Optical device, multi-chip module, and method of forming an optical device

Abstract

Examples described herein relate to an optical device having an integrated light emitting structure for generating light, and a waveguide integrated capacitor for monitoring the light. The light emitting structure can emit light when electricity is applied to the optical device. The waveguide integrated capacitor can be formed below the light emitting structure to monitor the light emitted by the light emitting structure. The waveguide integrated capacitor includes a waveguide region that carries at least a portion of the light. The waveguide region includes one or more photon absorption sites, which cause the generation of free charge carriers related to the intensity of the light confined in the waveguide region, thereby causing a change in the conductivity of the waveguide region.

Description

[0001] Government Rights Statement

[0002] This invention was made with government support under Award No. DE-AR0001039 awarded by DOE, Office of ARPA-E. The government has certain rights in this invention. Technical Field

[0003] The present disclosure relates to the field of optical technology, and more particularly to an optical device, a multi-chip module, and a method for forming the optical device. Background Art

[0004] Optical systems include optical devices that can generate, process, and / or carry optical signals from one point to another. In certain embodiments, optical systems (such as optical communication systems) can facilitate data communication over longer distances with higher bandwidth using smaller cable widths (or diameters) compared to communication systems using electrical wires. In optical communication systems, light can be generated by a light source (such as a laser). In some optical systems, an external light monitoring device (such as a photodiode) is used to monitor the light generated by the light source. Summary of the invention

[0005] According to one aspect of the present disclosure, an optical device is provided, comprising: a light emitting structure for emitting light when electricity is applied to the optical device; a waveguide integrated capacitor formed below the light emitting structure to monitor the light emitted by the light emitting structure, wherein the waveguide integrated capacitor comprises a waveguide region carrying at least a portion of the light, and wherein the waveguide region comprises one or more photon absorption sites, the one or more photon absorption sites being used to absorb photons of the portion of the light carried in the waveguide region and cause generation of free charge carriers related to the intensity of the light confined in the waveguide region based on the absorbed photons, thereby causing a change in conductance of the waveguide region, the change in conductance being proportional to the intensity of the portion of the light carried in the waveguide region; and a monitoring circuit, the monitoring circuit being configured to monitor the intensity of the light emitted by the light emitting structure without extracting the light to the outside of the optical device, the monitoring circuit being configured to apply a reference voltage to the waveguide integrated capacitor and the waveguide region and to measure a current flowing through the waveguide region, wherein a change in the current is proportional to a change in conductance of the waveguide region, the change in conductance being indicative of the intensity of the light confined in the waveguide region.

[0006] According to another aspect of the present disclosure, a multi-chip module is provided, comprising: an electronic chip; and a photonic chip, the photonic chip being coupled to the electronic chip so as to be communicatively coupled with the electronic chip, the photonic chip comprising an optical device, the optical device comprising: a light emitting structure, the light emitting structure comprising an optical gain region to emit light when electricity is applied to the optical device; and a waveguide integrated capacitor, the waveguide integrated capacitor being formed under the light emitting structure to monitor the light emitted by the light emitting structure, wherein the waveguide integrated capacitor comprises: a waveguide region, the waveguide region carrying at least a portion of the light, a first buffer semiconductor region; an insulating layer, the insulating layer being disposed between the waveguide region and the first buffer semiconductor region. between regions, wherein the waveguide region includes one or more photon absorption sites, the one or more photon absorption sites causing the generation of free charge carriers related to the intensity of light confined in the waveguide region, thereby causing a change in the conductance of the waveguide region; and a monitoring circuit, the monitoring circuit is coupled to the photonic chip to monitor the light intensity inside the optical device without diverting any part of the light to the outside of the waveguide region, the monitoring circuit is configured to apply a reference voltage to the waveguide integrated capacitor and the waveguide region and measure a current flowing through the waveguide region, wherein a change in the current is proportional to a change in the conductance of the waveguide region, and the change in conductance is indicative of the intensity of the light confined in the waveguide region.

[0007] According to another aspect of the present disclosure, a method for forming an optical device is provided, comprising: providing a substrate; forming a waveguide integrated capacitor using the substrate, wherein the waveguide integrated capacitor includes a waveguide region, the waveguide region including one or more photon absorption sites; forming a light emitting structure above the waveguide integrated capacitor, wherein the light emitting structure is used to emit light when electricity is applied to the optical device, wherein the waveguide region includes at least a portion of the light generated by the light emitting structure, and the one or more photon absorption sites absorb photons of the portion of the light carried in the waveguide region and cause generation of free charge carriers related to the intensity of the light confined in the waveguide region based on the absorbed photons, thereby causing a change in conductance of the waveguide region, the conductance change being proportional to the intensity of the portion of the light carried in the waveguide region; and providing a monitoring circuit, the monitoring circuit being configured to monitor the intensity of light emitted by the light emitting structure without extracting the light outside the optical device, the monitoring circuit being configured to apply a reference voltage to the waveguide integrated capacitor and the waveguide region and measure a current flowing through the waveguide region, wherein a change in the current is proportional to a change in conductance of the waveguide region, the conductance change being indicative of the intensity of the light confined in the waveguide region. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Various examples will be described below with reference to the following drawings.

[0009] Figure 1 An example optical device having a light emitting structure and a waveguide-integrated capacitor for monitoring the light is depicted.

[0010] Figure 2 A cross-sectional view of an example optical device is depicted.

[0011] Figure 3 A top view of an example optical device is depicted.

[0012] Figure 4 A top view of another example optical device is depicted.

[0013] Figure 5 A cross-sectional view of an example optical device is depicted.

[0014] Figure 6 A cross-sectional view of another example optical device is depicted.

[0015] Figure 7 A block diagram of an example optical system with an example optical arrangement is depicted.

[0016] Figure 8 Depicted is a block diagram of an example multi-chip module having an electronic chip and a photonic chip having an example optical device.

[0017] Fig. 9 A flow chart of an example method of making an example optical device is depicted.

[0018] Fig.10 A flow chart depicts another example method of manufacturing an example optical device.

[0019] It should be emphasized that in the drawings, the various features are not drawn to scale. In fact, in the drawings, the sizes of the various features have been arbitrarily increased or reduced for clarity of discussion. DETAILED DESCRIPTION

[0020] The following detailed description refers to the accompanying drawings. Where possible, the same reference numerals are used in the drawings and the following description to refer to the same or similar parts. It will be clearly understood that the drawings are for illustration and description purposes only. Although several examples are described in this document, modifications, adaptations and other embodiments are possible. Therefore, the following detailed description does not limit the disclosed examples. On the contrary, the proper scope of the disclosed examples may be defined by the appended claims.

[0021] The optical system may include various optical devices (e.g., components) such as, but not limited to, a light source (e.g., a laser), an optical modulator, an optical filter, an optical amplifier, an optical coupler, a waveguide, an optical combiner, an optical multiplexer, an optical demultiplexer, an optical resonator, or a photodetector (e.g., a photodiode). Some optical systems may include light monitoring circuitry to monitor optical signals included within one or more such optical components. Such monitoring of light may be useful to correct certain operating parameters, such as bias conditions in the presence of varying environmental conditions or aging of the optical device.

[0022] A common technique used in some optical monitoring circuits requires the use of one or more optical splitters to extract a small portion of the light from the optical component. The extracted light may be routed to one or more separate photodetectors (e.g., photodiodes), which convert the extracted light into an electrical signal (e.g., a current). This extraction of light and routing the extracted light to separate photodetectors may result in a loss of useful optical power. Further, the photodetectors used to convert light into electrical signals may not be properly calibrated, resulting in inaccurate measurements of light. In addition, in optical systems having several optical components (e.g., light sources cascaded in a long chain, ring resonators, etc.), the use of the above-mentioned optical monitoring techniques may result in increased optical losses. Additionally, the above-mentioned optical monitoring techniques may suffer from the uncertainty of the splitting ratios in the individual splitters used, even if the designs of these splitters are similar. In addition, the light from the splitters may be routed across the chip to the photodetectors, which may result in further uncertainty in power levels or unavoidable waveguide crossings. In some embodiments, the use of additional structural elements (such as a separate photodetector) may require additional space, thereby increasing the overall footprint of the optical system and / or requiring compromises in the internal structure and / or efficiency of the ring resonator.

[0023] According to one or more examples presented herein, an optical device (such as an optical light source) is provided that includes on-chip monitoring of photon density inside a cavity of the optical device without extracting portions of the light into separate detectors, thereby reducing losses and negative effects from light reflections. The footprint of the example optical device is small and compatible with heterogeneous III-V on Silicon.

[0024] An example optical device includes a light emitting structure to emit light when electricity is applied to the optical device. Further, the optical device includes a waveguide integrated capacitor formed integrally with the structure of the optical device. In particular, the waveguide integrated capacitor can be a metal oxide semiconductor (MOS) capacitor formed below the light emitting structure to monitor the light emitted by the light emitting structure without extracting the light out of the optical device (e.g., to a separate photodetector downstream of the light emitting structure). In some examples, the waveguide integrated capacitor includes a waveguide region that carries at least a portion of the light emitted by the light emitting structure. The waveguide region includes one or more photon absorption sites that cause the generation of free charge carriers related to the intensity of the light confined in the waveguide region, thereby causing a change in the conductance of the waveguide region.

[0025] In some examples, a monitoring circuit may be electrically coupled to the optical device to monitor light confined within the optical device. In particular, the monitoring circuit may be electrically coupled to (multiple) waveguide integrated capacitors at one or more monitoring sites within the optical device to cause the generation of electrical signals representing the intensity of light included at corresponding monitoring sites in the optical device. Using the electrical signals generated via the (multiple) waveguide integrated capacitors, the monitoring circuit may be configured to determine optical parameters such as, but not limited to, the efficiency of the optical device. The use of waveguide integrated capacitors may obviate the need for a separate photodiode to monitor light, thereby making the footprint of an optical system employing the proposed optical device compact and reduced in complexity.

[0026] Referring now to the accompanying drawings, Figure 1 , an example optical device 100 is presented. The optical device 100 may be a light source, such as a laser, which may be disposed in an optical system (not shown) for generating light and providing light to other optical devices in the optical system. Figure 1 The optical device 100 may include electrical contacts 102A, 102B, 102C, a light emitting structure 104, and a waveguide integrated capacitor 106. Figure 1 In the example depicted in , three electrical contacts 102A-102C are shown for illustration purposes. In some other examples, the optical device 100 may include fewer or more electrical contacts. The optical device 100 may receive power and / or a reference monitoring voltage through one or more of the electrical contacts 102A-102C.

[0027] When power is applied to the optical device 100 through one or more of the electrical contacts 102A-102C, the light emitting structure 104 can emit light. The light emitting structure 104 can be a region of semiconductor material(s) that generates light based on the excitation of charge carriers (e.g., electrons) due to the electric field caused by the applied power across the light emitting structure. For example, the light emitting structure 104 can be a diode, such as a light emitting diode. In some other examples, the light emitting structure 104 can include a heterogeneous quantum well structure or a quantum dot structure to generate light. Additional details of the light emitting structure 104 are incorporated herein by reference. Figure 5-6 to describe.

[0028] The waveguide integrated capacitor 106 may be a MOS capacitor formed within the device structure of the optical device 100, rather than a photodiode used with a conventional optical device, which is built outside the conventional optical device and receives light through a drop port. The waveguide integrated capacitor 106 may help detect light included within the optical device 100 without diverting any portion of the light to the outside of the optical device 100. In one example, the waveguide integrated capacitor 106 may include a photon absorption site (see Figure 2 ), these photon absorption sites may cause the generation of free charge carriers that are related to the intensity of the optical signal inside the optical device 100. As will be appreciated, the generation of free charge carriers may cause a change (e.g., an increase) in the conductance of a given region (e.g., a waveguide region) of the optical device. The change in conductance of the given region may cause a change in the current passing through the given region, which may be detected by the monitoring circuit ( Figure 1 Not shown, see Figure 4 ) to monitor. Additional details regarding example waveguide integrated capacitors (such as waveguide integrated capacitor 106) are as follows Figure 2 Give a description.

[0029] Reference now Figure 2, presents a cross-sectional view 200 of an example optical device 202. The optical device 202 may be an example representative of the optical device 100, and includes a light emitting structure 204 and a waveguide integrated capacitor 206. In some examples, the optical device 202 may include a waveguide region 207, a first buffer semiconductor region 208, and an insulating layer 210. The waveguide region 207, the first buffer semiconductor region 208, and the insulating layer 210 together define a metal oxide semiconductor (MOS) capacitor (also referred to herein as a waveguide integrated capacitor 206). In particular, the waveguide region 207 is used as a portion of the waveguide integrated capacitor 206. The insulating layer 210 may be formed between the waveguide region 207 and the first buffer semiconductor region 208, such that the insulating layer 210 may act as an electrical insulator between two conductive regions (e.g., the waveguide region 207 and the first buffer semiconductor region 208).

[0030] Optical device 202 may be formed using substrate 212. In some examples, substrate 212 may be a silicon-on-insulator (SOI) substrate, which may include a base substrate layer 216, a base oxide layer 214, and a device layer 218. Base substrate layer 216 may be made of a semiconductor material, such as silicon (Si). Other examples of materials that may be used to form base substrate layer 216 may include III-V semiconductors, such as indium phosphide (InP), germanium (Ge), gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium gallium arsenide (InGaAs), indium arsenide (InAs), or combinations thereof. Further, as Figure 2 As depicted in , the substrate 212 may include a base oxide layer 214 disposed on an underlying base substrate layer 216. For example, the base oxide layer 214 may be formed by oxidizing the substrate 212. Figure 2 In an embodiment, for a base substrate layer 216 made of silicon, the base oxide layer 214 may include silicon dioxide (SiO2), which may be formed in the presence of oxygen at a temperature in the range of 900°C to 1380°C. In some examples, the base oxide layer 214 may be a buried oxide (BOX) layer (e.g., SiO2 may be buried in the base substrate layer 216). In some examples, the SiO2 layer may be buried in the base substrate layer 216 to a depth ranging from less than 100 nm to several microns from the wafer surface, depending on the application. Other examples of the base oxide layer 214 may include, but are not limited to, silicon nitride (Si3N4), aluminum oxide (Al2O3), hafnium dioxide (HfO2), diamond, silicon carbide (SiC), or combinations thereof.

[0031] Further, the substrate 212 may include a device layer 218 disposed on top of the base oxide layer 214. Figure 2In an example embodiment of the present invention, the device layer 218 is composed of silicon. The device layer 218 can be appropriately shaped (e.g., via techniques such as lithography and etching) to form one or more regions, such as a waveguide region 207 and a non-waveguide region 209 isolated via air trenches 219. The waveguide region 207 carries optical signals during operation of the optical device 202. In some examples, the waveguide region 207 can include a first type of doping (e.g., p-type doping) or be compensation doped to produce a net doping of the first type. In one example, the waveguide region 207 can represent a cross-section of an annular or ring-shaped optical waveguide (e.g., see Figure 4 In another example, the waveguide region 207 may represent a cross section of a linear optical waveguide (eg, see Figure 3 ). The waveguide region 207 may be undoped, thereby resulting in no signal being detected by a monitoring circuit (e.g., Figure 1 Improvement in the sensitivity of the reference variable voltage applied by the monitoring circuit 108) depicted in FIG.

[0032] As depicted in the enlarged view 222 of a portion 224 of the waveguide region 207, the waveguide region 207 may have one or more photon absorption sites 226. As used herein, the term "photon absorption site" may refer to a crystal defect or flaw in the bulk of the material of the waveguide region 207, a surface defect at a boundary of the waveguide region 207, or both. In some examples, the photon absorption site may be caused by a defect in the manufacturing process. In some examples, some photon absorption sites may be intentionally created. The photon absorption site 226 may absorb photons and cause the generation of free charge carriers related to the intensity of the optical signal impinging thereon within the waveguide region 207. The conductance of the waveguide region 207 depends on the amount of free charge carriers, such that an increase in the optical signal causes an increase in the conductance of the waveguide region 207.

[0033] The insulating layer 210 is disposed over the waveguide region 207 and / or the non-waveguide region 209. In particular, the insulating layer 210 is formed such that the insulating layer 210 is sandwiched between the waveguide region 207 and the first buffer semiconductor region 208. The insulating layer 210 may be formed of one or more dielectric materials, including but not limited to native oxides of the materials of the waveguide region 207 or the first buffer semiconductor region 208 or both, or external dielectric materials (such as high-k dielectrics or polymers, which may be formed by deposition, oxidation, wafer bonding or other dielectric coating methods). Other non-limiting examples of dielectric materials that may be used to form the insulating layer 210 may include SiO2, Si3N4, Al2O3, HfO2, polyimide, benzocyclobutene (BCB), or combinations thereof.

[0034] Further, the first buffer semiconductor region 208 may be made of a semiconductor material, such as a III-V semiconductor material. Examples of III-V semiconductor materials that may be used to form the first buffer semiconductor region 208 may include, but are not limited to, GaAs, gallium nitride (GaN), or indium nitride (InN). The first buffer semiconductor region 208 may be formed over the insulating layer 210 using techniques such as, but not limited to, deposition, wafer bonding, monolithic growth, or other manufacturing techniques. In some examples, the first buffer semiconductor region 208 may include a second type of doping (e.g., n-type doping) that is different from the first type of doping.

[0035] Light emitting structure 204 may represent an example of light emitting structure 104 and may be capable of generating light based on the excitation of charge carriers (e.g., electrons) due to an electric field induced across light emitting structure 204 by an electric force applied via metal contacts (described later). For example, light emitting structure 204 may be a diode, such as a light emitting diode. In some other examples, light emitting structure 204 may include a heterogeneous mass quantum well structure (see Figure 5 ) or quantum dot structures (see Figure 6 ) to generate light.

[0036] The light emitting structure 204 may be formed over at least a portion of the first buffer semiconductor region 208. In particular, the light emitting structure 204 may be formed on a surface of the first buffer semiconductor region 208 over the waveguide region 207. The light emitting structure 204 may include an optical gain region 236 and a second buffer semiconductor region 238. The optical gain region 236 may be formed over the waveguide integrated capacitor 206, more particularly, on a surface of the first buffer semiconductor region 208 over the waveguide region 207. The second buffer semiconductor region 238 may be formed over the optical gain region 236. The second buffer semiconductor region 238 may be made of a semiconductor material, such as a III-V semiconductor material, for example, GaAs, GaN, or InN. In some examples, the second buffer semiconductor region 238 may have a different type of doping compared to the first buffer semiconductor region 208. In particular, if the first buffer semiconductor region includes a second type (e.g., n-type) doping, the second buffer semiconductor region 238 may include a first type (e.g., p-type) doping. Forming the buffer semiconductor regions 208 and 238 with such different types of doping may reduce optical propagation losses within the optical device 202 .

[0037] Additionally, in some examples, the optical device 202 may include a first contact region 228, a second contact region 230, and a third contact region 231. Figure 2, contact regions 228, 230, and 231 are shown as being made of silicon. In some other examples, contact regions 228 and 230 may be made of other semiconductor materials, including but not limited to InP, Ge, GaAs, AlGaAs, InGaAs, or combinations thereof. The first contact region 228 may include a first type of doping and be disposed in contact with the waveguide region 207. Further, the second contact region 230 may include a second type of doping and be disposed in contact with the first buffer semiconductor region 208. The third contact region 231 may include a first type of doping and be disposed in contact with the second buffer semiconductor region 238. In particular, in some examples, the third contact region 231 may be formed above the second buffer semiconductor region 238.

[0038] Furthermore, in some examples, the optical device 202 may include metal contacts, such as a first metal contact 232, a second metal contact 234, and a third metal contact 235 (hereinafter collectively referred to as metal contacts 232-235). Figure 2 As depicted in , first metal contact 232 and second metal contact 234 are disposed in electrical contact with first contact region 228 and second contact region 230, respectively (e.g., in direct physical contact or via any intermediate conductive material). Third metal contact 235 is disposed in electrical contact with third contact region 231. In some examples, metal contacts 232, 234, and 235 may be formed on top of first contact region 228, second contact region 230, and third contact region 235, respectively (i.e., formed vertically above them). Examples of materials for forming metal contacts 232 and 234 may include, but are not limited to, copper (Cu), gold (Au), Al, and / or platinum (Pt). In an example, in an optical system (e.g., see Figure 7 ), the monitoring circuit can be electrically connected to the contact areas 228 and 230 via the corresponding metal contacts 232 and 234. Further, in order for the optical device 202 to generate light, operating power can be applied to the optical device 202 across the metal contacts 234 and 235.

[0039] For example, during operation, power (e.g., an operating voltage) may be applied to the optical device 202 across the metal contacts 234 and 235. The application of the operating voltage may cause light to be generated through the optical gain region 236. At least a portion of the generated light may be confined in the waveguide region 207, the first buffer semiconductor region 208, and the optical gain region 236. This confinement of light in the waveguide region 207 (also referred to as modal overlap) allows efficient coupling to passive regions where the first buffer semiconductor region 208 is etched away to create a laser mirror (not shown), or to other devices composed entirely of silicon in a photonic integrated circuit, such as waveguides, modulators, detectors, multiplexers, demultiplexers, etc.

[0040] The waveguide integrated capacitor 206 helps monitor the light confined to the waveguide region 207 without using any external photodiode or other device (such as, a beam splitter). In order to monitor the light emitted by the light emitting structure 204, a reference voltage is applied to the second contact region 230, and the current flowing through the first contact region is measured. As previously described, the photon absorption site 226 can absorb photons and cause the generation of free charge carriers related to the intensity of the optical signal impinging thereon inside the waveguide region 207. The conductance of the waveguide region 207 depends on the amount of free charge carriers, so that an increase in the optical signal causes the conductance of the waveguide region 207 to increase. Therefore, the current flowing through the waveguide integrated capacitor 206 can change. The change in current is proportional to the change in conductance of the waveguide region, which indicates the light emitted by the light emitting structure. As will be appreciated, the use of a waveguide integrated capacitor (such as, the waveguide integrated capacitor 206) can help detect light within an optical device without the need to divert any portion of the light outside the waveguide region 207. Further, in some examples, the use of waveguide integrated capacitors can eliminate the need for a separate photodiode to monitor light, thereby making the proposed optical system compact in footprint and reduced in complexity. In addition, in some examples, tasks such as operational monitoring and debugging can be easily performed in the proposed optical system by using waveguide integrated capacitors in optical components and using common monitoring circuits.

[0041] Go to Figure 3 , depicting a top view 300 of an example optical device 302. Optical device 302 is a linear light source (e.g., a laser). Optical device 302 may be an example representative of optical device 202 and may include Figure 2 One or more material regions similar to the material regions described for optical device 202 in FIG. 1 are shown in FIG. 1 for simplicity of illustration. Figure 3 Not all such regions are depicted in FIG. In some examples, instead of having a continuous contact region (such as along Figure 2 In the embodiment of the present invention, the contact area 228 is circumferential to the waveguide area 207, and the contact area can be divided into multiple segments to allow the light intensity to be monitored at corresponding positions inside the optical device 302. For example, the optical device 302 may include contact areas such as contact areas 304, 306 and contact area segments 308A, 308B, and 308C. For illustration purposes, Figure 3 In the top view 300 of FIG. 302 , contact regions 304, 306, waveguide region 307, and contact region segments 308A, 308B, and 308C are depicted. Although the optical device 302 is shown as including three contact region segments 308A-308C, it is contemplated within the scope of the present disclosure to use a fewer or greater number of contact region segments. The optical device 302 may have contact regions 304, 306, waveguide region 307, and contact region segments 308A, 308B, and 308C at several locations along the length “L” of the optical device 302. Figure 2 , more specifically, when taken at the locations of contact area segments 308A, 308B, and 308C. For example, a cross section of optical device 302 taken at example location 3-3 along contact area segment 308B may appear similar to Figure 2 2. Furthermore, the optical device 302 may include metal contacts (not shown) disposed in contact with each of the contact regions 304, 306 and the contact region segments 308A-308C.

[0042] Contact areas 304 and 306 are Figure 2 304 is provided along the length of the optical device 302 to contact a first buffer semiconductor region (not shown) of a waveguide integrated capacitor of the optical device 302. The contact region 306 is provided above a second buffer semiconductor region (similar to the second buffer semiconductor region 238, not shown) of the light emitting structure of the optical device 302. Further, the contact region segments 308A-308C represent Figure 2 In particular, the contact region segments 308A-308C are physically and / or electrically isolated from each other and are disposed above the waveguide region 307.

[0043] In one example, to measure light inside the optical device 302, a reference sinusoidal voltage may be applied to the contact region 304, and the current flowing through one or more of the contact region segments 308A-308C may be monitored via a monitoring circuit (not shown). As previously described, in a similar manner to that described with reference to the waveguide region 207, changes in light intensity inside the waveguide region 307 may also cause changes in the conductance of the waveguide region 307. Thus, the current flowing through the waveguide integrated capacitor of the optical device 302 may vary. The change in current is proportional to the change in conductance of the waveguide region 307, which is indicative of light emitted by the light emitting structure. Measurement of the current through the contact region segments 308A-308C may indicate the intensity of light included inside the waveguide region at the location of the corresponding contact region segment.

[0044] Reference now Figure 4 , presents a top view 400 of an example optical device 402. Optical device 402 may be a ring light source (e.g., a ring laser). Optical device 402 may be an example representative of optical device 202 and may include Figure 2 One or more material regions similar to the material regions described for optical device 202 in FIG. 1 are shown in FIG. 1 for simplicity of illustration. Figure 4 Not all such areas are depicted. Figure 4In the example implementation shown in , an optical device 402 is shown to include a coupling waveguide 401 and a ring laser waveguide 403. The coupling waveguide 401 may be disposed adjacent to and evanescently coupled to the ring laser waveguide 403. The coupling waveguide 401 may include output ports 405A and 405B. Light generated in the ring laser waveguide 403 may be coupled into the coupling waveguide 401 and may be supplied to other optical devices (not shown) via one or both of the output ports 405A and 405B. In some examples, the ring laser waveguide 403 may include a waveguide integrated capacitor (such as, Figure 2 406) to detect the light intensity inside the ring laser waveguide 403. In some examples, both the coupling waveguide 401 and the ring laser waveguide 403 may include a waveguide integrated capacitor.

[0045] With Figure 3 In a similar manner as described in , in optical device 402, one or more of the contact regions may be segmented into multiple segments to allow monitoring of light intensity at corresponding locations within optical device 402. For example, optical device 402 may include contact regions such as contact regions 404, 406 and contact region segments 408A, 408B, and 408C. Instead of having a single contact region such as along Figure 2 The optical device 402 includes contact area segments 408A, 408B, and 408C. For illustration purposes, Figure 4 In the top view 400 of the ring laser waveguide 403, contact regions 404, 406, waveguide region 407, and contact region segments 408A, 408B, and 408C are depicted. Although the optical device 302 is shown as including three contact region segments 408A-408C, it is contemplated within the scope of the present disclosure to use a fewer or greater number of contact region segments. The optical device 402 may also have contact regions 404, 406, waveguide region 407, and contact region segments 408A, 408B, and 408C at several locations along the annulus of the ring laser waveguide 403. Figure 2 , more specifically, when taken at the locations of contact area segments 408A, 408B, and 408C. For example, a cross section of optical device 402 taken at example location 4-4 along contact area segment 408B may appear similar to Figure 2 2. Furthermore, the optical device 402 may include metal contacts (not shown) disposed in contact with each of the contact regions 404, 406 and the contact region segments 408A-408C.

[0046] Contact areas 404 and 406 are Figure 24. The contact regions 404 and 406 are representative of the example of contact regions 230 and 231 of the optical device 402 and are arranged in a similar manner to the contact regions 230 and 231. In particular, the contact region 404 is arranged to contact the first buffer semiconductor region (not shown) of the waveguide integrated capacitor of the optical device 402 along the annulus of the optical device 402. Further, the contact region 406 is arranged above the second buffer semiconductor region (similar to the buffer semiconductor region 238, not shown) of the light emitting structure of the optical device 402. Further, the contact region segments 408A-408C represent Figure 2 In particular, the contact region segments 408A-408C are physically isolated from each other and are disposed above the waveguide region 407 along the circumference of the waveguide region 407.

[0047] In one example, to measure light inside the optical device 402, a reference sinusoidal voltage may be applied to the contact region 404, and the current through one or more of the contact region segments 408A-408C may be monitored via a monitoring circuit (not shown). As previously described, in a similar manner as described with reference to the waveguide region 207, changes in light intensity inside the waveguide region 407 may also cause changes in the conductance of the waveguide region 407. As a result, the current flowing through the waveguide integrated capacitor of the optical device 402 may vary. The change in current is proportional to the change in conductance of the waveguide region, which is indicative of light emitted by the light emitting structure. Measurement of the current through the contact region segments 408A-408C may indicate the intensity of light included inside the waveguide region at the location of the corresponding contact region segment.

[0048] Figure 5 Depicted is a cross-sectional view 500 of an optical device 502 according to an example. Figure 5 The optical device 502 may represent Figure 2 An example of an optical device 202 and may include one or more aspects of Figure 2 For the sake of brevity, one or more structural elements similar to those described in the above description will not be repeated herein. Figure 5 , the optical device 502 is shown to include a light emitting structure 504, a waveguide integrated capacitor 506, a waveguide region 507, a first buffer semiconductor region 508, an insulating layer 510, a substrate 512 (having a base substrate layer 516, a base oxide layer 514 and a device layer 518), a non-waveguide region 509, contact regions 528, 530, and metal contacts 532, 534.

[0049] Further, the light emitting structure 504 may include an optical gain region 536, a second buffer semiconductor region 538, a contact region 531, and a metal contact 535. The waveguide region 507 and the non-waveguide region 509 are formed in the device layer 518 of the substrate 512. The waveguide region 507 includes a Figure 2 The light emitting structure 504 may be formed on at least a portion of the first buffer semiconductor region 508. In particular, the light emitting structure 504 may be formed on a surface of the first buffer semiconductor region 508 above the waveguide region 507.

[0050] exist Figure 5 In the example of FIG. 5 , the optical gain region 536 in the light emitting structure 504 includes a quantum well structure. Figure 5 , the optical gain region 536 is shown to include a quantum well region 540. In particular, the quantum well region 540 is made of several III-V layers of different composition and doping to provide lateral carrier (electron and hole) confinement, and is also referred to as separate confinement heterostructures (SCH) and quantum wells (QW) or active regions. In the quantum well region 540, carriers are confined in one dimension but can move in the other two dimensions. The carrier distribution in the quantum well region 540 caused by the current through the optical gain region 536 promotes light generation or optical gain at wavelengths close to the band gap of the material constituting the quantum well region 540.

[0051] Figure 6 A cross-sectional view 600 of an example optical device 602 is depicted. Figure 6 The optical device 602 may represent Figure 2 An example of an optical device 202 and may include one or more aspects of Figure 2 For the sake of brevity, one or more structural elements similar to those described in the above description will not be repeated herein. Figure 6, an optical device 602 is shown to include a light emitting structure 604, a waveguide integrated capacitor 606, a waveguide region 607, a first buffer semiconductor region 608, an insulating layer 610, a substrate 612 (having a base substrate layer 616, a base oxide layer 614, and a device layer 618), a non-waveguide region 609, contact regions 628, 630, and metal contacts 632, 634. The light emitting structure 604 may include an optical gain region 636, a second buffer semiconductor region 638, a contact region 631, and a metal contact 635. The waveguide region 607 and the non-waveguide region 609 are formed in the device layer 618 of the substrate 612. The waveguide region 607 may include a substrate similar to Figure 2 The light emitting structure 604 may be formed on at least a portion of the first buffer semiconductor region 608. In particular, the light emitting structure 604 may be formed on a surface of the first buffer semiconductor region 608 above the waveguide region 607.

[0052] exist Figure 6 In the example of FIG. 6 , the optical gain region 636 in the light emitting structure 604 includes a quantum dot structure. Figure 3 6, the optical gain region 636 is shown to include a quantum dot region 640. The quantum dot region 640 is made of several III-V layers of different composition and doping to provide lateral carrier (electron and hole) confinement, and is also referred to as SCH, quantum dot, or active region. In particular, the quantum dot region 640 is confined in three dimensions and has a discrete energy spectrum like an atom. The carrier distribution in the quantum dot region 640 caused by the current through the optical gain region 636 promotes light generation or optical gain at wavelengths close to the band gap of the material constituting the quantum dot region 640.

[0053] Figure 7 An example optical system 700 is presented. Optical system 700 may include an optical device capable of generating light, such as optical device 202, and monitoring circuitry 702 to monitor light inside optical device 100. In some examples, without limiting the scope of the present disclosure, optical system 700 may include more than one optical device.

[0054] As previously described, the optical device 202 includes a light emitting structure 204 that generates light, and a waveguide integrated capacitor 206 that helps detect the intensity of light inside the optical device 202 without extracting the light outside the waveguide region 207. When a voltage is applied across the waveguide integrated capacitor 206, the photon absorption site 226 may cause the generation of free charge carriers that are related to the intensity of the optical signal inside the optical device. As will be appreciated, the generation of free charge carriers may cause a change (e.g., an increase) in the conductance of a given region (e.g., the waveguide region 207) within the corresponding optical component. The change in conductance of the given region may cause a change in the current passing through the given region, which change in current may be monitored by the monitoring circuit 702.

[0055] The monitoring circuit 702 may be electrically coupled to the waveguide integrated capacitor 206 at one or more monitoring sites. In some examples, the monitoring circuit 702 may cause the waveguide integrated capacitor 206 to generate an electrical signal indicating the light intensity at the monitoring point. To achieve the generation of the electrical signal, in some examples, the monitoring circuit 702 may include a lock-in amplifier 708 and a preamplifier 710. In some examples, the lock-in amplifier 708 may generate a reference variable voltage signal, such as a sinusoidal signal. For a given waveguide integrated capacitor, the lock-in amplifier 708 may determine the frequency of the reference variable voltage signal based on the conductance of the waveguide region in the given waveguide integrated capacitor and the capacitance of the given waveguide integrated capacitor. In one example, the lock-in amplifier 708 may determine the frequency (F0) of the reference variable voltage signal based on the example relationship of equation (1).

[0056]

[0057] Among them, G WG represents the conductance of the waveguide region 207 in the given waveguide integrated capacitor, and C represents the capacitance of the given waveguide integrated capacitor 206. In some other examples, the frequency (F0) of the reference variable voltage signal may be set to be greater than any value of .

[0058] The monitoring circuit 702 may apply a reference variable voltage signal having a frequency F0 to the waveguide integrated capacitor 206. As previously described, the conductance of the waveguide region 207 may vary depending on the intensity of the optical signal therein. Therefore, the current flowing through the waveguide region 207 may also vary. In particular, the magnitude of the current generated by the waveguide integrated capacitor 206 may be affected by the light intensity inside the waveguide region 207 because the conductance of the waveguide region at the monitoring site varies due to the presence of carriers generated by the absorption of photons at the photon absorption site 226.

[0059] The monitoring circuit 702 may measure an electrical signal (e.g., current) passing through the waveguide integrated capacitor 206, which in turn represents the intensity of light included inside the waveguide region 207. In some examples, the intensity of the current received by the monitoring circuit 702 from the waveguide integrated capacitor 206 may be weak. The preamplifier 710 may amplify the current for further processing by the lock-in amplifier 708.

[0060] Figure 8 A block diagram of an example multi-chip module 800 is depicted. In some examples, the multi-chip module 800 is implemented as a subsystem within an electronic system, such as, but not limited to, a computer (fixed or portable), a server, a storage system, a wireless access point, a network switch, a router, a docking station, a printer, or a scanner. Such an electronic system may be provided as a standalone product, a packaged solution, and may be utilized on a one-time complete product / solution purchase or a pay-per-use or consumption basis. In an example embodiment, the multi-chip module may include at least one electronic chip (such as, electronic chip 802) and at least one photonic chip (such as, photonic chip 804) mounted on a circuit board 806. The circuit board 806 may be a printed circuit board (PCB) including a plurality of conductive traces (not shown) to interconnect the electronic chip 802 and the photonic chip 804 to each other and to other components disposed on or outside the circuit board 806. Non-limiting examples of electronic chip 802 may include IC chips, such as but not limited to application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), processor chips (e.g., central processing units and / or graphics processing units), memory chips, wireless communication module chips, power supply chips or modules, electronic devices (e.g., capacitors, inductors, resistors, etc.). In one example, electronic chip 802 may be configured to operate as a photon controller. During operation of multi-chip module 800, electronic chip 802 may be configured to send data and / or control signals to photon chip 804 and receive data and / or control signals from photon chip 804.

[0061] The photonic chip 804 may include one or more optical devices, such as, but not limited to, optical detectors, optical filters, optical cables, waveguides, optical modulators, light sources (e.g., lasers), etc. The photonic chip 804 may be used as an optical receiver, optical transmitter, optical transceiver, optical communication, and / or processing medium for data and control signals received from the electronic chip. In some examples, for example, the photonic chip 804 may include, for example, Figure 2804, for the sake of brevity, the description of the optical device 202 is not repeated herein. It is also contemplated within the scope of the present disclosure to use other optical devices in the photonic chip 804, such as the optical devices 102, 302, 402, 502, or 602. Further, in some examples, the electronic chip 802 may also be used as a monitoring circuit (such as, Figure 7 802) to monitor light inside the optical device 202 of the photonic chip 804. In some other examples, the multi-chip module 800 may include additional electronic chips or circuits used as the monitoring circuit 702.

[0062] Fig. 9 Describes forming an optical device (such as, Figure 1 For illustration purposes, in conjunction with Figure 1 Method 900 is described herein, however, the method steps described herein may also be applied to the other example optical devices described above.

[0063] At box 902, a substrate is provided. In one example, the substrate can be an SOI substrate. Further, at box 904, the substrate can be used to form a waveguide integrated capacitor, such as waveguide integrated capacitor 106, wherein the waveguide integrated capacitor can include a waveguide region that includes one or more photon absorption sites. The photon absorption sites can be defects in the bulk of the material of the waveguide region, surface defects at the boundary of the waveguide region, or both. In some examples, the photon absorption sites can be caused by defects in the manufacturing process. In some examples, the photon absorption sites can be intentionally created. Further, at box 906, a light emitting structure (such as light emitting structure 104) can be formed above the waveguide integrated capacitor, wherein the light emitting structure emits light when electricity is applied to the optical device. Additional details of forming waveguide integrated capacitors and light emitting structures are combined Fig.10 The waveguide region includes at least a portion of the light generated by the light emitting structure, and the photon absorption sites cause the generation of free charge carriers related to the intensity of the light confined in the waveguide region, resulting in a change in the conductance of the waveguide region.

[0064] Reference now Fig.10 , forming an optical device (such as Figure 2 Example method 1000 of an optical device 202 (for illustration purposes, in conjunction with Figure 2 Method 1000 is described herein, however, the method steps described herein may also be applied to the other example optical devices described above.

[0065] At block 1002, a substrate, such as substrate 212, may be provided. Substrate 212 may be a SOI substrate having a base substrate layer 216, a base oxide layer 214, and a device layer 218. Further, at block 1004, substrate 212 may be used to form a waveguide integrated capacitor, such as waveguide integrated capacitor 206. In one example, forming waveguide integrated capacitor 206 may include, at block 1006, forming a waveguide region 207 and a non-waveguide region 209 into substrate 212. As previously described, in some examples, defects are intentionally formed into waveguide region 207 to have photon absorption sites, such as photon absorption site 226. In some cases, photon absorption site 226 is caused by a defect in a manufacturing process. Further, in some examples, waveguide region 207 may be lightly doped to achieve a first type of doping. In particular, the waveguide region 207 and the non-waveguide region 209 may be formed by photolithographically defining and masking areas for the waveguide region 207 and the non-waveguide region 209, and then chemically and / or mechanically etching the unmasked areas. Further, forming the waveguide integrated capacitor 206 may include: at box 1008, forming an insulating layer 210 over the waveguide region 207 and the non-waveguide region 209. For example, the insulating layer 210 may be formed using a thermal growth technique and / or using a deposition technique, such as chemical vapor deposition (CVD). In addition, forming the waveguide integrated capacitor 206 may include: at box 1010, forming a first buffer semiconductor region 208 over the insulating layer 210 using a thermal growth technique and / or using a deposition technique (such as, for example, CVD) or wafer bonding.

[0066] Furthermore, in some examples, method 1000 may include, at block 1012, forming a light emitting structure (such as light emitting structure 204) over waveguide integrated capacitor 206. Light emitting structure 204 may be formed by forming an optical gain region (such as optical gain region 236) and a second buffer semiconductor region (such as buffer semiconductor region 238). For example, at block 1014, optical gain region 236 may be formed over first buffer semiconductor region 208. As described earlier, optical gain region 236 may include a quantum well structure (see Figure 5 ) or quantum dot structures (see Figure 6 In particular, in some examples, an optical gain region 236 may be formed on a top surface of the first buffer semiconductor region 208 above the waveguide region 207 using techniques such as, but not limited to, thermal growth or CVD, wafer bonding, molecular beam epitaxy (MBE), for example. Further, at block 1016, a second buffer semiconductor region 238 may be formed above the optical gain region 236 using similar techniques used to form the first buffer semiconductor region 208.

[0067] In addition, in some examples, at block 1018, one or more contact regions, such as contact regions 228, 230, and 231, may be formed. Contact regions 228, 230, and 231 may be formed using techniques such as, but not limited to, thermal growth and / or CVD, wafer bonding, MBE, and doping with corresponding impurities. For example, contact regions 228 and 231 are doped to include a first type of doping, and contact region 230 is doped to include a second type of doping. Further, in some examples, at block 1020, metal contacts, such as metal contacts 232, 234, and 235, are formed over contact regions 228, 230, and 231, respectively.

[0068] The terms used herein are for the purpose of describing a specific example, and are not intended to be limited. Unless the context clearly indicates otherwise, the singular forms "one", "a kind of" and "the" as used herein are intended to also include plural forms. The term "another" as used herein is defined as at least the second or more. Unless otherwise indicated, the term "coupled to" as used herein is defined as connected, whether it is a direct coupling without any intervening element or an indirect coupling using at least one intervening element. For example, two elements may be coupled to each other mechanically, electrically, optically, or communicated through a communication channel, path, network or system. Further, the term "and / or" as used herein refers to and encompasses any and all possible combinations of associated enumerated items. It will also be understood that although the terms first, second, third, etc. can be used to describe various elements in this article, these elements should not be limited by these terms, because unless otherwise stated or the context indicates otherwise, these terms are only used to distinguish one element from another element. As used herein, the term "includes" means including but not limited to, and the term "including" means including but not limited to. The term "based on" means based at least in part on.

[0069] Although certain embodiments have been shown and described above, various changes may be made to form and details. For example, some features and / or functions described with respect to one embodiment and / or process may be relevant to other embodiments. In other words, the process, features, components and / or properties described with respect to one embodiment may be useful in other implementations. In addition, it should be understood that the systems and methods described herein may include various combinations and / or sub-combinations of components and / or features of the different embodiments described. In addition, the method blocks described in the various methods may be executed in series, in parallel, or in combination with series and in parallel. Further, the method blocks may also be executed in a different order than that depicted in the flow chart.

[0070] Further, in the foregoing description, numerous details are set forth to provide an understanding of the subject matter disclosed herein. However, embodiments may be practiced without some or all of these details. Other embodiments may include modifications, combinations, and variations of the details discussed above. The appended claims are intended to cover such modifications and variations.

Claims

1. An optical device, comprising: a light emitting structure for emitting light when electricity is applied to the optical device; a waveguide integrated capacitor formed below the light emitting structure to monitor light emitted by the light emitting structure, wherein the waveguide integrated capacitor includes a waveguide region that carries at least a portion of the light, and wherein the waveguide region includes one or more photon absorption sites for absorbing photons of the portion of the light carried in the waveguide region and causing generation of free charge carriers related to the intensity of the light confined in the waveguide region based on the absorbed photons, thereby causing a change in conductance of the waveguide region that is proportional to the intensity of the portion of the light carried in the waveguide region; and a monitoring circuit configured to monitor the intensity of light emitted by the light emitting structure without extracting the light outside the optical device, the monitoring circuit configured to apply a reference voltage to the waveguide integrated capacitor and the waveguide region and measure a current flowing through the waveguide region, wherein a change in the current is proportional to a change in conductance of the waveguide region, the change in conductance indicating the intensity of light confined in the waveguide region.

2. The optical device according to claim 1, wherein: The waveguide integrated capacitor further comprises a first contact region comprising a first type of doping and arranged in contact with the waveguide region.

3. The optical device according to claim 2, wherein: The waveguide integrated capacitor further includes a first buffer semiconductor region, and an insulating layer disposed between the waveguide region and the first buffer semiconductor region.

4. The optical device according to claim 3, wherein: The waveguide region includes a first type of doping and the first buffer semiconductor region includes a second type of doping.

5. The optical device according to claim 3, wherein: The waveguide integrated capacitor further includes a second contact region including a second type of doping and arranged in contact with the first buffer semiconductor region.

6. The optical device according to claim 5, wherein: In order to monitor the light emitted by the light emitting structure without extracting the light outside the optical device, a reference voltage is applied to the second contact area and a current flowing through the first contact area is measured, wherein a change in the current is proportional to a change in the conductance of the waveguide area, and the change in conductance is indicative of the light emitted by the light emitting structure.

7. The optical device according to claim 1, wherein: The waveguide integrated capacitor further includes a plurality of physically isolated contact region segments disposed in contact with the waveguide region.

8. The optical device according to claim 1, wherein: The light emitting structure comprises: an optical gain region formed above the waveguide integrated capacitor; and A second buffer semiconductor region is formed above the optical gain region.

9. The optical device according to claim 8, wherein: The optical gain region includes a quantum well structure.

10. The optical device according to claim 8, wherein: The optical gain region includes a quantum dot structure.

11. The optical device according to claim 1, wherein: The one or more photon absorption sites include at least one of a crystal defect in the bulk of the material of the waveguiding region and a surface defect at a boundary of the waveguiding region.

12. A multi-chip module, comprising: Electronic chips; as well as A photonic chip coupled to the electronic chip so as to be communicatively coupled with the electronic chip, the photonic chip comprising an optical device, the optical device comprising: a light emitting structure including an optical gain region to emit light when electricity is applied to the optical device; and a waveguide integrated capacitor formed below the light emitting structure to monitor light emitted by the light emitting structure, wherein the waveguide integrated capacitor comprises: a waveguide region, the waveguide region carrying at least a portion of the light, a first buffer semiconductor region; an insulating layer, the insulating layer being disposed between the waveguide region and the first buffer semiconductor region, wherein the waveguide region comprises one or more photon absorption sites, the one or more photon absorption sites causing generation of free charge carriers related to the intensity of light confined in the waveguide region, thereby causing a change in the conductance of the waveguide region; and a monitoring circuit coupled to the photonic chip to monitor the intensity of light inside the optical device without diverting any portion of the light outside the waveguide region, the monitoring circuit being configured to apply a reference voltage to the waveguide integrated capacitor and the waveguide region and measure a current flowing through the waveguide region, wherein a change in the current is proportional to a change in conductance of the waveguide region, the change in conductance being indicative of the intensity of light confined in the waveguide region.

13. The multi-chip module according to claim 12, wherein: The waveguide integrated capacitor further comprises: a first contact region comprising a first type of doping and disposed over the waveguide region; and A second contact region includes a second type of doping and is disposed over the first buffer semiconductor region.

14. The multi-chip module according to claim 12, wherein: The waveguide integrated capacitor further comprises: a physically isolated plurality of contact region segments of a first contact region, the first contact region comprising a first type of doping and being disposed over the waveguide region; and A second contact region includes a second type of doping and is disposed over the first buffer semiconductor region.

15. The multi-chip module according to claim 12, wherein: The optical gain region includes a quantum well structure or a quantum dot structure.

16. The multi-chip module according to claim 12, wherein: The light emitting structure further includes a second buffer semiconductor region formed over the optical gain region.

17. A method of forming an optical device, comprising: providing a substrate; forming a waveguide integrated capacitor using the substrate, wherein the waveguide integrated capacitor comprises a waveguide region, the waveguide region comprising one or more photon absorption sites; forming a light emitting structure over the waveguide integrated capacitor, wherein the light emitting structure is configured to emit light when electricity is applied to the optical device, wherein the waveguide region includes at least a portion of the light generated by the light emitting structure, and the one or more photon absorption sites absorb photons of the portion of the light carried in the waveguide region and cause generation of free charge carriers related to the intensity of the light confined in the waveguide region based on the absorbed photons, thereby resulting in a change in conductance of the waveguide region, the change in conductance being proportional to the intensity of the portion of the light carried in the waveguide region; and A monitoring circuit is provided, the monitoring circuit being configured to monitor the intensity of light emitted by the light emitting structure without extracting the light outside the optical device, the monitoring circuit being configured to apply a reference voltage to the waveguide integrated capacitor and the waveguide region and measure a current flowing through the waveguide region, wherein a change in the current is proportional to a change in conductance of the waveguide region, the change in conductance being indicative of the intensity of light confined in the waveguide region.

18. The method according to claim 17, wherein: Forming the waveguide integrated capacitor comprises: forming the waveguide region into the substrate; forming an insulating layer over the waveguide region; and A first buffer semiconductor region is formed over the insulating layer.

19. The method according to claim 18, wherein: Forming the light emitting structure above the waveguide integrated capacitor comprises: forming an optical gain region over the first buffer semiconductor region; and A second buffer semiconductor region is formed over the optical gain region.

20. The method according to claim 19, wherein: The optical gain region includes a quantum well structure or a quantum dot structure.

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