A Germanium-Silicon coupled quantum well electro-optic refractive index modulator based on strain modulation

Abstract

The present invention provides a germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain modulation, which includes a substrate layer, a buffer layer, a lower isolation layer, a coupled quantum well region, an upper isolation layer, a capping layer and an N electrode, an insulating dielectric layer, a right P electrode, and a left P electrode. It also includes two etching windows, a ridge waveguide structure and a suspended microbridge structure. Among them, the substrate layer has a suspended area; the coupled quantum well region includes multiple pairs of five-layer coupled quantum wells; the two etching windows are axially symmetrically distributed with respect to the ridge waveguide structure, and the buffer layer, the ridge waveguide structure, the N electrode, the right P electrode and the left P electrode between the two etching windows form a suspended microbridge structure. In summary, the present invention can move the optical absorption band edge and the peak value of the electro-optic refractive index change in the quantum well region to the mainstream optical communication C band, and at the same time achieve a larger electro-optic refractive index change, making the electro-optic refractive index modulator have higher modulation efficiency and greater practicality.

Description

Technical Field

[0001] The present invention relates to the field of integrated photonics technology, and particularly to a germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain regulation. Background Art

[0002] With the rapid growth of businesses such as the Internet of Things and big data, optical communication and optical interconnection have become the general trend of the development of the communication industry. Among them, the field of integrated optics has received great attention and development. Silicon-based optoelectronics is compatible with traditional CMOS processes and has become a favorable platform for realizing the integration of optoelectronic devices. Germanium-silicon quantum well materials, as an active material in integrated photonics, are expected to achieve the monolithic integration of various photonic devices and have been widely studied. Modulators are crucial devices in the communication field. Achieving a silicon-based optical modulator that is compatible with CMOS processes, has a low operating voltage, low loss, and operates in the mainstream optical communication C band has become a key research direction.

[0003] The patent with the publication number CN109343237B discloses a germanium-silicon quantum well electro-optic refractive index modulator and an integrated optoelectronic device, which solves the technical problems of coupling occurring when no voltage is applied, poor coupling effect, and difficulty in controlling the speed during the preparation process in the prior art. However, the working wavelength of the optical modulator is not in the mainstream optical communication C band, or a large strain needs to be applied to shift the absorption wavelength red shift to the C band. These problems all increase the difficulty of the process and reduce the practicality of the device. Therefore, comprehensively designing a germanium-silicon optical modulator that works in the C band and has a more stable strain structure has become the key issue at present. Summary of the Invention

[0004] In view of this, the present invention proposes a germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain regulation, which can move the optical absorption band edge and the peak value of the electro-optic refractive index change in the quantum well region to the mainstream optical communication C band, and at the same time achieve a larger electro-optic refractive index change, making the electro-optic refractive index modulator have a higher modulation efficiency and greater practicality. The technical solution of the present invention is realized as follows:

[0005] As Figure 1As shown in the figure, the strain-controlled germanium-silicon coupled quantum well electro-optic refractive index modulator includes a substrate layer 101, a buffer layer 102, a lower isolation layer 103, a coupled quantum well region 104, an upper isolation layer 105, a capping layer 106, and an N electrode 108, which are arranged in sequence from bottom to top. It also includes an insulating dielectric layer 107, a right P electrode 109, and a left P electrode 110. Among them, the outer peripheries of the buffer layer 102, the lower isolation layer 103, the coupled quantum well region 104, the upper isolation layer 105, and the capping layer 106 are coated with the insulating dielectric layer 107; after the N electrode 108 penetrates the insulating dielectric layer 107, it makes electrical contact with the capping layer 106; after the right P electrode 109 and the left P electrode 110 both penetrate the insulating dielectric layer 107, they make electrical contact with the buffer layer 102.

[0006] As Figure 2 shown in the figure, in the strain-controlled germanium-silicon coupled quantum well electro-optic refractive index modulator provided by the present invention, it further includes two etching windows 111, a ridge waveguide structure 112, a suspended microbridge structure 113, and a suspended area 114. Among them,

[0007] etching windows 111 are etched on the buffer layer 102, and the etching windows 111 are etched down to the underlying substrate layer 101;

[0008] As Figure 1 shown in the figure, the substrate layer 101 is isotropically wet-etched through the etching windows 111 to form a suspended area 114; in the present invention, the etching length a of the suspended area 114 is greater than the length of the etching windows 111, and the etching width (in the b direction) of the suspended area 114 is greater than the sum of the widths of the two etching windows 111 and the width of the suspended microbridge structure 113. The etching depth of the suspended area 114 is 20 - 70 μm, so that the bottom of the suspended microbridge structure 113 is completely suspended.

[0009] The width of each etching window 111 in the b direction is 80 - 250 μm.

[0010] The coupled quantum well region 104 includes multiple pairs of five-layer coupled quantum wells;

[0011] The lower isolation layer 103, the coupled quantum well region 104, the upper isolation layer 105, the capping layer 106, and a part of the buffer layer 102 are etched to form a ridge waveguide structure 112; the two etching windows 111 are axially symmetrically distributed with respect to the ridge waveguide structure 112. The buffer layer 102, the ridge waveguide structure 112, the N electrode 108, the right P electrode 109, and the left P electrode 110 between the two etching windows 111 form a suspended microbridge structure 113. The suspended height of the suspended microbridge structure 113 is the etching depth of the suspended area 114. As Figure 11, the width c of the suspended microbridge structure 113 is 4000 - 5000 nm, which is convenient for the growth of the right P electrode 109 and the left P electrode 110 on both sides of the ridge waveguide structure 112, while ensuring the stability of the microbridge structure and reducing the process difficulty.

[0012] Based on the above technical solutions, preferably, the coupled quantum well region 104 includes 4 - 8 pairs of five-layer coupled quantum wells. A single pair of five-layer coupled quantum wells includes three potential well layers and two inner barrier layers, and the three potential well layers and the two inner barrier layers are arranged alternately at intervals; outer barrier layers with the same germanium composition are also provided on the left and right sides of the five-layer coupled quantum wells, and the germanium composition of the inner barrier layers is higher than that of the outer barrier layers on both sides to enhance the coupling effect between the three quantum well layers inside each pair of coupled quantum wells.

[0013] More preferably, the thickness of the outer barrier layer is greater than that of the inner barrier layer; the thickness of the inner barrier layer is 1.5 - 5 nm, preferably 2 - 4 nm, to facilitate improving the coupling effect between the internal quantum well layers; however, limited by the actual growth process of the quantum well material epitaxial structure, the thickness of the inner barrier layer does not exceed 5 nm.

[0014] Each adjacent two pairs of five-layer coupled quantum well structures share a middle outer barrier layer. The inside of a single pair of five-layer coupled quantum wells in the coupled quantum well region 104 can be a symmetric structure or an asymmetric structure. The five-layer coupled quantum well structure changes the wave function distribution and transition energy of electrons and holes. When the external electric field strength changes, its absorption spectrum has a small shift in the absorption peak wavelength while the absorption coefficient changes. According to the Kramers-Kronig relation, this structure can achieve a larger electro-optic refractive index change; at the same time, the working wavelength can be tuned to the C band by applying a smaller uniaxial tensile strain value.

[0015] See Figure 1 , since the ridge waveguide structure 112 is formed by etching the lower isolation layer 103, the coupled quantum well region 104, the upper isolation layer 105, the capping layer 106, and the buffer layer 102, the ridge waveguide structure 112 is a ridge-shaped convex long strip structure with respect to the substrate layer 101 and the buffer layer 102. The width d of the narrowest part of the ridge waveguide structure 112 is 1000 - 2000 nm, which is convenient for the growth of the N electrode 108 and ensures the stability of the suspended microbridge structure 113; the etching depth of the side surface of the ridge waveguide structure 112 is limited downward into the buffer layer 102 to enable better ohmic contact of the P electrode. During the material growth process, due to the lattice mismatch between germanium and silicon, residual biaxial thermal tensile strain will be generated in the buffer layer 102, and the suspended microbridge structure 113 will concentrate the residual biaxial thermal tensile strain to the microbridge region to generate uniaxial tensile strain. By designing the size of the etching window 111, the introduced uniaxial tensile strain value can be changed, and the optical absorption band edge of the quantum well active region and the peak value of the electro-optic refractive index change can be effectively moved to the mainstream optical communication C band.

[0016] The material of the substrate layer 101 is silicon; the materials of the buffer layer 102, the lower isolation layer 103, the upper isolation layer 105 and the capping layer 106 are all germanium-silicon alloys; the material of the well layer in the coupled quantum well region 104 is germanium, and the material of the barrier layer is germanium-silicon alloy; the material of the insulating dielectric layer 107 is silicon oxide or silicon nitride.

[0017] The buffer layer 102 is used to release the stress generated during the growth process due to the lattice mismatch between the germanium-silicon material and the silicon substrate material, so as to ensure a high growth quality of the material in the upper quantum well region 104. Preferably, the buffer layer 102 is P-type doped with boron element, and the doping concentration is not less than 5×10 18 cm -3 ; the thickness of the buffer layer 102 is 300 - 400 nm, which can release the strain generated by the lattice mismatch, ensure a high growth quality of the coupled quantum well region 104, and at the same time, the optical field is preferably limited in the coupled quantum well region 104.

[0018] Preferably, the capping layer 106 is N-type doped with phosphorus element or arsenic element, and the doping concentration is not less than 5×10 18 cm -3 .

[0019] The lower isolation layer 103 is used to isolate the diffusion of P-type doped ions in the buffer layer 102 into the coupled quantum well region 104; the upper isolation layer 105 is used to isolate the diffusion of N-type doped ions in the capping layer 106 into the coupled quantum well region 104.

[0020] When designing the germanium component of the buffer layer 102, the lower isolation layer 103, the upper isolation layer 105 and the capping layer 106, the lattice constant should be made equivalent to the equivalent lattice constant of all the barrier regions and well regions in the coupled quantum well region 104 as a whole, so as to reduce the strain caused by the lattice mismatch in the quantum well region 104.

[0021] Since the coupled quantum well region 104 is relatively thick and there is a certain refractive index difference between it and the lower isolation layer 103, the upper isolation layer 105 and the buffer layer 102, the optical field is mainly limited to propagate in the coupled quantum well region 104 of the ridge waveguide structure 112, thereby realizing the optical modulation effect.

[0022] The buffer layer 102 and the capping layer 106 together with the coupled quantum well region 104 form a PIN structure for realizing carrier injection. After applying voltages to the N electrode 108, the right P electrode 109 and the left P electrode 110, a voltage perpendicular to the junction plane direction will be formed in the coupled quantum well region 104.

[0023] The working principle of the present invention is:

[0024] Based on the principle of the quantum-confined Stark effect in GeSi quantum well materials, when the voltage applied perpendicular to the junction plane of the quantum well material increases, the overlap factor of the electron and hole wave functions in the quantum well region decreases, and at the same time, the transition energy value between the electrons and holes decreases. Correspondingly, the absorption edge of the direct bandgap optical absorption spectrum in the quantum well region shifts towards the long-wavelength direction, and at the same time, the absorption intensity decreases. This principle can achieve the intensity modulation of the optical field by applying an external voltage. Based on the principle of the Kramers-Kronig relationship, when the absorption intensity in the material changes, it will cause a change in the refractive index of the material, that is, electro-optic refractive index change. Based on this principle, the phase modulation of the optical field can be achieved by changing the light intensity by applying a voltage.

[0025] Among them, the transition between the first electron energy state e1 and the first heavy-hole energy state HH1 dominates the first absorption band edge of the TE-mode light. Since the integrated waveguide mainly operates in the TE-mode single mode in practical applications, the transition between the e1-HH1 states is mainly concerned. When a uniaxial tensile strain is applied to the quantum well region, the energy band structure of the quantum well material changes, and the e1-HH1 transition energy decreases. Correspondingly, the absorption edge of the optical absorption spectrum shifts towards the long-wavelength direction. When an appropriate uniaxial tensile strain is applied, the working wavelengths of the intensity modulation and phase modulation of the GeSi quantum well modulator can be tuned to the C band.

[0026] Compared with the prior art, the electro-optic refractive index modulator of the present invention has the following beneficial effects:

[0027] 1. The suspended microbridge structure 113 used in the present invention can introduce an appropriate uniaxial tensile strain into the quantum well active region in the ridge waveguide structure 112, and shift the optical absorption band edge and the peak value of the electro-optic refractive index change in the quantum well region to the mainstream optical communication C band, thereby making the modulator more practical.

[0028] 2. The modulator works in the mainstream optical communication C band through the suspended microbridge structure 113, but the stability of the suspended microbridge structure 113 needs to be improved. Therefore, the present invention uses a five-layer coupled quantum well structure. Through the optimized design of the specific structure of the five-layer coupled quantum well, the working wavelength of the modulator can be tuned to the C band by applying a smaller uniaxial tensile strain, thereby making the suspended microbridge structure 113 more stable, reducing the process difficulty, and improving the stability and practicality of the modulator.

[0029] 3. To further improve the modulation efficiency of the modulator, the present invention optimizes the design of the five-layer coupled quantum well structure. A single pair of five-layer coupled quantum wells includes three potential well layers and two inner potential barrier layers; outer potential barrier layers with the same germanium composition are also provided on the left and right sides of the five-layer coupled quantum wells; the germanium composition of the two inner potential barrier layers is higher than that of the outer potential barrier layers on both sides. This design can enhance the coupling effect between the three potential well layers inside each pair of coupled quantum wells; compared with the existing quantum well structure, the modulator based on the five-layer coupled quantum well structure can achieve a larger electro-optic refractive index change, improving the modulation efficiency of the modulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0031] Figure 1 It is a three-dimensional structure schematic diagram of a germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain regulation according to the present invention;

[0032] Figure 2 is Figure 1 a schematic diagram of the epitaxial layer structure of the cross-section of the ridge waveguide structure;

[0033] Figure 3 It is a schematic diagram of a single symmetric five-layer coupled quantum well structure in Embodiment 1;

[0034] Figure 4 It is a light absorption spectrum diagram of a single symmetric five-layer coupled quantum well in Embodiment 1 for TE mode light under different electric field intensities;

[0035] Figure 5 It is a diagram of the electro-optic refractive index change of TE mode light by a single symmetric five-layer coupled quantum well in Embodiment 1 under an electric field intensity of 30 kV / cm;

[0036] Figure 6 It is a simulation diagram of the uniaxial tensile strain distribution introduced by the suspended microbridge structure in Embodiment 1 to the quantum well region;

[0037] Figure 7 It is a schematic diagram of a single asymmetric five-layer coupled quantum well structure in Embodiment 3;

[0038] Figure 8 It is a light absorption spectrum diagram of a single asymmetric five-layer coupled quantum well in Embodiment 3 for TE mode light under different electric field intensities;

[0039] Figure 9Electro - refractive index change diagram of TE - mode light for a single asymmetric five - layer coupled quantum well in Example 3 under an electric field strength of 40 kV / cm;

[0040] Figure 10 Simulation diagram of uniaxial tensile strain distribution introduced by the suspended micro - bridge structure in the quantum well region in Example 3;

[0041] Figure 11 Top - view structural schematic diagram of a germanium - silicon coupled quantum well electro - refractive index modulator based on strain regulation according to the present invention;

[0042] In the figure, there are substrate layer 101, buffer layer 102, lower isolation layer 103, coupled quantum well region 104, upper isolation layer 105, capping layer 106, insulating dielectric layer 107, N - electrode 108, right - hand P - electrode 109, left - hand P - electrode 110, etching window 111, ridge waveguide structure 112, suspended micro - bridge structure 113, and suspended region 114. Detailed implementation manners

[0043] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0044] Example 1

[0045] The present invention provides a germanium - silicon coupled quantum well electro - refractive index modulator based on strain regulation, including a substrate layer 101, a buffer layer 102, a lower isolation layer 103, a coupled quantum well region 104, an upper isolation layer 105, a capping layer 106, and an N - electrode 108 arranged in sequence from bottom to top, and further including an insulating dielectric layer 107, a right - hand P - electrode 109, a left - hand P - electrode 110, two etching windows 111, a ridge waveguide structure 112, and a suspended micro - bridge structure 113. The substrate layer 101 is etched to form a suspended region 114.

[0046] The doping concentration of the buffer layer 102 is 1×10 19 cm -3 ; the thickness of the buffer layer 102 is 300 nm, the doping concentration of the capping layer 106 is 5×10 18 cm -3 ; a uniaxial tensile strain of 1.1% is applied to the coupled quantum well region through the suspended micro - bridge structure.

[0047] The width of the narrowest part of the ridge waveguide structure 112 is 2000 nm, the width of the suspended microbridge structure 113 is 5000 nm, the coupled quantum well region 104 includes 4 pairs of five-layer coupled quantum wells, and the inside of a single pair of five-layer coupled quantum wells is a symmetric structure. A single pair of five-layer coupled quantum wells includes three potential well layers and two inner potential barrier layers; outer potential barrier layers with the same germanium composition are also arranged on the left and right sides of the five-layer coupled quantum wells; the germanium composition of the two inner potential barrier layers is higher than that of the outer potential barrier layers on both sides.

[0048] Such as Figure 3 is a schematic diagram of a single symmetric five-layer coupled quantum well structure. When a uniaxial tensile strain of 1.1% is applied, its optical absorption spectra of the TE mode under different externally applied reverse electric field intensities are as Figure 4 shown. It can be seen that applying a uniaxial tensile strain of 1.1% can move the optical absorption band edge of the quantum well and the peak value of the electro-optic refractive index change to around 1550 nm. And it can be known that when a reverse voltage perpendicular to the junction plane is applied, the optical absorption spectrum moves towards the long wavelength direction.

[0049] According to the Kramers-Kronig relationship, the electro-optic refractive index change of this structure for the TE mode light under an electric field intensity of 30 kV / cm is calculated as Figure 5 shown. It can be seen that a modulator based on this structure can achieve an electro-optic refractive index change of about 1.3% at a wavelength of 1555 nm.

[0050] Such as Figure 6 shown is a simulation diagram of the uniaxial tensile strain distribution introduced by the suspended microbridge structure 113 into the quantum well region. By optimizing the design of the size of the etching window 111 on the buffer layer 102, a suitable uniaxial tensile strain value can be applied in the coupled quantum well region. Such as Figure 6 the structure shown can achieve a uniaxial tensile strain value of 1.1%.

[0051] Embodiment 2

[0052] The present invention provides a germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain regulation, which includes a substrate layer 101, a buffer layer 102, a lower isolation layer 103, a coupled quantum well region 104, an upper isolation layer 105, a capping layer 106, and an N electrode 108 arranged in sequence from bottom to top, and also includes an insulating dielectric layer 107, a right P electrode 109, a left P electrode 110, two etching windows 111, a ridge waveguide structure 112, and a suspended microbridge structure 113. A suspended region 114 is etched on the substrate layer 101.

[0053] The doping concentration of the buffer layer 102 is 1×10 19 cm -3 ; the thickness of the buffer layer 102 is 300 nm, and the doping concentration of the capping layer 106 is 5×10 18 cm -3; A uniaxial tensile strain of 1.1% is applied to the coupled quantum well region through the suspended microbridge structure.

[0054] The width of the narrowest part of the ridge waveguide structure 112 is 1000 nm, the width of the suspended microbridge structure 113 is 4000 nm, the coupled quantum well region 104 includes 8 pairs of five-layer coupled quantum wells, and the inside of a single pair of five-layer coupled quantum wells is a symmetric structure. A single pair of the five-layer coupled quantum wells includes three potential well layers and two inner potential barrier layers, and outer potential barrier layers with the same germanium composition are also arranged on the left and right sides of the five-layer coupled quantum wells; the germanium composition of the two inner potential barrier layers is higher than that of the outer potential barrier layers on both sides.

[0055] In this embodiment, applying a 1.1% uniaxial tensile strain can shift its optical absorption band edge and the peak value of electro-optic refractive index change to around 1550 nm. When the reverse voltage applied perpendicular to the junction plane increases, the optical absorption spectrum shifts towards longer wavelengths.

[0056] The modulator in this embodiment can achieve an electro-optic refractive index change of approximately 1.3% at a wavelength of 1556 nm under an electric field strength of 30 kV / cm; therefore, the electro-optic refractive index change of the five-layer coupled quantum well structure is more significant than that of a traditional phase modulator, and this structure can achieve a higher modulation efficiency.

[0057] The modulator in this embodiment realizes a uniaxial tensile strain value of 1.1% through the suspended microbridge structure.

[0058] Embodiment 3

[0059] The present invention provides a germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain regulation, which includes a substrate layer 101, a buffer layer 102, a lower isolation layer 103, a coupled quantum well region 104, an upper isolation layer 105, a capping layer 106, and an N electrode 108 arranged in sequence from bottom to top, and also includes an insulating dielectric layer 107, a right P electrode 109, a left P electrode 110, two etching windows 111, a ridge waveguide structure 112, and a suspended microbridge structure 113. A suspended region 114 is etched on the substrate layer 101.

[0060] The doping concentration of the buffer layer 102 is 1×10 19 cm -3 ; The thickness of the buffer layer 102 is 300 nm, the doping concentration of the capping layer 106 is 5×10 18 cm -3 ; A uniaxial tensile strain of 1.1% is applied to the coupled quantum well region through the suspended microbridge structure.

[0061] The width of the narrowest part of the ridge waveguide structure 112 is 1200 nm, the width of the suspended microbridge structure 113 is 4500 nm, the coupled quantum well region 104 includes 6 pairs of five-layer coupled quantum wells, and the inside of a single pair of five-layer coupled quantum wells is an asymmetric structure. A single pair of the five-layer coupled quantum wells includes three potential well layers and two inner potential barrier layers, and outer potential barrier layers with the same germanium composition are also arranged on the left and right sides of the five-layer coupled quantum wells; the germanium composition of the two inner potential barrier layers is higher than that of the outer potential barrier layers on both sides.

[0062] Such as Figure 7 is a schematic diagram of a single asymmetric five-layer coupled quantum well structure. When a uniaxial tensile strain of 1.1% is applied, its TE-mode light absorption spectra at different externally applied reverse electric field intensities are as Figure 8 shown. It can be seen that applying a uniaxial tensile strain of 1.1% can shift the light absorption band edge of the quantum well and the peak of the electro-optic refractive index change to around 1550 nm, and it can also be seen that when a reverse voltage perpendicular to the junction plane is applied, the light absorption spectrum shifts towards longer wavelengths.

[0063] According to the Kramers-Kronig relationship, the electro-optic refractive index change of this structure for TE-mode light under an electric field intensity of 40 kV / cm is as Figure 9 shown. It can be seen that a modulator based on this structure can achieve an electro-optic refractive index change of approximately 1.3% at a wavelength of 1552 nm.

[0064] Such as Figure 10 shown is a simulation diagram of the uniaxial tensile strain distribution introduced by the suspended microbridge structure 113 to the quantum well region. By optimizing the design of the size of the etching window 111 on the buffer layer 102, a suitable uniaxial tensile strain value can be applied in the coupled quantum well region. Such as Figure 10 the structure shown can achieve a uniaxial tensile strain value of 1.1%.

[0065] Comparative Example 1: Without a suspended microbridge structure

[0066] A germanium-silicon coupled quantum well electro-optic refractive index modulator includes a substrate layer 101, a buffer layer 102, a lower isolation layer 103, a coupled quantum well region 104, an upper isolation layer 105, a capping layer 106, and an N electrode 108 arranged in sequence from bottom to top, and also includes an insulating dielectric layer 107, a right P electrode 109, a left P electrode 110, and a ridge waveguide structure 112.

[0067] The doping concentration of the buffer layer 102 in the modulator is 1×10 19 cm -3 ; the thickness of the buffer layer 102 is 300 nm, and the doping concentration of the capping layer 106 is 5×10 18 cm -3 .

[0068] The coupled quantum well region 104 includes 4 pairs of five-layer coupled quantum wells. A single pair of five-layer coupled quantum wells includes three potential well layers and two inner barrier layers. Outer barrier layers with the same germanium composition are provided on both the left and right sides of the five-layer coupled quantum wells; the germanium composition of the two inner barrier layers is higher than that of the outer barrier layers on both sides.

[0069] Through calculation, under the condition of not applying uniaxial tensile strain through the suspended microbridge structure, the absorption band edges of the symmetric five-layer coupled quantum wells and the asymmetric five-layer coupled quantum wells in the corresponding Examples 1 and 3 in this comparative example are located at approximately 1438 nm and approximately 1436 nm respectively, which are far from the mainstream optical communication wavelength of 1550 nm.

[0070] Comparative Example 2: It is not a five-layer coupled quantum well structure

[0071] A germanium-silicon quantum well electro-optic refractive index modulator based on strain regulation includes a substrate layer 101, a buffer layer 102, a lower isolation layer 103, a quantum well region 104, an upper isolation layer 105, a capping layer 106, and an N electrode 108 arranged in sequence from bottom to top. It also includes an insulating dielectric layer 107, a right P electrode 109, a left P electrode 110, two etching windows 111, a ridge waveguide structure 112, and a suspended microbridge structure 113. A suspended region 114 is etched on the substrate layer 101.

[0072] The doping concentration of the buffer layer 102 in the modulator is 1×10 19 cm -3 ; the thickness of the buffer layer 102 is 300 nm, and the doping concentration of the capping layer 106 is 5×10 18 cm -3 .

[0073] The width of the narrowest part of the ridge waveguide structure 112 is 1000 nm, the width of the suspended microbridge structure 113 is 4000 nm, the quantum well region 104 includes 4 pairs of ordinary quantum wells, and the single quantum well structure is 12 nm Si 0.19 Ge 0.81+ 10 nm Ge + 12 nm Si 0.19 Ge 0.81 .

[0074] When there is only the residual biaxial tensile strain during the material growth process, the absorption band edge of this structure is located at 1380 nm; it is necessary to apply a 1.6% uniaxial tensile strain to move the absorption band edge of the TE mode to the 1550 nm wavelength.

[0075] Comparative Example 3: The germanium composition of the two inner barrier layers is lower than that of the outer barrier layers on both sides

[0076] A germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain regulation, comprising a substrate layer 101, a buffer layer 102, a lower isolation layer 103, a coupled quantum well region 104, an upper isolation layer 105, a capping layer 106 and an N electrode 108 arranged in sequence from bottom to top, further comprising an insulating dielectric layer 107, a right P electrode 109, a left P electrode 110, two etching windows 111, a ridge waveguide structure 112 and a suspended microbridge structure 113. A suspended region 114 is etched on the substrate layer 101.

[0077] The doping concentration of the buffer layer 102 in the modulator is 1×10 19 cm -3 ; the thickness of the buffer layer 102 is 300 nm, and the doping concentration of the capping layer 106 is 5×10 18 cm -3 ; a uniaxial tensile strain of 1.1% is applied to the coupled quantum well region through the suspended microbridge structure.

[0078] The width of the narrowest part of the ridge waveguide structure 112 is 2000 nm, the width of the suspended microbridge structure 113 is 5000 nm, the coupled quantum well region 104 includes 8 pairs of five-layer coupled quantum wells, and the inside of a single pair of five-layer coupled quantum wells is a symmetric structure.

[0079] A single pair of five-layer coupled quantum wells includes three potential well layers and two inner potential barrier layers; outer potential barrier layers with the same germanium composition are also arranged on the left and right sides of the five-layer coupled quantum wells; the germanium composition of the two inner potential barrier layers is lower than that of the outer potential barrier layers on both sides. According to the basic principles of quantum mechanics, the overlap integral of the electron and hole wave function distributions in the coupled quantum wells affects the transition intensity between electrons and holes, thus affecting the electro-absorption spectrum; since the five-layer coupled quantum wells need to utilize the coupling effect between different potential well regions, when the germanium composition of the two inner potential barrier layers is lower than that of the outer potential barrier layers on both sides, the internal potential barrier will be higher, which is not conducive to the coupling between the three intermediate potential well layers and is not conducive to improving the modulation efficiency of the modulator.

[0080] Comparative example 4: Without a suspended microbridge structure and not a five-layer coupled quantum well structure

[0081] A germanium-silicon coupled quantum well electro-optic refractive index modulator, comprising a substrate layer 101, a buffer layer 102, a lower isolation layer 103, a coupled quantum well region 104, an upper isolation layer 105, a capping layer 106 and an N electrode 108 arranged in sequence from bottom to top, further comprising an insulating dielectric layer 107, a right P electrode 109, a left P electrode 110, and a ridge waveguide structure 112.

[0082] The doping concentration of the buffer layer 102 in the modulator is 1×10 19 cm -3 ; the thickness of the buffer layer 102 is 300 nm, and the doping concentration of the capping layer 106 is 5×10 18 cm-3 。

[0083] The coupled quantum well region 104 includes 8 pairs of triple-layer coupled quantum wells, and the triple-layer coupled quantum well structure is [12nm Si 0.15 Ge 0.85 +6nm Ge + 2nm Si 0.17 Ge 0.83 +12nm Ge + 12nm Si 0.15 Ge 0.85 .

[0084] In this structure, the operating wavelength of the modulator is around 1461 nm, and the electro-refractive index change of its quantum well is about 0.9% under an electric field strength of 30 kV / cm.

[0085] Comparative Example 5: Without a suspended microbridge structure, the germanium composition of the two inner barrier layers is lower than that of the outer barrier layers on both sides

[0086] A germanium-silicon coupled quantum well electro-refractive index modulator includes a substrate layer 101, a buffer layer 102, a lower isolation layer 103, a coupled quantum well region 104, an upper isolation layer 105, a capping layer 106, and an N electrode 108 arranged in sequence from bottom to top, and also includes an insulating dielectric layer 107, a right P electrode 109, a left P electrode 110, and a ridge waveguide structure 112.

[0087] The doping concentration of the buffer layer 102 in the modulator is 1×10 19 cm -3 ; the thickness of the buffer layer 102 is 300 nm, and the doping concentration of the capping layer 106 is 5×10 18 cm -3 .

[0088] The coupled quantum well region 104 includes 6 pairs of five-layer coupled quantum wells, and the internal structure of a single pair of five-layer coupled quantum wells is asymmetric. A single pair of five-layer coupled quantum wells includes three well layers and two inner barrier layers, and the three well layers and the two inner barrier layers are arranged alternately; outer barrier layers with the same germanium composition are also provided on the left and right sides of the five-layer coupled quantum wells, and the germanium composition of the inner barrier layers is lower than that of the outer barrier layers on both sides.

[0089] After calculation, the absorption band edge of the absorption spectrum of this quantum well structure is far from the mainstream optical communication C band. And according to the basic principles of quantum mechanics, the overlap integral of the electron and hole wave function distributions in the coupled quantum well affects the transition intensity between electrons and holes, thereby affecting the electro-absorption spectrum; since the five-layer coupled quantum well needs to utilize the coupling effect between different well regions, when the germanium composition of the two inner barrier layers is lower than that of the outer barrier layers on both sides, the internal barrier will be higher, which is not conducive to the coupling between the three middle well layers and is not conducive to improving the modulation efficiency of the modulator.

[0090] Comparative Example 6: It is not a five-layer coupled quantum well structure, and the germanium composition of the inner barrier layer is lower than that of the outer barrier layers on both sides.

[0091] A germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain regulation includes a substrate layer 101, a buffer layer 102, a lower isolation layer 103, a coupled quantum well region 104, an upper isolation layer 105, a capping layer 106, and an N electrode 108 arranged in sequence from bottom to top. It also includes an insulating dielectric layer 107, a right P electrode 109, a left P electrode 110, two etching windows 111, a ridge waveguide structure 112, and a suspended microbridge structure 113. The substrate layer 101 is etched to form a suspended region 114.

[0092] The doping concentration of the buffer layer 102 in the modulator is 1×10 19 cm -3 ; the thickness of the buffer layer 102 is 300 nm, and the doping concentration of the capping layer 106 is 5×10 18 cm -3 ; a uniaxial tensile strain of 1.1% is applied to the coupled quantum well region through the suspended microbridge structure.

[0093] The width of the narrowest part of the ridge waveguide structure 112 is 1200 nm, the width of the suspended microbridge structure 113 is 4500 nm, and the coupled quantum well region 104 includes 6 pairs of three-layer coupled quantum wells. A single pair of three-layer coupled quantum wells includes two wide barrier layers with the same germanium composition on the left and right, two intermediate thin quantum well layers, and an intermediate thin barrier layer; the germanium composition of the intermediate thin barrier layer is lower than that of the wide barrier layers on both sides.

[0094] According to the basic principles of quantum mechanics, the overlap integral of the electron and hole wave function distributions in the coupled quantum well affects the transition intensity between electrons and holes, thus affecting the electro-absorption spectrum; since the five-layer coupled quantum well needs to utilize the coupling effect between different quantum well regions, when the germanium composition of the intermediate thin barrier layer is lower than that of the wide barrier layers on both sides, it will result in a higher internal barrier, which is not conducive to the coupling between the three intermediate quantum well layers and is not beneficial to improving the modulation efficiency of the modulator.

[0095] In the present invention, when the corresponding uniaxial tensile strain is applied through the suspended microbridge structure, the optical absorption band edge and the peak value of the electro-optic refractive index change in the quantum well region can be moved to the mainstream optical communication C band. The five-layer coupled quantum well structure used in the present invention can achieve a larger electro-optic refractive index change compared with the existing quantum well structure; through the optimized design of the five-layer coupled quantum well structure, the working wavelength can be regulated to the C band by applying a smaller uniaxial tensile strain, reducing the process difficulty and effectively improving the modulation efficiency and practicality of the device.

[0096] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain modulation, which comprises a substrate layer (101), a buffer layer (102), a lower isolation layer (103), a coupled quantum well region (104), an upper isolation layer (105), a capping layer (106) and an N electrode (108) arranged successively from bottom to top, and further comprises an insulating dielectric layer (107), a right P electrode (109) and a left P electrode (110), wherein, The outer periphery of the buffer layer (102), the lower isolation layer (103), the coupled quantum well region (104), the upper isolation layer (105) and the capping layer (106) is coated with an insulating dielectric layer (107); after the N electrode (108) penetrates the insulating dielectric layer (107), it is in electrical contact with the capping layer (106); after the right P electrode (109) and the left P electrode (110) both penetrate the insulating dielectric layer (107), they are in electrical contact with the buffer layer (102); it is characterized in that: it further includes two etching windows (111), a ridge waveguide structure (112), a suspended microbridge structure (113) and a suspended region (114), wherein, Etching windows (111) are etched on the buffer layer (102), and the etching windows (111) are etched down to the underlying substrate layer (101); The underlying substrate layer (101) is etched through the etching windows (111) to form a suspended region (114); The coupled quantum well region (104) includes multiple pairs of five-layer coupled quantum wells; The lower isolation layer (103), the coupled quantum well region (104), the upper isolation layer (105), the capping layer (106) and a part of the buffer layer (102) are etched to form a ridge waveguide structure (112); The two etching windows (111) are axially symmetrically distributed with respect to the ridge waveguide structure (112), and the buffer layer (102), the ridge waveguide structure (112), the N electrode (108), the right P electrode (109) and the left P electrode (110) between the two etching windows (111) form a suspended microbridge structure (113).

2. The germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain regulation according to claim 1, characterized in that: The coupled quantum well region (104) includes 4-8 pairs of five-layer coupled quantum wells.

3. The germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain regulation according to claim 1, wherein: A single pair of the five-layer coupled quantum wells includes three potential well layers and two inner potential barrier layers, and the three potential well layers and the two inner potential barrier layers are arranged alternately at intervals.

4. The germanium-silicon coupled quantum well electro-optic refractive index modulator based on strain regulation according to claim 3, wherein: Outer potential barrier layers with the same germanium composition are further arranged on the left and right sides of the five-layer coupled quantum wells, and the germanium composition of the inner potential barrier layer is higher than that of the outer potential barrier layer.

5. The strain-controlled germanium-silicon coupled quantum well electro-optic refractive index modulator according to claim 4, wherein: The thickness of the outer potential barrier layer is greater than that of the inner potential barrier layer; the thickness of the inner potential barrier layer is 1.5-5 nm.

6. The electro - refractive index modulator based on strain - controlled germanium - silicon coupled quantum wells according to claim 3, characterized in that: The inside of a single pair of the five-layer coupled quantum wells is a symmetric structure or an asymmetric structure.

7. The electro - refractive index modulator based on strain - controlled germanium - silicon coupled quantum wells according to claim 1, wherein: The width of the narrowest part of the ridge waveguide structure (112) is 1000-2000 nm; the etching depth of the side surface of the ridge waveguide structure (112) is limited downward to the inside of the buffer layer (102).

8. The strain-regulated germanium-silicon coupled quantum well electro-optic refractive index modulator according to claim 1, wherein: The etching length of the suspended region (114) is greater than the length of the etching window (111), and the etching width of the suspended region (114) is greater than the sum of the widths of the two etching windows (111) and the width of the suspended microbridge structure (113), and the etching depth of the suspended region (114) is 20-70 μm.

9. The strain-regulated germanium-silicon coupled quantum well electro-optic refractive index modulator according to claim 8, wherein: The width of each etching window (111) is 80-250 μm; The width of the suspended microbridge structure (113) is 4000-5000 nm; the suspended height of the suspended microbridge structure (113) is the etching depth of the suspended region (114).

10. The electro - refractive index modulator based on strain - controlled germanium - silicon coupled quantum wells according to claim 1, wherein: The buffer layer (102) is doped with boron element in a P type; the capping layer (106) is doped with phosphorus element or arsenic element in an N type.

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