Monitor photodiode, photonic integrated circuit, optoelectronic system, and method

Abstract

SOLUTION: A monitor photodiode (1) that absorbs up to 5% of the optical radiation to which it is exposed when the monitor photodiode is in use, includes a layer stack (5) having a semiconductor-based core layer (6), a semiconductor-based absorption layer (9), and a semiconductor-based cladding layer (12) provided with an elevated elongated portion (15), in which the semiconductor-based absorption layer and the elevated elongated portion are positioned relative to one another such that, when the monitor photodiode is in use, overlap between the mode field of optical radiation present in the semiconductor-based core layer and the semiconductor-based absorption layer results in up to 5% optical absorption. There are also provided a PIC (100) including a monitor photodiode according to the present invention, an optoelectronic system (200) including such a PIC, and a method for manufacturing a monitor photodiode.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to a monitor photodiode for absorbing up to 5% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use. The present invention also relates to a photonic integrated circuit (PIC) including a monitor photodiode according to the present invention. The present invention further relates to an optoelectronic system including a PIC according to the present invention. The optoelectronic system according to the present invention may be used, for example but not limited to, in telecommunications applications, light detection and ranging (LIDAR) or sensor applications. The present invention further relates to a method of manufacturing a monitor photodiode according to the present invention. [Background technology]

[0002] In many optoelectronic systems, which may be used, for example, but not limited to, telecommunications applications, light detection and ranging (lidar), or sensor applications, a monitor photodiode is used to accurately measure the optical output radiation of a semiconductor laser, for example, for purposes of optical monitoring and / or optical control. For efficiency reasons, the monitor photodiode should typically absorb or tap at most 5% of the optical output radiation of the semiconductor laser, i.e., just enough of the optical radiation to establish an electrical signal that can be reliably measured by sensing electronics. Tapping or absorbing more than 5% of the optical radiation to which the monitor photodiode is exposed can result in additional insertion loss.

[0003] Known manufacturing platforms for producing photonic integrated components such as the monitor photodiodes described above and / or PICs containing such components do not yet offer the capabilities, e.g., in terms of lithographic resolution, that known manufacturing platforms for electronic integrated components can achieve. The lithographic resolution limitations of known manufacturing platforms for photonic integrated components mean that it is not possible to use the same sequence of process steps to manufacture the monitor photodiodes described above, which are capable of absorbing up to 5% of the optical radiation to which they are exposed, and RF photodiodes, which are capable of absorbing, for example, 50% to 80% of the optical radiation to which they are exposed. As a result of these lithographic resolution limitations and the significant differences in the functionality of monitor photodiodes and RF photodiodes, these components have different architectures. Due to their different architectures, the manufacturing processes for monitor photodiodes and RF photodiodes each involve a different number and / or type of process steps. The numerous different manufacturing processes that must be supported by a manufacturing platform to enable the manufacture of a wide variety of photonic components with diverse functionalities and / or performance characteristics complicates the manageability of such a manufacturing platform. Therefore, there is a need to improve the manageability of such manufacturing platforms by reducing the number of different manufacturing processes required. Summary of the Invention

[0004] It is an object of the present invention to provide a monitor photodiode that can be manufactured using the same number and / or type of process steps as those that allow the manufacture of photodiodes with significantly different functions and / or performance characteristics, such as the RF photodiodes described above. In this way, a monitor photodiode according to the present invention can reduce the number of different manufacturing processes required, thereby improving the manageability of a manufacturing platform that allows the manufacture of a variety of photonic components with diverse functions and / or performance characteristics. In addition, a monitor photodiode according to the present invention can proactively avoid or at least reduce other disadvantages associated with the manufacturing platforms described above, such as long lead times and high costs.

[0005] It is also an object of the present invention to provide a PIC that includes a monitor photodiode according to the present invention.

[0006] It is another object of the present invention to provide an optoelectronic system including a PIC according to the present invention, which may be used in, for example, but not limited to, telecommunications applications, lidar, or sensor applications.

[0007] It is yet another object of the present invention to provide a method for fabricating a monitor photodiode according to the present invention.

[0008] Aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims as appropriate and not merely as explicitly set out in the claims. Furthermore, all features may be substituted by technical equivalents.

[0009] At least one of the above objects provides a monitor photodiode comprising a substrate having a first surface and a second surface disposed opposite and spaced from the first surface, and a layer stack disposed on the second surface of the substrate, the layer stack absorbing at most 5% of optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use, the layer stack comprising: a semiconductor-based core layer having a third surface disposed facing toward the second surface of the substrate and a fourth surface disposed facing away from the third surface, the semiconductor-based core layer being configured to guide optical radiation when the monitor photodiode is in use and having a first surface area A1; a semiconductor-based absorber layer having a fifth surface disposed facing toward the second surface of the substrate and a sixth surface disposed facing away from the fifth surface; a first width W1 as viewed transverse to the propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use; a first length L1 as viewed in a propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use, the first length L1 being at least equal to 3 μm; a semiconductor-based absorber layer having a second surface area A2=W1*L1 that is smaller than the first surface area A1 of the semiconductor-based core layer; a seventh surface disposed facing toward the second surface of the substrate; and an eighth surface disposed facing away from the seventh surface, a second width W2 as viewed in a direction transverse to the propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use and parallel to the sixth surface of the semiconductor-based absorption layer; a second length L2 as viewed in a propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use, the second length L2 being at least equal to the first length L1 of the semiconductor-based absorption layer; an eighth surface configured with an elevated elongated portion; and a semiconductor-based cladding layer having an eighth surface configured with an elevated elongated portion; the elevated elongated portion of the semiconductor-based cladding layer and the semiconductor-based absorbing layer are positioned relative to one another such that an overlap between a mode field MF of optical radiation present in the semiconductor-based core layer and the semiconductor-based absorbing layer results in absorption of up to 5% of the optical radiation when the monitor photodiode is in use; This is achieved by a monitor photodiode.

[0010] As described above, the manageability of a manufacturing platform for producing photonic integrated components can be improved by reducing the number of different manufacturing processes required to produce various photonic components with diverse functions and / or performance characteristics. In this way, the manufacturing platform can provide as many functions as possible with the minimum number of manufacturing steps. Achieving the latter typically requires trade-offs. For example, the laser gain section and the SOA booster amplifier can achieve their best performance if the PL wavelengths for the laser gain section and the SOA booster amplifier are different from each other. This can be achieved at the cost of additional epitaxial growth steps, which increase the complexity and cost of the manufacturing process. However, by choosing the same PL wavelength for the laser gain section and the SOA booster amplifier and accepting a small degradation in performance for both the laser gain section and the SOA booster amplifier, the additional epitaxial growth steps can be avoided, thus improving the manageability of the manufacturing platform as a whole.

[0011] A similar trade-off can be envisioned for fabricating a monitor photodiode according to the present invention configured to absorb up to 5% of the optical radiation to which the monitor photodiode is exposed when in use, and an RF photodiode configured to absorb 50% to 80% of the optical radiation to which the RF photodiode is exposed when in use. Ideally, such an RF photodiode would have a semiconductor-based absorber layer configured to have as small a surface area as possible to provide the RF photodiode with the lowest possible overall capacitance, while still being capable of absorbing 50% to 80% of the optical radiation to which the RF photodiode is exposed when in use. This requirement regarding the surface area of ​​the semiconductor-based absorber layer imposes limitations on the specific length and width of the RF photodiode. When using a fabrication process that limits the width of the RF photodiode to, for example, 1.5 μm, an appropriate length for the RF photodiode needs to be established that can absorb 50% to 80% of the optical radiation to which the RF photodiode is exposed when in use, while maintaining the RF photodiode's overall capacitance as low as possible. If the RF photodiode has a responsivity of, for example, 0.8 A / W, which corresponds to an absorption of about 65% of the optical radiation to which the RF photodiode is exposed when in use, the RF photodiode will typically have a maximum length on the order of 25 μm.

[0012] There are several options for providing different optical tapping or absorption capabilities for the RF photodiode and the monitor photodiode. To achieve, for example, 1% absorption or tapping of the optical radiation to which the monitor photodiode is exposed, a first option is to configure the monitor photodiode to have a length significantly shorter than the length of the RF photodiode described above, which has an exemplary width of 1.5 μm and a maximum length on the order of 25 μm. Preferably, the length of the monitor photodiode is as short as possible. The shortest possible length of the monitor photodiode is determined by the lithographic resolution limits of the manufacturing platform. Below the lithographic resolution limits, the manufacturing process is no longer reliable. If the shortest possible length of the monitor photodiode, for example, 5 μm, is not small enough to tap or absorb 1% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use, other options are required.

[0013] If the RF photodiode has the aforementioned length L of, for example, 25 μm, and is required to absorb, for example, 65% of the optical radiation to which it is exposed when the RF photodiode is in use, then the absorption coefficient α of the RF photodiode is 420 cm -1 (≈1825 dB / cm) can be found by solving the equation for absorption coefficient α, 1-exp(-αL) = 0.65. If the monitor photodiode has a length L, say 5 μm, and is required to absorb, say, 1% of the optical radiation to which it is exposed when in use, then the absorption coefficient α of the monitor photodiode is 20 cm -1By solving the equation for the absorption coefficient α, 1−exp(−αL)=0.01, it can be seen that the absorption coefficient α has a value of approximately 87 dB / cm. Based on the large difference between the aforementioned values ​​of the absorption coefficient α of the RF photodiode and the monitor photodiode, it can be concluded that the semiconductor-based absorption layers of the RF photodiode and the monitor photodiode typically have different material compositions and / or are located at different distances from the respective semiconductor-based core layers in order to achieve suitable performance of the RF photodiode and the monitor photodiode. Furthermore, it will be apparent that any selection of a value for the absorption coefficient α between the aforementioned values ​​to reach a trade-off regarding the absorption coefficient α of the monitor photodiode and the RF photodiode will result in a degradation of the performance of at least one of the monitor photodiode and the RF photodiode.

[0014] A second option for achieving the aforementioned value of the absorption coefficient α that enables the desired performance of the RF photodiode and the monitor photodiode is to provide semiconductor-based absorption layers with different material compositions for the RF photodiode and the monitor photodiode. As a result, the manufacturing processes used to manufacture the RF photodiode and the monitor photodiode each require different epitaxial growth steps to achieve the different material compositions for the semiconductor-based absorption layers of the RF photodiode and the monitor photodiode. As a result of the different epitaxial growth steps, it will be apparent that the RF photodiode and the monitor photodiode cannot be manufactured using the same manufacturing process.

[0015] A third option for achieving the aforementioned values ​​of the absorption coefficient α that enable the desired performance of the RF photodiode and the monitor photodiode is to provide the RF photodiode and the monitor photodiode with semiconductor-based absorption layers having the same material composition. In this case, different epitaxial growth steps are still required to fabricate the semiconductor-based absorption layers of the RF photodiode and the monitor photodiode, because different overlaps are required between the mode field of the optical radiation present in the RF photodiode's semiconductor-based absorption layer and the mode field of the optical radiation present in the RF photodiode's semiconductor-based core layer and between the mode field of the optical radiation present in the monitor photodiode's semiconductor-based absorption layer and the semiconductor-based core layer. The different overlaps can be achieved by positioning the semiconductor-based absorption layer and the semiconductor-based core layer of the RF photodiode at a first distance from each other and the semiconductor-based absorption layer and the semiconductor-based core layer of the monitor photodiode at a second distance from each other. It will be apparent that the first distance and the second distance must be different from each other to achieve the aforementioned exemplary values ​​for the desired absorption of the RF photodiode and the monitor photodiode. Those skilled in the art will understand that to achieve 1% absorption or tapping of optical radiation, the second distance is significantly greater than the first distance to limit overlap between the semiconductor-based absorption layer of the monitor photodiode and the mode field of optical radiation present in the semiconductor-based core layer of the monitor photodiode when the monitor photodiode is in use.

[0016] As a result of having to use different epitaxial growth steps to fabricate the semiconductor-based absorption layers of each of the RF photodiode and the monitor photodiode, the complexity of the manufacturing platform increases and the manageability of the manufacturing platform decreases.

[0017] By patterning the semiconductor-based absorption layer of the monitor photodiode according to the present invention, it is possible to fabricate, using a manufacturing process including the same process steps, a monitor photodiode capable of absorbing up to 5% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use, and an RF photodiode capable of absorbing 50% to 80% of the optical radiation to which the RF photodiode is exposed when the RF photodiode is in use. It is understood that the absorption of the monitor photodiode can be changed by adjusting the second surface area A2 of the semiconductor-based absorption layer and / or the relative positioning of the tall, elongated portion of the semiconductor-based cladding layer and the semiconductor-based absorption layer. If the second surface area A2 of the semiconductor-based absorption layer and the first surface area A1 of the semiconductor-based core layer are the same, the monitor photodiode will in fact be configured as an RF photodiode capable of absorbing 50% to 80% of the optical radiation to which the RF photodiode is exposed when the RF photodiode is in use.

[0018] Based on the above, the monitor photodiode according to the present invention allows for a reduction in the number of different manufacturing processes of a manufacturing platform used to manufacture the above-mentioned monitor photodiodes and RF photodiodes having sufficiently different desired performance characteristics, thereby increasing the manageability of the manufacturing platform, which allows for the manufacture of a variety of photonic components having diverse functional and / or performance characteristics.

[0019] In an embodiment of the monitor photodiode according to the present invention, the second width W2 of the elongated portion is in the range of 200 nm to 10 μm, and the first width W1 of the semiconductor-based absorption layer is in the range of 0.1 W2 to 0.5 W2. In this manner, the overlap between the semiconductor-based absorption layer of the monitor photodiode and the mode field of optical radiation present in the semiconductor-based core layer of the monitor photodiode when the monitor photodiode is in use can be adjusted to enable the monitor photodiode to absorb or tap at most 5% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use.

[0020] In an embodiment of the monitor photodiode according to the present invention, the semiconductor-based absorber layer is provided with a slot constructed and arranged to divide the semiconductor-based absorber layer into a first portion and a second portion, the first portion and the second portion being separated and spaced apart from one another when viewed in a direction transverse to a propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use and parallel to the second surface of the substrate; a third width W3 as viewed in a direction transverse to the propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use and parallel to the fourth surface of the semiconductor-based core layer, the third width W3 being in the range of 0.95W2 to 3W2 depending on a desired value of overlap between a mode field MF of the optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use and at least one of the first portion and the second portion of the semiconductor-based absorption layer; a third length L3 as viewed in the propagation direction S of the optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use, the third length L3 being equal to the first length L1 of the semiconductor-based absorption layer; With slot, provided.

[0021] Providing the above-defined slot in the semiconductor-based absorption layer provides another method for controlling overlap between the semiconductor-based absorption layer of the monitor photodiode and the mode field of optical radiation present in the semiconductor-based core layer of the monitor photodiode when the monitor photodiode is in use, thereby achieving the monitor photodiode absorbing or tapping at most 5% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use.

[0022] The third width W3 of the slot can be selected depending on the desired amount of optical absorption resulting from overlap between the mode field MF of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use and at least one of the first and second portions of the semiconductor-based absorbing layer. The amount of optical absorption is given by the formula exp(-αΓL1), where α is the absorption coefficient of the semiconductor-based material constituting the absorbing layer, i.e., the first and second portions, Γ is the overlap between the semiconductor-based absorbing layer, i.e., at least one of the first and second portions, and the mode field of optical radiation present in the semiconductor-based core layer of the monitor photodiode when the monitor photodiode is in use, and L1 is the length of the semiconductor-based absorbing layer, i.e., the first and second portions. As noted above, L1 is preferably the minimum length that can be reliably realized by the manufacturing platform used. The overlap Γ is a function of the second width W2 of the tall, elongated portion of the semiconductor-based cladding layer.

[0023] It will be appreciated that no process steps need to be added to the manufacturing process for the monitor photodiode to provide the slots in the semiconductor-based absorption layer, as the slots can be provided as part of the process steps for removing the semiconductor-based absorption layer over any passive areas, and therefore, the manageability of the manufacturing platform is not reduced as a result of providing the slots in the semiconductor-based absorption layer.

[0024] In an embodiment of the monitor photodiode according to the present invention, The layer stack includes a semiconductor-based spacer layer disposed between the semiconductor-based core layer and the semiconductor-based absorber layer, the semiconductor-based spacer layer having a ninth surface disposed facing toward the fourth surface of the semiconductor-based core layer and a tenth surface disposed facing away from the ninth surface, the semiconductor-based spacer layer having a third surface area A3 equal to the first surface area A1 of the semiconductor-based core layer, and the semiconductor-based spacer layer having a first thickness T1 as viewed in a direction transverse to the ninth surface, the first thickness T1 being in a range from 40 nm to 100 nm. The semiconductor-based spacer layer provides an additional degree of freedom in controlling overlap between the semiconductor-based absorber layer and a mode field of optical radiation present in the semiconductor-based core layer of the monitor photodiode when the monitor photodiode is in use. Experiments have shown that selecting a semiconductor-based spacer layer thickness T1 in the above range allows an example RF photodiode having a length of 25 μm and a width of 1.5 μm to absorb 50% to 80% of the optical radiation to which the example RF photodiode is exposed when the example RF photodiode is in use, and an example monitor photodiode having a length of 5 μm and a width of 1.5 μm to absorb or tap at most 5% of the optical radiation to which the example monitor photodiode is exposed when the example RF photodiode is in use. It is understood that the example RF photodiode and the example monitor photodiode can be fabricated using the same fabrication process.

[0025] In an embodiment of a monitor photodiode according to the present invention, the semiconductor-based spacer layer is a p-type doped InP-based layer, which may be configured to be optically transparent with respect to the optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use.

[0026] In an embodiment of a monitor photodiode according to the present invention, the substrate is an n-type doped InP-based layer.

[0027] In an embodiment of the monitor photodiode according to the present invention, the semiconductor-based core layer is unintentionally doped In. x Ga 1-x As y P 1-y The semiconductor-based core layer is configured to guide the optical radiation present in the monitor photodiode when it is in use.

[0028] In an embodiment of a monitor photodiode according to the invention, the semiconductor-based absorption layer has a second thickness T2 as viewed transverse to the fifth surface, the second thickness T2 being in the range of 75 nm to 150 nm.

[0029] In an embodiment of the monitor photodiode according to the invention, the semiconductor-based absorption layer is p-type doped or unintentionally doped In. x Ga 1-x As layer. p-type doped or unintentionally doped In x Ga 1-x The As layer absorption layer can be configured to absorb the optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use. Experiments have shown that such p-type doped or unintentionally doped In layers with a thickness T2 of 100 nm can be used. x Ga 1-x The As absorption layer enables an example RF photodiode having a length of 25 μm and a width of 1.5 μm to absorb 65% of the optical radiation to which the example RF photodiode is exposed when the example RF photodiode is in use, while such p-type doped or unintentionally doped In x Ga 1-xThe As absorption layer enables an example monitor photodiode having a length of 5 μm and a width of 1.5 μm to absorb or tap 1% of the optical radiation to which the example monitor photodiode is exposed when the example monitor photodiode is in use. It is understood that the example RF photodiode and the example monitor photodiode may be fabricated using the same fabrication process.

[0030] In an embodiment of a monitor photodiode according to the present invention, the semiconductor-based cladding layer is a p-type doped InP-based layer, which may be configured to be optically transparent with respect to the optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use.

[0031] The p-type doped InP-based cladding layer may be p-type doped or unintentionally doped InP as described above. x Ga 1-x It will be appreciated that this may be used to fill slots provided in a semiconductor-based absorbing layer, which may be an As layer.

[0032] According to another aspect of the present invention, there is provided a PIC including a monitor photodiode according to the present invention, the PIC being a hybrid-integrated PIC or a monolithically integrated PIC. Based on the above, those skilled in the art will appreciate that a PIC according to the present invention can benefit from the advantages provided by a monitor photodiode according to the present invention.

[0033] An advantage of the hybrid integrated PIC is that the monitor photodiode can be, for example, an InP-based monitor photodiode combined with a Si-based optoelectronic device. Hence, the PIC according to the present invention can be used in any semiconductor technology field, such as the field of silicon photonics.

[0034] Another advantage of the hybrid integrated PIC according to the present invention is that the monitor photodiode is replaceable, which may be necessary, for example, in the event of a malfunction of the monitor photodiode or after failure of the monitor photodiode.

[0035] An advantage of monolithically integrated PICs is that both active and passive optoelectronic devices can be integrated on the same semiconductor substrate, e.g., an InP-based substrate. Furthermore, monolithic integration of active and passive optoelectronic devices may be less cumbersome and may require less die area than hybrid integration of active and passive optoelectronic devices.

[0036] According to another aspect of the present invention, there is provided an optoelectronic system including a PIC according to the present invention, the optoelectronic system being one of a transmitter, a receiver, a transceiver, a coherent transmitter, a coherent receiver, and a coherent transceiver. The optoelectronic system may be used, for example, but not limited to, in telecommunications applications, light detection and ranging (LIDAR), or sensor applications. Based on the above, one skilled in the art will appreciate that any of the above-mentioned transmitters, receivers, and transceivers can benefit from the advantages provided by a PIC according to the present invention that includes a monitor photodiode according to the present invention.

[0037] According to another aspect of the present invention, there is provided a method for fabricating a monitor photodiode that absorbs at most 5% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use, comprising the steps of: providing a substrate having a first surface and a second surface disposed opposite and spaced from the first surface; providing a layer stack on the second surface of the substrate, wherein providing the layer stack includes: epitaxially growing a semiconductor-based core layer having a third surface disposed facing toward the second surface of the substrate and a fourth surface disposed facing away from the third surface, the semiconductor-based core layer being configured to guide optical radiation when the monitor photodiode is in use and having a first surface area A1; epitaxially growing a semiconductor-based absorber layer having a fifth surface disposed facing toward the second surface of the substrate and a sixth surface disposed facing away from the fifth surface; performing a first lithography process followed by a first etching process; a first width W1 as viewed in a direction transverse to a propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use and parallel to the fourth surface of the semiconductor-based core layer; a first length L1 as viewed in a propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use, the first length L1 being at least equal to 3 μm; and configuring the semiconductor-based absorption layer to have the semiconductor-based absorber layer having a second surface area A2=W1*L1 that is smaller than the first surface area A1 of the semiconductor-based core layer; epitaxially growing a semiconductor-based cladding layer having a seventh surface disposed facing toward the second surface of the substrate and an eighth surface disposed facing away from the seventh surface; performing a second lithography process followed by a second etching process; a second width W2 as viewed in a direction transverse to the propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use and parallel to the sixth surface of the semiconductor-based absorption layer; a second length L2 as viewed in a propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use, the second length L2 being at least equal to the first length L1 of the semiconductor-based absorption layer; configuring an eighth surface of the semiconductor-based cladding layer to have an elevated elongated portion having a Including, A method is provided in which the elevated elongated portion of the semiconductor-based cladding layer and the semiconductor-based absorption layer are positioned relative to one another such that when the monitor photodiode is in use, an overlap between the mode field MF of optical radiation present in the semiconductor-based core layer and the semiconductor-based absorption layer results in absorption of up to 5% of the optical radiation.

[0038] In this way, a first exemplary embodiment of a monitor photodiode according to the present invention can be manufactured, which allows for the advantages mentioned above.

[0039] In an embodiment of the method according to the present invention, a first lithography process followed by a first etching process is performed; a slot in the semiconductor-based absorber layer constructed and arranged to divide the semiconductor-based absorber layer into a first portion and a second portion, the first portion and the second portion being separated and spaced apart from one another when viewed in a direction transverse to a propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use and parallel to the second surface of the substrate; a third width W3 as viewed in a direction transverse to the propagation direction S of optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use and parallel to the fourth surface of the semiconductor-based core layer, the third width W3 being in the range of 0.95W2 to 3W2 depending on a desired value of overlap between a mode field MF of the optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use and at least one of the first portion and the second portion of the semiconductor-based absorption layer; a third length L3 as viewed in the propagation direction S of the optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use, the third length L3 being equal to the first length L1 of the semiconductor-based absorption layer; You will be provided with a slot with

[0040] In this way, a second exemplary embodiment of a monitor photodiode according to the present invention can be manufactured, enabling the advantages mentioned above.

[0041] In an embodiment of the method according to the present invention, Providing a layer stack epitaxially growing a semiconductor-based spacer layer after epitaxially growing the semiconductor-based core layer and before growing the semiconductor-based absorption layer, the semiconductor-based spacer layer having a ninth surface disposed facing toward the fourth surface of the semiconductor-based core layer and a tenth surface disposed facing away from the ninth surface, the semiconductor-based spacer layer having a third surface area A3 equal to the first surface area A1 of the semiconductor-based core layer.

[0042] As mentioned above, the semiconductor-based spacer layer provides an additional degree of freedom in controlling the overlap between the semiconductor-based absorption layer and the mode field of the optical radiation present in the semiconductor-based core layer of the monitor photodiode when the monitor photodiode is in use. The semiconductor-based spacer layer may be a p-type doped InP-based layer that may be configured to be optically transparent with respect to the optical radiation present in the semiconductor-based core layer when the monitor photodiode is in use. [Brief explanation of the drawings]

[0043] Further features and advantages of the present invention will become apparent from the description of exemplary, non-limiting embodiments of a monitor photodiode, a PIC, an optoelectronic system, and a method for manufacturing a monitor photodiode according to the present invention.

[0044] Those skilled in the art will understand that the embodiments of the monitor photodiode, the PIC, the optoelectronic system, and the method for manufacturing the monitor photodiode are merely exemplary in nature and should not be construed as limiting the scope of protection in any way. Those skilled in the art will understand that alternative or equivalent embodiments of the monitor photodiode, the PIC, the optoelectronic system, and the method for manufacturing the monitor photodiode are conceivable and can be put into practice without departing from the scope of protection of the present invention.

[0045] Reference is made to the figures in the accompanying drawings, which are schematic in nature and therefore not necessarily drawn to scale. Furthermore, like reference numerals refer to like or similar parts. In the accompanying drawings, [Figure 1A] 1 shows a schematic top view of a first exemplary non-limiting embodiment of a monitor photodiode according to the present invention; [Figure 1B] 1B shows a schematic cross-sectional view of a first exemplary non-limiting embodiment of a monitor photodiode along line AB shown in FIG. 1A. [Figure 2A] 2 shows a schematic top view of a second exemplary non-limiting embodiment of a monitor photodiode according to the present invention; [Figure 2B] 2B shows a schematic cross-sectional view of a second exemplary non-limiting embodiment of a monitor photodiode along line AB shown in FIG. 2A. [Figure 3] 10 is a simulation of the numerical value of optical overlap between a semiconductor-based absorption layer of a monitor photodiode according to a second exemplary, non-limiting embodiment of the monitor photodiode and a mode field of optical radiation present in a semiconductor-based core layer of the monitor photodiode when the monitor photodiode is in use, the numerical value of optical overlap being dependent on the value of the second width W2 of the elevated, elongated portion of the semiconductor-based cladding layer of the monitor photodiode and the third width W3 of the slot provided in the semiconductor-based absorption layer. [Figure 4]1 shows a schematic top view of a first exemplary, non-limiting embodiment of a PIC according to the present invention including a monitor photodiode according to the present invention; [Figure 5] 1 shows a schematic top view of a first exemplary, non-limiting embodiment of an optoelectronic system according to the present invention, including a PIC according to the present invention; [Figure 6A] 1 is a flow diagram of a first exemplary non-limiting embodiment of a method for fabricating a monitor photodiode according to the present invention. [Figure 6B] FIG. 4 is a flow diagram of a second exemplary non-limiting embodiment of a method for fabricating a monitor photodiode according to the present invention. [Figure 6C] FIG. 10 is a flow diagram of a third exemplary non-limiting embodiment of a method for fabricating a monitor photodiode according to the present invention. [Figure 6D] FIG. 10 is a flow diagram of a fourth exemplary non-limiting embodiment of a method for fabricating a monitor photodiode according to the present invention. Detailed Description of the Invention

[0046] FIG. 1A is a schematic top view of a first exemplary, non-limiting embodiment of a monitor photodiode 1 according to the present invention for absorbing up to 5% of the optical radiation to which the monitor photodiode 1 is exposed when the monitor photodiode 1 is in use, and FIG. 1B is a schematic cross-sectional view of the first exemplary, non-limiting embodiment of the monitor photodiode 1 along line AB shown in FIG. 1A.

[0047] The monitor photodiode 1 includes a substrate 2 having a first surface 3 and a second surface 4 disposed opposite and spaced from the first surface 3, and a layer stack 5 disposed on the second surface 4 of the substrate 2. The substrate 2 may be an n-type doped InP-based layer.

[0048] The layer stack 5 includes a semiconductor-based core layer 6 having a third surface 7 disposed opposite and in contact with the second surface 4 of the substrate 2. The semiconductor-based core layer 6 also has a fourth surface 8 disposed opposite and spaced apart from the third surface 7. The semiconductor-based core layer 6 has a first surface area A1 and is configured to guide optical radiation when the monitor photodiode 1 is in use. The mode field MF and propagation direction S of the optical radiation are shown schematically in FIGS. 1A and 1B. The semiconductor-based core layer 6 includes an unintentionally doped InN layer 6 that may be configured to guide optical radiation present therein when the monitor photodiode 1 is in use. x Ga 1-x As y P 1-y It may be a layer.

[0049] According to a first exemplary, non-limiting embodiment of the monitor photodiode 1 shown in FIGS. 1A and 1B , the layer stack 5 includes a semiconductor-based spacer layer having a ninth surface disposed facing toward and in contact with the fourth surface 8 of the semiconductor-based core layer 6. The semiconductor-based spacer layer 17 also has a tenth surface 19 disposed facing away from the ninth surface 18. The semiconductor-based spacer layer 17 has a third surface area A3 equal to the first surface area A1 of the semiconductor-based core layer 6. The semiconductor-based spacer layer 17 has a first thickness T1 as viewed transversely to the ninth surface 18. The first thickness T1 is in the range of 40 nm to 100 nm. The semiconductor-based spacer layer 17 may be a p-type doped InP-based layer that can be configured to be optically transparent with respect to the optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use.

[0050] The layer stack 5 includes a semiconductor-based absorber layer 9 having a fifth surface 10 positioned facing toward and in contact with the tenth surface 19 of the semiconductor-based spacer layer 17. The semiconductor-based absorber layer 9 also has a sixth surface 11 positioned facing away from the fifth surface 10. The semiconductor-based absorber layer 9 has a first width W1 when viewed in a direction transverse to the propagation direction S of optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use and parallel to the fourth surface 8 of the semiconductor-based core layer 6. The semiconductor-based absorber layer 9 has a first length L1 when viewed in the propagation direction S of optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use. The first length L1 is at least equal to 3 μm. The semiconductor-based absorber layer 9 has a second surface area A2=W1*L1 that is smaller than the first surface area A1 of the semiconductor-based core layer 6. The semiconductor-based absorber layer 9 has a second thickness T2 when viewed in a direction transverse to the fifth surface 10. The second thickness T2 is in the range of 75 nm to 150 nm. The semiconductor-based absorption layer 9 is a p-type doped or unintentionally doped In semiconductor-based core layer 6 that can be configured to absorb optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use. x Ga 1-x It can be an As layer.

[0051] The layer stack 5 includes a semiconductor-based cladding layer 12 having a seventh surface 13 disposed facing the second surface 4 of the substrate 2 in contact with the tenth surface 19 of the semiconductor-based spacer layer 17 and facing the sixth surface 11 of the semiconductor-based absorber layer 9. The semiconductor-based cladding layer 12 also has an eighth surface 14 disposed facing away from the seventh surface 13. The eighth surface 14 is configured to have an elongated portion 15 having a second width W2 when viewed in a direction transverse to the propagation direction S of optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use and parallel to the sixth surface 11 of the semiconductor-based absorber layer 9. The elongated portion 15 has a second length L2 when viewed in the propagation direction S of optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use. The second length L2 is at least equal to the first length L1 of the semiconductor-based absorber layer 9.

[0052] The elongated portion 15 of the semiconductor-based cladding layer 12 and the semiconductor-based absorption layer 9 are positioned relative to one another such that an overlap between the mode field MF of optical radiation present in the semiconductor-based core layer 6 and the semiconductor-based absorption layer 9 when the monitor photodiode 1 is in use results in absorption of up to 5% of the optical radiation. It is understood that the second width W2 of the elongated portion 15 of the semiconductor-based cladding layer 12 is in the range of 200 nm to 10 μm, and the first width W1 of the semiconductor-based absorption layer 9 is in the range of 0.1W2 to 0.5W2. In this manner, the overlap between the semiconductor-based absorption layer 9 and the mode field MF of optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use can be adjusted so that the monitor photodiode 1 absorbs or taps up to 5% of the optical radiation to which the monitor photodiode 1 is exposed when the monitor photodiode 1 is in use.

[0053] It will be appreciated that the semiconductor-based spacer layer 17 provides an additional degree of freedom in controlling the overlap between the semiconductor-based absorbing layer 9 and the mode field MF of the optical radiation by selecting an appropriate value for the first thickness T1 of the semiconductor-based spacer layer 17 from the range of 40 nm to 100 nm.

[0054] The semiconductor-based cladding layer 12 may be a p-type doped InP-based layer that may be configured to be optically transparent with respect to the optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use.

[0055] A portion 20 of the mode field MF corresponding to the desired overlap between the mode field MF and the semiconductor-based absorption layer 9 is shown in the mode field MF shown schematically in Figure 1A. With reference to Figure 1A, it will be understood that the semiconductor-based absorption layer 9, which would not be visible in a top view of the monitor photodiode 1, is drawn with dashed lines to give an impression of its size and position in relation to the tall, elongated portion 15 of the semiconductor-based cladding layer 12.

[0056] As described above, by patterning the semiconductor-based absorption layer 9 of the monitor photodiode 1, it is possible to fabricate a monitor photodiode capable of absorbing up to 5% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use, and an RF photodiode capable of absorbing 50% to 80% of the optical radiation to which the RF photodiode is exposed when the RF photodiode is in use, using a manufacturing process including the same process steps. It will be appreciated that the absorption of the monitor photodiode 1 can be changed by adjusting the second surface area A2 of the semiconductor-based absorption layer 9 and / or the relative positioning of the tall, elongated portion 15 of the semiconductor-based cladding layer 12 and the semiconductor-based absorption layer 9. If the second surface area A2 of the semiconductor-based absorption layer 9 and the first surface area A1 of the semiconductor-based core layer 6 are the same, the monitor photodiode will in fact be configured as an RF photodiode capable of absorbing 50% to 80% of the optical radiation to which the RF photodiode is exposed when the RF photodiode is in use.

[0057] Based on the above, the monitor photodiode 1 allows for a reduction in the number of different manufacturing processes of a manufacturing platform used to manufacture the above-mentioned monitor photodiodes and RF photodiodes with sufficiently different desired performance characteristics. As a result, the monitor photodiode 1 according to the present invention allows for an improved manageability of a manufacturing platform that allows for the manufacture of a variety of photonic components with diverse functional and / or performance characteristics.

[0058] 2A is a schematic top view of a second exemplary, non-limiting embodiment of a monitor photodiode 1 according to the present invention, and FIG. 2B is a schematic cross-sectional view of the second exemplary, non-limiting embodiment of the monitor photodiode 1 taken along line AB shown in FIG. 2A. According to the second exemplary, non-limiting embodiment of the monitor photodiode 1, the semiconductor-based absorption layer 9 is provided with a slot 16 configured and arranged to divide the semiconductor-based absorption layer 9 into a first portion 9a and a second portion 9b. The first portion 9a and the second portion 9b are separated and spaced apart from each other when viewed in a direction transverse to the propagation direction S of optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use and parallel to the second surface 4 of the substrate 2. As mentioned above, the semiconductor-based core layer 6 is formed of unintentionally doped In. x Ga 1-x As y P 1-y It may be a layer.

[0059] The slot 16 has a third width W3 when viewed in a direction transverse to the propagation direction S of the optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use and parallel to the fourth surface 8 of the semiconductor-based core layer 6. The third width W3 ranges from 0.95W2 to 3W2 depending on the desired amount of optical overlap between the mode field MF of the optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use and at least one of the first portion 9a and the second portion 9b of the semiconductor-based absorbing layer 9. The third width W3 of the slot 16 can be selected depending on the desired amount of optical absorption resulting from the optical overlap. The amount of optical absorption is given by the formula exp(-αΓL1), where α is the amount of, for example, p-doped or unintentionally doped In that constitutes the semiconductor absorbing layer 9, i.e., the first portion 9a and the second portion 9b. x Ga 1-xwhere As is the absorption coefficient of the semiconductor-based material, Γ is the optical overlap between the semiconductor-based absorption layer 9, i.e., at least one of the first portion 9a and the second portion 9b, and the mode field of the optical radiation present in the semiconductor-based core layer 6 of the monitor photodiode 1 when the monitor photodiode 1 is in use, and L1 is the length of the semiconductor-based absorption layer 9, i.e., the first portion 9a and the second portion 9b. As mentioned above, L1 is preferably the minimum length that can be reliably realized by the manufacturing platform used. The optical overlap Γ is a function of the second width W2 of the tall, elongated portion 15 of the semiconductor-based cladding layer 12.

[0060] The slot 16 has a third length L3 as viewed in the propagation direction S of the optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use. The third length L3 is equal to the first length L1 of the semiconductor-based absorption layer 9.

[0061] Providing slots 16 in the semiconductor-based absorption layer 9 provides another method for controlling the optical overlap between the semiconductor-based absorption layer 9, i.e., at least one of the first portion 9a and the second portion 9b, and the mode field MF of the optical radiation present in the semiconductor-based core layer 6 of the monitor photodiode 1 when the monitor photodiode 1 is in use, thereby achieving the monitor photodiode 1 absorbing or tapping at most 5% of the optical radiation to which the monitor photodiode 1 is exposed when the monitor photodiode 1 is in use.

[0062] It will be appreciated that, because the slots 16 may be provided as part of a process step for removing the semiconductor-based absorption layer 9 over any passive areas (not shown), no process steps need to be added to the manufacturing process for the monitor photodiode 1 to provide the slots 16 in the semiconductor-based absorption layer 9. Hence, the manageability of the manufacturing platform is not reduced as a result of providing the above-described slots 16 in the semiconductor-based absorption layer 9.

[0063] Additionally, according to a second exemplary, non-limiting embodiment of the monitor photodiode 1, it is understood that the cladding layer 12, which may be a p-type doped InP-based layer, is used to fill the slot 16 and is in contact with a tenth surface 19 of the semiconductor-based spacer layer 17, which may also be a p-type doped InP-based layer.

[0064] 3 shows a simulation of the optical overlap between at least one of the first portion 9a and the second portion 9b of the semiconductor-based absorption layer 9 of the monitor photodiode 1 according to the second exemplary non-limiting embodiment shown in FIGS. 2A and 2B and the mode field MF of the optical radiation present in the semiconductor-based core layer 6 of the monitor photodiode 1 when the monitor photodiode 1 is in use. The optical overlap value depends on the second width W2 of the elongated, high portion 15 of the semiconductor-based cladding layer 12 and the third width W3 of the slot 16 provided in the semiconductor-based absorption layer 9. FIG. 3 shows that the optical overlap is approximately 1% when the ratio W3 / W2 is equal to 1. By selecting a ratio W3 / W2 greater than 1, the optical overlap can be reduced to a value less than 1%. In this way, optical absorption can also be reduced.

[0065] 4 is a schematic top view of a first exemplary, non-limiting embodiment of a PIC 100 according to the present invention including a monitor photodiode 1 according to the present invention. The monitor photodiode 1 may be construed as being monolithically integrated with other optoelectronic devices (not shown) of the PIC 100.

[0066] According to an exemplary, non-limiting embodiment of the PIC (not shown), the monitor photodiode can be integrated in a hybrid manner with other optoelectronic devices of the PIC. An advantage of allowing hybrid integration of the monitor photodiode according to the invention is that the monitor photodiode can be used in any semiconductor technology field, such as the field of silicon photonics. Another advantage of allowing hybrid integration of the monitor photodiode according to the invention is that the monitor photodiode is replaceable. Replacing the monitor photodiode may be necessary, for example, in the event of a malfunction of the monitor photodiode or after a failure of the monitor photodiode.

[0067] An advantage of monolithically integrating a monitor photodiode with other optoelectronic devices (not shown) on the same semiconductor substrate, as shown schematically in FIG. 4, is that the monolithic integration of the monitor photodiode 1 with other optoelectronic devices may be less cumbersome and may require less die area than hybrid integration. As a result, the cost associated with monolithic integration of active and passive optoelectronic devices may be less than the cost associated with hybrid integration of the same. Additionally, monolithic integration may result in a smaller footprint for the PIC 100, which is beneficial in terms of reducing the cost of the PIC.

[0068] The PIC 100 may be an InP-based PIC. Those skilled in the art will appreciate that the majority of general-purpose technology platforms for PICs, particularly those that may be applied to telecommunications, lidar, or sensor applications, use wafers that include InP-based semiconductor materials. InP-based technology allows for the monolithic integration of both active components, e.g., light-generating and / or light-absorbing optics, and passive components, e.g., light-guiding and / or light-switching optics, in a PIC on a single die.

[0069] Based on the above, one skilled in the art will appreciate that a PIC 100 according to the present invention can benefit from the advantages provided by a monitor photodiode 1 according to the present invention.

[0070] 5 is a schematic diagram of a first exemplary, non-limiting embodiment of an optoelectronic system 200 in accordance with the present invention, including a PIC 100 in accordance with the present invention. The optoelectronic system 200 may be used, for example, but not limited to, in telecommunications applications, lidar, or sensor applications. The optoelectronic system 200 may be, for example, one of a transmitter, a receiver, a transceiver, a coherent transmitter, a coherent receiver, and a coherent transceiver. Based on the above, one skilled in the art will appreciate that the optoelectronic system 200 in accordance with the present invention may benefit from the advantages provided by the PIC 100 in accordance with the present invention.

[0071] FIG. 6A is a flow diagram of a first exemplary, non-limiting embodiment of a method 300 for fabricating a monitor photodiode according to this invention.

[0072] Step 301 includes providing a substrate 2 having a first surface 3 and a second surface 4 disposed facing away from the first surface 3 .

[0073] Step 302 includes providing a layer stack 5 on the second surface 4 of the substrate 2, and providing the layer stack 5 includes steps 303-307.

[0074] Step 303 includes epitaxially growing a semiconductor-based core layer 6 having a third surface 7 disposed facing toward the second surface 4 of the substrate 2 and a fourth surface 8 disposed facing away from the third surface 7, the semiconductor-based core layer 6 being configured to guide optical radiation when the monitor photodiode 1 is in use. The semiconductor-based core layer 6 has a first surface area A1.

[0075] Step 304 includes epitaxially growing a semiconductor-based absorber layer 9 having a fifth surface 10 disposed facing toward the second surface 4 of the substrate 2 and a sixth surface 11 disposed facing away from the fifth surface 10.

[0076] Step 305 includes performing a first lithography process followed by a first etching process to configure the semiconductor-based absorption layer 9 to have a first width W1 as viewed in a direction transverse to the propagation direction S of optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use and parallel to the fourth surface 8 of the semiconductor-based core layer 6, and a first length L1 as viewed in the propagation direction S of optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use, the first length L1 being at least equal to 3 μm. The semiconductor-based absorption layer 9 has a second surface area A2=W1*L1 that is smaller than the first surface area A1 of the semiconductor-based core layer 6.

[0077] Step 306 includes epitaxially growing a semiconductor-based cladding layer 12 having a seventh surface 13 positioned facing toward the second surface 4 of the substrate 2 and an eighth surface 14 positioned facing away from the seventh surface.

[0078] Step 307 includes performing a second lithography process followed by a second etching process to configure the eighth surface 14 of the semiconductor-based cladding layer 12 to have an elongated portion 15 having a second width W2 when viewed in a direction transverse to the propagation direction S of the optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use and parallel to the sixth surface 11 of the semiconductor-based absorber layer 9, and a second length L2 when viewed in the propagation direction S of the optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use, the second length L2 being at least equal to the first length L1 of the semiconductor-based absorber layer 9. The elongated portion 15 of the semiconductor-based cladding layer 12 and the semiconductor-based absorber layer 9 are positioned relative to each other such that an overlap between a mode field MF of the optical radiation present in the semiconductor-based core layer 6 and the semiconductor-based absorber layer 9 when the monitor photodiode 1 is in use results in absorption of optical radiation of up to 5%.

[0079] By continuing to perform steps 301-307 of the first exemplary, non-limiting embodiment of method 300, an exemplary, non-limiting embodiment of a monitor photodiode according to the present invention can be fabricated that enables the above-mentioned advantages by absorbing up to 5% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use.

[0080] 6B shows a flow diagram of a second exemplary, non-limiting embodiment of a method 300 for fabricating a monitor photodiode according to the present invention. Steps 301, 302, 303, 304, 306, and 307 are the same as those described above with respect to the first exemplary, non-limiting embodiment of the method 300 shown in FIG. 6A. In addition, it is understood that step 308 is performed instead of step 305 according to the first exemplary, non-limiting embodiment of the method 300.

[0081] Step 308 includes performing a first lithography process followed by a first etching process to provide a slot 16 in the semiconductor-based absorber layer 9 that is configured and arranged to divide the semiconductor-based absorber layer 9 into a first portion 9a and a second portion 9b. The first portion 9a and the second portion 9b are separated and spaced apart from each other when viewed in a direction transverse to the propagation direction S of optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use and parallel to the second surface 4 of the substrate 2. The slot 16 has a third width W3 when viewed in a direction transverse to the propagation direction S of optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use and parallel to the fourth surface 8 of the semiconductor-based core layer 6. The third width W3 ranges from 0.95W2 to 3W2 depending on the desired amount of overlap between a mode field MF of optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use and at least one of the first portion 9a and the second portion 9b of the semiconductor-based absorber layer 9. The slot 16 has a third length L3 as viewed in the propagation direction S of the optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use. The third length L3 is equal to the first length L1 of the semiconductor-based absorption layer 9.

[0082] By sequentially performing steps 301, 302, 303, 304, 308, 306, and 307 of the second exemplary, non-limiting embodiment of method 300, another exemplary, non-limiting embodiment of a monitor photodiode according to the present invention can be fabricated that enables the above-mentioned advantages by allowing absorption of up to 5% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use.

[0083] 6C shows a flow diagram of a third exemplary, non-limiting embodiment of a method 300 for fabricating a monitor photodiode 1 according to the present invention. Steps 301, 302, 305, 306, and 307 are the same as those described above with respect to the first exemplary, non-limiting embodiment of the method 300 shown in FIG. 6A.

[0084] Step 309 includes epitaxially growing a semiconductor-based core layer 6 having a third surface 7 disposed facing toward and in contact with the second surface 4 of the substrate 2. The semiconductor-based core layer 6 has a fourth surface 8 disposed facing away from the third surface 7. The semiconductor-based core layer 6 is configured to guide optical radiation when the monitor photodiode 1 is in use. The semiconductor-based core layer 6 has a first surface area A1.

[0085] Step 310 includes epitaxially growing a semiconductor-based spacer layer 17 having a ninth surface 18 disposed facing toward and in contact with the fourth surface 8 of the semiconductor-based core layer 6. The semiconductor-based spacer layer 17 has a tenth surface 19 disposed facing away from the ninth surface 18. The semiconductor-based spacer layer 17 has a third surface area A3 equal to the first surface area A1 of the semiconductor-based core layer 6.

[0086] Step 311 includes epitaxially growing a semiconductor-based absorber layer 9 having a fifth surface 10 disposed facing toward and in contact with tenth surface 19 of semiconductor-based spacer layer 17. Semiconductor-based absorber layer 9 has a sixth surface 11 disposed facing away from fifth surface 10.

[0087] By sequentially performing steps 301, 302, 309, 310, 311, 305, 306, and 307 of the third exemplary, non-limiting embodiment of method 300, yet another exemplary, non-limiting embodiment of a monitor photodiode according to the present invention can be fabricated that enables the above-mentioned advantages by allowing absorption of up to 5% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use.

[0088] 6D shows a flow diagram of a fourth exemplary, non-limiting embodiment of a method 300 for fabricating a monitor photodiode 1 according to the present invention. Steps 301, 302, 308, 306, and 307 are the same as those described above with respect to the second exemplary, non-limiting embodiment of the method 300 shown in FIG. 6B. Furthermore, steps 309, 310, and 311 are the same as those described above with respect to the third exemplary, non-limiting embodiment of the method 300 shown in FIG. 6C.

[0089] By sequentially performing steps 301, 302, 309, 310, 311, 308, 306, and 307 of the fourth exemplary, non-limiting embodiment of method 300, yet another exemplary, non-limiting embodiment of a monitor photodiode according to the present invention can be fabricated that enables the above-mentioned advantages by allowing absorption of up to 5% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use.

[0090] The present invention can be summarized as relating to a monitor photodiode 1 for absorbing up to 5% of the optical radiation to which the monitor photodiode is exposed when the monitor photodiode is in use. The monitor photodiode includes a layer stack 5 having a semiconductor-based core layer 6, a semiconductor-based absorption layer 9, and a semiconductor-based cladding layer 12 provided with an elevated elongated portion 15. The semiconductor-based absorption layer and the elevated elongated portion are arranged relative to each other such that, when the monitor photodiode is in use, an overlap between the mode field of the optical radiation present in the semiconductor-based core layer and the semiconductor-based absorption layer results in an optical absorption of up to 5%. The present invention also relates to a PIC 100 including a monitor photodiode 1 according to the present invention, an optoelectronic system 200 including such a PIC 100, and a method for manufacturing the monitor photodiode 1.

[0091] It will be apparent to those skilled in the art that the scope of the present invention is not limited to the above-described embodiments, and that numerous amendments and modifications thereto are possible without departing from the scope of the present invention as defined in the appended claims. In particular, specific features of various aspects of the present invention can be combined. Aspects of the present invention can be further advantageously enhanced by adding features described for other aspects of the present invention. While the present invention has been illustrated and described in detail in the drawings and specification, such illustration and description should be interpreted as illustrative or exemplary only and not restrictive.

[0092] The present invention is not limited to the disclosed embodiments. By studying the features, the description, and the appended claims, modifications to the disclosed embodiments can be understood and achieved by those skilled in the art in practicing the claimed invention. In the claims, the word "comprises" does not exclude other steps or elements, and the indefinite articles "a" or "an" do not exclude a plurality. The fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the present invention.

Claims

1. 1. A monitor photodiode (1) comprising: a substrate (2) having a first surface (3) and a second surface (4) arranged facing away from the first surface (3); and a layer stack (5) arranged on the second surface (4) of the substrate (2), the layer stack (5) absorbing at most 5% of optical radiation to which the monitor photodiode (1) is exposed when the monitor photodiode (1) is in use, the layer stack (5) comprising: a semiconductor-based core layer (6) having a third surface (7) arranged facing towards the second surface (4) of the substrate (2) and a fourth surface (8) arranged facing away from the third surface (7), the semiconductor-based core layer (6) being configured to guide optical radiation when the monitor photodiode (1) is in use and having a first surface area A １ the semiconductor-based core layer (6) having a semiconductor-based absorption layer (9) having a fifth surface (10) arranged facing towards the second surface (4) of the substrate (2) and a sixth surface (11) arranged facing away from the fifth surface (10), a first width W transverse to the propagation direction S of the optical radiation present in the semiconductor-based core layer 6 when the monitor photodiode 1 is in use; １ and, a first length L as seen in the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use; １ and the first length L is at least equal to 3 μm. １ and, The first surface area A of the semiconductor-based core layer (6) １ a second smaller surface area A ２ =W １ *L １ a semiconductor-based absorption layer (9) having a seventh surface (13) arranged facing towards the second surface (4) of the substrate (2), and an eighth surface (14) arranged facing away from the seventh surface (13), a second width W as viewed in a direction transverse to the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use and parallel to the sixth surface (11) of the semiconductor-based absorption layer (9); ２ and, a second length L as viewed in the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use; ２ wherein the first length L of the semiconductor-based absorption layer (9) １ The second length L is at least equal to ２ and the semiconductor-based cladding layer (12) having the eighth surface (14) configured with an elevated elongated portion (15); the elongated portion (15) of the semiconductor-based cladding layer (12) and the semiconductor-based absorption layer (9) are arranged relative to each other such that an overlap between the mode field MF of the optical radiation present in the semiconductor-based core layer (6) and the semiconductor-based absorption layer (9) results in an absorption of at most 5% of the optical radiation when the monitor photodiode (1) is in use; The monitor photodiode (1).

2. A monitor photodiode (1) according to claim 1, The second width W of the elongated portion (15) ２ is in the range of 200 nm to 10 μm, and the first width W of the semiconductor-based absorption layer (9) １ is 0.1W ２ from 0.5W ２ In the range of The monitor photodiode (1).

3. A monitor photodiode (1) according to claim 1, the semiconductor-based absorption layer (9) is provided with a slot (16) constructed and arranged to divide the semiconductor-based absorption layer (9) into a first portion (9a) and a second portion (9b), the first portion (9a) and the second portion (9b) being separated and spaced apart from each other when viewed in the direction transverse to the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use and parallel to the second surface (4) of the substrate (2); a third width W as viewed in the direction transverse to the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use and parallel to the fourth surface (8) of the semiconductor-based core layer (6); ３ 0.95 W depending on the desired value of overlap between the mode field MF of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use and at least one of the first portion (9a) and the second portion (9b) of the semiconductor-based absorption layer (9). ２ From 3W ２ The third width W ３ and, a third length L as viewed in the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use; ３ wherein the first length L of the semiconductor-based absorption layer (9) １ the third length L ３ and, provided with said slot (16), The monitor photodiode (1).

4. A monitor photodiode (1) according to claim 1, The layer stack (5) includes a semiconductor-based spacer layer (17) disposed between the semiconductor-based core layer (6) and the semiconductor-based absorption layer (9), the semiconductor-based spacer layer (17) having a ninth surface (18) disposed facing toward the fourth surface (8) of the semiconductor-based core layer (6) and a tenth surface (19) disposed facing away from the ninth surface (18), the semiconductor-based spacer layer (17) having a first surface area A １ A third surface area A equal to ３ and the semiconductor-based spacer layer (17) has a first thickness T as viewed transverse to the ninth surface (18). １ and the first thickness T １ is in the range of 40 nm to 100 nm, The monitor photodiode (1).

5. A monitor photodiode (1) according to claim 2, The layer stack (5) includes a semiconductor-based spacer layer (17) disposed between the semiconductor-based core layer (6) and the semiconductor-based absorption layer (9), the semiconductor-based spacer layer (17) having a ninth surface (18) disposed facing toward the fourth surface (8) of the semiconductor-based core layer (6) and a tenth surface (19) disposed facing away from the ninth surface (18), the semiconductor-based spacer layer (17) having a first surface area A １ A third surface area A equal to ３ and the semiconductor-based spacer layer (17) has a first thickness T as viewed transverse to the ninth surface (18). １ and the first thickness T １ is in the range of 40 nm to 100 nm, The monitor photodiode (1).

6. A monitor photodiode (1) according to claim 3, The layer stack (5) includes a semiconductor-based spacer layer (17) disposed between the semiconductor-based core layer (6) and the semiconductor-based absorption layer (9), the semiconductor-based spacer layer (17) having a ninth surface (18) disposed facing toward the fourth surface (8) of the semiconductor-based core layer (6) and a tenth surface (19) disposed facing away from the ninth surface (18), the semiconductor-based spacer layer (17) having a first surface area A １ A third surface area A equal to ３ and the semiconductor-based spacer layer (17) has a first thickness T as viewed transverse to the ninth surface (18). １ and the first thickness T １ is in the range of 40 nm to 100 nm, The monitor photodiode (1).

7. A monitor photodiode (1) according to claim 4, the semiconductor-based spacer layer (17) is a p-type doped InP-based layer; The monitor photodiode (1).

8. A monitor photodiode (1) according to claim 6, the semiconductor-based spacer layer (17) is a p-type doped InP-based layer; The monitor photodiode (1).

9. A monitor photodiode (1) according to claim 1, The substrate (2) is an n-type doped InP-based layer, The monitor photodiode (1).

10. A monitor photodiode (1) according to claim 1, The semiconductor-based core layer (6) is unintentionally doped with In ｘ Ga １－ｘ As ｙ P １－ｙ The layer is The monitor photodiode (1).

11. A monitor photodiode (1) according to claim 1, The semiconductor-based absorbing layer (9) has a second thickness T as viewed transversely to the fifth surface (10). ２ and the second thickness T is in the range of 75 nm to 150 nm. ２ have, The monitor photodiode (1).

12. A monitor photodiode (1) according to claim 3, The semiconductor-based absorbing layer (9) has a second thickness T as viewed transversely to the fifth surface (10). ２ and the second thickness T is in the range of 75 nm to 150 nm. ２ have, The monitor photodiode (1).

13. A monitor photodiode (1) according to claim 1, The semiconductor-based absorption layer (9) is p-type doped or unintentionally doped In ｘ Ga １－ｘ As layer, The monitor photodiode (1).

14. A monitor photodiode (1) according to claim 1, The semiconductor-based cladding layer (12) is a p-type doped InP-based layer. The monitor photodiode (1).

15. A photonic integrated circuit PIC (100) including a monitor photodiode (1) according to claim 1, The PIC (100) is a hybrid integrated PIC or a monolithically integrated PIC; Said PIC (100).

16. An optoelectronic system (200) including the PIC (100) of claim 15, the optoelectronic system (200) being one of a transmitter, a receiver, a transceiver, a coherent transmitter, a coherent receiver, and a coherent transceiver; The optoelectronic system (200).

17. 1. A method (300) for manufacturing a monitor photodiode (1) that absorbs at most 5% of the optical radiation to which the monitor photodiode (1) is exposed when the monitor photodiode (1) is in use, comprising: providing a substrate (2) having a first surface (3) and a second surface (4) arranged opposite and spaced from said first surface (3); providing a layer stack (5) on the second surface (4) of the substrate (2), wherein providing the layer stack (5) comprises: a semiconductor-based core layer (6) having a third surface (7) arranged facing towards the second surface (4) of the substrate (2) and a fourth surface (8) arranged facing away from the third surface (7), the semiconductor-based core layer (6) being configured to guide optical radiation when the monitor photodiode (1) is in use and having a first surface area A １ epitaxially growing said semiconductor-based core layer (6) having epitaxially growing a semiconductor-based absorber layer (9) having a fifth surface (10) arranged facing towards the second surface (4) of the substrate (2) and a sixth surface (11) arranged facing away from the fifth surface (10); performing a first lithography process followed by a first etching process; a first width W as viewed in a direction transverse to the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use and parallel to the fourth surface (8) of the semiconductor-based core layer (6); １ and, a first length L as seen in the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use; １ and the first length L is at least equal to 3 μm. １ and, and configuring said semiconductor-based absorption layer (9) to have The semiconductor-based absorption layer (9) is formed on the first surface area A of the semiconductor-based core layer (6). １ a second smaller surface area A ２ =W １ *L １ and configuring said semiconductor-based absorption layer (9) with epitaxially growing a semiconductor-based cladding layer (12) having a seventh surface (13) disposed facing toward the second surface (4) of the substrate (2) and an eighth surface (14) disposed facing away from the seventh surface (13); performing a second lithography process followed by a second etching process; a second width W as viewed in a direction transverse to the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use and parallel to the sixth surface (11) of the semiconductor-based absorption layer (9); ２ and, a second length L as viewed in the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use; ２ wherein the first length L of the semiconductor-based absorption layer (9) １ The second length L is at least equal to ２ and, and configuring the eighth surface (14) of the semiconductor-based cladding layer (12) to have an elevated elongated portion (15) having the elongated portion (15) of the semiconductor-based cladding layer (12) and the semiconductor-based absorption layer (9) are arranged relative to each other such that when the monitor photodiode (1) is in use, an overlap between the mode field MF of the optical radiation present in the semiconductor-based core layer (6) and the semiconductor-based absorption layer (9) results in an absorption of optical radiation of at most 5%. The method (300).

18. 20. The method (300) of claim 17, comprising: the first lithography process followed by the first etching process is performed; a slot (16) in the semiconductor-based absorption layer (9) constructed and arranged to divide the semiconductor-based absorption layer (9) into a first portion (9a) and a second portion (9b), the first portion (9a) and the second portion (9b) being separated and spaced apart from each other when viewed in the direction transverse to the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use and parallel to the second surface (4) of the substrate (2); a third width W as viewed in the direction transverse to the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use and parallel to the fourth surface (8) of the semiconductor-based core layer (6); ３ 0.95 W depending on the desired value of overlap between the mode field MF of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use and at least one of the first portion (9a) and the second portion (9b) of the semiconductor-based absorption layer (9). ２ From 3W ２ The third width W ３ and, a third length L as viewed in the propagation direction S of the optical radiation present in the semiconductor-based core layer (6) when the monitor photodiode (1) is in use; ３ wherein the first length L of the semiconductor-based absorption layer (9) １ the third length L ３ and, providing said slot (16) with Method (300).

19. 20. The method (300) of claim 17, comprising: Providing said layer stack (5) comprises: epitaxially growing a semiconductor-based spacer layer (17) after epitaxially growing the semiconductor-based core layer (6) and before growing the semiconductor-based absorption layer (9), the semiconductor-based spacer layer (17) having a ninth surface (18) arranged facing toward the fourth surface (8) of the semiconductor-based core layer (6) and a tenth surface (19) arranged facing away from the ninth surface (18), the semiconductor-based spacer layer (17) covering the first surface area A of the semiconductor-based core layer (6); １ A third surface area A equal to ３ and epitaxially growing the silicon nitride film having a thickness of 1000 nm to 1000 nm. The method (300).

20. 20. The method (300) of claim 18, comprising: Providing said layer stack (5) comprises: epitaxially growing a semiconductor-based spacer layer (17) after epitaxially growing the semiconductor-based core layer (6) and before growing the semiconductor-based absorption layer (9), the semiconductor-based spacer layer (17) having a ninth surface (18) arranged facing toward the fourth surface (8) of the semiconductor-based core layer (6) and a tenth surface (19) arranged facing away from the ninth surface (18), the semiconductor-based spacer layer (17) covering the first surface area A of the semiconductor-based core layer (6); １ A third surface area A equal to ３ and epitaxially growing the silicon nitride film having a thickness of 1000 nm to 1000 nm. The method (300).

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