CN108963752B - Electrically Driven Lasers Based on Circular Photonic Crystal Nanobeam Resonators - Google Patents

Abstract

The invention discloses an electric drive laser based on a circular photonic crystal nano-beam resonant cavity. The laser sequentially comprises a Si-based substrate and thermally oxidized SiO from bottom to top ₂ Layer, si waveguide, BCB layer, siO ₂ Layer, P-doped layer, active region, N-doped layer, siO ₂ A coating layer; the Si-based substrate, the thermally oxidized SiO ₂ The Si waveguides jointly form an SOI waveguide structure; the P doped layer, the active region and the N doped layer are etched into a nano beam resonant cavity altogether; the upper part of the P doped layer is plated with strip-shaped upper electrodes parallel to the Si waveguide on two sides of the nano beam resonant cavity, and the upper part of the nano beam resonant cavity is plated with lower electrodes along two ends of the Si waveguide direction. The invention uses the circular photon crystal nanometer beam as the resonant cavity of the laser, and improves the high-speed and low-energy consumption performance of the laser by further reducing the volume of the active area of the optical interconnection VCSEL.

Description

Electrically Driven Lasers Based on Toroidal Photonic Crystal Nanobeam Resonators

technical field

The invention belongs to the technical field of optoelectronics, and in particular relates to an electrically driven laser that further improves the high-speed performance and low energy consumption performance of an optical interconnection laser.

Background technique

Lasers are the core components of optical interconnects. How to obtain lasers with smaller volume, higher modulation speed and lower energy consumption is the key technology for the development of this field. At present, the high-speed and low-energy lasers are mainly vertical cavity surface emitting lasers (VCSEL), which are used in short-distance optical interconnections of big data centers, server clusters and petascale supercomputers. At present, the data transmission rate of 850 nm–VCSEL has reached 25 Gb/s and 28 Gb/s on single-channel Ethernet and fiber channel; the error-free transmission of 71 Gbit/s achieved in 2015 is the highest transmission speed of lasers at present, but the transmission energy consumption is too high due to high driving current.

According to the evaluation and prediction of the International Technology Roadmap for Semiconductors (ITRS), the energy consumption of communication light sources must be reduced by ~100 fJ/bit to maintain the economic and ecological viability of Internet and cloud computing services. The current lowest energy consumption high-speed VCSEL is ~95 fJ/bit required for 50 Gb/s error-free bit transmission by 850 nm–VCSEL at room temperature. Lowest energy consumption high-speed 980 nm– VCSEL at 85°C high-temperature operation is 139 fJ/bit required for 35 Gb/s error-free transmission.

The application of lasers on silicon-based chips (on-chip) optical interconnection directly requires that the characteristic scale of lasers is close to that of electronic devices, and the energy consumption is less than that of mature electrical interconnections, and the energy consumption is required to be on the order of 10 fJ/bit. The energy consumption of a laser is positively correlated with its size. The energy consumption of the order of 10 fJ/bit directly requires the mode volume of the laser to be smaller. VCSEL obviously cannot meet this requirement.

Therefore, how to further reduce the volume of the active region to improve the performance of the laser is of great significance for short-distance data transmission. Photonic crystals are formed by periodic arrangements of dielectrics with different dielectric constants, which can effectively regulate photons at the micro-nano scale. The resonant cavity formed has the advantages of high quality factor, small mode volume, and easy integration. It has been used in ultra-low threshold lasers, nonlinear optics, quantum optics and other fields. The photonic crystal microcavity laser has a high Purcell factor, and the spontaneous emission coupling coefficient is improved. The high spontaneous emission coupling coefficient can significantly reduce the laser threshold, and can increase the relaxation oscillation frequency, thereby increasing the modulation bandwidth and improving the modulation performance and dynamic energy consumption performance. Therefore, photonic crystal micro-nano cavity laser is an effective way to achieve low threshold and low energy consumption.

Contents of the invention

The object of the present invention is to provide a photonic crystal nano-beam laser structure which can further improve the high-speed and low-energy-consumption performance of optical interconnection lasers, so as to make up for the deficiencies in the prior art.

For the high-speed modulation performance of the laser in the present invention, the modulation bandwidth is limited by thermal limitation, damping limitation and relaxation oscillation frequency. The laser in the present invention breaks through the bandwidth limitation from three aspects: the photonic crystal nano-beam structure, the quantum well structure of the InP-based heteroepitaxial structure and the electrical injection structure.

Working principle of the present invention:

At present, the nanobeam cavities used in microcavity lasers are circular hole-shaped photonic crystal nanobeam cavities. Based on the progress of micro-nano technology, the ring-shaped photonic crystal nanobeam cavity with a slightly complex structure can provide higher Q value and smaller mode volume V. The annular photonic crystal nanobeam cavity has two types of circular holes on the symmetry axis and circular holes on both sides of the symmetry axis. The structure can be divided into a gradient area and a mirror area. The radius of the ring in the gradient area changes regularly, and the radius of the ring in the mirror area remains unchanged. The nanobeam cavities of these two structures have high quality factors and small mode volumes. Combining the rate equation and high-speed modulation theory to optimize parameters, a resonator suitable for high-speed and low-energy photonic crystal nanobeam lasers is designed. Using a high-quality one-dimensional photonic crystal nanobeam structure as a resonator, compared with the semiconductor resonator used in the current optical interconnect light source VCSEL, it can provide a higher quality factor and smaller mode volume, and can realize a micro-nano cavity laser with a lower threshold, higher modulation rate, and lower dynamic energy consumption than VCSEL.

At the same time, the present invention proposes a current injection structure on both sides of the plane, which is beneficial to the high-speed operation and high-efficiency current injection of the laser. Using the characteristics of different electron mobility and hole mobility, electrons are injected at both ends of the beam, and holes are injected at both sides of the beam. The p-i-n electric injection structure suitable for high-speed lasers, the proposed structure can allow more carriers to pass through the nano-beam cavity region and participate in radiative composite light emission.

In addition, the present invention adopts the scheme of wafer bonding and low refractive index dielectric material coating. By placing the nano-beam cavity on the upper part of the SOI waveguide, and separating the SOI waveguide and the nano-beam cavity with a BCB layer and a _SiO2 layer, this structure can realize evanescent wave coupling. At the same time, the entire structure is covered with _SiO2 to reduce thermal resistance and improve thermal performance. While solving the problem of heat dissipation, it can also protect the structure from the influence of the external environment.

Based on said principle, and in order to achieve the above object, the concrete technical scheme that the present invention takes is:

An electrically driven laser based on a ring-shaped photonic crystal nanobeam resonator, the laser consists of a Si-based substrate, a thermally oxidized SiO₂layer, Si waveguide, BCB layer, SiO₂layer, P-doped layer, active region, N-doped layer, SiO₂cladding layer; wherein, the Si-based substrate, the thermally oxidized SiO₂, the Si waveguide together constitutes an SOI waveguide structure; the P-doped layer, the active region, and the N-doped layer jointly carve out a nanobeam resonator; the upper part of the P-doped layer is plated with strip-shaped upper electrodes parallel to the Si waveguide on both sides of the nanobeam resonator, and the upper part of the nanobeam resonator is plated with lower electrodes at both ends along the direction of the Si waveguide; the nanobeam resonator is placed on the upper part of the SOI waveguide structure and passed through the BCB layer and SiO₂layers separated; the nanobeam resonator and SOI structure composed of dual mesa filled SiO₂For the cladding layer, the electrode window is etched by ICP, and the GSG-Pad electrode is evaporated by E-Beam to achieve a coplanar electrode structure.

Further, the SOI waveguide structure is prepared by CMOS technology: first, the cleaved SOI sheet is cleaned and dried, the _SiO2 layer is thermally oxidized, and the pattern is prepared by electron beam exposure, and then the mask pattern is transferred to the silicon layer by ICP dry etching.

Further, the nano-beam resonator is a series of nano-beam resonators etched by wet etching to strip the NIP structure of the InP substrate, which is a III-V group semiconductor material, etc. by dry etching.

Further, the nanobeam resonator structure is located on the axis of symmetry, and can be divided into a gradient region of the nanobeam cavity and a mirror region of the nanobeam cavity. The radius of the ring in the gradient region changes regularly, and the radius of the ring in the mirror region remains unchanged. The nanobeam resonator of this structure has a higher quality factor and a smaller mode volume; the ring has an inner diameter and an outer diameter.

Further, the SOI waveguide structure and the nanobeam resonator are bonded through the BCB layer and the _SiO2 intermediate layer, and the nanobeam resonator is vertically coupled to the underlying SOI waveguide structure to achieve directional output of light. The performance of the structure can be optimized by optimizing the waveguide width and _SiO2 thickness.

Further, the size of the SOI waveguide structure is the same as that of the BCB layer and the SiO ₂ layer, and the size of the nanobeam resonant cavity is smaller than that of the SOI waveguide structure.

Further, the size of each layer of the nanobeam resonator cavity is slightly different, the width of the P-doped layer is slightly smaller than that of the SOI waveguide structure, and larger than that of the active region and the N-doped layer, and the size of each layer is the same in length.

Further, the SiO ₂ cladding layer is a low-refractive-index material, which is used to solve the problem of heat dissipation and improve the thermal performance of the device.

Further, the upper and lower electrodes achieve good ohmic contact by optimizing the electrode sputtering conditions, alloy composition and rapid thermal annealing conditions, so as to reduce the contact resistance, increase the cut-off bandwidth, and improve the modulation bandwidth of the laser.

Advantages and beneficial effects of the present invention:

The invention utilizes the annular photonic crystal nano-beam as the resonant cavity of the laser, and further reduces the volume of the active area of the optical interconnection VCSEL to improve the high-speed and low-energy consumption performance of the laser.

In the present invention, electrons are injected at both ends of the nanobeam resonator and holes are injected at both sides of the beam. The new point injection structure of the nanobeam cavity laser utilizes the difference in mobility between electrons and holes, and serves as a coplanar electrode, which helps to achieve high-speed modulation rate. At the same time, the scheme of wafer bonding and low refractive index dielectric material _SiO2 coating solves the problem of thermal insulation in the air bridge electrical injection structure used by most photonic crystal nanolasers at present, and improves the modulation bandwidth by solving thermal limitations. Compared with direct bonding and SiO ₂ interlayer bonding process, BCB layer bonding is less difficult, can maintain better bonding interface flatness and less interface vacancies, and is fully compatible with the CMOS process of Si material. As a laser resonator, the nanobeam cavity is used to achieve high Q value and low mode volume, optimize parasitic parameters, increase Q value, and achieve high modulation bandwidth.

Compared with VCSEL, the invention can provide higher quality factor and smaller mode volume, and can realize lower threshold value, higher modulation speed and lower dynamic energy consumption than VCSEL. The improvement of the modulation bandwidth of the high-speed low-energy VCSEL is limited by the parasitic bandwidth and its own structure, but the invention overcomes the problems existing in the VCSEL.

Compared with the two-dimensional photonic crystal microcavity, the present invention is easier to realize the p-i-n junction as an electric injection light-emitting device, and more carriers participate in the radiation recombination light emission through the nano-beam cavity, and the laser is smaller in size and higher in integration degree, and is easy to integrate with silicon nano-waveguide and other functional photonic devices.

In addition, the present invention is expected to obtain high-speed electrically driven photonic crystal nanobeam laser technology, realize high-speed, low-threshold, and low-energy-consumption one-dimensional photonic crystal lasers, and help to solve the problem of lack of high-speed and low-energy light sources in the field of optical interconnection on silicon substrates, which is of great significance for realizing high-efficiency and low-cost interconnection.

Description of drawings

Fig. 1 is a schematic diagram of the overall cross-sectional structure of the present invention.

Fig. 2 is a schematic plan view of the annular photonic crystal nanobeam resonator cavity of the present invention.

Among them, 1-Si-based substrate, 2-thermally oxidized _SiO2 layer, 3-Si waveguide, 4-BCB layer, 5- _SiO2 layer, 6-P doped layer, 7-active region, 8-N doped region, 9- _SiO2 cladding layer, 10-lower electrode, 11-upper electrode, 12-gradient region of nanobeam cavity, 13-mirror region of nanobeam cavity, 14-ring inner diameter, 15-ring outer diameter.

Detailed ways

The present invention will be further explained and described below through specific embodiments in conjunction with the accompanying drawings.

Example:

如图1所示，一种基于圆环形光子晶体纳米梁谐振腔的电驱动激光器，该激光器由下至上依次包括Si基衬底1、热氧化SiO ₂层2、Si波导3、BCB层4、SiO ₂层5、P掺杂层6、有源区7、N掺杂层8、SiO ₂包覆层9；其中，所述Si基衬底1、所述热氧化SiO ₂ 2、所述Si波导3共同构成SOI波导结构；所述P掺杂层6、所述有源区7、所述N掺杂层8共刻出纳米梁谐振腔；所述P掺杂层6上部在纳米梁谐振腔两侧镀有与Si波导3平行的条状上电极11，所述纳米梁谐振腔上部沿Si波导3方向两端镀有下电极10；所述纳米梁谐振腔置于SOI波导3结构上部且通过BCB层4和SiO ₂层5隔开；所述纳米梁谐振腔和SOI波导结构组成的双台面填充SiO ₂包覆层9，利用ICP刻蚀开电极窗口，通过E-Beam蒸镀GSG-Pad电极，以实现共面电极结构。 The SiO ₂ cladding layer is a material with a low refractive index, which is used to solve the problem of heat dissipation and improve the thermal performance of the device. The upper electrode 11 and the lower electrode 10 realize good ohmic contact by optimizing the electrode sputtering conditions, alloy components and rapid thermal annealing conditions, so as to reduce the contact resistance, increase the cut-off bandwidth, and improve the modulation bandwidth of the laser.

The SOI waveguide structure is prepared by CMOS technology: firstly, the cleaved SOI sheet is cleaned and dried, the SiO ₂ layer 5 is thermally oxidized, the pattern is prepared by electron beam exposure, and the mask pattern is transferred to the silicon layer by ICP dry etching.

The nano-beam resonator is a NIP structure stripped of an InP substrate by wet etching, which is a group III-V semiconductor material, and a series of nano-beam resonators carved by dry etching and other processes; the dimensions of each layer of the nano-beam resonator are slightly different. The width of the P-doped layer is slightly smaller than that of the SOI waveguide structure, and larger than that of the active region 7 and N-doped layer 8, and the dimensions of each layer are the same in length.

As shown in Figure 2, the nanobeam resonator structure is located on the axis of symmetry and can be divided into a gradient region 12 of the nanobeam cavity and a mirror image region 13 of the nanobeam cavity. The radius of the ring in the gradient region 12 of the nanobeam cavity changes regularly, and the radius of the ring in the mirror region 13 of the nanobeam cavity remains unchanged. The nanobeam resonator of this structure has a higher quality factor and a smaller mode volume; the ring is provided with an inner diameter 14 and an outer diameter 15.

The SOI waveguide structure and the nanobeam resonator are bonded through the BCB layer and the _SiO2 intermediate layer, and the nanobeam resonator cavity is vertically coupled with the SOI waveguide structure below to realize directional output of light. The performance of the structure can be optimized by optimizing the width of the SOI waveguide structure and the thickness of SiO2; the SOI waveguide structure is the same size as the BCB layer 4 and the _SiO2 layer ₅ , and the size of the nanobeam resonator cavity is smaller than the SOI waveguide structure.

Claims (8)

1. An electrically driven laser based on a ring-shaped photonic crystal nanobeam resonator, characterized in that the laser comprises a Si-based substrate (1), a thermally oxidized SiO₂layer (2), Si waveguide (3), BCB layer (4), SiO₂layer (5), P-doped layer (6), active region (7), N-doped layer (8), SiO₂cladding layer (9); wherein, the Si-based substrate (1), the thermally oxidized SiO₂(2), the Si waveguide (3) together constitute an SOI waveguide structure; the P-doped layer (6), the active region (7), and the N-doped layer (8) co-carve out a nanobeam resonant cavity; the upper part of the P-doped layer (6) is plated with strip-shaped upper electrodes (11) parallel to the Si waveguide (3) on both sides of the nanobeam resonator, and the upper part of the nanobeam resonator is plated with lower electrodes (10) at both ends along the direction of the Si waveguide (3); the nanobeam resonator is placed on the SOI The upper part of the I-waveguide structure and through the BCB layer (4) and SiO₂layer (5); the nanobeam resonator and the SOI waveguide structure consist of a double-mesa filled SiO₂The cladding layer (9); the nano-beam resonator is a series of nano-beam resonators carved out by using wet etching to strip the NIP structure of the InP substrate and using a dry etching process; the nano-beam resonator structure is located on the axis of symmetry and is divided into a gradient area (12) of the nano-beam cavity and a mirror image area (13) of the nano-beam cavity. diameter (14) and ring outer diameter (15). 2. The electrically driven laser according to claim 1, characterized in that the laser uses ICP to etch the electrode window, and evaporates the GSG-Pad electrode by E-Beam to realize a coplanar electrode structure. 3. The electrically driven laser as claimed in claim 1, wherein the SOI waveguide structure is prepared by a CMOS process: first, the cleaved SOI sheet is cleaned and dried, the _SiO layer is thermally oxidized, and the pattern is prepared by electron beam exposure, and then the mask pattern is transferred to the silicon layer by ICP dry etching. 4. The electrically driven laser as claimed in claim 1, wherein the SOI waveguide structure and the nanobeam resonator are bonded through the BCB layer and the _SiO2 intermediate layer, and the nanobeam resonator is vertically coupled with the SOI waveguide structure below to realize the directional output of light. 5. The electrically driven laser according to claim 1, characterized in that the size of the SOI waveguide structure is the same as that of the BCB layer (4) and the SiO ₂ layer (5), and the size of the nanobeam resonator is smaller than that of the SOI waveguide structure. 6. The electrically driven laser according to claim 1, characterized in that the dimensions of each layer of the nanobeam resonator are different, the P-doped layer is smaller than the SOI waveguide structure in width, and larger than the active region (7) and N-doped layer (8), and the dimensions of each layer are the same in length. 7. The electrically driven laser according to claim 1, characterized in that the SiO ₂ cladding layer (9) is a low refractive index material. 8. The electrically driven laser according to claim 1, characterized in that, the upper electrode (11) and the lower electrode (10) realize ohmic contact by optimizing electrode sputtering conditions, alloy components and rapid thermal annealing conditions, so as to reduce contact resistance, increase cut-off bandwidth, and increase the modulation bandwidth of the laser.