exposed by this patterning. Similar to the second electrode 110, the first electrode 109 may be formed by an electron beam evaporation method and a lift-off method.

  Next, the electric field control layer 106, the bonding metal layer 108, the multiplication layer 105, and the second contact layer 103 are patterned by a known lithography technique and etching technique (wet etching or the like) to obtain a mesa shape having a smaller diameter. Further, an antireflection layer 111 made of a dielectric multilayer film is formed on the back surface of the substrate 101 so that the transmittance at a desired wavelength is almost 100%.

  Here, it is important that the thickness of the bonded metal layer 108 integrated after bonding is equal to or less than the length of the mean free path of electrons. During the operation (voltage application) of the avalanche photodiode in the first embodiment described above, the light absorption layer 104 has an electric field strength of several tens to several hundreds kV / cm because depletion proceeds. For this reason, the photocarrier generated by light absorption has high kinetic energy while traveling through the light absorption layer 104, and is in a so-called hot carrier state. Furthermore, the mean free path of electrons in Au constituting the bonding metal layer 108 is said to be about several tens of nm (see Non-Patent Document 10).

  Therefore, if the bonding metal layer 108 is made of Au and the layer thickness is set to 10 nm or less, which is the length of the mean free path of electrons, photocarriers are hardly affected by Au in the bonding metal layer 108. It reaches the multiplication layer 105 and is injected.

  Next, the avalanche photodiode in the first embodiment will be described in more detail.

  InAs, which is a material used for the multiplication layer 105, has a high ionization rate because the ionization rate of holes is close to 0 in principle, and as a result, the ionization rate ratio that is the dominant factor of GBP is almost 0. Material. However, InAs has a very small band gap (0.36 eV). For this reason, when an optical communication wavelength is incident, light that has not been absorbed by the light absorption layer 104 made of InGaAs reaches the multiplication layer 105 made of InAs, and light absorption occurs in the multiplication layer 105. . At this time, in the multiplication layer 105, an electron-hole pair accompanying the light absorption generated in the multiplication layer 105 is generated together with the electrons injected from the light absorption layer 104. For this reason, even though InAs having a hole ionization rate close to 0 is used as the multiplication layer 105, essentially constant holes are generated. As a result, the ionization rate ratio increases from 0, and the GBP is reduced. Invite.

  In order to prevent the above-described state, in Embodiment Mode 1, light is first incident from the substrate 101 side, and the reflective structure layer 107 is provided between the light absorption layer 104 and the multiplication layer 105. With this configuration, light incidence on the multiplication layer 105 can be suppressed, and a high GBP inherent in the multiplication layer 105 can be realized.

  InAs, the electric field strength at which avalanche breakdown occurs is 20-30 kV / cm (Non-patent Document 10), which is very small compared to about 250 kV / cm, which is the breakdown electric field strength of InGaAs. In this case, when a voltage is applied to the avalanche photodiode, the multiplication layer 105 made of InAs reaches the breakdown electric field strength before reaching the electric field strength at which electrons are saturated in the InGaAs of the light absorption layer 104. End up. As a result, the high speed performance of the avalanche photodiode is impaired.

  In order to solve this problem, an electric field control layer 106 made of an n-type compound semiconductor is provided between the light absorption layer 104 and the multiplication layer 105, thereby adjusting the electric field profile of the avalanche photodiode when a voltage is applied. The electric field profile at this time is shown in FIG.

  In the first embodiment, the “High-Low electric field profile” in which the electric field strength of the light absorption layer 104 is “high” and the electric field strength of the multiplication layer 105 is “low” when a voltage is applied. With this electric field profile, the electric field strength in the light absorption layer 104 is sufficient to allow the electrons to reach the saturation speed, and the electric field strength in the multiplication layer 105 is changed to an electric field suitable for avalanche multiplication. Strength. The balance of the electric field intensity of the light absorption layer 104 and the multiplication layer 105 in this electric field intensity profile can be arbitrarily adjusted by the layer thickness and doping concentration of the n-type electric field control layer 106.

As described above, according to the first embodiment, the multiplication layer of the avalanche photodiode can be formed of a semiconductor that does not cause ionization due to hole collision when a voltage is applied, and has high gain and broadband device characteristics. A photodiode can be obtained.

[Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a cross-sectional view schematically showing the configuration of the avalanche photodiode in the second embodiment of the present invention. FIG. 7 is a band diagram showing a change in the band gap in the stacking direction of the avalanche photodiode according to the second embodiment of the present invention.

  In this avalanche photodiode, first, a first contact layer 202 made of a p-type compound semiconductor formed on a substrate 201 and a second contact layer 203 made of an n-type compound semiconductor formed on the substrate 201. And a light absorption layer 204 made of a III-V group compound semiconductor formed between the first contact layer 202 and the second contact layer 203.

  The avalanche photodiode includes a multiplication layer 205 made of an undoped compound semiconductor formed between the light absorption layer 204 and the second contact layer 203, and between the light absorption layer 204 and the multiplication layer 205. Two electric field control layers 206a and 206b made of the formed n-type compound semiconductor are provided. In the second embodiment, the reflective structure layer 207 having a semiconductor multilayer structure formed between the multiplication layer 205 and the light absorption layer 204 is formed between the multiplication layer 205 and the light absorption layer 204. And a bonding metal layer 208.

  In the second embodiment, the electron transit layer 212 made of an undoped compound semiconductor formed between the second contact layer 203 and the multiplication layer 205 is formed between the electron transit layer and the multiplication layer. And an electric field control layer 213 made of an n-type compound semiconductor. Unlike the electric field control layer 206a and the electric field control layer 206b, the electric field control layer 213 is newly provided.

Here, in the avalanche photodiode, first, the junction metal layer 208 has a thickness equal to or less than the length of the electron mean free path. The multiplication layer 205 is made of a compound semiconductor that does not cause ionization by hole collision when a voltage is applied. Note that a first electrode 209 formed to be connected to the first contact layer 202 and a second electrode 210 formed to be connected to the second contact layer 203 are provided. An antireflection layer 211 is formed on the back surface of the substrate 201 opposite to the first contact layer 202.

  In the second embodiment, the first contact layer 202 is formed in contact with the substrate 201, the light absorption layer 204 is formed in contact with the first contact layer 202, and is reflected on the light absorption layer 204. The structure layer 207 is formed in contact, the electric field control layer 206a is formed on the reflective structure layer 207, the bonding metal layer 208 is formed on the electric field control layer 206a, and the bonding metal layer 208 is formed on the bonding metal layer 208. The electric field control layer 206b is formed in contact, the multiplication layer 205 is formed on the electric field control layer 206b, and a new electric field control layer 213 is formed on the multiplication layer 205, and the electric field control layer 213 is formed. The case where the electron transit layer 212 is formed in contact with the second contact layer 203 on the electron transit layer 212 is described. In this configuration, light is incident from the substrate 201 side. Further, the case where the light absorption layer 204 is undoped is described.

  In the second embodiment, the electric field control layer is composed of an n-type compound semiconductor in which impurities are introduced in a state where the band offset from the light absorption layer 204 to the multiplication layer 205 does not inhibit carrier travel, and the junction metal The electric field control layer 206a on the light absorption layer 204 side and the electric field control layer 206b on the multiplication layer 205 side are formed with the layer 208 as a boundary. Therefore, in the second embodiment, the bonding metal layer 208 is formed between the electric field control layer 206a formed on the light absorption layer 204 side and the electric field control layer 206b formed on the multiplication layer 205 side. . The electric field control layer is composed of an n-type compound semiconductor in which impurities are introduced in a state where the band offset from the light absorption layer 204 to the multiplication layer 205 does not inhibit carrier travel, and the light absorption layer of the bonding metal layer 208 It may be formed on at least one side of 204 side and multiplication layer 205 side.

  For example, the substrate 201 is made of semi-insulating InP, the first contact layer 202 is made of p-type InGaAsP, and the light absorption layer 204 is made of InGaAs. The second contact layer 203 is made of n-type InAs, the multiplication layer 205 is made of undoped InAs, the electric field control layer 206a is made of n-type InAlGaAs, and the electric field control layer 206b is What is necessary is just to be comprised from n-type InAs. Further, the electron transit layer 212 may be made of InAs, and the electric field control layer 213 may be made of n-type InAs.

  The reflection structure layer 207 may be a Bragg distribution reflection structure made of InAlGaAs whose composition is periodically changed. Moreover, the 1st electrode 209 should just be comprised from the 3 layer laminated film of a titanium layer / platinum layer / gold layer. Moreover, the 2nd electrode 210 should just be comprised from Al, for example. The antireflection layer 211 may be composed of a dielectric multilayer film.

  Next, a method for manufacturing the avalanche photodiode in the second embodiment will be described. First, as shown in FIG. 7A, a first contact layer 202 made of p-type InGaAsP, which is a group III-V compound semiconductor, is formed on a semi-insulating substrate (first substrate) 101 made of InP. Then, a light absorption layer 204 made of InGaAs, which is a III-V group compound semiconductor, is formed on the first contact layer 202. Further, a reflective structure layer 207 composed of a plurality of InAlGaAs layers whose composition is periodically changed is formed on the light absorption layer 204. In addition, a III-V group compound semiconductor is formed on the reflective structure layer 207. An electric field control layer 206a made of some n-type InAlGaAs is formed. These may be formed by epitaxial growth using a well-known metal organic chemical vapor deposition method.

Further, as shown in FIG. 7B, an n-type second contact layer 203 made of InAs is formed on a substrate (second substrate) 230 made of InAs, and on the second contact layer 203. An electron transit layer 212 made of InAs is formed, an electric field control layer 213 made of n-type InAs is formed on the electron transit layer 212, and a multiplication layer 205 made of undoped InAs is formed on the electric field control layer 213. In addition, an electric field control layer 206b made of n-type InAs is formed on the multiplication layer 205. For example, each layer may be epitaxially grown sequentially on the substrate 230 by a well-known metal organic chemical vapor deposition method. InAs is a semiconductor that does not cause ionization by holes collide when a voltage is applied.

  Next, the formation side of the light absorption layer 204 of the substrate 201 and the formation side of the multiplication layer 205 of the substrate 230 are directly bonded to each other via a metal layer (bonding metal layer). to paste together. For example, a metal layer (joining metal layer) made of Au with a thickness of several nm is formed on the surface 261a of the electric field control layer 206a and the surface 261b of the electric field control layer 206b by an electron beam evaporation method or a sputtering method. Next, the formed metal layers are directly joined (see Non-Patent Document 8). For example, in a processing apparatus in which a metal layer is formed, the surfaces of the metal layers may be brought into contact with each other and bonded by applying a predetermined pressure. This joining can be performed at about room temperature (about 23 ° C.).

  By this bonding, the formation side of the light absorption layer 204 of the substrate 201 (electric field control layer 206a) and the formation side of the multiplication layer 205 of the substrate 201 (electric field control layer 206b) are bonded metal as shown in FIG. A state of being bonded through the layer 208 is obtained. Note that the metal layer may be attached in a state where the metal layer is formed over one surface of the electric field control layer 206a and the electric field control layer 206b.

  Next, the substrate 230 is removed (peeled) from the second contact layer 203. For example, the substrate 230 is removed by polishing, etching, or the like. Next, the second electrode 210 is formed on the second contact layer 203 exposed by removing the substrate 230. For example, a resist mask pattern having an opening is formed in a region to be the second electrode 210, and a three-layer laminated film of platinum layer / titanium layer / gold layer is formed thereon by electron beam evaporation. Thereafter, if the resist mask pattern is removed, the second electrode 210 that is in ohmic contact with the second contact layer 203 can be formed. This is a manufacturing method called a so-called lift-off method.

  Next, the light absorption layer 204, the reflective structure layer 207, the electric field control layer 206a, the bonding metal layer 208, the electric field control layer 206b, the multiplication layer 205, and the electric field control layer are formed by a known lithography technique and etching technique (wet etching or the like). 213, the electron transit layer 212, and the second contact layer 203 are patterned and processed into a desired mesa shape (for example, a cylindrical shape). Next, a first electrode 209 is formed on the first contact layer 202 exposed by this patterning. Similar to the second electrode 210, the first electrode 209 may be formed by an electron beam evaporation method and a lift-off method.

  Next, the second contact layer 203 is patterned by a known lithography technique and etching technique (wet etching or the like) to obtain a mesa shape having a smaller diameter. Further, an antireflection layer 211 made of a dielectric multilayer film is formed on the back surface of the substrate 201 so that the transmittance at a desired wavelength is almost 100%.

  Here, it is important that the thickness of the bonding metal layer 208 integrated after bonding is equal to or less than the length of the mean free path of electrons. During the operation (voltage application) of the avalanche photodiode in the second embodiment described above, the light absorption layer 204 has an electric field strength of several tens to several hundreds kV / cm because depletion proceeds. For this reason, the photocarrier generated by light absorption has high kinetic energy while traveling through the light absorption layer 204, and is in a so-called hot carrier state. Further, the mean free path of electrons in Au constituting the bonding metal layer 208 is said to be about several tens of nm (see Non-Patent Document 10).

  Therefore, if the bonding metal layer 208 is made of Au and the layer thickness is set to 10 nm or less, which is the length of the mean free path of electrons, photocarriers are hardly affected by Au in the bonding metal layer 208. It reaches the multiplication layer 205 and is injected.

  Next, the avalanche photodiode in the third embodiment will be described in more detail.

  The second embodiment is greatly different from the first embodiment described above in that an electron transit layer 212 and another electric field control layer 213 are newly added to the configuration of the first embodiment described above. This point will be described.

  The 3 dB band of an avalanche photodiode is generally determined by GBP, carrier travel band, and CR band due to element resistance and capacitance. In order to realize a high CR band of the element, it is important to reduce the element capacitance by increasing the width of the depletion layer in the element. For this reason, by providing the undoped electron transit layer 212 between the multiplication layer 205 and the second contact layer 203, it is possible to expand the depletion layer width of the element and reduce the element capacitance.

  Further, when the electron transit layer 212 and the multiplication layer 205 are continuously arranged, the multiplication layer 205 and the electron transit layer 212 are formed of the same InAs, so that the layer thickness of the multiplication layer 205 is effectively enlarged. Will be equivalent to In this configuration, the GBP is also determined by the layer thickness of the multiplication layer 205, so that the GBP decreases. Here, by inserting another n-type electric field control layer 213 between the multiplication layer 205 and the electron transit layer 212, the electric field strength of the electron transit layer 212 is lowered relative to the multiplication layer 205. It becomes possible.

  FIG. 8 shows an electric field intensity profile of the avalanche photodiode according to the second embodiment configured as described above. The light absorption layer 204, the multiplication layer 205, and the electron transit layer 212 have a “High-Low-Low” electric field intensity profile in this order. As a result, avalanche multiplication is selectively generated only in the multiplication layer 205, and electrons can be drifted and moved in the electron transit layer 212 with a lower electric field strength. It becomes possible to prevent. At the same time, the edge breakdown in the multiplication layer 205 made of InAs can be suppressed.

  By the way, as described above, bonding by the bonding metal layer 208 is performed. However, in such a Seto number, a semiconductor / metal interface is formed, and a finite Schottky barrier is generated at these interfaces. On the other hand, by performing impurity doping on the surface of the semiconductor layer in contact with the junction metal layer 208, the Schottky barrier height at the metal / semiconductor interface can be adjusted, and the charge transfer at the semiconductor / metal interface can be stabilized. In the embodiment described above, the connection metal layer 208 is brought into contact with the n-type electric field control layer, and the above-described effects are obtained.

As described above, also in the second embodiment, the avalanche photodiode multiplication layer of the avalanche photodiode can be composed of a semiconductor that does not cause ionization due to hole collision when a voltage is applied, and has a high gain and broadband device characteristics. A diode is obtained.

As described above, according to the present invention, since the reflective structure layer having a semiconductor multilayer structure is provided between the light absorption layer and the multiplication layer, the intrusion of light into the multiplication layer is suppressed. It becomes so that, the multiplication layer of an avalanche photodiode, so ionization by holes collide when a voltage is applied Ru can consist semiconductor does not occur.

  As described in the section of the background art and the problem to be solved by the invention, in order to realize an avalanche photodiode having a higher GBP, a material having a smaller ionization rate ratio is selected as a material constituting the multiplication layer. It is important to do. However, in conventional avalanche photodiodes, materials such as InP and InAlAs that are lattice-matched to InGaAs used for the light absorption layer are used for the multiplication layer, and there is a limit to the reduction of the ionization rate ratio in the multiplication layer. was there. InAs is a material that can realize GBP, but because it has a large lattice constant difference from InGaAs of the light absorption layer, it cannot be stably grown on the InP substrate and with the InGaAs light absorption layer, so that the communication wavelength band It was difficult to operate as an avalanche photodiode conforming to

On the other hand, since InAs, HgCdTe, etc. have a small band gap and do not cause ionization due to hole collision in principle, it has been reported that the multiplication layer can be brought into a state with a very small ionization ratio by using these. Yes. However, since these materials have a smaller band gap than InGaAs, when an optical communication wavelength of 1.55 μm to 1.3 μm band is incident, light absorption occurs in the multiplication layer in addition to the light absorption layer. Holes are generated in the multiplication layer. In this case, InAs and HgCdTe do not cause ionization due to hole collision in principle, and thus, although they are materials that enable high GBP, holes are induced in the multiplication layer, and effectively There was a problem of having a certain ionization rate ratio and a decrease in GBP.

  Furthermore, when the band gap of the multiplication layer material is smaller than the band gap of the light absorption layer, the multiplication layer breaks before the electric field strength in the light absorption layer reaches the electron saturation speed when a voltage is applied to the avalanche photodiode. It will cause down. For this reason, electrons cannot be sufficiently accelerated before the breakdown of the avalanche photodiode, resulting in a problem that a high-speed avalanche photodiode cannot be realized.

  According to the present invention, the restrictions due to the lattice constant of the material selection of the light absorption layer material and the multiplication layer material are eliminated, and the band gap limitation of the material selection of the light absorption layer material and the multiplication layer material is also eliminated. Can be eliminated.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, in the above-described embodiment, the example in which the multiplication layer is formed from InAs has been described. However, the present invention is not limited to this. For example, the multiplication layer is formed from a II-VI group semiconductor such as HgCdTe having a very low ionization ratio. It may be configured. Further, although Au is used as the bonding metal, other metal material systems such as Ti and Mo may be used. Further, in order to realize high speed and high sensitivity of the element, it may have a loading type structure.

  In the above-described embodiment, the case where the metal organic vapor phase epitaxy method is used for forming the semiconductor layer has been described as an example. However, the semiconductor layer may be formed by using a molecular beam epitaxy method or the like. In addition, although the PIN structure is given as an example of the light absorption layer, the non-lower light absorption layer may be an MIC structure (Non-Patent Document 11) or a single traveling carrier (UTC) structure (Non-Patent Document 12). It is good. In addition, as a device structure of the avalanche photodiode, a so-called “inverted avalanche photodiode structure” (Non-patent Document 13) is given as an example. However, the device structure is not limited to this, and an n-type contact layer is an underlayer structure. Also good.

  In the above-described embodiment, the metal-metal bonding is exemplified as the wafer bonding method. However, the present invention is not limited to this, and the surface of the layer to be bonded in the vacuum chamber is irradiated with Ar plasma. Other bonding methods such as “surface activation method” may be used such as bonding by exposing and activating dangling bonds. In this case, it is not necessary to use the bonding metal layer, and the problem of the Schottky barrier does not occur.

  DESCRIPTION OF SYMBOLS 101 ... Board | substrate, 102 ... 1st contact layer, 103 ... 2nd contact layer, 104 ... Light absorption layer, 105 ... Multiplication layer, 106 ... Electric field control layer, 107 ... Reflective structure layer, 108 ... Joining metal layer, 109 ... 1st electrode, 110 ... 2nd electrode, 111 ... Antireflection layer.

Claims (10)

Forming a p-type first contact layer made of a compound semiconductor on a first substrate;
Forming a light absorption layer made of a III-V compound semiconductor on the first contact layer;
Forming a second contact layer made of an n-type compound semiconductor on the second substrate;
Forming a multiplication layer made of an undoped compound semiconductor on the second contact layer;
Forming a reflective structure layer composed of a semiconductor multilayer structure disposed between the light absorption layer and the multiplication layer;
Forming an electric field control layer made of an n-type compound semiconductor disposed between the reflective structure layer and the multiplication layer;
The first contact layer and the light absorption layer are formed on the first substrate by bonding the light absorption layer formation side of the first substrate and the multiplication layer formation side of the second substrate. , The reflective structure layer, the electric field control layer, the multiplication layer, and the second contact layer are stacked in this order,
Removing a selected one of the first substrate and the second substrate;
Connecting and forming a first electrode to the first contact layer;
And at least a step of connecting and forming a second electrode to the second contact layer,
The method of manufacturing an avalanche photodiode, wherein the multiplication layer is made of a semiconductor that is not ionized by hole collision when a voltage is applied. In the manufacturing method of the avalanche photodiode of Claim 1,
The light absorption layer formation side of the first substrate and the multiplication layer formation side of the second substrate are bonded together via a bonding metal layer, and the bonding metal layer is an average of electrons in the bonded state. A method of manufacturing an avalanche photodiode, characterized in that the thickness is equal to or less than the length of a free stroke. In the manufacturing method of the avalanche photodiode according to claim 2,
The electric field control layer is composed of an n-type compound semiconductor in which impurities are introduced in a state where a band offset from the light absorption layer to the multiplication layer does not inhibit carrier travel in a bonded state, and the first substrate And an avalanche photodiode manufacturing method comprising forming the avalanche photodiode on at least one side of the second substrate. In the manufacturing method of the avalanche photodiode according to claim 3,
The electric field control layer is formed on each of the first substrate side and the second substrate side, and the bonding via the bonding metal layer is performed on the electric field control layer formed on the first substrate side and the second substrate side. A method of manufacturing an avalanche photodiode, comprising: bonding an electric field control layer formed on a substrate side through the bonding metal layer. In the manufacturing method of the avalanche photodiode of any one of Claims 1-4,
Forming an electron transit layer made of an undoped compound semiconductor between the second contact layer and the multiplication layer on the second substrate;
And a step of forming another electric field control layer made of an n-type compound semiconductor between the electron transit layer on the second substrate and the multiplication layer. A method for manufacturing an avalanche photodiode . A first contact layer made of a p-type compound semiconductor formed on a substrate;
A second contact layer made of an n-type compound semiconductor formed on the substrate;
A light absorption layer made of a III-V compound semiconductor formed between the first contact layer and the second contact layer;
A multiplication layer made of an undoped compound semiconductor formed between the light absorption layer and the second contact layer;
An electric field control layer made of an n-type compound semiconductor formed between the light absorption layer and the multiplication layer;
A reflective structure layer composed of a semiconductor multilayer structure formed between the light absorption layer and the multiplication layer;
A first electrode formed in connection with the first contact layer;
And at least a second electrode formed in connection with the second contact layer,
The amplifying layer is made of a compound semiconductor that does not cause ionization due to hole collision when a voltage is applied. The avalanche photodiode according to claim 6,
An avalanche photo comprising a bonding metal layer formed between the multiplication layer and the light absorption layer, wherein the bonding metal layer has a thickness equal to or less than the length of the mean free path of electrons. diode. The avalanche photodiode according to claim 7,
The electric field control layer is composed of an n-type compound semiconductor into which impurities are introduced in a state where a band offset from the light absorption layer to the multiplication layer does not inhibit carrier travel, and the light absorption layer of the junction metal layer The avalanche photodiode is formed on at least one of the side of the multiplication layer and the side of the multiplication layer. The avalanche photodiode according to claim 8,
The electric field control layer is formed on each of the light absorption layer side and the multiplication layer side of the bonding metal layer, and the bonding metal layer is formed on the electric field control layer formed on the light absorption layer side and the multiplication layer. An avalanche photodiode characterized by being sandwiched between an electric field control layer formed on the double layer side. The avalanche photodiode according to any one of claims 6 to 9,
An electron transit layer made of an undoped compound semiconductor formed between the second contact layer and the multiplication layer;
An avalanche photodiode comprising: an electric field control layer made of an n-type compound semiconductor formed between the electron transit layer and the multiplication layer.

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