JP6726248B2 - Semiconductor light receiving element and photoelectric fusion module - Google Patents

Description

The present invention relates to a semiconductor light receiving element and an optoelectronic fusion module, for example, a semiconductor light receiving element used in optical fiber communication, and an optoelectronic fusion module in which an optical circuit and an electric circuit are fused.

Currently, FTTH (Fiber to the Home) systems, particularly PON (Passive Optical Network) systems, which are being introduced at present, often use a single-core bidirectional communication module that performs bidirectional communication with a single optical fiber. .. This single-core bidirectional communication module realizes miniaturization by mounting electronic devices such as LDs (Laser Diodes) and PDs (Photo Diodes), which have conventionally been individually mounted, on the substrate surface of an optical circuit. There is.

The optical circuit employs an optical waveguide using Si as a material. For example, there is known a Si wire waveguide using Si as a core and SiO ₂ having a refractive index extremely smaller than that of Si as a cladding. Since the Si wire waveguide has an extremely large difference in refractive index between the core and the clad, it is possible to strongly confine light in the core. As a result, the optical device using the Si wire waveguide can form a very fine submicron-order waveguide, such as a small curved waveguide having a bend radius reduced to about 1 μm. .. Therefore, the Si wire waveguide has attracted attention as a technology that has the potential to combine Si electronic devices and optical devices on the same chip.

By the way, the semiconductor light receiving element is preferably integrated with the Si wire waveguide. That is, it is preferable to form the semiconductor light receiving element on the SOI (Silicon On Insulator) substrate on which the Si wire waveguide is formed. In Non-Patent Document 1, a top Si layer of an SOI substrate is doped with impurities to a Si core formed by a semiconductor process so as to have a p-type conductivity type, and for example, Ge absorption on the p-type Si core. A semiconductor light receiving element for long wavelength (1550 nm) in which regions are stacked is disclosed. This semiconductor light receiving element has a conductivity type (that is, n type) opposite to that of the Si core by adding impurities to the Ge surface, and a waveguide having an i type region between the p type region and the n type region is present. A photodiode having a PIN structure (hereinafter, also referred to as PIN-PD) is configured.

The photosensitivity R of the PIN-PD (value [A/W] obtained by dividing the generated current Iph by the input light power Pin to the PD [A/W]) is generally e[C] for the elementary electron content, η for the external quantum efficiency, and the Planck constant Where h[m ² kg/s] and the frequency of light are ν[/s], they are expressed by the following equation.
R=eη/(hν)

From the above formula, when light with a wavelength of 1490 nm is received, even if the external quantum efficiency can be increased to the ideal state of 1, the upper limit of the light receiving sensitivity of PIN-PD is about 1.2 [A/W]. I know there is. Therefore, Non-Patent Document 2 discloses a waveguide-type avalanche photodiode (hereinafter, also referred to as APD) that can obtain a higher photosensitivity than PIN-PD by utilizing the avalanche breakdown phenomenon of the diode. ..

The APD disclosed in Non-Patent Document 2 has a structure in which a high reverse bias voltage is applied to the PIN-PD, and the carriers are multiplied in the Ge absorption layer and outside the region where the carriers are generated by light absorption. It has become. The APD having this structure has an advantage that it can be easily manufactured, but since a high electric field is applied to the Ge absorption region, a dark current due to a tunnel current increases in the Ge absorption region, and there is a disadvantage that Ge is easily broken down.

Next, the APD disclosed in Non-Patent Document 3 is an APD devised to overcome the disadvantages of the APD disclosed in Non-Patent Document 2, and is generally called an SAM structure APD. .. The SAM structure is characterized in that an absorption region composed of a non-doped Ge layer and a multiplication region composed of a non-doped Si layer are separated. Due to this feature, the internal electric field due to the high reverse bias voltage is applied to the multiplication region made of the non-doped Si layer according to the ratio of the electric resistance of the absorption region made of the non-doped Ge layer and the electric resistance of the multiplication region made of the non-doped Si layer. Applied efficiently. Since tunnel current is less likely to occur in Si having a band gap larger than that of Ge, the APD disclosed in Non-Patent Document 3 can suppress the dark current more than the APD having the PIN structure disclosed in Non-Patent Document 2. In addition, it is possible to prevent Ge from dielectric breakdown.

Furthermore, the structure of the APD disclosed in Non-Patent Document 4 is generally called a SACM structure, and has a structure in which a charge region is added to the SAM structure. In the SACM structure, the electric field applied to the absorption region composed of the non-doped Ge layer by the charge region composed of the p ⁻ --Si layer is compared with the electric resistance of the multiplication region composed of the absorption region composed of the non-doped Ge layer and the non-doped Si layer. Can be kept lower than As a result, in the SACM structure, the electric field can be concentratedly applied to the multiplication region made of the non-doped Si layer. That is, in the ACM having the SACM structure, Ge is more difficult to be dielectrically broken down than in the APD having the SAM structure, and a high electric field can be applied to the multiplication region with a low applied voltage.

Tao Yin, Rami Cohen, Mike M. Morse, Gadi Sarid, Yoel Chetrit, Doron Rubin,and Mario J. Paniccia, “31GHz Ge nip waveguide photodetectors on Silicone-on-Insulator substrate”,OPTICS EXPRESS,Vol.15,No. 21, 2007, pp.13965-13971 HT Chen, J. Verbist, P. Verheyen, P. De Heyn, G. Lepage, J. De Coster, P. Absil, X. Yin, J. Bauwelinck, J. Van Campenhout, and G. Roelkens,”High sensitivity 10Gb/s Si photonic receiver based on a low-voltage waveguide-coupled Ge avalanche photodetector”, OPTICS EXPRESS, Vol.23, No.2, 2015, pp.815 MS Carroll, K. Childs, R. Jarecki, T. Bauer, and K. Saiz, “Ge-Si separate absorption and multiplication avalanche photodiode for Geiger mode single photon detection”, Applied physics letters, Vol.93, 2008, pp. 183511 Y. Kang, Z. Huang, Y. Saado, J. Campbell, A. Pauchard, J. Bowers, M.J. Paniccia, “High Performance Ge/Si Avalanche Photodiodes Development in Intel”, OSA/OFC/NFOEC 2011,OWZ1.pdf

However, also in the SACM structure APD of Non-Patent Document 4, if the reverse bias voltage applied to the APD increases, the internal electric field generated in the Ge absorption region also increases accordingly. Therefore, if the reverse bias voltage is increased above a certain level in order to increase the multiplication factor, the dielectric breakdown electric field of Ge is exceeded, and the problem of APD damage remains.
In addition, as shown in FIG. As shown in 3, when the reverse bias voltage (Bias) is increased to increase the multiplication factor, the gain (Gain) increases rapidly. This indicates that it is difficult to stabilize the gain with the conventional SACM structure APD. Therefore, an APD having a gradual change in gain with respect to a change in reverse bias voltage has been required.

The present invention has been made in order to solve such a problem, and provides a semiconductor light receiving element and an optoelectronic fusion module that can moderate the slope of change in gain with respect to change in reverse bias voltage. The purpose is to do.

To achieve the above object, the present invention is a semiconductor light receiving device of the waveguide for receiving the optical signal through the formed optical waveguide supporting substrate (101) on (103), absorbs the pre-SL signal light and the absorption region (109) and a charge region (105) and the multiplication region and the (108) is formed as an avalanche photodiode SACM structure that separates the said charge region (105), the multiplication is one The low concentration region (106) is joined to the region (108) and the other end is joined to the low concentration region (106) of the same first conductivity type (for example, p type) as the charge region (105), and the low concentration region (106) is One end facing the junction surface with the charge region (105) is joined with the first contact region (107) of the first conductivity type, and the multiplication region (108) is joined with the charge region (105). One end facing the surface is joined to a region (104) of a second conductivity type (for example, n type) different from the first conductivity type, and the absorption region (109) includes the charge region (105) and the It is formed so as to be bonded to both of the low concentration regions (106), and the carrier concentration of the low concentration region is higher than the carrier concentration of the charge region . The reference numerals and characters in the parentheses are the reference numerals and the like given in the embodiments, and do not limit the present invention.

According to this, the charge region, the low concentration region, and the first contact region are of the first conductivity type. Further, the charge region and the low concentration region have different carrier concentrations. Therefore, a built-in potential is generated at the boundary between the charge region and the low concentration region. Further, the absorption region is joined to both the charge region and the low concentration region. Therefore, in the absorption region, an internal electric field that depends on the built-in potential is generated. Since the built-in potential is a small value, there is no dielectric breakdown in the absorption region.

The first contact region of the first conductivity type and the low-concentration region are in contact with each other, and the charge region, the multiplication region, and the region of the second conductivity type form a pin structure. Therefore, by applying a reverse bias voltage to the device, the depletion layer width W associated with the pin structure is widened. As a result, the increase of the internal electric field applied to the multiplication region is moderated, and the slope of the change in gain with respect to the change in reverse bias voltage is also moderated.

According to the present invention, the slope of the change in gain can be made gentle with respect to the change in reverse bias voltage.

It is sectional drawing which shows the cross section perpendicular|vertical to the optical axis of the semiconductor light receiving element which is 1st Embodiment of this invention. It is a top view of the semiconductor light receiving element which is a 1st embodiment of the present invention. 4 is a flowchart for explaining a method for manufacturing the semiconductor light receiving element that is the first embodiment of the present invention. It is explanatory drawing (1) explaining the manufacturing method of the semiconductor light receiving element which is 1st Embodiment of this invention. FIG. 6 is an explanatory view (2) for explaining the method for manufacturing the semiconductor light receiving element according to the first embodiment of the present invention. It is explanatory drawing (3) explaining the manufacturing method of the semiconductor light receiving element which is 1st Embodiment of this invention. FIG. 6 is an explanatory view (4) for explaining the method for manufacturing the semiconductor light receiving element according to the first embodiment of the present invention. It is explanatory drawing (5) explaining the manufacturing method of the semiconductor light receiving element which is 1st Embodiment of this invention. It is explanatory drawing (6) explaining the manufacturing method of the semiconductor light receiving element which is 1st Embodiment of this invention. It is explanatory drawing (7) explaining the manufacturing method of the semiconductor light receiving element which is 1st Embodiment of this invention. FIG. 8 is an explanatory view (8) for explaining the method for manufacturing the semiconductor light receiving element according to the first embodiment of the present invention. It is explanatory drawing (9) explaining the manufacturing method of the semiconductor light receiving element which is 1st Embodiment of this invention. FIG. 9 is an explanatory view (10) illustrating the method for manufacturing the semiconductor light receiving element according to the first embodiment of the present invention. FIG. 9 is an explanatory view (10) illustrating the method for manufacturing the semiconductor light receiving element according to the first embodiment of the present invention. It is explanatory drawing (11) explaining the manufacturing method of the semiconductor light receiving element which is 1st Embodiment of this invention. FIG. 3 is a yz sectional view parallel to the optical axis for explaining the operation of the semiconductor light receiving element according to the first embodiment of the present invention. FIG. 3 is an xy cross-sectional view perpendicular to the optical axis for explaining the operation of the semiconductor light receiving element that is the first embodiment of the present invention. It is a figure which shows the relationship between the reverse voltage applied to the semiconductor light receiving element which is 1st Embodiment of this invention, and the electric field strength of a multiplication region. It is sectional drawing which shows the cross section perpendicular|vertical to the optical axis of the semiconductor light receiving element which is 2nd Embodiment of this invention. It is a top view of a semiconductor light receiving element which is a 2nd embodiment of the present invention. It is explanatory drawing (1) explaining the manufacturing method of the semiconductor light receiving element which is 2nd Embodiment of this invention. It is explanatory drawing (2) explaining the manufacturing method of the semiconductor light receiving element which is 2nd Embodiment of this invention. It is explanatory drawing (3) explaining the manufacturing method of the semiconductor light receiving element which is 2nd Embodiment of this invention. It is explanatory drawing (4) explaining the manufacturing method of the semiconductor light receiving element which is 2nd Embodiment of this invention. It is explanatory drawing (5) explaining the manufacturing method of the semiconductor light receiving element which is 2nd Embodiment of this invention. FIG. 9 is a yz sectional view parallel to the optical axis for explaining the operation of the semiconductor light receiving element which is the second embodiment of the present invention. FIG. 6 is an xy cross-sectional view perpendicular to the optical axis for explaining the operation of the semiconductor light receiving element that is the second embodiment of the present invention. It is sectional drawing which shows the cross section perpendicular|vertical to the optical axis of the semiconductor light receiving element which is 3rd Embodiment of this invention. It is a block diagram of the photoelectric fusion module to which the semiconductor light receiving element which is each embodiment of this invention is applied.

Hereinafter, an embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings. It should be noted that the drawings are merely schematic representations so that the present invention can be fully understood. Further, in each drawing, common or similar components are designated by the same reference numerals, and duplicate description thereof will be omitted.

(First embodiment)
1 is a sectional view showing a cross section perpendicular to an optical axis of a semiconductor light receiving element according to a first embodiment of the present invention, and FIG. 2 is a plan view of a semiconductor light receiving element according to a first embodiment of the present invention. It is a figure. FIG. 1 shows an xy plane sectional view when light propagates in the z direction, and FIG. 2 shows an xz plane.

The semiconductor light receiving element 100a includes a Si substrate 101 as a supporting substrate, a lower cladding 102, a Si slab waveguide 103, an n-Si region 104, a p ^-- Si charge region 105, and a p-Si low concentration region 106. A p ⁺ -Si contact region 107, an i-Si multiplication region 108 as a multiplication region, an i-Ge absorption region 109, and two Al electrodes 110 and 110. The n-Si region 104 is composed of an n ⁺ -Si contact region 104a and an n-Si low concentration region 104b. In the plan view of FIG. 2, the Si slab waveguide 103 is connected to the Si wire waveguide 115.

The Si substrate 101 has a thickness t ₁ =775 [μm]. The lower clad 102 is deposited on the entire surface of the Si substrate 101, and is SiO ₂ having a thickness t ₂ =3 [μm]. The Si slab waveguide 103 and the Si wire waveguide 115 are Si formed on the lower clad 102 with a thickness t ₃ =220 [nm].

The n-Si region 104, the p ^-- Si charge region 105, the p-Si low-concentration region 106, and the p ⁺ -Si contact region 107 are formed with the same thickness t ₃ =220 nm as the Si slab waveguide 103. The carrier concentration is 4×10 ²⁰ [cm ⁻³ ] in the n ⁺ -Si contact region 104a, 1×10 ¹⁹ in the n-Si low concentration region 104b, and 4×10 in the p ⁻ −Si charge region 105. ¹⁷ [cm ⁻³ ], the p-Si low concentration region 106 is 1×10 ¹⁹ [cm ⁻³ ] and the p ⁺ −Si contact region 107 is 4×10 ²⁰ [cm ⁻³ ].

p ^- -Si charge region 105 has one end joined to the i-Si multiplication region 108, the other end the ^p - bonded to the p-Si low concentration regions 106 of the same conductivity type as -Si charge region 105. Further, p-Si low concentration regions ^106, p - end opposite the junction surface between the -Si charge region 105 ^is bonded to the p + -Si contact region 107. The i-Si multiplication region 108 has a second conductivity type (n-type) n-Si low-concentration region 104b having a second conductivity type different from the first conductivity type at one end facing the junction surface with the p ^-- Si charge region 105. To join. As described above, the p ⁻ --Si charge region 105 and the p − Si low concentration region 106 are in contact with each other, which is a feature different from the APD having the conventional SACM structure. The n-type region is formed by ion-implanting P (phosphorus), for example, and the p-type region is formed by ion-implanting B (boron), for example.

The i-Si multiplication region 108 is non-doped silicon formed between the n-Si region 104 and the p ^-- Si charge region 105.

i-Ge absorption region ^109, p - is formed on the -Si charge region 105 and p-Si low concentration regions 106 - -Si charge region 105 and p-Si so as to straddle the boundary between the low-concentration region 106 ^p .. The i-Ge absorption region 109 has a thickness t ₇ =500 [nm].

The Al electrodes 110 and 110 are formed on the n ⁺ -Si contact region 104a and the p ⁺ -Si contact region 107, and have a thickness t ₄ =1 μm. The n ⁺ -Si contact region 104a is included in the n-Si low-concentration region 104b while being exposed on the upper surface of the Si slab waveguide 103. The upper cladding 111 covers the Si slab waveguide 103 and the i-Ge absorption region 109, and is formed so that the two Al electrodes 110 and 110 are exposed. The upper cladding 111 is, for example, SiO ₂ having a thickness t ₈ =1 [μm].

FIG. 3 is a flow chart for explaining the method of manufacturing the semiconductor light receiving element according to the first embodiment of the present invention.
The manufacturer first prepares an SOI (Silicon On Insulator) substrate 113 (FIG. 4A) (S1), forms a silicon layer (S2 to S6), forms a hard mask layer (S7), and selects a Ge selective growth window. Are formed (S8), and the i-Ge absorption region 109 is selectively grown (S10a). The recess formation (S9) and steps S10b to S13b indicated by broken lines will be described in the second embodiment. After S10a, the manufacturer forms the upper clad 111 (S11a), a contact hole (S12a), and the Al electrodes 110 and 110 (S13a).

In the above-described formation of the silicon layer (S2 to S6), the manufacturer forms the Si slab waveguide 103 on the SOI substrate 113 (S2) and forms the n-Si region 104 (S3), and p- The Si low-concentration region 106 is formed (S4), the p ⁺ -Si contact region 107 is formed (S5), and the p ⁻ -Si charge region 105 and the i-Si multiplication region 108 are formed (S6). ..

4A to 4L are explanatory views (11) illustrating the method for manufacturing the semiconductor light receiving element according to the first embodiment of the present invention. Hereinafter, a method for manufacturing the semiconductor light receiving element 100a will be described in detail.
In FIG. 4A (S1), the manufacturer shows that the lower clad 102 made of SiO ₂ having a thickness t ₂ =3 [μm] and the lower clad 102 are formed on the surface of the Si substrate 101 having a thickness t ₁ =775 [μm]. An SOI substrate 113 in which a top Si layer 112 having a thickness t ₃ =220 [nm] is laminated on the surface is prepared.

In FIG. 4B (S2), the top Si layer 112 is patterned by using photolithography and dry etching to form the Si slab waveguide 103.

In FIG. 4C (S3), the manufacturer partially ion-implants, for example, P (phosphorus) into the inside of the Si slab waveguide 103 by using a resist mask formed by photolithography, and then the n-Si region 104. To form. That is, the manufacturer forms the n-Si low concentration region 104b, and further forms the n ⁺ -Si contact region 104a by changing the ion implantation region and the concentration.

In FIG. 4D (S4), the manufacturer uses a resist mask formed by photolithography, and the inside of the Si slab waveguide 103 is removed so as to exclude the opposite end 117 of the n-Si low concentration region 104b. Then, for example, B (boron) is ion-implanted to form the p-Si low concentration region 106.

In FIG. 4E (S5), the manufacturer uses a resist mask formed by photolithography to partially implant, for example, B (boron) into the p-Si low-concentration region 106 to p ⁺ -Si contact. A region 107 is formed.

In FIG. 4F (S6), the manufacturer uses the resist mask formed by photolithography to contact the p-Si low-concentration region 106, on the n-Si low-concentration region 104b side, and in the n-Si low-concentration region. For example, B (boron) is ion-implanted so as not to contact the concentration region 104b to form the p ^-- Si charge region 105. Thereby, the non-doped i-Si multiplication region 108 is simultaneously formed.

In FIG. 4G (S7), a hard mask layer 202 (for example, a SiO ₂ film) that functions as a Ge selective growth mask is deposited by, for example, a chemical vapor deposition method.

As shown in FIG. 4H (S8), the manufacturer uses photolithography and dry etching to pattern the hard mask layer 202 to form the Ge selective growth window 118. In this case, Ge selective growth window 118, in view of the Ge selective growth of the next ^step, p - straddle the boundary between the -Si charge region 105 and the p-Si low concentration regions ^106, p - -Si charge region 105 and p- The Si low concentration region 106 is formed so as to be exposed.

As shown in FIG. 4I (S10a), the manufacturer selectively grows the i-Ge absorption region 109 having a thickness t ₇ =500 [nm] in the Ge selective growth window 118 (FIG. 4H). Next, in FIG. 4J (S11b), for example, a SiO ₂ film is deposited by chemical vapor deposition to a thickness t ₈ =1 [μm] to form the upper clad 111.

As shown in FIG. 4K (S12a), the manufacturer patterns the upper clad 111 by photolithography and dry etching. As a result, contact holes 114, 114 are formed on the surface of the n ⁺ -Si contact region 104a and the surface of the p ⁺ -Si contact region 107.

As shown in FIG. 4L (S13a), the manufacturer forms an Al film by sputtering so as to cover the two contact holes 114, 114, and further forms an Al electrode 110 by patterning by photolithography and dry etching. .. As a result, the semiconductor light receiving element 100a is formed.

(Explanation of operation)
FIG. 5 is a yz sectional view parallel to the optical axis for explaining the operation of the semiconductor light receiving element according to the first embodiment of the present invention. FIG. 6 is an xy sectional view perpendicular to the optical axis for explaining the operation of the semiconductor light receiving element according to the first embodiment of the present invention.

The operation of the semiconductor light receiving element 100a will be described below with reference to FIGS. Semiconductor photodetector 100a is, i-Ge absorption region 109 and ^p - since the i-Si multiplication region 108 as -Si charge region 105 and multiplication region is separated, may be referred to as SACM structure. However, the operation is slightly different from the conventional SACM structure.

First, as shown in FIG. 5, the signal light 116 propagating through the Si wire waveguide 115 and the Si slab waveguide 103 is evanescently coupled to the i-Ge absorption region 109 and propagates through the i-Ge absorption region 109.

Next, as shown in FIG. 6, the i-Ge absorption region 109 absorbs signal light and generates electrons and holes as carriers. ^Further, p - the boundary between the -Si charge region 105 and the p-Si low concentration region 106 generates a built-in potential due to concentration difference. i-Ge absorption region ^109, p - so deposited on the surface of the -Si-charge regions 105 and p-Si low concentration regions 106, the internal electric field due to the built-in potential is generated. Therefore, electrons generated in the i-Ge absorption region 109, the internal electric ^field, p - drift in the direction of -Si charge region 105, holes, drift in the direction of the p-Si low concentration regions 106.

When the p-Si low concentration region 106 has an acceptor concentration of 1×10 ¹⁹ [cm ⁻³ ] and the p ⁻ −Si charge region 105 has an acceptor concentration of 4×10 ¹⁷ [cm ⁻³ ], the built-in potential is 0.083. It becomes [V]. The built-in potential does not depend on the reverse bias voltage applied to the device.

Thus, according to the semiconductor light-receiving element 100a, the intensity of the internal electric field of the i-Ge absorption region 109 is ^p - uniquely by built-in potential at the boundary between the -Si charge region 105 and the p-Si low concentration region 106 Decided. Therefore, the strength of the internal electric field of the i-Ge absorption region 109 is not dependent on the magnitude of the reverse bias voltage applied to the element. In other words, most of the reverse bias voltage applied to the device is applied to the i-Si multiplication region 108. That is, the internal electric field of the i-Si multiplication region 108 is high.

^Then, p - electrons that reach the -Si charge region ^105, p - through drifting the -Si charge region 105 and reaches the i-Si multiplication region 108. The electrons that have reached the i-Si multiplication region 108 are accelerated in drift by the high internal electric field of the i-Si multiplication region 108, and avalanche multiplication occurs. A large number of electrons and holes are generated due to the avalanche multiplication.

The electrons multiplied in the i-Si multiplication region 108 drift as they are and reach the n-Si region 104. The electrons that have reached the n-Si region 104 are output to the external circuit as a generated current via the Al electrode 110.

At the same time, holes generated in the i-Si multiplication region 108, the electrons drift in the opposite ^direction, p - to reach the -Si charge region 105. After that, the holes reaching the p ⁻ −Si charge region 105 drift, pass through the p − Si low-concentration region 106, and reach the p ⁺ −Si contact region 107. The holes that have reached the p ⁺ -Si contact region 107 are output to the external circuit as a generated current via the Al electrode 110.

On the other hand, the holes generated in the i-Ge absorption region 109 and reaching the p-Si low concentration region 106 drift inside the p-Si low concentration region 106 and reach the p ⁺ -Si contact region 107. The holes reaching the p ⁺ -Si contact region 107 are output to the external circuit as a generated current through the Al electrode 110 together with the holes generated in the i-Si multiplication region 108.

The multiplication factor of each carrier has a unique value according to the semiconductor material. The multiplication factor of Si is about 10 times larger for electrons than for holes. Further, in an avalanche photodiode using Ge and Si, it is efficient to make the Ge side p-type and the Si side n-type so that electrons can be multiplied in the i-Si multiplication region 108.

Further, the p ^-- Si charge region 105 and the p--Si low concentration region 106 are in contact with each other. Therefore, in the semiconductor light receiving element 100a, the p ^-- Si charge region 105, the i--Si multiplication region 108, and the n--Si low concentration region 104b form a pin structure. The semiconductor light receiving device 100a is different from the conventional SACM structure APD in that the depletion layer associated with the pin structure can be expanded by applying a reverse bias voltage to the device.

In general, the depletion layer width W of a diode is expressed by the following equation.
W=√[-{(2kε ₀ /q)(1/N _D +1/N _A )(v _D +vb)}]
Here, κ: relative permittivity, ε ₀ : permittivity of vacuum, q: electron charge (negative value), N _D : donor concentration, N _A : acceptor concentration, v _D : built-in potential, vb: reverse direction Voltage. As shown in the above equation, the depletion layer width W becomes wider as the dopant concentration of the donor or acceptor is lower.

FIG. 7 is a diagram showing the relationship between the reverse voltage applied to the semiconductor light receiving element according to the first embodiment of the present invention and the electric field strength in the multiplication region. The horizontal axis represents the applied reverse voltage [V], and the vertical axis represents the electric field strength [V/μm] of the i-Si multiplication region 108. As parameters, the present embodiment (multiplication region width 0 μm), the present embodiment (multiplication region width 0.1 μm), the present embodiment (multiplication region width 0.2 μm), and the conventional SACM structure are used. APD (multiplication region width 0.2 μm).

In the conventional ACM having the SACM structure, the width of the depletion layer applied to the i-Si multiplication region does not change due to the increase or decrease of the applied reverse voltage. Therefore, in the APD having the conventional SACM structure, the electric field strength applied to the i-Si multiplication region increases linearly with the increase of the applied reverse voltage. On the other hand, in the present embodiment (multiplication region width 0 μm), the depletion layer of the pn junction is generated, and the depletion layer width W widens as the applied reverse voltage increases. The increase in electric field strength is moderate. In other words, in the APD having the conventional SACM structure, the electric field strength applied to the i-Si multiplication region 108 is sharper than that in the present embodiment (the multiplication region width is 0 μm). Further, by providing the i-Si multiplication region 108 and increasing the width thereof, the electric field strength is reduced.

(Explanation of effects)
As described above, according to the semiconductor light-receiving element 100a of the present embodiment, ^p + -Si contact region 107 in the horizontal direction in this order, p-Si low concentration regions ^106, p - -Si charge region 105, i-Si up The double region 108 and the n-Si low-concentration region 104b are arranged in contact with each other. The semiconductor light receiving element 100a is, p-Si low concentration regions 106 and ^p - across the boundary between the -Si charge region 105, p-Si low concentration regions 106 and ^p - to the surface of the -Si-charge region 105 i- The Ge absorption region 109 is formed. With these, the semiconductor light receiving element 100a solves the above-described problems and has the following operational effects.

(1) internal electric field of the i-Ge absorption region 109, regardless of the applied reverse voltage to the ^element, p - uniquely determined by the built-in potential between the -Si charge region 105 and the p-Si low concentration region 106 .. Therefore, the i-Ge absorption region 109 is not subject to dielectric breakdown due to an increase in reverse voltage applied to the device.

(2) Since the p ^-- Si charge region 105 and the p--Si low concentration region 106 are in contact with each other, the p ^-- Si charge region 105, the i-Si multiplication region 108 and the n ⁺ -Si contact region 104 are formed. It constitutes a p-i-n structure. Therefore, by applying a reverse bias voltage to the device, the depletion layer width W associated with the pin structure is widened. As a result, the increase of the internal electric field applied to the i-Si multiplication region 108 becomes gentle, and the slope of the change in gain with respect to the change in reverse bias voltage also becomes gentle.

(Second embodiment)
Although the i-Ge absorption region 109 of the semiconductor light receiving device 100a of the first embodiment is formed on the upper surface of the Si slab waveguide 103, a recess is formed in the Si slab waveguide 103 and the i-Ge is formed in this recess. The absorption region 209 can also be formed.

(Description of configuration)
FIG. 8 is a sectional view showing a section perpendicular to the optical axis of the semiconductor light receiving element according to the second embodiment of the present invention. FIG. 9 is a plan view of a semiconductor light receiving element that is the second embodiment of the present invention.
Hereinafter, with respect to the structure of the semiconductor light receiving element 100b, differences from the semiconductor light receiving element 100a (FIG. 1) of the first embodiment will be described.

Semiconductor photodetector 100b ^is, p - -Si charge region 205 and the p-Si low concentration regions 206 and the recess 217 is formed. The depth of the recess 217 is t ₉ . The i-Ge absorption region 209 is formed in the recess 217, and its thickness is also t ₉ . The shape of the upper clad 211 is different from that of the upper clad 111 (FIG. 1) of the first embodiment.

10A to 10E are explanatory views illustrating the method for manufacturing the semiconductor light receiving element according to the second embodiment of the present invention. Hereinafter, a method for manufacturing the semiconductor light receiving element 100b will be described with reference to these explanatory diagrams. Since S1 to S8 of FIG. 3 are the same as FIGS. 4A to 4H of the first embodiment, first, the device configuration created in the step of FIG. 4H (S8) will be described.

In the step of FIG. 4H ^(S8), p + -Si contact region 107, p-Si low concentration regions ^106, p - -Si charge region 105, i-Si multiplication region 108, n-Si region 104 is formed There is. The n-Si region 104 is composed of an n ⁺ -Si contact region 104a and an n-Si low concentration region 104b. Further, a hard mask layer 202 is formed, and in this hard mask layer 202, a Ge selective growth window 118 is formed on the surfaces of the p-Si low concentration region 106 and the p ^-- Si charge region 105.

In FIG. 10A (S9), using the hard mask layer 202 as a mask, the region of the Ge selective growth window 118 of the Si slab waveguide 103 is partially dry etched to form a recess 217 having a depth t ₉ . As a result, the p ^-- Si charge region 205 and the p--Si low concentration region 206 are formed.

In FIG. 10B (S10b), the i-Ge absorption region 209 is selectively grown in the recess 217 (FIG. 10A). Thereby, the i-Ge absorption region 209 having the thickness t ₉ is formed.

In FIG. 10C (S11b), for example, a SiO ₂ film is deposited by the chemical vapor deposition method to form the upper clad 211.

As shown in FIG. 10D (S12b), the upper cladding 211 is patterned by photolithography and dry etching. As a result, contact holes 114, 114 are formed on the surface of the n ⁺ -Si contact region 104a and the surface of the p ⁺ -Si contact region 107.

As shown in FIG. 10E (S13b), an Al film is formed by sputtering so as to cover the two contact holes 114, 114, and further, Al electrodes 110, 110 are formed by patterning by photolithography and dry etching. As a result, the semiconductor light receiving element 100b is formed.

(Explanation of operation)
FIG. 11 is a yz sectional view parallel to the optical axis for explaining the operation of the semiconductor light receiving element according to the second embodiment of the present invention. FIG. 12 is an xy sectional view perpendicular to the optical axis for explaining the operation of the semiconductor light receiving element according to the second embodiment of the present invention.

The operation principle of the semiconductor light receiving element 100b is substantially the same as that of the semiconductor light receiving element 100a of the first embodiment.
First, as shown in FIG. 11, the signal light 116 propagating through the Si wire waveguide 115 and the Si slab waveguide 103 is butt-joined to the i-Ge absorption region 209 and propagates through the i-Ge absorption region 209. To do.

As shown in FIG. 12, the i-Ge absorption region 209 absorbs the signal light 116 and generates electrons and holes as carriers. ^Further, p - built-in potential is generated at the boundary between the -Si charge region 205 and the p-Si low concentration regions 206. Along the internal electric field of the i-Ge absorption region 209 which the built-in potential results, electrons ^p - in the direction of -Si charge region 205, holes drift toward the p-Si low concentration regions 206.

^Then, p - electrons reaching the -Si charge region ^205, p - through drifting the -Si charge region 205 and reaches the i-Si multiplication region 108. The drift of electrons that have reached the i-Si multiplication region 108 is accelerated by the high internal electric field of the i-Si multiplication region 108. A large number of electrons and holes are generated by the avalanche multiplication in the i-Si multiplication region 108.

The electrons multiplied in the i-Si multiplication region 108 drift as they are, reach the n-Si region 104, and are output to the external circuit as a generated current through the Al electrode 110. At the same time, holes generated in the i-Si multiplication region 108, ^p drifted in a direction opposite to the electron - after reaching the -Si charge region 205, p through the p-Si low concentration regions 206 and drift ^It reaches the ⁺ -Si contact region 107, and is output to the external circuit as a generated current via the Al electrode 110.

The holes generated in the i-Ge absorption region 209 and reaching the p-Si low concentration region 206 drift inside the p-Si low concentration region 206 and reach the p ⁺ -Si contact region 107. The holes reaching the p ⁺ -Si contact region 107 are output to the external circuit as a generated current through the Al electrode 110 together with the holes generated in the i-Si multiplication region 108.

(Explanation of effects)
As described above, according to the semiconductor light receiving element 100b, the same effect as that of the semiconductor light receiving element 100a of the first embodiment can be obtained, and the signal light propagating through the Si slab waveguide is i-Ge absorbed. By performing the butt joint coupling with the region 209, the coupling efficiency becomes higher than that of the semiconductor light receiving element 100a that performs the evanescent coupling. Further, since the semiconductor light receiving element 100b is butt-joint-coupled, the polarization dependence of the coupling can be reduced more than the semiconductor light-receiving element 100a.

(Third Embodiment)
Although the semiconductor light receiving device 100a of the first embodiment has the multiplication region, the i-Si multiplication region 108 is not provided as in the case of the present embodiment (width of multiplication region 0 μm) of FIG. A configuration is also possible. That is, the width of the i-Si multiplication region 108 can be set to 0 (zero).

FIG. 13 is a sectional view showing a section perpendicular to the optical axis of the semiconductor light receiving element according to the third embodiment of the present invention.
Semiconductor photodetector 100c includes a Si substrate 101 as a support substrate, a lower clad 102, the Si slab waveguide 103, the n-Si region ^104, p - and -Si charge region 105, p-Si low concentration region 106 And a p ⁺ -Si contact region 107, an i-Ge absorption region 109, and two Al electrodes 110 and 110. The n-Si region 104 is composed of an n ⁺ -Si contact region 104a and an n-Si low concentration region 104b. ^That, p - -Si charge region 105 has one end joined to the n-Si low concentration region 104b, the other end is joined to the p-Si low concentration regions 106.

Even with such a configuration, a depletion layer is generated when a reverse bias voltage is applied to the p ^-- Si charge region 105 and the n-Si low concentration region 104b. Further, as in each of the above-described embodiments, when the reverse bias voltage is increased, the width of the depletion layer is increased and the increase of the internal electric field is moderated. That is, the slope of the change in gain with respect to the change in reverse bias voltage also becomes gentle.

(Photoelectric fusion module)
FIG. 14 is a configuration diagram of an optoelectronic fusion module to which the semiconductor light receiving element according to each embodiment of the present invention is applied.
The optoelectronic fusion module 200 is, for example, a one-core bidirectional communication module used in a PON system, and an optical circuit 210 and an electric circuit 220 are formed on the surface of a lower clad 102 laminated on a Si substrate 101. .. Here, the optical circuit 210 is composed of a spot size converter 213 and a wavelength multiplexer/demultiplexer 212, and the wavelength multiplexer/demultiplexer 212 is composed of a Si thin wire waveguide 115 as an optical waveguide. Further, the electric circuit 220 includes the semiconductor light receiving element 100 (100a, 100b, 100c), a laser diode 222 as a semiconductor light emitting element, a transimpedance amplifier 221 as an electronic circuit, and a monitor photodiode 223. .. In other words, the optoelectronic fusion module 200 has a configuration in which the Si thin-film waveguide 115 and the semiconductor light receiving element 100 (100a, 100b, 100c) are coupled to each other, and the optical circuit 210 and the electric circuit 220 are integrated. Has been done.

The wavelength multiplexer/demultiplexer 212 guides the signal light emitted from the laser diode 222 to the spot size converter 213 and makes the signal light guided from the spot size converter 213 incident on the semiconductor light receiving element 100. In addition, since bidirectional communication is performed with one optical fiber, the wavelength of the light incident on the monitoring photodiode 223 blocks the wavelength of the light emitted by the laser diode provided at the other end of the optical fiber. I am trying. For example, when the transmission wavelength of the laser diode 222 is 1.310 nm and the reception wavelength of the semiconductor light receiving element 100 (100a, 100b, 100c) is 1.55 nm, the semiconductor light receiving element 100 (100a, 100b, 100c) is incident. As for the wavelength of light, the wavelength of 1.310 nm of the light emitted by the laser diode provided at the other end of the optical fiber is blocked. The Si wire waveguide 115 is an optical waveguide in which the core material is silicon and the clad material is quartz, and the light path can be bent sharply as compared with the conventionally used quartz optical waveguide.

The spot size converter 213 is for coupling an optical fiber (not shown) and a silicon wire waveguide, and uses a tapered taper type. That is, the spot size converter 213 has a function of converting the size of the beam spot of light, and is provided to reduce the optical power loss at the light input/output. A taper type spot size conversion is used between the laser diode 222 and the waveguide, and a grating type is used between the semiconductor light receiving element 100 (100a, 100b, 100c) and the waveguide.

The transimpedance amplifier 221 is an electronic circuit that converts the current generated by the semiconductor light receiving element 100 (100a, 100b, 100c) into a voltage while virtually grounding the voltage across the semiconductor light receiving element 100 (100a, 100b, 100c). ..
The monitoring photodiode 223 is for monitoring the optical output of the laser diode 222 and performing feedback control, and is arranged close to the laser diode 222.

(Modification)
The present invention is not limited to the above-described embodiment, and various modifications such as the following are possible.
(1) Although the charge regions of the semiconductor light receiving elements 100a, 100b, 100c of the above-described embodiments are p-type, they may be n-type. At this time, the charge region, the first contact region, and the low concentration region are n-type, and the second contact region is p-type.

(2) Although the semiconductor light receiving elements 100a, 100b, 100c of the above-described embodiments use Al electrodes, the present invention is not limited to this as long as it is a metal material capable of forming ohmic contact with Si or Ge. For example, Cu or the like is also possible. In the semiconductor light receiving elements 100a, 100b, 100c, SiO ₂ is used as the material of the upper claddings 111, 211, but the material is not limited to this as long as it is a transparent material having a smaller refractive index than Si and Ge in the used wavelength range. For example, SiON or the like is also possible.

(3) In the semiconductor light receiving devices 100a, 100b, 100c of the above-described respective embodiments, the configuration and the manufacturing method in which the Ge layer is selectively grown directly on the Si layer have been described, but the SiGe mixed layer is formed between the Si layer and the Ge layer. A crystal layer or the like may be selectively grown. Similarly, a protective layer such as a Si layer may be provided on the Ge layer.

(4) In the semiconductor light receiving devices 100a, 100b, 100c of the above-described embodiments, the Ge layer selective growth on the Si layer has been described, but the combination of materials is not limited to this. For example, in addition to selective growth of a SiGe mixed crystal layer on a Si layer, it is possible to combine materials that can be selectively grown on a base material.

100a, 100b Semiconductor light receiving element 101 Si substrate (supporting substrate)
102 lower clad 103 Si slab waveguide 104 n-Si region 104a n ⁺ -Si contact region 104b n-Si low-concentration region 105, 205 p ⁻ -Si charge region 106, 206 p-Si low-concentration region 107 p ⁺ -Si Contact region 108 i-Si multiplication region 109, 209 i-Ge absorption region 113 SOI substrate 115 Si wire waveguide 200 Photoelectric fusion module 217 recess

Claims (5)

A waveguide type semiconductor light receiving element for receiving signal light through an optical waveguide formed on a supporting substrate,
Before SL and the absorption region and the charge region and the multiplication region absorbs signal light is formed as an avalanche photodiode SACM structure that is separate,
One end of the charge region is joined to the multiplication region, and the other end is joined to the same low-concentration region of the first conductivity type as the charge region,
One end of the low-concentration region facing the junction surface with the charge region is joined to the first contact region of the first conductivity type,
The multiplication region is
One end facing the joint surface with the charge region is joined to a region of a second conductivity type different from the first conductivity type,
The absorption region is
It is formed by joining to both the charge region and the low concentration region ,
The semiconductor light receiving element characterized in that the carrier concentration in the low concentration region is higher than the carrier concentration in the charge region . The semiconductor light receiving element according to claim 1, wherein
Recesses are formed in both the charge region and the low concentration region,
The semiconductor light receiving element characterized in that the absorption region is formed in the recess. The semiconductor light receiving element according to claim 1 or 2, wherein
The optical waveguide has a core integrally formed with the multiplication region. The semiconductor light receiving element according to any one of claims 1 to 3,
The first conductivity type is p-type,
A semiconductor light receiving element characterized in that the second conductivity type is an n type. A photoelectric fusion module in which both a waveguide type semiconductor light receiving element in which a waveguide for receiving signal light is formed and an optical waveguide for guiding the signal light to the waveguide are integrally formed on a supporting substrate. There
Before SL and the absorption region and the charge region and the multiplication region absorbs signal light is formed as an avalanche photodiode SACM structure that is separate,
One end of the charge region is joined to the multiplication region, and the other end is joined to the same low-concentration region of the first conductivity type as the charge region,
One end of the low-concentration region facing the junction surface with the charge region is joined to the first contact region of the first conductivity type,
The multiplication region is
One end facing the joint surface with the charge region is joined to a region of a second conductivity type different from the first conductivity type,
The absorption region is
It is formed by joining to both the charge region and the low concentration region,
The carrier concentration of the low concentration region is higher than the carrier concentration of the charge region,
The optoelectronic module, wherein a core of the optical waveguide is integrally formed with the multiplication region.

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