Monolithic III-V/Si Waveguide Phase Modulator

Abstract

Example embodiments relate to monolithic III-V/Si waveguide phase modulators. One embodiment includes a monolithic integrated phase modulator that includes a waveguide for propagating light. The waveguide for propagating light includes a waveguide base made of a first conductivity type Si-based semiconductor material. The waveguide for propagating light also includes at least one groove formed in a surface of the waveguide base. Further, the waveguide for propagating light includes an epitaxial region formed on the waveguide base in the at least one groove. The epitaxial region is made of a second conductivity type III-V semiconductor material. The waveguide base and the epitaxial region form a monolithically integrated junction diode that is a phase modulation region for light propagated through the waveguide.

Claims

1. A monolithic integrated phase modulator comprising: a waveguide for propagating light, comprising: a waveguide base made of a first conductivity type Si-based semiconductor material; at least one groove formed in a surface of the waveguide base; and an epitaxial region formed on the waveguide base in the at least one groove, wherein the epitaxial region is made of a second conductivity type III-V semiconductor material, and wherein the waveguide base and the epitaxial region form a monolithically integrated junction diode that is a phase modulation region for light propagated through the waveguide.

2. The monolithic integrated phase modulator according to claim 1, wherein the waveguide further comprises: a plurality of grooves formed in the surface of the waveguide base and arranged one after the other along a light propagation direction of the waveguide; and a plurality of epitaxial regions each made of the second conductivity type III-V semiconductor material, wherein epitaxial regions are formed on the waveguide base in each of the plurality of grooves, and wherein the waveguide base and each of the epitaxial regions form the monolithically integrated junction diode.

3. The monolithic integrated phase modulator according to claim 2, wherein each epitaxial region together with the waveguide base is a separate phase modulation region for the light propagated through the waveguide.

4. The monolithic integrated phase modulator according to claim 2, wherein adjacent grooves are distanced by a subwavelength pitch.

5. The monolithic integrated phase modulator according to claim 2, wherein each epitaxial region is arranged to guide at least a part of the light propagated through the waveguide.

6. The monolithic integrated phase modulator according to claim 2, further comprising: a first lead electrically contacting the waveguide base, wherein the first lead is made of the first conductivity type Si-based semiconductor material; and a second lead electrically contacting each epitaxial region, wherein the second lead is made of a second conductivity type Si-based semiconductor material.

7. The monolithic integrated phase modulator according to claim 6, wherein the second lead comprises a sidewall region of the waveguide that electrically contacts each epitaxial region, and wherein the sidewall region of the waveguide of the second lead is made of the second conductivity type Si-based semiconductor material.

8. The monolithic integrated phase modulator according to claim 7, wherein: the epitaxial region has a doping level between 110.sup.16 cm.sup.3 and 510.sup.18 cm.sup.3; the first conductivity type Si-based semiconductor material has a doping level between 110.sup.17 cm.sup.3 and 110.sup.19 cm.sup.3; or the sidewall region has a doping level between 110.sup.17 cm.sup.3 and 110.sup.19 cm.sup.3.

9. The monolithic integrated phase modulator according to claim 6, wherein each epitaxial region and the waveguide base are arranged to be depleted when the junction diode is reversely biased by applying a reverse potential across the first lead and the second lead.

10. The monolithic integrated phase modulator according to claim 1, wherein the at least one groove is a V-groove or a U-groove.

11. The monolithic integrated phase modulator according to claim 1, wherein at least one sidewall of the at least one groove is arranged along a (111)-facet of the waveguide base.

12. The monolithic integrated phase modulator according to claim 1, wherein the epitaxial region has a doping profile that includes a doping level of the second conductivity type that changes in a direction from a surface of the interface between the epitaxial region and the waveguide base to a further surface of the epitaxial region.

13. The monolithic integrated phase modulator according to claim 12, wherein the doping profile comprises: lower doping levels of the second conductivity type near the interface and near the further surface of the epitaxial region; and a higher doping level of the second conductivity type between the lower doping levels.

14. A method for producing a monolithic integrated phase modulator, comprising: forming a waveguide for propagating light by: forming a waveguide base from a Si-based semiconductor material; doping the waveguide base to be of a first conductivity type; forming at least one groove in a surface of the waveguide base; and epitaxially growing a region of a second conductivity type III-V semiconductor material on the waveguide base in the at least one groove, wherein the waveguide base and the epitaxially grown region form a monolithically integrated junction diode that is a phase modulation region for light propagated through the waveguide.

15. A method of operating a monolithic integrated phase modulator, wherein the monolithic integrated phase modulator comprises: a waveguide for propagating light, comprising: a waveguide base made of a first conductivity type Si-based semiconductor material; at least one groove formed in a surface of the waveguide base; and an epitaxial region formed on the waveguide base in the at least one groove, wherein the epitaxial region is made of a second conductivity type III-V semiconductor material, wherein the waveguide base and the epitaxial region form a monolithically integrated junction diode that is a phase modulation region for light propagated through the waveguide, and wherein the method comprises: propagating light through the waveguide; and reversely biasing the monolithically integrated junction diode to modulate a phase of the light propagated through the waveguide based on a reverse bias potential.

16. The method according to claim 15, wherein the waveguide further comprises: a plurality of grooves formed in the surface of the waveguide base and arranged one after the other along a light propagation direction of the waveguide; and a plurality of epitaxial regions each made of the second conductivity type III-V semiconductor material, wherein epitaxial regions are formed on the waveguide base in each of the plurality of grooves, and wherein the waveguide base and each of the epitaxial regions form the monolithically integrated junction diode.

17. The method according to claim 16, wherein each epitaxial region together with the waveguide base is a separate phase modulation region for the light propagated through the waveguide.

18. The method according to claim 16, wherein adjacent grooves are distanced by a subwavelength pitch.

19. The method according to claim 16, wherein each epitaxial region is arranged to guide at least a part of the light propagated through the waveguide.

20. The method according to claim 16, wherein the monolithic integrated phase modulator further comprises: a first lead electrically contacting the waveguide base, wherein the first lead is made of the first conductivity type Si-based semiconductor material; and a second lead electrically contacting each epitaxial region, wherein the second lead is made of a second conductivity type Si-based semiconductor material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The above described aspects and implementations will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

[0054] FIG. 1 shows a waveguide of a monolithic integrated phase modulator, wherein the waveguide includes a monolithically integrated junction diode, according to example embodiments.

[0055] FIG. 2 shows a monolithic phase modulator, according to example embodiments.

[0056] FIG. 3 shows another monolithic integrated phase modulator, according to example embodiments.

[0057] FIG. 4 shows a carrier density profile in a monolithic integrated phase modulator, with and without reverse bias applied to the leads, according to example embodiments.

[0058] FIG. 5A shows a specific carrier density with and without reverse bias, according to example embodiments.

[0059] FIG. 5B shows a simulated band diagram vertical cut through the waveguide, according to example embodiments.

[0060] FIG. 5C shows an optical mode profile in the waveguide, according to example embodiments.

[0061] FIG. 6A shows a refractive index profile in the waveguide for a specific carrier density profile, according to example embodiments.

[0062] FIG. 6B shows a change of the refractive index and the absorption coefficient, respectively, with a change of the carrier density, according to example embodiments.

[0063] FIG. 7A shows a bias voltage-induced change of the refractive index, according to example embodiments.

[0064] FIG. 7B shows a bias voltage-induced change of a figure of merit of the modulator, according to example embodiments.

[0065] FIG. 8A shows a bias voltage-induced change of phase shifter loss in the light modulation region of the monolithic integrated phase modulator, according to example embodiments.

[0066] FIG. 8B shows a bias voltage-induced change of a figure of merit of the modulator, according to example embodiments.

[0067] FIG. 9 shows a conceptual process flow for producing a monolithic integrated phase modulator, according to example embodiments.

DETAILED DESCRIPTION

[0068] FIG. 1 shows a basic waveguide 11 of a monolithic integrated phase modulator 10 according to example embodiments. FIG. 1 particularly shows only the waveguide 11, since the waveguide 11 includes the core elements of the disclosure. The monolithic integrated phase modulator 10 will be explained in more detail with respect to FIG. 2 and FIG. 3. A possible fabrication flow of the modulator 10 will be explained with respect to FIG. 9.

[0069] The waveguide 11 of the modulator 10 includes a waveguide base 12 and an epitaxial region 13, which is grown within a groove 14 formed in a surface of the waveguide base 12. The waveguide base 12 is made of a first conductivity type Si-based semiconductor material, for instance, p-type Si and/or SiGe. The epitaxial region 13 is made of a second conductivity type III-V semiconductor material, for instance, n-type InP, GaAs, InGaAs, and/or InGaAsP, i.e. the epitaxial region 13 can include either a single- or multi-material stack.

[0070] The groove 14 may be a groove fabricated by etching or another trench formation technique. The groove 14 may be a V-groove or U-groove (as shown in the example of FIG. 1). The epitaxial region 13 is an epitaxially grown region on the waveguide base 12. The epitaxial region 13 and the waveguide base 12 form a monolithically integrated junction diode 15, particularly a p-n junction diode. This is indicated in FIG. 1 by the double-sided arrow across the (p-n) junction of the junction diode 15, i.e. across the interface between the epitaxial region 13 and the waveguide base 12. The junction diode 15 is monolithically integrated in the waveguide 11, because the waveguide base 12 and the epitaxial layer 13 are monolithically formed on top of each other during one and the same process flow.

[0071] The junction diode 15 is arranged to be reversely biased, for instance, by applying a reverse potential to the leads, which contact the waveguide base 12 and the epitaxial region 13, respectively. Possible details of such leads are explained with respect to FIG. 2 and FIG. 3. When the junction diode 15 is biased reversely, depletion regions form in the waveguide base 12 and the epitaxial region 13, particularly starting from the interface. Due to the lower effective mass, depletion regions are stronger in the epitaxial region 13. Because of the change of the electron and hole densities in the junction diode 15, light propagating through the waveguide 11 can be phase modulated based on the above-described effect of plasma dispersion. The III-V epitaxial region 13 makes the phase modulation particularly efficient.

[0072] FIG. 2 shows a monolithic integrated phase modulator 10 according to example embodiments, which includes a waveguide 11 that builds on the basic waveguide 11 shown in FIG. 1. Accordingly, same elements in FIG. 1 and FIG. 2 are labelled with the same reference signs and have likewise functions.

[0073] FIG. 2 shows particularly an X cross section (upper drawing) and a Y cross section (lower drawing) of the modulator 10. In the X-Y-Z coordinate system, it is assumed that Z indicates the growth direction of the modulator 10, particularly of the epitaxial region 13, and that Y indicates the light propagation direction through the waveguide 11.

[0074] The waveguide 11 of the modulator 10 shown in FIG. 2 includes again the epitaxial region 13 grown in the groove 14 on the waveguide base 12. The groove 14 is in FIG. 2, e.g., a V-groove. The sidewalls of the V-groove 14 may be arranged along (111)-facets of the Si-based waveguide base 12.

[0075] As shown in the X cross section, the waveguide 11 further includes a sidewall region 23, which electrically contacts the epitaxial region 13. As can be seen, the sidewall region 23 is a part of the waveguide 11 next to the waveguide base 12 and next to the epitaxial layer 13. The side sidewall region 23 is of the second conductivity type, for instance, with a doping level of between 110.sup.17 cm.sup.3 and 110.sup.19 cm.sup.3, particularly 110.sup.18 cm.sup.3. Notably, at the same time the second conductivity type epitaxial region 13 has a doping level between 110.sup.16 cm.sup.3 and 510.sup.18 cm.sup.3, and the first conductivity type Si-based semiconductor material of the waveguide base 12 has a doping level between 110.sup.17 cm.sup.3 and 110.sup.19 cm.sup.3, particularly 110.sup.18 cm.sup.3.

[0076] As also shown in the X cross section, the modulator 10 further includes a first lead 21 electrically contacting the waveguide base 12 from the side, i.e. laterally along the X direction. Further, the modulator 10 includes a part of a second lead 22 electrically contacting the sidewall region 23 from the side, i.e. laterally along the X direction. In particular, the sidewall region 23 is also a part of the second lead 22 and electrically contacts the epitaxial region 13. The first lead 21 is of the first conductivity type with an example doping level between 110.sup.18 cm.sup.3 and 110.sup.20 cm.sup.3, particularly 110.sup.19 cm.sup.3. The part of the second lead 22 excluding the sidewall region 23 is of the second conductivity type with an example doping level between 110.sup.18 cm.sup.3 and 110.sup.20 cm.sup.3, particularly 110.sup.19 cm.sup.3. That is, this part of the second lead 22 may have a higher doping level then the sidewall region 23.

[0077] Further, metal contacts may be implemented on the first lead 21 and second lead 22, respectively, in order to interface with the modulator 10. For instance, one end of the first lead 21 may contact the waveguide base 12 and one end of the second lead 22 may contact the epitaxial region 13, while the other end of each lead 21, 22 is contacted by a metal contact. The metal contacts particularly extend to a surface of the modulator 10.

[0078] The X cross section also shows that the leads 21 and 22 may each include a thicker region (in Z direction) and a thinner region (in Z direction). The thicker regions can be contacted from the outside of the modulator 10, e.g. a connection between the optical modulator 10 and leads in a packaging thereof may be established. The thinner regions contact the waveguide base 12 and sidewall region 23, respectively.

[0079] Some dimensions of the modulator 10 are shown in FIG. 2, namely a distance d between the thicker regions and the thinner regions of the leads 21 and 22, a thickness t of the thinner regions of the leads 21 and 22, a height h2 of the thicker regions of the lead 21 or lead 22 and the waveguide 11, a width w1 of the waveguide 11, a height h1 between a top surface of the waveguide 11 and a top surface of the thinner regions of the leads 21 and 22, and a width w2 of the sidewall region 23.

[0080] In an example of the modulator 10, d=600-800 nm (e.g. 750 nm), t=50-100 nm (e.g. 70 nm), h2=150-300 nm (e.g. 220 nm), w1=425-525 nm (e.g. 475 nm), h1=100-200 nm (e.g. 150 nm), and/or w2=25-75 nm (e.g. 50 nm).

[0081] As shown in the Y cross section, the modulator 10 of FIG. 2 includes one epitaxial region 13 in one groove 14 formed in the surface of the waveguide base 12, which groove extends along the light propagation direction of the waveguide 11 (Y direction). The epitaxial region 13 and the waveguide base 12 form accordingly one monolithic integrated junction diode 15, which is the (single) light modulation region of the modulator 10. The modulator 10 of FIG. 2 allows modulating the phase of the light propagating through the waveguide 11 in this light modulation region with high-speed and efficiency.

[0082] FIG. 3 shows a monolithic integrated phase modulator 10 according to example embodiments, which builds on the phase modulator 10 shown in FIG. 2, and includes a waveguide 11 that builds on the basic waveguide 11 shown in FIG. 1. Same elements in FIG. 1, FIG. 2, and FIG. 3 are indicated with the same reference signs and have likewise functions.

[0083] FIG. 3 shows, like FIG. 2, an X cross section (upper drawing) and a Y cross section (lower drawing) of the modulator 10. In the X-Y-Z coordinate system, it is again assumed that Z is along the growth direction of the modulator 10, particularly of the epitaxial region 13, and that Y is along the light propagation direction through the waveguide 11.

[0084] In contrast to the monolithic integrated phase modulator 10 shown in FIG. 2, the waveguide 11 of the monolithic integrated phase modulator 10 shown in FIG. 3 includes a plurality of grooves 14 and a plurality of epitaxial regions 13, wherein one epitaxial region 13 is formed on the waveguide base 12 in each of the grooves 14.

[0085] Since the X cross section shown in FIG. 3 is through one particular epitaxial region 13, it is identical to the X cross section shown in FIG. 2. It can be seen that the monolithic integrated phase modulator 10 shown in FIG. 3 also includes the first lead 21 and the second lead 22 having the sidewall region 23. Conductivity types, doping levels, and dimensions as indicated in the X cross section of the modulator 10 shown in FIG. 3, may be the same as described above with respect to the modulator 10 shown in FIG. 2.

[0086] The difference between the modulators 10 shown in FIG. 2 and FIG. 3, respectively, can be seen in the Y cross section. Here, the plurality of grooves 14 formed in the surface of the waveguide base 12, which are arranged one after the other along a light propagation direction of the waveguide 11 (Y direction), and the plurality of epitaxial regions 13 formed in these grooves 14 can be seen. Each epitaxial region 13 forms a monolithically integrated junction diode 15, particularly a p-n junction diode, with the waveguide base 12. It can be seen that each epitaxial region 13 is contacted electrically by the sidewall region 23 of the second lead 22. Thus, a reverse bias can be collectively applied to all junction diodes 15 (accordingly, in this example the diodes 15 may be regarded to be one junction diode 15). It is also be possible to provide separate sidewall regions 23, and thus separate second leads 22, wherein each second lead 22 contacts one epitaxial region or a subset of epitaxial regions 13. Thus, junction diodes 15 could be (reversely) biased independently.

[0087] FIG. 4 shows a carrier density profile in a monolithic integrated phase modulator 10 according to example embodiments, particularly according to the modulator 10 shown in FIG. 1 with an InP epitaxial region 13 and a Si waveguide base 12. The left side of FIG. 4 shows the modulator 10 without reverse bias applied to the leads 21 and 22 (0V), and the right side shows the modulator 10 with a reverse bias applied to the leads 21 and 22 (1.5V). In particular, the zero bias and reverse bias conditions are shown for four different carrier densities of the epitaxial region 13 of the waveguide 11, namely (from top to bottom) N.sub.D=110.sup.18 cm.sup.3, 510.sup.17 cm.sup.3, 110.sup.17 cm.sup.3 and 110.sup.16 cm.sup.3. The carrier density distribution in the waveguide 11 is shown in grey shading according to the key shown on the rightmost side of FIG. 4.

[0088] The carrier profiles are derived by electrical simulations of the modulator 10, in order to demonstrate the concept of the disclosure. As shown, the reverse bias is able to deplete the InP epitaxial region 13 and the waveguide base 12 in the III-V/Si monolithic junction diode 15, specifically at its III-V/Si interface. This depletion through reverse biasing can modulate the light propagating through the waveguide 11. In particular, FIG. 4 shows that at carrier densities of N.sub.D=110.sup.18 cm.sup.3 (in FIG. 4 the notation 1E18 cm.sup.3 is used), and N.sub.D=510.sup.17 cm.sup.3 and the epitaxial region 13 is not yet depleted at zero bias condition, but depletes partially at reverse bias condition. At a carrier density of N.sub.D=110.sup.17 cm.sup.3, the epitaxial region 13 is already partially depleted at zero bias condition, and fully depletes at reverse bias condition. At a carrier density of N.sub.D=110.sup.16 cm.sup.3, the epitaxial region 13 is already fully depleted at zero bias condition and thus also at reverse bias condition.

[0089] The simulations shown in FIG. 4 are for the case of InP as the III-V semiconductor material of the epitaxial layer 13, but other III-V semiconductor materials such as GaAs, InGaAs, InGaAsP, etc. can be used likewise.

[0090] FIG. 5A shows again a specific carrier density, namely N.sub.D=110.sup.18 cm.sup.3 with and without reverse bias applied. Further, FIG. 5B shows a band diagram vertical cut simulation at this carrier density through the waveguide 11, as indicated by the vertical lines through the waveguide 11 in FIG. 5A. Again, the epitaxial region 13 of the waveguide 11 is made of InP and the waveguide base 12 of Si. It can be seen that at reverse bias conditions (dashed lines in FIG. 5B), the conduction and valence bands of both the InP epitaxial region 13 and the Si waveguide base 12 are pulled upwards (to higher potential energies (eV)), so that depletion regions are formed at least at the InP/Si interface.

[0091] FIG. 5C shows an optical mode profile of light propagated through the waveguide 11. From the optical mode profile simulation, it can be derived that most of the light is confined in the epitaxial region 13, which is in the form of a V-groove. Thus, most of the light passes through the lower effective mass III-V semiconductor material, where it can be phase modulated more efficiently and with lower optical loss.

[0092] FIG. 6A shows a carrier density profile in the waveguide 11 at a carrier density of again N.sub.D=110.sup.18 cm.sup.3 in the epitaxial region 13. Beneath that, FIG. 6A shows a refractive index profile for the carrier density profile. It can be seen, how the refractive index is different in the InP epitaxial region 13 and the Si waveguide base 12, respectively, but also how it is different within the epitaxial region 13 in differently depleted/populated areas.

[0093] FIG. 6B shows a change of the refractive index n and a change of the absorption coefficient , respectively, in dependence of a change of the carrier density. n and were calculated considering the plasma dispersion effect, band-filling effects, bandgap shrinkage effects, and inter-valence band absorption. It can be seen that the refractive index change in the InP material is much steeper in the region between carrier densities of 110.sup.17 cm.sup.3 and 110.sup.18 cm.sup.3, where the refractive index change can be linearly fitted, than for the Si material. Due to this more rapid change of the refractive index, the modulation performance of the modulator 10 is higher than for a modulator that is made only from a Si-based semiconductor material.

[0094] It can further be seen that the absorption coefficient behaves linearly in both semiconductor materials, but is in absolute numbers always lower in the InP epitaxial region 13 than in the Si waveguide base 12. This is due to the higher mobility of the epitaxially grown III-V semiconductor material. This effect more than compensates the influence of the lower effective mass of this III-V semiconductor material (compared to the Si in the waveguide base 12) to the absorption coefficient.

[0095] FIG. 7A shows (on the left hand side) changes in the effective refractive index n.sub.eff for different bias condition and different carrier densities, calculated by overlapping the optical mode with the carrier distribution. FIG. 7B shows further (on the right hand side) changes of V.sub.L, which is a measure of the voltage V.sub. per length L in cm, which may affect a phase shift of the light propagating through the waveguide 11. Thus, it is a figure-of-merit of the modulator 10.

[0096] FIG. 8A shows a calculated phase shifter loss (left hand side) and FIG. 8B shows a calculated V.sub.L (right hand side), the latter being a product of the absorption coefficient and V.sub.L, and thus another representative figure-of-merit of the modulator 10.

[0097] FIGS. 7A-8B demonstrate the effective modulation characteristics, which can be obtained with the modulator 10, owing to the small effective mass in the III-V semiconductor material of the epitaxial region 13. Notably, the obtained representative figure-of-merit VL is impressively low compared to a conventional Si-based optical modulator (several tens of dB-V).

[0098] The monolithic integrated phase modulator 10 can be generally produced with the method that forms the waveguide 11 by: forming a waveguide base 12 from a Si-based semiconductor material and doping the waveguide base 12 to be of a first conductivity type; then forming at least one groove 14 in a surface of the waveguide base 12 and epitaxially growing a region 13 of a second conductivity type III-V semiconductor material on the waveguide base 12 in the groove 14, particularly an epitaxial region 13 in each groove 14, if there are multiple grooves in the waveguide base 12 surface. Accordingly, the general production method can produce the modulator 10 with one epitaxial region 13 shown in FIG. 2 and the modulator 10 with multiple epitaxial regions 13 shown in FIG. 3.

[0099] FIG. 9 shows a specific example of a process flow 900 for such a production method. The at least one III-V semiconductor material may be grown in the groove by SAG.

[0100] In particular, in a step 901, the region that will later be the waveguide 11 (shown generally in FIG. 1) is formed, for instance, by etching Si-based semiconductor material, e.g. p-Si. Likewise, the regions that would later be the leads 21 and 22 may be formed in this way.

[0101] In step 902, dopants were implanted into the Si-based semiconductor material and activation is done. In particular, as indicated by the different shadings, the leads 21 and 22 can be formed by doping them to be highly-doped p-Si (lead 21) and highly-doped n-Si (lead 22), respectively. Further, the waveguide 11 region can be doped to form the sidewall region 23 to be moderately doped n-Si. The remainder of the waveguide region 11 (i.e. the waveguide base 12) can be doped to be a moderately doped p-Si region. Particularly, the doping of the waveguide base 12 and the sidewall region 23, respectively, may be selected high enough to make it electrically low resistive, but at the same time low enough to minimize optical losses.

[0102] In step 903 an oxide 90 can be deposited over the semi-finished modulator structure. The oxide 90 may for instance be Sift.

[0103] In step 904 at least one groove 14 is formed by a trench formation technique like dry and/or wet etching. The groove 14 shown in FIG. 9 is an example V-shape. However, it may also have a U-shape or other suitable shape.

[0104] In step 905, the III-V semiconductor material of the second conductivity type (here, for example, n-type InP) is grown into the at least one groove 14 on the groove surfaces. The growth is an epitaxial growth, and forms the epitaxial region 13. The second conductivity type doping of the epitaxial region 13 can be performed in-situ, and the doping level and profile can be controlled. The doping profile may change in a direction from the surface of the interface between the epitaxial region 13 and the n-type Si to a further surface of the epitaxial region 13. In particular, as schematically shown in FIG. 9, moderately doped n-InP and highly doped n-InP may be grown in the epitaxial region 13.

[0105] Due to a potential impact of defect density near the III-V/Si interface, to avoid/mitigate this impact, a doping profile (low-high-low) may be designed from the interface to top surface of the epitaxial layer 13. In other words, as shown in FIG. 9 in steps 905 and 906, moderately doped n-InP 13a could be grown near the interface and near the top surface of the epitaxial region 13, and highly doped n-InP 13b may be grown between the moderately doped regions. Such a design can be optimized to maximize the depletion in high-quality regions in III-V semiconductor material of the epitaxial region 13, not near the III-V/Si interface.

[0106] In step 906, chemical-mechanical planarization (CMP) can be performed of the III-V semiconductor material in particular, and a final protective oxide deposition can be applied.

[0107] In contrast to the process flow 900 shown in FIG. 9, so far reported III-V/insulator/Si modulator structures all use wafer bonding to fabricate the structure, which makes the process not fully Si-compatible. Here, III-V semiconductor material growth using SAG can be used for high film quality in the epitaxial region 13. The process flow 900 of FIG. 9 can be implemented in large Si wafer (300 mm and even larger).

[0108] In summary, the present disclosure presents an improved monolithic integrated phase modulator 10, particular in terms of modulation efficiency and loss performance, and an improved high-volume production method.