Monolithic silicon III-V optoelectronic phase modulator with ridge waveguide

Abstract

The present disclosure relates to the field of electro-optical devices. Specifically, the present disclosure provides a monolithically integrated electro-optical phase modulator fabricated using a III-V semiconductor process on silicon. The phase modulator includes a silicon-based n-type substrate base layer and a III-V n-type ridge waveguide for propagating light, wherein the ridge waveguide protrudes from and extends along the n-type substrate base layer. In addition, the phase modulator includes one or more insulating layers provided on the ridge waveguide, and a silicon-based p-type cap layer provided on the one or more insulating layers, at least above the ridge waveguide, wherein the one or more insulating layers have a total thickness of 1-100 nm.

Description

Technical Field

[0001] The present disclosure relates to the field of electro-optical devices, and in particular to the field of electro-optical modulators. This disclosure proposes a monolithically integrated electro-optical phase modulator based on a ridge waveguide-on-silicon III-V semiconductor process. This disclosure also provides a method for manufacturing the electro-optical phase modulator, and a Mach-Zehnder modulator including at least one such electro-optical phase modulator. Background Art

[0002] Electro-optic modulators (EOMs) are fundamental building blocks in silicon (Si) photonics and are used to modulate light, such as by modulating its phase. Conventional Si-based optical phase modulators utilize the free-carrier plasma dispersion effect to achieve phase modulation by modulating the carrier density in the light-propagating material.

[0003] However, the efficiency of this conventional silicon-based phase modulator is inherently limited by the effective mass of the carriers in the silicon-based material, as the amount of carrier modulation is inversely proportional to the effective mass. Therefore, some work has been devoted to using III-V semiconductor materials instead of silicon-based materials and to taking advantage of their lower effective mass.

[0004] As an example, III-V / silicon hybrid phase modulators can be manufactured using a wafer bonding process, which is however a problematic process for higher volume manufacturing.

[0005] As another example, monolithically integrated III-V / silicon hybrid phase modulators can be fabricated using a process that epitaxially grows III-V semiconductor materials on silicon, a process that is more favorable for large-scale production. However, in this example, the phase modulator often suffers from performance degradation due to the low crystal quality of the epitaxially grown III-V semiconductor material. Summary of the Invention

[0006] In light of the above-mentioned shortcomings, embodiments of the present invention aim to provide an improved electro-optical phase modulator. Specifically, the goal is to provide a monolithically integrated optical phase modulator that exploits the relatively low effective mass of III-V semiconductor materials without suffering the performance degradation associated with the excessively low crystal quality of these III-V semiconductor materials. The process used to manufacture the electro-optical phase modulator should also be more favorable for high-volume production. Furthermore, the electro-optical phase modulator should be suitable for implementation in various optical blocks, such as Mach-Zehnder modulators.

[0007] This object is achieved by the embodiments of the invention presented in the appended independent claims. Advantageous realizations of these embodiments are defined in the dependent claims.

[0008] Specifically, to overcome the problems of the exemplary phase modulators described above, embodiments of the present invention propose a monolithic on-silicon III-V electro-optical phase modulator including a ridge waveguide for propagating light.

[0009] A first aspect of the present disclosure provides a monolithically integrated electro-optical phase modulator, wherein the phase modulator includes, in an optical modulation region, a silicon-based n-type base layer; an n-type ridge waveguide for propagating light, wherein the ridge waveguide protrudes from and extends along the n-type base layer and is made of a III-V semiconductor material; one or more insulating layers provided on the ridge waveguide, wherein the one or more insulating layers have a total thickness in the range of 1-100 nm; and a silicon-based p-type cladding layer provided on the one or more insulating layers at least above the ridge waveguide, wherein the n-type ridge waveguide, the one or more insulating layers, and the p-type cladding layer together form a monolithically integrated semiconductor-insulator-semiconductor (SIS) capacitor, which is used to phase modulate light propagating along the ridge waveguide in the optical modulation region.

[0010] The phase modulator of the first aspect is a monolithically integrated optical phase modulator that exploits the relatively low effective mass of the III-V semiconductor material of the ridge waveguide. However, the phase modulator does not suffer from the excessively low crystal quality of the III-V semiconductor material. This is likely because the ridge waveguide can cause defects in the semiconductor material to be trapped at its base (particularly in the portion where the ridge waveguide does not propagate the majority of the light to be phase modulated). Specifically, light primarily propagates at the interface defining the SIS capacitor (i.e., at the top of the ridge waveguide), where the light can be phase modulated.

[0011] Furthermore, the process for fabricating the electro-optical phase modulator may be advantageous for high volume production because epitaxy may be used and wafer bonding is not necessary.

[0012] In one implementation, the phase modulator further includes: one or more first contacts provided on the n-type base layer; and one or more second contacts provided on the p-type cladding layer; wherein a voltage applied between the one or more first contacts and the one or more second contacts causes light propagating along the ridge waveguide to be phase modulated in the light modulation region.

[0013] The first and second contacts thus allow for control of the phase modulation of light in the light modulation region of the phase modulator, for example, allowing for control of whether the light phase is modulated at all and / or the intensity with which the light phase is modulated. The first and second contacts can specifically control the charge state of the SIS capacitor. The p-type silicon-based cap layer and the one or more insulating layers can thus function as a gate contact and a gate insulator, respectively, to modify the carrier density in the top region of the n-type ridge waveguide.

[0014] In one implementation of the phase modulator, the one or more insulating layers and the p-type cladding layer are planar and provided on a planar top surface of the ridge waveguide.

[0015] This implementation enables a single manufacturing process. For example, the ridge waveguide can be embedded in a dielectric material and chemical mechanical polishing (CMP) can be used to provide a common flat surface, onto which one or more insulating layers can then be provided with high quality and precision.

[0016] In one implementation of the phase modulator, the one or more insulating layers and the p-type cladding layer are wrapped around the top of the ridge waveguide.

[0017] This implementation allows for more efficient and precise control of the carrier density in the ridge waveguide.

[0018] In one implementation of the phase modulator, the ridge waveguide, one or more insulating layers, and the p-type cladding layer are surrounded by or embedded in a dielectric material.

[0019] This isolates the SIS capacitor from its surroundings and thereby can improve the performance of the phase modulator. Specifically, the phase of light propagating in the ridge waveguide can be efficiently and accurately modulated in the modulation region.

[0020] In one implementation, the phase modulator includes, in an optical transition region, a silicon-based non-intentionally doped (NID) base layer; an n-type ridge waveguide protruding from and extending along the NID base layer; one or more insulating layers provided on the ridge waveguide; and a silicon-based NID capping layer provided on the one or more insulating layers and over at least a portion of the ridge waveguide.

[0021] The optical transition region allows light propagating in the ridge waveguide to be guided out of the optical modulation region, for example, to couple the light to another waveguide or provide the light to some other optical block of the optical system. Note that the NID base layer and the n-type base layer can be formed from a selectively n-doped base layer. For example, the top layer of the SOI substrate can be selectively n-doped, and the ridge waveguide can thus be formed across the doped and undoped regions of the top layer. Similarly, the NID cap layer and the p-type cap layer can be formed from a selectively p-doped cap layer.

[0022] In one implementation, the phase modulator further includes: a silicon-based waveguide formed on the NID substrate or adjacent to the ridge waveguide.

[0023] The silicon-based waveguide may be made of silicon or silicon nitride, for example.The silicon-based waveguide may be used to guide light to and from a modulation region of a phase modulator.

[0024] In one implementation of the phase modulator, a ridge waveguide and a silicon-based waveguide are configured and arranged such that light propagating along one of the waveguides is coupled into the other of the waveguides.

[0025] For example, the silicon-based waveguide can be tapered, or have tapered ends, or can be curved to support and / or customize the coupling. The silicon-based waveguide can be placed at a predetermined distance from the ridge waveguide and can have one or more determined dimensions to enable efficient coupling of light from one waveguide to another.

[0026] In one implementation of the phase modulator, the NID cover is tapered in the light transition region.

[0027] This supports coupling from ridge waveguides to silicon-based waveguides and vice versa.

[0028] In one implementation of the phase modulator, the ridge waveguide is partially arranged in a groove formed in an n-type and / or NID-based layer; and / or the ridge waveguide is grown on a V-groove formed in an n-type and / or NID-based layer.

[0029] This has the advantage that defects can be efficiently trapped in the bottom of the ridge waveguide (e.g., the portion arranged in the trench or groove). This can result in a significant reduction in defects in the top of the ridge waveguide, closer to or where the SIS capacitor is formed. For example, aspect ratio trapping (ART) techniques can be used to reduce defects. The silicon V-groove improves the quality of the III-V semiconductor material grown for the ridge waveguide, thereby further improving the performance of the phase modulator.

[0030] In one implementation of the phase modulator, an n-type and / or NID-based layer is formed from a top layer of a silicon-on-insulator substrate.

[0031] In one implementation of the phase modulator, the ridge waveguide includes a narrower bottom portion disposed on an n-type and / or NID base layer and a wider top portion disposed above the bottom portion; and the wider top portion has a rectangular cross section or a triangular cross section.

[0032] The narrower and wider portions support ART of defects in the lower portion of the ridge waveguide.

[0033] In one implementation of the phase modulator, the ridge waveguide includes two portions protruding side by side from an n-type and / or NID base layer.

[0034] This may further enable a particularly efficient wrapping of one or more insulating layers and cover layers around the ridge waveguide and thereby enable a particularly efficient modulation of the charge carrier density in the ridge waveguide.

[0035] A second aspect of the present disclosure provides a Mach-Zehnder modulator comprising: an optical input and an optical output; a first waveguide arm and a second waveguide arm, wherein each waveguide arm connects the optical input with the optical output; and one or more phase modulators according to the first aspect or any implementation form thereof, wherein at least one of the phase modulators is arranged in the first waveguide arm and / or the second waveguide arm.

[0036] Thus, the electro-optical phase modulator of the first aspect is suitable for implementation in optical building blocks such as the Mach-Zehnder modulator of the second aspect.Mach-Zehnder modulators exploit the advantages of phase modulator(s) and can modulate light with high performance.

[0037] A third aspect of the present disclosure provides a method for manufacturing a monolithically integrated electro-optical phase modulator, wherein, in order to manufacture a light modulation region of the phase modulator, the method includes: providing a silicon-based n-type base layer; growing an n-type ridge waveguide for propagating light, wherein the ridge waveguide protrudes from the n-type base layer and extends along the n-type base layer and is made of a III-V semiconductor material; forming one or more insulating layers on the ridge waveguide, wherein the one or more insulating layers have a total thickness in the range of 1-100 nm; and forming a silicon-based p-type cladding layer at least above the ridge waveguide on the one or more insulating layers, wherein the n-type ridge waveguide, the one or more insulating layers, and the p-type cladding layer together form a monolithically integrated semiconductor-insulator-semiconductor (SIS) capacitor, which is used to phase modulate light propagating along the ridge waveguide in the light modulation region.

[0038] The method of the second aspect achieves the same advantages as the phase modulator of the first aspect and can be extended by corresponding implementations as described above for the phase modulator of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The above aspects and implementations are explained in the following detailed description with reference to the accompanying drawings:

[0040] Figure 1 A Mach-Zehnder modulator according to an embodiment of the present invention is shown, which exemplarily comprises two phase modulators according to the present invention.

[0041] Figure 2 SIS capacitors in a phase modulator according to an embodiment of the present invention are shown.

[0042] Figure 3 A phase modulator according to an embodiment of the present invention is shown with planar insulating layer(s) and cover layers, in particular the light modulating region of the phase modulator.

[0043] Figure 4Another phase modulator according to an embodiment of the present invention is shown having planar insulating layer(s) and cover layers, in particular the light modulating region of the phase modulator.

[0044] Figure 5 Another phase modulator according to an embodiment of the present invention is shown having planar insulating layer(s) and cover layers, in particular the light modulating region of the phase modulator.

[0045] Figure 6 A phase modulator according to an embodiment of the present invention is shown having non-planar insulating layer(s) and cover layers, in particular a light modulating region of the phase modulator.

[0046] Figure 7 Another phase modulator according to an embodiment of the present invention is shown having non-planar insulating layer(s) and cover layers, specifically the light modulating region of the phase modulator.

[0047] Figure 8 Another phase modulator according to an embodiment of the present invention is shown having non-planar insulating layer(s) and cover layers, specifically the light modulating region of the phase modulator.

[0048] Figure 9 A phase modulator according to an embodiment of the present invention is shown, specifically an optical transition region of the phase modulator.

[0049] Figure 10 Another phase modulator according to an embodiment of the present invention is shown, specifically the light transition region of the phase modulator.

[0050] Figure 11 The steps of a first integrated flow for manufacturing a phase modulator according to an embodiment of the present invention are shown.

[0051] Figure 12 The steps of a first integrated flow for manufacturing a phase modulator according to an embodiment of the present invention are shown.

[0052] Figure 13 The steps of a first integrated flow for manufacturing a phase modulator according to an embodiment of the present invention are shown.

[0053] Figure 14 The steps of a second integrated flow for manufacturing a phase modulator according to an embodiment of the present invention are shown.

[0054] Figure 15 The steps of a second integrated flow for manufacturing a phase modulator according to an embodiment of the present invention are shown. DETAILED DESCRIPTION

[0055] Figure 1An example of how the phase modulator 20 according to an embodiment of the present invention may be used is shown. Specifically, Figure 1 The Mach-Zehnder modulator 10 according to an embodiment of the present invention is schematically shown. The Mach-Zehnder modulator 10 exemplarily includes two phase modulators 20.

[0056] Specifically, the Mach-Zehnder modulator 10 includes an optical input 11 and an optical output 12. The line between the optical input 11 and the optical output 12 represents a silicon-based (e.g., silicon or silicon nitride) waveguide. The Mach-Zehnder modulator 10 further includes two waveguide arms, namely a first waveguide arm 13 and a second waveguide arm 14. Each waveguide arm 13, 14 connects the optical input 11 to the optical output 12.

[0057] The Mach-Zehnder modulator 10 is shown with one phase modulator 20 arranged in the first waveguide arm 13 and another phase modulator 20 arranged in the second waveguide arm 14. In general, the Mach-Zehnder modulator 10 may include at least one phase modulator 20 in at least one waveguide arm 13, 14. Each phase modulator 20 includes a waveguide transition (i.e., an optical transition region) and a phase shifter (i.e., an optical modulation region). Group III-V semiconductor materials are specifically used to form ridge waveguides in the optical modulation region and the optical transition region, as explained in more detail below.

[0058] Figure 2 FIG2 shows a cross section of an electro-optical phase modulator 20 according to an embodiment of the present invention, specifically a cross section of a SIS capacitor formed in the optical modulation region of the phase modulator 20. The phase modulator 20 is a monolithically integrated phase modulator 20, i.e. Figure 2 All elements shown can be grown on top of each other in one manufacturing process flow.The phase modulator 20 is thus a monolithic on-silicon III-V optical phase shifter.

[0059] In the light modulation region, the phase modulator 20 includes a silicon-based n-type base layer 21, a silicon-based n-type base layer 21 protruding from the n-type base layer 21 and extending along the n-type base layer 21 (here, at the time of entering the n-type base layer 21). Figure 2 An n-type ridge waveguide 22 (extending in a flat direction), one or more insulating layers 23 provided on the ridge waveguide 22, and a silicon-based p-type cladding layer 24 provided on the one or more insulating layers 23 at least above the ridge waveguide 22.

[0060] The silicon-based n-type layer 21 may be made of silicon or silicon nitride. For example, the layer may be a top layer of an SOI substrate, wherein the top layer is n-doped at least in the light modulation region of the phase modulator 20 .

[0061] The ridge waveguide 22 is configured to propagate light specifically along its extension direction on the substrate 21. The ridge waveguide 22 is made of a III-V semiconductor material. For example, it may include gallium arsenide (GaAs), indium gallium arsenide (InGaAs), indium phosphide (InP), and / or indium gallium phosphide (InGaAsP). The III-V semiconductor material may be doped with silicon (Si), germanium (Ge), selenium (Se), and / or tellurium (Te).

[0062] The one or more insulating layers 23 have a total thickness in the range of 1-100 nm, in particular in the range of 1-50 nm, more particularly less than 40 nm. The very thin one or more insulating layers 23 allow the optical mode of light to be confined to the top of the ridge waveguide 22, in particular in the SIS capacitor 25. The highest light intensity of this mode can even exist at the insulating layer 23, while the optical mode can diffuse from the top area of ​​the ridge waveguide 22 into the cover layer 24. At the same time, the thin insulating layer 23 can still act as a gate insulator, thereby allowing the carrier density in the top area of ​​the ridge waveguide 22 to be modified. The one or more insulating layers 23 can be transparent to light propagating along the ridge waveguide 22. The one or more insulating layers 23 may include an aluminum oxide (Al2O3) layer and / or a silicon oxide (SiO2) layer and / or a hafnium oxide (HfO2) layer and / or a high-k dielectric material layer.

[0063] The p-type silicon-based capping layer 24 may include a p-type polycrystalline silicon (poly-Si) layer, a p-type silicon layer, a p-type polycrystalline silicon germanium (poly-SiGe) layer, and / or a p-type silicon germanium (SiGe) layer.

[0064] Figure 3 FIG. 1 shows a cross section of a light modulation region of a phase modulator 20 according to an embodiment of the present invention. The embodiment is constructed on Figure 2 In the embodiment shown. Figure 2 and Figure 3 The same elements in FIG are marked with the same reference numerals and can be implemented in the same manner. Specifically, Figure 3 A phase modulator with planar insulating layer(s) 23 and a planar cover layer 24 is shown.

[0065] As in Figure 2As shown in FIG, an n-type doped III-V semiconductor material ridge waveguide 22 can be epitaxially grown on a highly n-type doped silicon-based base layer 21, such as a top layer of an SOI substrate. The SOI substrate may include a silicon substrate, a buried oxide (BOX) having a thickness of approximately 2 μm, and a silicon top layer having a thickness of 200-250 nm (e.g., approximately 215 nm). However, in the case where the n-type base layer 21 is formed on the top layer of the SOI substrate, the silicon top layer may have a reduced thickness of approximately 50-60 nm. One or more insulating layers 23 may be formed on the planarized III-V semiconductor material of the ridge structure 22, and in this embodiment, a dielectric material 33 is formed that surrounds or embeds the ridge waveguide 22 and the planarized surface of the III-V semiconductor material. A capping layer 24 is provided on the one or more insulating layers 23. As shown, the dielectric material 33 may further surround or also embed the one or more insulating layers 23 and the p-type top cap layer 24.

[0066] In addition, one or more first contacts 31 may be provided on the n-type substrate base layer 21, and one or more second contacts 32 may be provided on the p-type cladding layer 24. Specifically, metal contacts 31, 32 may be provided on these doped layers and may be configured to provide electrical signal terminals. By applying a bias voltage to one of the contacts 31, 32 and grounding the other contact 32, 31, carriers can be significantly modulated at the interface of the SIS capacitor 25. As a result, the voltage applied between the one or more first contacts 31 and the one or more second contacts 32 can cause light propagating along the ridge waveguide 22 to be phase-modulated in the light modulation region.

[0067] The optical mode of light can be confined in the SIS capacitor 25, as Figure 3 As depicted by the circles in FIG, the highest light intensity can exist at the insulating layer 23 (unlike, for example, in laser diode or photodiode applications), where the III-V semiconductor material of the ridge waveguide 22 is transparent to light wavelengths that can be used for optical communications. Therefore, the electrons at the insulating layer / n-type III-V semiconductor material interface can be mainly attributed to the efficient light modulation, and the holes at the p-type silicon base layer / insulating layer interface.

[0068] Figure 3 The illustrated ridge waveguide 22 further includes a narrower bottom portion disposed on the n-type base layer 21 and a wider top portion disposed above the bottom portion. The bottom portion may have a width of 50-100 nm (e.g., approximately 70 nm) and a height of 200-250 nm (e.g., approximately 215 nm), while the wider portion may have a width of up to 400-500 nm (e.g., 450 nm) (at the widest portion, here the triangular top portion) and a height of 300-350 nm (e.g., approximately 325 nm).

[0069] Furthermore, the ridge waveguide 22, specifically the narrower portion thereof, is partially arranged in the groove 110 formed in the n-type base layer 21 (see also Figure 11 and Figure 14 The ridge waveguide 22, specifically its narrower portion, can be grown (e.g., epitaxially) on the V-grooves formed in the n-type base layer 21. That is, the ART technique can be applied to form the ridge waveguide 22 and can trap defects in the narrower bottom portion. The wider top portion can therefore be defect-free, or at least contain significantly fewer defects. Because the optical mode of light propagating in the ridge waveguide 22 is located in the wider top portion, better performance is achieved.

[0070] exist Figure 3 In an exemplary embodiment, the one or more insulating layers 23 include aluminum oxide. The capping layer 24 further includes p-type polysilicon. The n-type base layer 21 includes silicon. The first contact 31 and the second contact 32 are made of metal.

[0071] Figure 4 FIG. 2 shows a cross section of a light modulation region of another phase modulator 20 according to an embodiment of the present invention. Figure 2 The embodiment shown and with Figure 3 The illustrated embodiments share elements. Figure 2 、 Figure 3 and Figure 4 The same elements in FIG are marked with the same reference numerals and can be implemented in the same manner. Specifically, Figure 4 Another phase modulator is shown having planar insulating layer(s) 23 and a cover layer 24 .

[0072] respectively Figure 3 and Figure 4 The difference between the embodiments of the phase modulator 20 shown in FIG. 1 is that Figure 3 The top of the ridge waveguide 22 has a triangular cross section, and Figure 4 It has a rectangular cross section. The rectangular cross section may benefit from an improved waveguide transition to another silicon-based waveguide (described later). The top portion of the rectangle may have a height of 100-200 nm (e.g., about 150 nm) and a width of 400-500 nm (e.g., about 450 nm), while the bottom portion may have dimensions of about Figure 3 Same as in.

[0073] Figure 5 FIG. 2 shows a cross section of a light modulation region of another phase modulator 20 according to an embodiment of the present invention. Figure 2 The embodiment shown and with Figure 3 The illustrated embodiments share elements. Figure 2 、 Figure 3 and Figure 5The same elements in FIG are marked with the same reference numerals and can be implemented in the same manner. Specifically, Figure 5 Another phase modulator 20 is shown having planar insulating layer(s) 23 and a cover layer 24 .

[0074] In principle, Figure 5 The phase modulator 20 shown has Figure 3 The same concept as the phase modulator 20 shown. However, in Figure 5 In the phase modulator 20 , as depicted, the number of contacts 31 , 32 is reduced. Specifically, the phase modulator 20 includes only one first contact 31 connected to the n-type base layer 21 and only one second contact connected to the p-type cladding layer 24 .

[0075] Figure 6 FIG. 2 shows a cross section of a light modulation region of another phase modulator 20 according to an embodiment of the present invention. Figure 2 The embodiment shown and with Figure 5 The illustrated embodiments share some elements. Figure 2 、 Figure 5 and Figure 6 The same elements in FIG are marked with the same reference numerals and can be implemented in the same manner. Specifically, Figure 6 The phase modulator 20 includes a non-planar insulating layer(s) 23 and a non-planar cladding layer 24. The insulating layer(s) 23 and the p-type cladding layer 24 are wrapped around the top of the ridge waveguide 22, respectively.

[0076] Figure 7 FIG. 2 shows a cross section of a light modulation region of another phase modulator 20 according to an embodiment of the present invention. Figure 2 The embodiment shown and with Figure 6 The illustrated embodiments share some elements. Figure 2 、 Figure 6 and Figure 7 The same elements in FIG are marked with the same reference numerals and can be implemented in the same manner. Specifically, Figure 7 The phase modulator 20 includes a non-planar insulating layer(s) 23 and a cover layer 24. One or more insulating layers 23 and a p-type cover layer 24 are wrapped around the top of the ridge waveguide 22. Figure 6 Compared with the phase modulator, Figure 7 The phase modulator 20 does not have a ridge waveguide 22 that is wider at the top than at its narrower bottom. Instead, the bottom and top of the ridge waveguide 22 have similar or identical widths.

[0077] Figure 8 FIG. 2 shows a cross section of a light modulation region of another phase modulator 20 according to an embodiment of the present invention. Figure 2 The embodiment shown and with Figure 7 The illustrated embodiments share some elements. Figure 2 、 Figure 7 and Figure 8 The same elements in FIG are marked with the same reference numerals and can be implemented in the same manner. Specifically, Figure 7 The phase modulator 20 includes non-planar insulating layers 23 and a cover layer 24. One or more insulating layers 23 and a p-type cover layer 24 are wrapped around the top of the ridge waveguide 22. Specifically, the ridge waveguide 22 in this embodiment includes two parts that protrude side by side from the n-type base layer 21. Each of the two parts is wrapped by one or more insulating layers 23 and a cover layer 24.

[0078] Figure 9 (a) shows a top view of the light modulation region ("phase shifter") and light transition region ("waveguide transition") of another phase modulator 20 according to an embodiment of the present invention (contacts / metal layers are omitted). Figure 9 (b) shows Figure 9 The specific light transition region of the phase modulator 20 of (a) is along Figure 9 (a) is a cross section of the dashed line shown.

[0079] like Figure 9 As shown in FIG. 2( b ), in the optical transition region, the phase modulator 20 includes a silicon-based NID base layer 91, an n-type ridge waveguide 22 protruding from and extending along the NID base layer 91, one or more insulating layers 23 provided on the ridge waveguide 22, and a silicon-based NID cap layer 94 provided on the one or more insulating layers 23 and above at least a portion of the ridge waveguide 22. The NID base layer 91 in the optical transition region and the n-type base layer 21 in the optical modulation region can be formed from the same layer (e.g., the top layer of an SOI substrate) provided with different undoped regions (for NID) and doped regions (for n-type). Similarly, the NID cap layer 94 in the optical transition region and the p-type cap layer 24 in the optical modulation region can be formed from the same layer provided with different undoped regions (for NID) and doped regions (for p-type).

[0080] In the light transition region, a ridge waveguide may be formed on the NID base layer 91 in a manner similar to that in which it is formed on the n-type base layer 21 in the light modulation region. Specifically, the ridge waveguide 22 may be partially disposed in a groove 110 formed in the NID base layer 91, and / or the ridge waveguide 22 may be grown on a V-groove formed in the NID base layer 91. The groove 110 and / or the V-groove may extend along the base layer across an undoped region (for NID) and a doped region (for n-type).

[0081] The optical transition region of the phase modulator 20 can be beneficial for establishing a low-loss optical path between the silicon-based waveguide 95 and the III-V ridge waveguide 22. Specifically, the (passive) silicon-based waveguide 95 can be formed on or by the NID substrate 91 adjacent to the ridge waveguide 22. The ridge waveguide 22 and the silicon-based waveguide 95 are configured and arranged so that light propagating along one of the waveguides 22, 95 is coupled into the other of the waveguides 22, 95. For example, the center of the silicon-based waveguide 95 can be about 200-350nm from the bottom of the ridge waveguide 22, for example about 315nm. The silicon-based waveguide 95 can include a tapered end and / or can be curved to support the coupling. The silicon-based waveguide 95 can be a directional linear taper and / or can be an advanced adiabatic coupler to support the coupling. Thus, as Figure 9 As shown in (b), the optical mode moves when light is coupled from the silicon-based waveguide 95 into the ridge waveguide 22 until the insulating layer(s) 23 are located in the middle of the optical mode.

[0082] Figure 10 (a) shows a top view of the light modulation region (“phase shifter”) and the light transition region (“waveguide transition”) of another phase modulator 20 according to an embodiment of the present invention. Figure 10 (b) and 10 (c) show the specific locations of the light transition region of the phase modulator 20. Figure 10 (a) Cross section of the two dashed lines shown. Figure 9 and Figure 10 The same elements in FIG. 1 are marked with the same reference numerals and can be implemented identically.

[0083] Figure 10 (a) shows that the NID cover layer 94 can be tapered in the light transition region. Figure 10 (c) shows an optical transition region in which a silicon-based waveguide 95 is formed adjacent to the ridge waveguide 22 . Figure 10 (b) shows a light transition region in which the silicon-based waveguide 95 is not formed, but only the NID base layer 91 is formed to support the ridge waveguide 22 .

[0084] Figure 11-13 FIG. 1 shows a first integrated solution for manufacturing a phase modulator 20 according to an embodiment of the present invention. Specifically, Figure 11 Steps 1-4 of the first integration scheme are shown, Figure 12 Steps 5-8 are shown, and Figure 13 Steps 9 and 10 are shown.

[0085] In step 1, a SOI substrate including a NID silicon top layer is provided. In step 2, the NID silicon top layer of the SOI is n-doped to form an n-type (silicon) base layer 21.

[0086] In step 3, a cavity is patterned into the n-type base layer 21, the cavity is filled with a dielectric material (e.g., silicon oxide), the dielectric material is etched, and a silicon V-groove 110 is formed through the etched dielectric material into the n-type base layer 21. In step 4, a III-V semiconductor material ridge waveguide 22 is grown onto the silicon V-groove, particularly using ART growth.

[0087] In step 5, one or more insulating layers 23 are formed (e.g., gate oxide may be deposited). Illustratively, the one or more insulating layers 23 wrap around the top of the ridge waveguide 22. In step 6, a silicon nitride layer 120 and a dielectric material (e.g., silicon oxide) are deposited (wrapped around the one or more insulating layers 23 and the top of the ridge waveguide 22).

[0088] In step 7 , the dielectric material is planarized to form a planar surface together with the top surface of the silicon nitride 120 . In step 8 , the silicon nitride 120 is etched to expose the top surface of the one or more insulating layers 23 .

[0089] In step 9, a p-type silicon-based capping layer 24 (e.g., polysilicon) is provided on the flat top surface and thus on the exposed one or more insulating layers 23. Note that the capping layer 24 does not wrap around the top of the ridge waveguide 22. In step 10, a first contact 31 and a second contact 32 are formed, for example, by depositing metal layers. Thus, the phase modulator 20 is manufactured.

[0090] Figure 14-15 A second integrated solution for manufacturing the phase modulator 20 according to an embodiment of the present invention is shown. Specifically, Figure 14 Steps 1-4 of the second integration scheme are shown, and Figure 15 Steps 5-8 are shown.

[0091] In step 1, as in the first integration scheme, a SOI substrate including a NID silicon top layer is provided. In step 2, the NID silicon top layer of the SOI is n-doped to form an n-type (silicon) base layer 21.

[0092] In step 3, similar to the first integration scheme, a hole is patterned into the n-type base layer 21 (compared to the first integration scheme, the n-type base layer 21 is removed on the right side of the SOI substrate, as shown in the figure). The hole is filled with a dielectric material (e.g., silicon oxide), the dielectric material is etched, and a silicon V-groove 110 is formed through the etched dielectric material into the n-type base layer 21. In step 4, a III-V semiconductor material ridge waveguide is grown onto the silicon V-groove, particularly using ART growth.

[0093] In step 5, as in the first integration scheme, one or more insulating layers 23 are formed (e.g., gate oxide may be deposited). Illustratively, the one or more insulating layers 23 wrap around the top of the ridge waveguide 22. In step 6, a p-type silicon-based capping layer 24 (e.g., polysilicon) is provided that wraps around the one or more insulating layers 23 and the top of the ridge waveguide 22.

[0094] In step 7, the p-type cladding layer 24 is patterned (the portion of the cladding layer 24 on the left side of the SOI substrate is removed above the n-type base layer 21). An implantation step (right side) is then performed to form a p+ region in the p-type cladding layer 24, and a dielectric material (e.g., silicon dioxide) is deposited to surround or embed the ridge waveguide 22. Furthermore, one or more insulating layers 23 are wrapped around the top of the ridge waveguide 22, and a cladding layer 24 is wrapped around the one or more insulating layers 23 and the top of the ridge waveguide 22. In step 8, a first contact 31 and a second contact 32 are formed, for example, by depositing metal layers. Thus, the phase modulator 20 is manufactured.

[0095] As discussed above, according to various embodiments of the present invention, a highly manufacturable and efficient III-V (hybrid) phase modulator 20 on silicon can be realized. The phase modulator 20 can be realized by implementing III-V on silicon using (nano)ridge waveguides. Embodiments of the present invention provide a way to manufacture efficient and low-loss III-V hybrid optical modulators on silicon in silicon photonics in a manufacturable manner.

Claims

1. A monolithically integrated electro-optical phase modulator, wherein the phase modulator comprises, in an optical modulation region: Silicon-based n-type base layer; an n-type ridge waveguide for propagating light, wherein the ridge waveguide protrudes from the n-type base layer and extends along the n-type base layer and is made of a III-V semiconductor material; one or more insulating layers provided on the ridge waveguide, wherein the one or more insulating layers have a thickness in the range of 1-100 nm in total; as well as a silicon-based p-type cladding layer provided on the one or more insulating layers at least above the ridge waveguide, The n-type ridge waveguide, the one or more insulating layers, and the p-type cladding layer collectively form a monolithically integrated semiconductor-insulator-semiconductor capacitor for phase modulating light propagating along the ridge waveguide in the light modulation region.

2. The phase modulator according to claim 1, further comprising: one or more first contacts provided on the n-type base layer; as well as one or more second contacts provided on the p-type cladding layer; Wherein a voltage applied between the one or more first contacts and the one or more second contacts causes light propagating along the ridge waveguide to be phase modulated in the light modulation region.

3. The phase modulator according to claim 1, wherein: The one or more insulating layers and the p-type cladding layer are planar and provided on a planar top surface of the ridge waveguide.

4. The phase modulator according to claim 1, wherein: The one or more insulating layers and the p-type cladding layer wrap around the top of the ridge waveguide.

5. The phase modulator according to claim 1, wherein: The ridge waveguide, the one or more insulating layers, and the p-type cladding layer are surrounded by or embedded in a dielectric material.

6. The phase modulator of claim 1 , wherein the phase modulator comprises, in a light transition region: Silicon-based non-intentionally doped NID substrate; the n-type ridge waveguide protruding from the NID base layer and extending along the NID base layer; the one or more insulating layers provided on the ridge waveguide; as well as A silicon-based NID capping layer is provided on the one or more insulating layers over at least a portion of the ridge waveguide.

7. The phase modulator according to claim 6, further comprising: A silicon-based waveguide is formed on or from the NID substrate adjacent to the ridge waveguide.

8. The phase modulator according to claim 7, wherein: The ridge waveguide and the silicon-based waveguide are configured and arranged such that light propagating along one of the waveguides is coupled into the other of the waveguides.

9. The phase modulator according to claim 6, wherein: The NID cover is tapered in the light transition region.

10. The phase modulator according to claim 6, wherein: The ridge waveguide is partially arranged in a groove formed in the n-type base layer and / or the NID base layer; and / or The ridge waveguide is grown on a V-groove formed in the n-type base layer and / or the NID base layer.

11. The phase modulator according to claim 6, wherein: The n-type base layer and / or the NID base layer is formed from a top layer of a silicon-on-insulator substrate.

12. The phase modulator according to claim 6, wherein: The ridge waveguide includes a narrower bottom portion disposed on the n-type base layer and / or the NID base layer, and a wider top portion disposed above the bottom portion; and The wider top portion has a rectangular cross section or a triangular cross section.

13. The phase modulator of claim 6, wherein: The ridge waveguide includes two portions protruding side by side from the n-type base layer and / or the NID base layer.

14. A Mach-Zehnder modulator comprising: Light input and light output; a first waveguide arm and a second waveguide arm, wherein each waveguide arm connects the optical input with the optical output; as well as One or more phase modulators as claimed in any one of claims 1 to 13, At least one of the phase modulators is arranged in the first waveguide arm and / or the second waveguide arm.

15. A method for manufacturing a monolithically integrated electro-optical phase modulator, wherein to manufacture a light modulating region of the phase modulator, the method comprises: Providing a silicon-based n-type base layer; growing an n-type ridge waveguide for propagating light, wherein the ridge waveguide protrudes from and extends along the n-type base layer and is made of a III-V semiconductor material; forming one or more insulating layers on the ridge waveguide, wherein the one or more insulating layers have a total thickness in the range of 1-100 nm; and forming a silicon-based p-type cladding layer on the one or more insulating layers at least above the ridge waveguide, The n-type ridge waveguide, the one or more insulating layers, and the p-type cladding layer collectively form a monolithically integrated semiconductor-insulator-semiconductor capacitor for phase modulating light propagating along the ridge waveguide in the light modulation region.

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