Abstract:
A photonic integrated circuit including: at least one photonic component being suitable for operation with a plurality of photons and including an operational material having a bandgap energy close to the energy of the photons; and, at least one photonic component being suitable for operation with the plurality of photons, including an operational material having a bandgap energy substantially higher than the photons and being adjacent to the at least one photonic component including an operational material having a bandgap energy close to the energy of the photons. The at least one photonic component including an operational material having a bandgap energy substantially higher than the photons includes at least one amorphous silicon based alloy material.

Description:
RELATED APPLICATION  
       [0001]    This Application claims priority of U.S. Patent application Ser. No. 60/287,277, filed Apr. 27, 2001, entitled DISC/RING RESONATOR IR DETECTOR FOR PHOTONIC COMMUNICATIONS, the entire disclosure of which is hereby incorporated by reference as if being set forth in its entirety herein. 
     
    
     
       FIELD OF INVENTION  
         [0002]    The present invention relates generally to Photonic Integrated Circuits (PICs) and methods for making the same.  
         BACKGROUND OF THE INVENTION  
         [0003]    The use of Photonic Integrated Circuits (PICs) including III-V semiconductor compound photonic components or devices is desirable. Such circuits may be monolithic in nature. One example of such a PIC may take the form of an optical crossconnect including a large number of channel counts.  
           [0004]    Coupling between active and passive components represents a fundamental difficulty to be overcome in integrating guided-wave photonic devices into PICs. Active components are those that generally require the bandgap of the operational material be close to the photon energy, such as a laser diode, a semiconductor optical amplifier (SOA) or an electroabsorption modulator, for example. Passive components generally exhibit a bandgap energy of an operational material to be substantially higher than a propagating photon, and may take the form of a waveguide based connector, splitter, coupler, optoelectronic switch or wavelength filtering element or wavelength selective element, such as a demultiplexer, for example.  
           [0005]    Integration of active and passive components generally requires use of different materials. However, because of stringent lattice matching requirements for crystalline materials, integration of heterogeneous materials with different optical properties may be difficult.  
           [0006]    Existing approaches to integrating active and passive components are believed to generally not be effective, leading to poor coupling and high losses, for example. As a result, efforts in integrating a large number of optoelectronic functions on a single chip may be problematic, particularly in telecommunications devices, for example.  
           [0007]    Two general approaches include butt coupling and directional coupling. In butt coupling, the waveguide core stack may be selectively removed using chemical etching for example. An aligned passive waveguide structure may then be regrown. Drawbacks of such joints include the use of the growth step, in addition to difficulties associated with reproducing joint geometries, for example. Alternatively, a largely continuous passive waveguide structure having an active layer formed thereon may be used. The active layer may be selectively etched away in those portions intended to be passive.  
           [0008]    Alternatively, a selective area growth (SAG) process leveraging differences in growth rates and masks may be used.  
           [0009]    In vertical directional coupling, coupling between different epitaxial layers in the vertical plane serving as distinct waveguides may be utilized. Nonetheless, it is believed that each of these methods exhibits shortcomings. For example, the use of epitaxial growth in a manufacturing process limits choices of suitable materials. Losses at coupling points, such as butt joint interfaces, are typically significant, on the order of approximately 2-3 dB/interface for example. Further, typically realized poor manufacturing yields, that may be on the order of about 20%, also lead to high costs associated with these techniques.  
           [0010]    Accordingly, it is highly desirable to provide PICs including active and passive devices and methods for making for them.  
         SUMMARY OF INVENTION  
         [0011]    A photonic integrated circuit including: at least one photonic component being suitable for operation with a plurality of photons and including an operational material having a bandgap energy close to the energy of the photons; and, at least one photonic component being suitable for operation with the plurality of photons, including an operational material having a bandgap energy substantially higher than the photons and being adjacent to the at least one photonic component including an operational material having a bandgap energy close to the energy of the photons; wherein, the at least one photonic component including an operational material having a bandgap energy substantially higher than the photons includes at least one amorphous silicon based alloy material. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0012]    Understanding of the present invention will be facilitated by consideration of the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, wherein like numerals refer to like parts and in which:  
         [0013]    [0013]FIG. 1 illustrates a cross-sectional view of an a-Si material/III-V active device heterogeneous integration according to an aspect of the present invention;  
         [0014]    [0014]FIG. 2 illustrates a chart presenting achievable refractive indices as a function of a ratio of CH 4  to SiH 4  used in a PECVD process to form a waveguide material including a-SiC x  using conventional techniques;  
         [0015]    [0015]FIG. 3 illustrates a chart presenting achievable refractive indices as a function of a ratio of N 2  to SiH 4  used in a PECVD process to form a waveguide material including a-SiN x  using conventional techniques;  
         [0016]    [0016]FIG. 4 illustrates a PIC according to an aspect of the present invention;  
         [0017]    [0017]FIG. 5 illustrates a typical modal loss as a function of core index; and,  
         [0018]    FIGS.  6 - 9  illustrate some non-limiting examples of possibilities for Photonic Integrated Circuits (PICs) according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other elements found in typical photonic devices, Photonic Integrated Circuits (PICs), optical waveguides and manufacture methods relating thereto. Those of ordinary skill in the art will recognize that other elements are desirable and/or required in order to implement the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. The disclosure herein is directed to all such variations and modifications to such devices, PICs, waveguides and methods known to those skilled in the art.  
         [0020]    According to an aspect of the present invention, amorphous silicon (a-Si) materials may be used to provide flexible, index matched, low loss waveguide coupling to active and passive device components in a monolithically integrated optoelectronic product. According to an aspect of the present invention, amorphous silicon (a-Si) materials, including a-Si:H and a-Si:F based alloys such as a-SiC x  where 0&lt;x&lt;1, a-SiN y  where 0&lt;y&lt;1.33, a-SiO z  where 0&lt;z&lt;2 and a-SiGe w  where 0&lt;w&lt;1 may be utilized to form waveguides for integrating active and passive components in optoelectronic products. Because of their amorphous nature, a-Si materials do not have the lattice match requirements of crystalline materials. Furthermore, the ability to tune the optical index substantially continuously, from 1.5 to 4 for example, provides for improved index matching and low loss waveguide coupling to active components as compared to conventional techniques.  
         [0021]    According to an aspect of the present invention, a-Si material, such as a-Si:H or a-Si:F alloy based, waveguides may be fabricated using Plasma Enhanced Chemical Vapor Deposition (PECVD), resulting in a low intrinsic optical absorption coefficient (approximately 0.1 cm −1  at 1.55 μm), allowing the development of low-loss waveguide structures. The electronic and optical characteristics of a-Si materials may be altered depending on the waveguide formation method, such as sputtering or PECVD. For example, sputtered a-Si has been generally characterized as having a high density of states in the forbidden band and optical absorption coefficients greater than 10 cm −1  at 1.55 μm. However, PECVD a-Si materials may exhibit lower absorption coefficients in the infrared wavelengths, such as in the range of 1.3 and 1.55 μm.  
         [0022]    In the case of such a-Si materials, optical absorption at an operating wavelength of 1.55 μm is desirably low, leading to low loss and good optical transmission properties as will be understood by those possessing an ordinary skill in the pertinent arts. For example, the absorption coefficient corresponding to a-Si:H may be approximately 0.1 cm −1 , advantageously providing for waveguide losses on the order of approximately 0.5 dB/cm at 1.55 μm, for example.  
         [0023]    Further, by mixing the main gas that undergoes plasma assisted decomposition in the a-Si material PECVD process, such as SiH 4 , with other chemicals, such as CH 4 , CO 2 , N 2 , NH 3  or N 2 O, wider energy gaps may be achieved with lower refractive indices.  
         [0024]    [0024]FIG. 1 illustrates a cross-sectional view of an a-Si/III-V semiconductor active device heterogeneous integration  10  according to an aspect of the present invention. The integration  10  includes a substrate  20 , active device  30 , that may include multiple quantum well (MQW) layer  40 , and a-Si material waveguide  50 .  
         [0025]    Substrate  20  may take the form of any suitable conventional semiconductor substrate such as InP, GaAs or GaN for example or c-Si, which may form a base structure for a PIC. Active device  30  may take the form of a conventional type III-V semiconductor active component or device, such as a semiconductor laser for example. The formation and use of such substrates and active devices are well understood by those possessing an ordinary skill in the pertinent arts.  
         [0026]    Waveguide  50  may be formed of amorphous silicon (a-Si) material, including a-Si:H and a-Si:F based alloys such as a-SiCx where 0&lt;x&lt;1, a-SiN y  where 0&lt;y&lt;1.33, a-SiO z  where 0&lt;z&lt;2 and a-SiGe w  where 0&lt;w&lt;1 thereof. Waveguide  50  may be suitable for use in an operating range such as 1.3 or 1.55 μm. The formation and use of such waveguides is well understood by those possessing an ordinary skill in the pertinent arts.  
         [0027]    For example, waveguide  50  may take the form of an a-Si alloy material layer having a refractive index of approximately 3.4 deposited upon an a-Si alloy material under-cladding layer having a refractive index of approximately 3.2 in turn deposited on a c-Si wafer. The a-Si alloy undercladding layer may be approximately 1 μm thick, while the a-Si:H alloy core may be approximately 0.5 μm thick. An a-Si alloy material layer having a refractive index of approximately 3.2 may be provided as an overcladding layer, and have a thickness of approximately 1 μm for example. The a-Si alloy under- and overcladding may be formed using RF or DC plasma assisted decomposition of SiH 4  or N 2  (see FIG. 4), for example. In the case of N 2 , an N 2  to SiH 4  flow ratio of approximately 0.9 may be used while the substrate temperature is held at approximately 250° C. To form the a-Si alloy core layer, the N 2  to SiH 4  flow ratio may be approximately 0.45, while the substrate temperature is held at approximately 250° C. Processing pressure may be approximately 1.5 torr, while the 13.56-MHz RF power is held approximately at 50 W, for example.  
         [0028]    The waveguide, and core thereof, may be defined using standard photolithographic patterning of the planar amorphous stack and plasma etching, for example. A standard planarization step, such as mechanical polishing may be used to further reduce coupling losses, for example.  
         [0029]    Referring still to FIG. 1, use of a-Si material waveguide  50  in integration  10  provides several advancements in the art. For example, the refractive index of the a-Si waveguide  50  may be readily tuned to be compatible with a variety of III-V semiconductor active components. Further, use of a-Si materials generally provides for ready integration of active type III-V semiconductor devices, low optical coupling loss, the ability to use relatively low temperature processing technologies, as compared to epitaxial growth for example, that may be on the order of 250° C., and the ability to realize relatively low cost, high yield manufacturing processes.  
         [0030]    Referring now to FIG. 2, there is shown a chart illustrating achievable refractive indices as a function of a ratio of CH 4  to SiH 4  used in a PECVD process to form a waveguide including a-SiC x . Referring now also to FIG. 3, there is shown a chart illustrating achievable refractive indices as a function of a ratio of N 2  to SiH 4  used in a PECVD process to form a waveguide material including a-SiN y , Thus, a-Si material waveguide  50  may be formed such as to have a desired refractive index being suitable for use with a particular type III-V semiconductor device, such as device  30  (FIG. 1).  
         [0031]    Referring now to FIG. 4, there is illustrated a PIC  600  according to an aspect of the present invention. PIC  600  generally includes substrate  650  having active device  610  and passive device  620  formed thereon. Substrate  650  may take any suitable form, such as c-Si or suitable semiconductor compound, for example. Active device  610  may take the form of a semiconductor laser, for example, including multiple quantum wells. Device  620  may take the form of a waveguide, such as an a-SiN y  waveguide. Device  610  may include a contact  630  and mirror  640  as is conventionally understood by those possessing an ordinary skill in the pertinent arts.  
         [0032]    According to an aspect of the present invention, the interface between devices  610 ,  620  may be indexed matched as is conventionally understood, and device  620  may provide a low optical absorption consistently with as has been set forth with regard to FIGS.  1 - 3 . Further, a low interface reflection may be achieved and be desirable for use with active component  610 , as for example where the difference in refractive index (Δn)&lt;0.01, reflectivity (R)&lt;10 −5 . Further, use of PECVD for formation of the device  620  provides for improved surface conformation with device  610  at the device  610 ,  620  interface, and low interface scattering loss, as opposed to sputtering for example. For example, referring now to FIG. 5, there is shown a typical modal loss as a function of core index. Referring again to FIGS. 2 and 3, as will be apparent to one possessing an ordinary skill in the pertinent arts, core indexes represented in FIG. 5 may be achieved using SiH 4  and CH 4  or N 2  in a PECVD process.  
         [0033]    Referring to FIGS.  6 - 9  there are shown some non-limiting examples of possibilities for Photonic Integrated Circuits (PICs) according to the present invention.  
         [0034]    Referring now also to FIG. 6, there is shown a block-diagrammatic representation of a monolithically integrated tunable laser module  800  according to an aspect of the present invention. The phase and the distributed Bragg reflector grating regions  810 ,  820  of tunable laser module  800  can be realized using index matched plasma enhanced chemical vapor deposited a-Si material. Additionally, a gain region  830  may be realized using conventional type III-V semiconductor materials, for example.  
         [0035]    Referring now also to FIG. 7, there is shown a waveguide  950  coupled to a transmission source  910 , such as a laser. Coupler  960  is coupled to optical detectors  930 ,  940 . The waveguide  950  and coupler  960  may be made from plasma enhanced chemical vapor deposited a-Si materials, while laser  910  and detectors  930 ,  940  may be made of III-V semiconductor materials as is conventionally understood.  
         [0036]    Referring now also to FIG. 8, there is shown a PIC  1000  according to an aspect of the present invention including a waveguide  1010  coupling laser  1020  and electroabsorption modulator  1030 . Waveguide  1010  may be made from index matched plasma enhanced chemical vapor deposited a-Si material, while laser  1020  and EA modulator  1030  are made of type III-V semiconductor materials, for example.  
         [0037]    Referring now also to FIG. 11, there is shown a general illustration of a PIC  1100  according to an aspect of the present invention. PIC  1100  generally includes a substrate  1105  having active components  1110 , 1120  and passive component  1130  optically coupling devices  1110  and  1120  to one another formed thereon. Substrate  1105  may take the form of c-Si. Active components  1110 ,  1120  may take the form of type III-V semiconductor active devices. Passive component  1130  may take the form of a plasma enhanced chemical vapor deposited amorphous silicon (a-Si) material waveguide, such as a-Si:H and a-Si:F based alloys like a-SiC x  where 0&lt;x&lt;1, a-SiN y  where 0&lt;y&lt;1.33, a-SiO z  where 0&lt;z&lt;2 and a-SiGe w  where 0&lt;w&lt;1. Components  1110 ,  1120  may be formed using conventional techniques. Waveguide  1130  may then be formed using plasma enhanced chemical vapor deposition consistently with as has been set forth herein. As will be recognized by those possessing an ordinary skill in the pertinent art, as lower processing temperatures associated with the formation of waveguide  1130  may be used, as compared to epitaxial growth for example, formation of waveguide  1130  should not adversely effect formed devices  110 ,  1120 .  
         [0038]    It will be apparent to those skilled in the art that various modifications and variations may be made in the apparatus and process of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modification and variations of this invention provided they come within the scope of the appended claims and their equivalents.