Optical semiconductor element, optical receiver, and optical transceiver

Abstract

To improve the response speed of optical semiconductor elements.SOLUTION: An optical semiconductor element includes a first semiconductor layer having a first band gap and a second semiconductor layer having a second band gap smaller than the first band gap and formed on the first semiconductor layer. The first semiconductor layer includes a first conductive region of a first polarity, a second conductive region of a second polarity, and a first non-conductive region provided between the first conductive region and the second conductive region. The second semiconductor layer includes a third conductive region of the first polarity and a second non-conductive region. The third conductive region is in contact with the first conductive region and the first non-conductive region. The second non-conductive region is in contact with at least one of the second conductive region or the first non-conductive region without contacting the first conductive region.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an optical semiconductor element that converts an optical signal into an electrical signal, an optical receiver including an optical semiconductor element, and an optical transmitter / receiver including an optical semiconductor element. [Background technology]

[0002] An optical receiver (or an optical transceiver equipped with an optical receiver) is one of the key devices for realizing high-speed optical communication. An optical receiver includes a photoreceiver that converts a received optical signal into an electrical signal. Therefore, in order to realize high-speed optical communication, a photoreceiver capable of high-speed operation is required.

[0003] The light receiver is realized by, for example, an optical semiconductor element such as a photodiode. In recent years, optical semiconductor elements manufactured by silicon photonics have been attracting attention.

[0004] A photodiode includes an absorption layer that absorbs light and generates electron-hole pairs. The electrons and / or holes generated in the absorption layer are output via electrodes, resulting in an electrical signal that represents the intensity of the input light. That is, the received optical signal is converted into an electrical signal.

[0005] A photodiode having a germanium layer as an absorption layer has been proposed. For example, a photodetector described in Patent Document 1 has an N-type silicon layer, a germanium layer, and a P-type silicon layer, and an optical signal is absorbed in the germanium layer. An electrical signal is generated from the absorbed optical signal. Then, the electrical signal is output to the outside of the photoreceiver via the N-type silicon layer and the P-type silicon layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-111363 A Summary of the Invention [Problem to be solved by the invention]

[0007] In a photodiode with a germanium layer as an absorption layer, electrons and holes generated in the germanium layer flow into the N-type silicon layer and the P-type silicon layer, respectively. At this time, holes are trapped at the heterointerface between the germanium layer and the P-type silicon layer. This slows down the movement speed of the holes due to the spatial field effect, limiting the response speed to changes in the intensity of the input light.

[0008] An object of one aspect of the present invention is to improve the response speed of an optical semiconductor element. [Means for solving the problem]

[0009] An optical semiconductor device according to one embodiment of the present invention comprises a first semiconductor layer having a first band gap and a second semiconductor layer having a second band gap smaller than the first band gap and formed on the first semiconductor layer. The first semiconductor layer comprises a first conductive region of a first polarity, a second conductive region of a second polarity, and a first non-conductive region provided between the first conductive region and the second conductive region. The second semiconductor layer comprises a third conductive region of the first polarity and a second non-conductive region. The third conductive region is in contact with the first conductive region and the first non-conductive region. The second non-conductive region is in contact with at least one of the second conductive region or the first non-conductive region without being in contact with the first conductive region. Effect of the Invention

[0010] According to the above aspect, the response speed of the optical semiconductor element is improved. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating an example of a structure of a photodiode. [Diagram 2]FIG. 13 is a diagram showing another example of the structure of a photodiode. [Diagram 3] 1 is a diagram showing an example of an optical semiconductor element according to an embodiment of the present invention; [Figure 4] 3 is a diagram illustrating the operation of the optical semiconductor element shown in FIG. 2. [Diagram 5] 4A to 4C are diagrams illustrating the operation of the optical semiconductor element according to the embodiment shown in FIG. [Figure 6] FIG. 13 is a diagram showing an example of a simulation result of an OE response to frequency. [Figure 7] FIG. 1 shows an example of measurement results for OE response versus frequency. [Figure 8] FIG. 2 is a diagram showing an example of an optical semiconductor element according to a first variation. [Figure 9] FIG. 13 is a diagram showing an example of an optical semiconductor element according to a second variation. [Figure 10] FIG. 13 is a diagram showing an example of an optical semiconductor element according to a third variation. [Figure 11] 13 is a diagram showing an example of an optical semiconductor element according to a fourth variation. FIG. [Figure 12] FIG. 13 is a diagram showing an example of an optical semiconductor element according to a fifth variation. [Figure 13] FIG. 13 is a diagram showing an example of an optical semiconductor element according to a sixth variation. [Figure 14] 1 is a diagram showing an example of an optical transceiver in which an optical semiconductor element according to an embodiment of the present invention is mounted; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 1 shows an example of the structure of a photodiode. This photodiode includes a p-type light absorbing layer 101, an n-type electrode layer 102, a carrier transport layer 103, a p-type carrier blocking layer 104, an anode electrode 105, a cathode electrode 106, and a semi-insulating substrate 107.

[0013] Generally, in semiconductor materials, the drift velocity of holes is slower than that of electrons. Therefore, the carrier transit time is limited by the drift velocity of holes. Therefore, the photodiode shown in Figure 1 adopts a Uni-Traveling Carrier Photodiode (UTC-PD) structure to shorten the carrier transit time.

[0014] Light incident from the semi-insulating substrate 107 side passes through the n-type electrode layer 102 and the carrier travel layer 103, and is absorbed in the p-type light absorbing layer 101. Then, pairs of electrons and holes are generated in the p-type light absorbing layer 101. Of the pairs of electrons and holes generated in the p-type light absorbing layer 101, the electrons diffuse to the carrier travel layer 103 and reach the cathode electrode 106 via the n-type electrode layer 102. As a result, an induced current is generated in an external circuit. The holes flow into the anode electrode 105, so they hardly contribute to the induced current. In this way, the photodiode shown in FIG. 1 uses only electrons as carriers. This improves the response speed.

[0015] However, in the structure shown in FIG. 1, a metal material (i.e., the anode electrode 105) is provided near the p-type light absorption layer 101. Therefore, a part of the input light is absorbed by the anode electrode 105. Here, when the input light is absorbed by the metal material, electrons and holes are not generated. That is, ineffective absorption occurs. Therefore, the conversion efficiency from the input light to carriers is poor, and the light receiving sensitivity is low. In addition, there are many layers formed on the substrate (n-type electrode layer 102, carrier traveling layer 103, p-type light absorption layer 101, p-type carrier block layer 104), and the manufacturing process is complicated.

[0016] 2 shows another example of the structure of a photodiode, which includes a SiO2 layer 111, a p-type silicon layer 112, an intrinsic silicon layer 113, an n-type silicon layer 114, a germanium layer 115, a waveguide layer 117, a passivation layer 118, and metal contact electrodes 119 and 120.

[0017] The germanium layer 115 is an intrinsic germanium region and is used as a light absorbing layer. The germanium layer 115 is in contact with the p-type silicon layer 112, the intrinsic silicon layer 113, and the n-type silicon layer 114. The germanium layer 115 may include a p-type germanium layer 116. In this case, the p-type germanium layer 116 is in contact with the p-type silicon layer 112. The metal contact electrode 119 is used as an anode electrode and is in contact with the p-type silicon layer 112. The metal contact electrode 120 is used as a cathode electrode and is in contact with the n-type silicon layer 114.

[0018] Input light is guided to the germanium layer 115 via the waveguide layer 117. Electron-hole pairs are generated in the germanium layer 115. Of the electron-hole pairs generated in the germanium layer 115, the electrons reach the metal contact electrode 120 via the n-type silicon layer 114. As a result, an induced current is generated in an external circuit. Note that when the germanium layer 115 includes the p-type germanium layer 116, the electric field strength in the germanium layer 115 increases, and the drift speed of the electrons increases. The holes flow into the p-type silicon layer 112.

[0019] 2, holes generated in the germanium layer 115 pass through the heterointerface between the germanium layer 115 and the p-type silicon layer 112. At this time, holes accumulate at this interface, and the response speed decreases due to the spatial field effect. Note that "intrinsic" means that the impurity concentration is sufficiently low and the material can be considered as an intrinsic semiconductor.

[0020] <Embodiment> 3 shows an example of an optical semiconductor device according to an embodiment of the present invention. The optical semiconductor device 10 according to the embodiment of the present invention is a photoreceiver (or a photodiode) that converts input light into an electrical signal.

[0021] FIG. 3(a) is a cross-sectional view of the optical semiconductor element 10. FIG. 3(b) is a top view of the optical semiconductor element 10. Here, FIG. 3(a) shows the AA cross section shown in FIG. 3(b). Note that FIG. 3(b) is for explaining the arrangement of the waveguide, and FIG. 3(a) and FIG. 3(b) do not correspond exactly. For example, in FIG. 3(b), the SiO2 layer 17 shown in FIG. 3(a) is omitted.

[0022] The optical semiconductor element 10 is formed on the surface of a silicon substrate 11. That is, the optical semiconductor element 10 is manufactured by silicon photonics.

[0023] A BOX (Buried Oxide) layer 12 is formed on the upper surface of a silicon substrate 11. The BOX layer 12 is an insulating film and is realized by, for example, SiO2.

[0024] The silicon (Si) layer 13 is formed on the upper surface of the BOX layer 12. The thickness of the silicon layer 13 is not particularly limited, but is, for example, about 0.2 μm. The silicon layer 13 also includes a p-type silicon region (p_Si) 13p, an n-type silicon region (n_Si) 13n, an intrinsic silicon region (i_Si) 13i shown in Fig. 3(a), and an optical waveguide 13w shown in Fig. 3(b). That is, the p-type silicon region 13p, the n-type silicon region 13n, the intrinsic silicon region 13i, and the optical waveguide 13w belong to the same semiconductor layer (i.e., the silicon layer 13).

[0025] The p-type silicon region 13p is formed by selectively doping the silicon layer 13 with a p-type impurity. The p-type impurity may be, for example, boron, aluminum, gallium, or indium. The n-type silicon region 13n is formed by selectively doping the silicon layer 13 with an n-type impurity. The n-type impurity may be, for example, phosphorus, arsenic, or antimony.

[0026] The p-type silicon region 13p and the n-type silicon region 13n each contain an impurity to such an extent that they can be used as conductive regions. Although not particularly limited, the impurity concentration of the p-type silicon region 13p and the n-type silicon region 13n is preferably 1×10 17 / cm 3 The above is assumed.

[0027] As shown in FIG. 3(a), the intrinsic silicon region 13i is formed between the p-type silicon region 13p and the n-type silicon region 13n. The intrinsic silicon region 13i is a silicon region with a sufficiently low concentration of impurities. Here, "intrinsic" means a pure state that does not contain impurities. However, in this specification, a semiconductor with an impurity concentration low enough to be considered as a non-conductive region may be called an intrinsic semiconductor. In this embodiment, the impurity concentration of the intrinsic silicon region 13i is 1×10 16 / cm 3 The intrinsic silicon region 13i is an example of a non-conductive region.

[0028] A germanium (Ge) layer 14 is formed on the upper surface of the silicon layer 13. Here, the band gap of germanium is smaller than the band gap of silicon. That is, a second semiconductor layer (here, the germanium layer 14) having a second band gap smaller than the first band gap is formed on the upper surface of a first semiconductor layer (here, the silicon layer 13) having a first band gap. Note that the band gap of silicon is 1.11 eV, and the band gap of germanium is 0.67 eV. The band gap represents the energy difference between the top of the valence band and the bottom of the conduction band.

[0029] The germanium layer 14 includes a p-type germanium region (p_Ge) 14p. In this embodiment, the germanium layer 14 includes a p-type germanium region 14p and an intrinsic germanium region (i_Ge) 14i. However, the germanium layer 14 does not have to include the intrinsic germanium region 14i. That is, the germanium layer 14 may be composed of only the p-type germanium region 14p. The germanium layer 14 is used as a light absorption layer of a photodiode.

[0030] The p-type germanium region 14p is formed by adding a p-type impurity to the germanium layer 14. For example, boron, aluminum, gallium, or indium may be added as the p-type impurity. The p-type germanium region 14p contains the impurity to an extent that it can be used as a conductive region. Although not particularly limited, the impurity concentration of the p-type germanium region 14p is preferably 1×10 17 / cm 3 The intrinsic germanium region 14i is a germanium region having a sufficiently low impurity concentration. In this embodiment, the impurity concentration of the intrinsic germanium region 14i is 1×10 16 / cm 3 The intrinsic germanium region 14i is an example of a non-conductive region.

[0031] The p-type germanium region 14p is formed so as to be in contact with the p-type silicon region 13p and the intrinsic silicon region 13i. Although the p-type germanium region 14p is not in contact with the n-type silicon region 13n in the embodiment shown in FIG.

[0032] In this embodiment, the intrinsic germanium region 14i is formed so as to be in contact with the intrinsic silicon region 13i and the n-type silicon region 13n, as shown in Fig. 3(a). However, the intrinsic germanium region 14i may be formed so as to be in contact with the n-type silicon region 13n without being in contact with the intrinsic silicon region 13i. In either case, the intrinsic germanium region 14i is formed on the upper surface of the silicon layer 13 so as not to be in contact with the p-type silicon region 13p. That is, the germanium layer 14 is formed so that the p-type silicon region 13p and the intrinsic germanium region 14i are not in contact with each other.

[0033] The electrode 15 is an anode electrode of the photodiode, and is in contact with the p-type silicon region 13p of the silicon layer 13. The electrode 16 is a cathode electrode of the photodiode, and is in contact with the n-type silicon region 13n of the silicon layer 13. A SiO2 layer 17 is formed between the electrode 15 and the germanium layer 14. A SiO2 layer 17 is also formed between the electrode 16 and the germanium layer 14.

[0034] When the optical semiconductor device 10 having the above structure is used as a photoreceiver, a predetermined reverse bias voltage is applied to it. As an example, the electrode 15 used as the anode electrode is grounded to the ground potential, and a predetermined positive voltage (e.g., 3 V) is applied to the electrode 16 used as the cathode electrode. In this case, the reverse bias voltage generates electric field lines from the electrode 16 toward the electrode 15. Some of these electric field lines pass through the germanium layer 14.

[0035] The input light is guided to the optical semiconductor device 10 via the optical waveguide 13w shown in Fig. 3(b). Here, the optical waveguide 13w is a part of the silicon layer 13 shown in Fig. 3(a). Therefore, the input light is guided to the intrinsic silicon region 13i, the p-type silicon region 13p, and the n-type silicon region 13n. Furthermore, the input light propagates from the silicon layer 13 to the germanium layer 14.

[0036] The input light is absorbed in the germanium layer 14. That is, the germanium layer 14 acts as a light absorbing layer of the photodiode. Then, in the germanium layer 14, electron-hole pairs are generated in an amount corresponding to the intensity of the input light.

[0037] When the optical semiconductor device 10 is used as a photoreceiver, a predetermined reverse bias voltage is applied. Thus, electrons and holes generated in the germanium layer 14 move within the semiconductor region based on the electric field generated by the reverse bias voltage. Specifically, electrons move from the germanium layer 14 through the intrinsic silicon region 13i and the n-type silicon region 13n to the electrode 16. Holes diffuse from the germanium layer 14 into the p-type silicon region 13p. At this time, some of the holes may diffuse from the germanium layer 14 through the intrinsic silicon region 13i into the p-type silicon region 13p.

[0038] If the silicon layer 13 does not include the intrinsic silicon region 13i, the p-type silicon region 13p and the n-type silicon region 13n will be in contact with each other. In this case, a depletion layer will be generated at the interface of the pn junction. The depletion layer acts as a capacitor and weakens the electric field caused by the reverse bias voltage. That is, when depletion is formed, the movement speed of carriers (electrons and / or holes) will be slowed down. For this reason, the optical semiconductor device 10 includes the intrinsic silicon region 13i between the p-type silicon region 13p and the n-type silicon region 13n. As a result, the influence of the depletion layer is mitigated. Also, the intrinsic silicon region 13i acts as a carrier travel layer.

[0039] In this way, when light is incident on the optical semiconductor device 10, electron-hole pairs are generated in the germanium layer 14. The generated electrons and holes then move to the electrodes 16 and 15, respectively. As a result, an induced current is generated in the external circuit connected to the electrodes 15 and 16. In other words, a current or voltage according to the intensity of the input light can be detected.

[0040] <Effects> Next, the effects of the structure according to the embodiment of the present invention will be described below by comparing the structure shown in FIG.

[0041] Fig. 4 is a diagram for explaining the operation of the optical semiconductor element shown in Fig. 2. Fig. 4(a) shows the path along which carriers (electrons and holes) generated due to input light move. Fig. 4(b) shows an example of the energy band of the optical semiconductor element shown in Fig. 2. It is assumed that a predetermined reverse bias voltage is applied to electrodes 119 and 120. In Fig. 4(b), black circles and white circles represent electrons and holes, respectively.

[0042] 2, electron-hole pairs are generated in the germanium layer 115. Of the electron-hole pairs generated in the germanium layer 115, electrons reach the metal contact electrode 120 via the n-type silicon layer 114. This generates an induced current in an external circuit connected to the electrodes 119 and 120.

[0043] Holes diffuse from the germanium layer 115 to the p-type silicon layer 112. At this time, the holes generated in the germanium layer 115 pass through the heterointerface between the germanium layer 115 and the p-type silicon layer 112. However, a barrier that prevents the diffusion of holes exists at this interface. Therefore, holes are trapped near this interface, and the response speed is reduced due to the spatial field effect.

[0044] FIG. 5 is a diagram for explaining the operation of the optical semiconductor element 10 according to the embodiment of the present invention shown in FIG. 3. FIG. 5(a) shows the path along which carriers (electrons and holes) generated due to input light move. FIG. 5(b) and FIG. 5(c) show an example of the energy band of the optical semiconductor element shown in FIG. 3. It is assumed that a predetermined reverse bias voltage is applied to the electrodes 15 and 16. In addition, in FIG. 5(b) and FIG. 5(c), the black circles and the white circles represent electrons and holes, respectively.

[0045] When light is incident on the optical semiconductor element shown in Fig. 3, electron-hole pairs are generated in the germanium layer 14. Here, the electrons generated in the germanium layer 14 can move to the electrode 16 via two paths shown in Fig. 5(a). Specifically, the electrons can move via path R1 from the germanium layer 14 to the n-type silicon region 13n without passing through the intrinsic silicon region 13i, and path R2 from the germanium layer 14 to the n-type silicon region 13n via the intrinsic silicon region 13i.

[0046] The holes generated in the germanium layer 14 diffuse to the p-type silicon region 13p. At this time, the holes generated in the germanium layer 14 pass through the heterointerface between the germanium layer 14 and the p-type silicon region 13p. A barrier that prevents the diffusion of holes exists at this interface. However, in the optical semiconductor element 10 shown in FIG. 3 or FIG. 5, the germanium layer 14 in contact with this heterointerface is the p-type germanium region 14p. A large number of holes exist in the p-type germanium region 14p. Therefore, the holes generated in the germanium layer 14 easily overcome the barrier in the process of diffusion from the germanium layer 14 to the p-type silicon region 13p. That is, the accumulation of holes is unlikely to occur at the heterointerface between the germanium layer 14 and the p-type silicon region 13p. As a result, compared to the structure shown in FIG. 2, in the optical semiconductor element 10 according to the embodiment shown in FIG. 3, the diffusion speed of holes (or the movement speed of holes) is faster, and a high-speed response of the photodiode is realized. In particular, at high optical inputs, hole accumulation at the heterointerface between the germanium layer 14 and the p-type silicon region 13p becomes significant, and therefore, it is expected that the optical semiconductor device 10 according to the embodiment shown in FIG. 3 will operate at a significantly higher speed than the structure shown in FIG. 2.

[0047] In addition, the carriers moving in the carrier travel layer (i.e., the intrinsic silicon region 13i) in the path R2 are electrons, and as shown in the energy band of Fig. 5(c), the structure can be considered equivalent to a uni-traveling carrier photodiode (UTC-PD). Here, the travel speed of electrons is faster than that of holes, so the structure shown in Fig. 3 is expected to increase the speed.

[0048] The germanium layer 14 does not necessarily have to include the intrinsic germanium region 14i. That is, the germanium layer 14 may be composed of only the p-type germanium region 14p. However, the configuration in which the germanium layer 14 includes the intrinsic germanium region 14i has the following advantages.

[0049] (1) By appropriately designing the widths (or ratios) of the p-type germanium regions 14p and the intrinsic germanium regions 14i, the response speed, which is determined by the sum of the drift process and the diffusion process, can be maximized. (2) The p-type germanium region 14p is formed, for example, by doping the germanium layer 14 with a p-type impurity. At this time, if there is an error in the shape or position of a mask used to dope the p-type impurity, the p-type impurity may be doped into the n-type silicon region 13n. In this case, the characteristics of the n-type silicon region 13n may be deteriorated. Therefore, by providing the intrinsic germanium region 14i, it is possible to prevent the p-type impurity from being doped into the n-type silicon region 13n.

[0050] Figure 6 shows an example of the simulation result of the OE response to frequency. The simulation conditions are as follows: Input light wavelength: 1.55μm Bias voltage: -3V Width of germanium layer (14): 2 μm Thickness of germanium layer (14): 0.3 μm Width of p-type germanium region (14p): 1 μm Width of silicon layer (13): 21 μm Thickness of silicon layer (13): 0.22 μm Distance between p-type silicon region (13p) and n-type silicon region (13n): 0.4 μm

[0051] The above simulation conditions are common to the structure shown in Fig. 2 and the structure according to the embodiment shown in Fig. 3. However, in the embodiment, the p-type germanium region 14p is in contact with the p-type silicon region 13p and the intrinsic silicon region 13i, and the intrinsic germanium region 14i is not in contact with the p-type silicon region 13p. In contrast, in the structure shown in Fig. 2, the width of the p-type germanium region (116) is 0.2 µm, and the germanium layer 115, which is the intrinsic germanium region, is in contact with the p-type silicon region (112).

[0052] According to the above simulation, the OE response characteristic deteriorates as the frequency increases in both structures. However, the OE response characteristic of the structure according to the embodiment shown in Figure 3 is improved compared to the structure shown in Figure 2. In this simulation, the -3 dB band of the OE response is improved by about 10 GHz.

[0053] Figure 7 shows an example of the measurement results for the OE response to frequency. Figure 7(a) shows the OE response characteristics for input light that results in a photodiode output current of 0.1 mA. Figure 7(b) shows the OE response characteristics for input light that results in a photodiode output current of 3 mA. The measurement conditions are as follows: Temperature: 25℃ Input light wavelength: 1.55μm Bias voltage: -3V Width of germanium layer (14): 0.8 μm Thickness of germanium layer (14): 0.15 μm Width of silicon layer (13): 21 μm Thickness of silicon layer (13): 0.22 μm Distance between p-type silicon region (13p) and n-type silicon region (13n): 0.4 μm

[0054] The above measurement conditions are common to the structure shown in Fig. 2 and the structure according to the embodiment shown in Fig. 3. However, in the embodiment, the p-type germanium region 14p is in contact with the p-type silicon region 13p and the intrinsic silicon region 13i, and the intrinsic germanium region 14i is not in contact with the p-type silicon region 13p. In contrast, in the structure shown in Fig. 2, the germanium layer 115, which is an intrinsic germanium region, is in contact with the p-type silicon region (112).

[0055] According to the above measurement results, by adopting the structure of the embodiment shown in Fig. 3, the bandwidth is improved compared to the structure shown in Fig. 2. Specifically, as shown in Fig. 7(a), when the power of the input light is low, the bandwidth is improved by about 8.2 GHz. Also, as shown in Fig. 7(b), when the power of the input light is high, the bandwidth is improved by about 10.3 GHz. Note that, according to the structure of the embodiment, even when the output current of the photodiode is large (i.e., when the power of the input light is high), the -3 dB bandwidth exceeds 70 GHz, so that an optical signal of 130 Gbaud can be received using this optical semiconductor element.

[0056] Thus, the structure according to the embodiment of the present invention can achieve a faster response speed than the structure shown in Fig. 2. In addition, in the structure according to the embodiment of the present invention, as shown in Fig. 3, no metal electrodes (i.e., electrodes 15, 16) are provided near the region that absorbs input light (i.e., germanium layer 14). Therefore, unlike the structure shown in Fig. 1, there is less reactive absorption by the metal electrodes, and the efficiency of conversion from optical signals to electrical signals is high.

[0057] Furthermore, in the structure according to the embodiment of the present invention, the optical waveguide (optical waveguide 13w in FIG. 3) that propagates input light is formed in the same process as silicon layer 13. In contrast to this, in the structure shown in FIG. 2, the waveguide layer 117 is formed in a process different from that for the silicon layers (112-114). Therefore, the manufacturing process of optical semiconductor device 10 according to the embodiment of the present invention is simpler than that of the structure shown in FIG. 2.

[0058] <Variations> FIG. 8 shows an example of an optical semiconductor device according to the first variation. In the optical semiconductor device 10B according to the first variation, the p-type germanium region 14p contacts the p-type silicon region 13p and the intrinsic silicon region 13i. The intrinsic germanium region 14i contacts the intrinsic silicon region 13i. That is, unlike the structure shown in FIG. 3, the intrinsic germanium region 14i does not contact the n-type silicon region 13n. In this case, electrons generated in the germanium layer 14 move to the electrode 16 via the path R2 shown in FIG. 5. That is, the electrons generated in the germanium layer 14 pass through the carrier travel layer (intrinsic silicon region 13i) and the n-type silicon region 13n to reach the electrode 16.

[0059] 9 shows an example of an optical semiconductor device according to the second variation. In an optical semiconductor device 10C according to the second variation, a p-type germanium region 14p contacts a p-type silicon region 13p, an intrinsic silicon region 13i, and an n-type silicon region 13n. In addition, an intrinsic germanium region 14i contacts an n-type silicon region 13n without contacting the p-type silicon region 13p and the intrinsic silicon region 13i.

[0060] FIG. 10 shows an example of an optical semiconductor element according to the third variation. In the optical semiconductor element 10D according to the third variation, the silicon layer 13 includes a p+ type silicon region 13px, a p type silicon region 13p, an intrinsic silicon region 13i, an n type silicon region 13n, and an n+ type silicon region 13nx. The intrinsic silicon region 13i is provided between the p type silicon region 13p and the n type silicon region 13n. In addition, a p+ type silicon region 13px having a higher impurity concentration than the p type silicon region 13p is provided in the p type silicon region 13p or at an end of the p type silicon region 13p, and an n+ type silicon region 13nx having a higher impurity concentration than the n type silicon region 13n is provided in the n type silicon region 13n or at an end of the n type silicon region 13n. The p+ type silicon region 13px is formed by, for example, further adding a p type impurity to the p type silicon region 13p. The n + -type silicon region 13nx is formed, for example, by further adding an n-type impurity to the n-type silicon region 13n.

[0061] Electrode 15 contacts p+ type silicon region 13px. Electrode 16 contacts n+ type silicon region 13nx. In this way, the impurity concentration of the semiconductor region where electrodes 15 and 16 contact is high, so that the contact resistance is small and high-speed operation of the photodiode is achieved.

[0062] FIG. 11 shows an example of an optical semiconductor element according to the fourth variation. In the optical semiconductor element 10E according to the fourth variation, the p-type silicon region 13p and the n-type silicon region 13n are selectively formed in a region close to the upper surface of the silicon layer 13. That is, the region close to the bottom surface of the silicon layer 13 is formed of the same non-conductive material as the intrinsic silicon region 13i. In other words, the intrinsic silicon region 13i is formed between the p-type silicon region 13p and the n-type silicon region 13n in a region close to the upper surface of the silicon layer 13, and is formed throughout the region close to the bottom surface of the silicon layer 13. Here, the upper surface of the silicon layer 13 is a surface of the silicon layer 13 including a region in contact with the germanium layer 14, and the bottom surface of the silicon layer 13 is a surface of the silicon layer 13 facing the upper surface of the silicon layer 13.

[0063] The p-type silicon region 13p and the n-type silicon region 13n are each formed by doping and diffusing impurities so that the impurities do not reach the bottom surface of the silicon layer 13. This structure suppresses reactive absorption caused by doping of impurities, thereby improving the efficiency of conversion from an input optical signal to an electrical signal.

[0064] FIG. 12 shows an example of an optical semiconductor element according to the fifth variation. In the optical semiconductor element 10F according to the fifth variation, the silicon layer 13 has a recess. That is, a "dent" is formed in the upper surface portion of the silicon layer 13. The recess is formed, for example, by selectively removing the upper surface portion of the silicon layer 13. At this time, the upper surface portion of the intrinsic silicon region 13i is removed. In addition, in the vicinity of the intrinsic silicon region 13i, the upper surface portions of the p-type silicon region 13p and the n-type silicon region 13n are each removed. The germanium layer 14 is formed on the recess. The p-type germanium region 14p contacts the p-type silicon region 13p and the intrinsic silicon region 13i, and the intrinsic germanium region 14i contacts the n-type silicon region 13n and the intrinsic silicon region 13i.

[0065] With this structure, the input light is tightly confined within the waveguide and electron-hole pairs are efficiently generated, thereby improving the operating speed of the photodiode.

[0066] 13 shows an example of an optical semiconductor element according to the sixth variation. In the optical semiconductor element 10G according to the sixth variation, the silicon layer 13 has trenches. The trenches are formed in the upper surface of the silicon layer 13 in the p-type silicon region 13p and the n-type silicon region 13n, respectively. The trenches are formed in positions that do not contact the germanium layer 14. In this embodiment, the regions in which the trenches are formed are filled with SiO2.

[0067] With this structure, the input light is tightly confined within the waveguide and electron-hole pairs are efficiently generated, thereby improving the operating speed of the photodiode.

[0068] <Optical transmitter / receiver> 14 shows an example of an optical transceiver in which an optical semiconductor device according to an embodiment of the present invention is mounted. The optical transceiver 50 according to the embodiment of the present invention includes an optical transmitter 60 and an optical receiver 70. The optical transceiver 50 is provided with local light generated by a light source (not shown). The local light is continuous light having a predetermined wavelength.

[0069] The optical transmitter 60 includes a pair of IQ modulators 61. The IQ modulator 61 includes a pair of Mach-Zehnder interferometers. A drive signal is provided to the IQ modulator 61 from a drive circuit (not shown). The drive signal represents transmission data. The IQ modulator 61 generates a modulated optical signal by modulating local light with the drive signal. The modulated optical signals generated by the pair of IQ modulators 61 are combined by a polarization beam combiner. As a result, a polarization multiplexed optical signal is generated.

[0070] The optical receiver 70 includes a 90-degree optical hybrid circuit 71 and a plurality of optical receivers 72. Here, it is assumed that the optical transceiver 50 receives a polarization multiplexed optical signal transmitted from another node. The polarization multiplexed optical signal is split by a polarization beam splitter into an X-polarized component and a Y-polarized component, the polarizations of which are orthogonal to each other. The 90-degree optical hybrid circuit 71 uses local light to extract an I (In-Phase) component signal and a Q (Quadrature) component signal for each polarization component. As a result, four optical components (XI, XQ, YI, YQ) are extracted from the received optical signal. Each optical component (XI, XQ, YI, YQ) is converted into an electric signal by the optical receiver 72. That is, an electric field information signal representing the electric field of the received optical signal is generated.

[0071] The electric field information signal is guided to a data recovery circuit (not shown). The data recovery circuit recovers data by detecting the phase and amplitude of the optical signal based on the electric field information signal. The data recovery circuit may include a phase recoverer, a discriminator, an error corrector, etc.

[0072] In the optical receiver 70 having the above structure, the optical receiver 72 is realized by the optical semiconductor element 10 (or 10B to 10G) according to the embodiment of the present invention. Here, the response speed of the semiconductor element 10 is improved. Therefore, the optical transceiver 50 or the optical receiver 70 can receive a wideband optical signal. [Explanation of symbols]

[0073] 10 Optical semiconductor elements 13 Silicon layer 13p p-type silicon region 13n n-type silicon region 13i Intrinsic Silicon Region 13w optical waveguide 14 Germanium layer 14p p-type germanium region 14i Intrinsic germanium region 15, 16 electrodes 50 Optical Transmitter / Receiver 70 Optical Receiver 72 Receiver

Claims

1. a first semiconductor layer having a first band gap; a second semiconductor layer having a second bandgap smaller than the first bandgap and formed on the first semiconductor layer; The first semiconductor layer is a first conductive region of a first polarity; a second conductive region of a second polarity; and a first non-conductive region disposed between the first conductive region and the second conductive region; The second semiconductor layer is a third conductive region of the first polarity; and a second non-conductive region; the third conductive region contacts the first conductive region and the first non-conductive region; The second non-conductive region is in contact with at least one of the second conductive region or the first non-conductive region without being in contact with the first conductive region. An optical semiconductor element comprising:

2. The first semiconductor layer includes a waveguide that propagates input light to the optical semiconductor element.

2. The optical semiconductor element according to claim 1 .

3. a first electrode in contact with the first conductive region; a second electrode in contact with the second conductive region.

2. The optical semiconductor element according to claim 1 .

4. the third conductive region contacts the first conductive region, the first non-conductive region, and the second conductive region; The second non-conductive region contacts the second conductive region without contacting the first conductive region and the first non-conductive region.

2. The optical semiconductor element according to claim 1 .

5. a first high concentration region having the first polarity and a higher impurity concentration than the first conductive region is formed in the first conductive region without contacting the first non-conductive region; a second high concentration region having the second polarity and a higher impurity concentration than the second conductive region is formed within the second conductive region without contacting the first non-conductive region; The first high concentration region and the second high concentration region are in contact with electrodes.

2. The optical semiconductor element according to claim 1 .

6. the first conductive region and the second conductive region are formed on an upper surface portion of the first semiconductor layer; The bottom surface of the first semiconductor layer is formed of a non-conductive material.

2. The optical semiconductor element according to claim 1 .

7. A recess is provided in an upper surface of the first semiconductor layer, The second semiconductor layer is formed in the recess.

2. The optical semiconductor element according to claim 1 .

8. The first semiconductor layer has a trench at a position on the upper surface thereof that is not in contact with the second semiconductor layer.

2. The optical semiconductor element according to claim 1 .

9. The impurity concentration of the first conductive region, the second conductive region, and the third conductive region is 1×10 １７ / cm ３ That's all. The impurity concentration of the first non-conductive region and the second non-conductive region is 1×10 １６ / cm ３ is less than or equal to 2. The optical semiconductor element according to claim 1 .

10. the first semiconductor layer is formed of silicon; the second semiconductor layer is formed of germanium; The first polarity is p-type. The second polarity is n-type 2. The optical semiconductor element according to claim 1 .

11. an optical circuit for extracting an I (In-Phase) component signal and a Q (Quadrature) component signal from a received optical signal; a plurality of optical semiconductor elements that convert the I component signal and the Q component signal into an electrical signal, Each optical semiconductor element is a first semiconductor layer having a first band gap; a second semiconductor layer having a second bandgap smaller than the first bandgap and formed on the first semiconductor layer; The first semiconductor layer is a first conductive region of a first polarity; a second conductive region of a second polarity; and a first non-conductive region disposed between the first conductive region and the second conductive region; The second semiconductor layer is a third conductive region of the first polarity; and a second non-conductive region; the third conductive region contacts the first conductive region and the first non-conductive region; the second non-conductive region is in contact with at least one of the second conductive region or the first non-conductive region without being in contact with the first conductive region; the I component signal is input to the second semiconductor layer of a first optical semiconductor element of the plurality of optical semiconductor elements; The Q component signal is input to the second semiconductor layer of a second optical semiconductor element of the plurality of optical semiconductor elements.

1. An optical receiver comprising:

12. An optical transceiver including an optical transmitter and an optical receiver, The optical receiver includes: an optical circuit for extracting an I (In-Phase) component signal and a Q (Quadrature) component signal from a received optical signal; a plurality of optical semiconductor elements that convert the I component signal and the Q component signal into an electrical signal, Each optical semiconductor element is a first semiconductor layer having a first band gap; a second semiconductor layer having a second bandgap smaller than the first bandgap and formed on the first semiconductor layer; The first semiconductor layer is a first conductive region of a first polarity; a second conductive region of a second polarity; and a first non-conductive region disposed between the first conductive region and the second conductive region; The second semiconductor layer is a third conductive region of the first polarity; and a second non-conductive region; the third conductive region contacts the first conductive region and the first non-conductive region; the second non-conductive region is in contact with at least one of the second conductive region or the first non-conductive region without being in contact with the first conductive region; the I component signal is input to the second semiconductor layer of a first optical semiconductor element of the plurality of optical semiconductor elements; The Q component signal is input to the second semiconductor layer of a second optical semiconductor element of the plurality of optical semiconductor elements.

1. An optical transceiver comprising:

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