Four-corner incidence germanium-silicon photoelectric detector

Abstract

The invention discloses a four-corner incidence germanium-silicon photoelectric detector, which comprises a silicon slab waveguide, the silicon ridge waveguide is arranged on the silicon slab waveguide; the strip waveguide is connected with the silicon ridge waveguide; a germanium layer disposed on the silicon ridge waveguide; a doped germanium layer disposed on the germanium layer; a pair of contact electrodes disposed on the silicon slab waveguide; and the germanium upper electrode is arranged on the doped germanium layer, and the germanium upper electrode and the contact electrode collect photon-generated carriers generated by the germanium layer. The strip waveguide is provided with four waveguide areas, and the four waveguide areas are respectively connected with four vertex angles of the silicon ridge waveguide; an optical signal is quartered, is input from the four-way strip waveguide, is propagated along the transmission direction, and is gradually and uniformly coupled into germanium at the same time. The germanium layer generates current after absorbing the optical signal, and conversion of the photoelectric signal is completed. According to the photoelectric detector, the uniformity of light absorption of the germanium layer is improved by changing the incident structure of light, so that the saturation power of the photoelectric detector is enhanced.

Description

Technical Field

[0001] The present invention belongs to the field of photoelectric detectors, and more specifically, relates to a four-corner incident germanium silicon photoelectric detector. Background Art

[0002] Microwave photonics uses optical integration technology to generate and transmit microwave signals, and up-converts radio frequency signals to the optical frequency band. It has the characteristics of large bandwidth, low loss, and low electromagnetic interference. These characteristics give microwave photonics unique advantages and have attracted widespread attention in the academic community. One of the most important indicators of microwave photonic links is the largest possible spurious-free dynamic range, in which photodetectors play a vital role, requiring photodetectors to have the largest possible saturation power.

[0003] The light-absorbing materials of photodetectors include germanium, group III-V materials, graphene, etc. Compared with group III-V materials and other materials, germanium can be directly epitaxially grown on silicon and is compatible with existing CMOS processes. At the same time, other optoelectronic devices on silicon are also relatively mature. Silicon-based germanium photodetectors can be integrated with other optoelectronic devices on silicon, and can have a high degree of integration. In addition, germanium has good thermal conductivity and is less prone to thermal breakdown than group III-V elements, which is crucial to the high saturation power performance of photodetectors. Therefore, germanium silicon photodetectors have unique advantages among many types of photodetectors.

[0004] At present, the main limiting factor of the saturation power of germanium silicon photodetectors is the uneven absorption of light by germanium. At present, the incident mode of traditional germanium silicon photodetectors is that a single incident waveguide is directly connected to the front end of germanium. Since the propagation direction of the incident light directly overlaps with the bottom of the germanium area, the absorption of light inside the germanium after it is output from the incident waveguide will decay exponentially. A large amount of light accumulates at the front end of the germanium, but the tail of the germanium lacks sufficient light absorption. After the germanium layer absorbs light, a large number of electron-hole pairs are excited, called photogenerated carriers. Under the action of an external electric field, these electron-hole pairs will quickly drift toward the corresponding electrodes and move in a directional manner to form a current. However, since the front end of the germanium absorbs excessive light, a large number of electron-hole pairs will accumulate, which will generate a reverse electric field opposite to the external electric field, weakening the effect of the external electric field, weakening the drift motion of the electron-hole pairs, and the generated current of the germanium layer tends to saturate at the front end. The output power of the photodetector is positively correlated with the output current. At this time, even if the input power of the optical signal is increased, since the front end is already saturated, the light reaching the tail is obtained after exponential decay, and the proportion is very small. The response photocurrent is also very weak, causing the overall output photocurrent of the germanium silicon photodetector to reach saturation prematurely.

[0005] In summary, the demand for spurious-free dynamic range in fields such as microwave photonics and analog photonic links is further increasing, but the existing technical solutions have the problem of uneven distribution of germanium absorbed light and restricted saturation power, so further improvement is needed. Summary of the invention

[0006] The purpose of the present invention is to provide a four-corner incident germanium silicon photodetector to overcome the current problem that the optical signal is difficult to be uniformly absorbed in the germanium layer, thereby limiting the saturation power of the photodetector.

[0007] A four-corner-incident germanium silicon photodetector, comprising:

[0008] Silicon slab waveguide;

[0009] A silicon ridge waveguide disposed on the silicon slab waveguide;

[0010] a strip waveguide connected to the silicon ridge waveguide;

[0011] a germanium layer disposed on the silicon ridge waveguide;

[0012] a doped germanium layer disposed on the germanium layer;

[0013] A pair of contact electrodes disposed on the silicon slab waveguide;

[0014] A germanium upper electrode disposed on the doped germanium layer;

[0015] The strip waveguide has four waveguide regions, including a first waveguide region, a second waveguide region, a third waveguide region and a fourth waveguide region, and the four waveguide regions are respectively connected to the four vertex corners of the silicon ridge waveguide; after being divided into four equal parts, the optical signal is respectively incident on the four waveguide regions, and then coupled to the germanium layer and absorbed by the germanium layer.

[0016] The bottom surface area of ​​the germanium layer is smaller than the top surface area of ​​the silicon ridge waveguide. A gap is left between the bottom surface edge of the germanium layer and the top surface edge of the silicon ridge waveguide, and the gap is greater than the width of each waveguide area in the four waveguide areas.

[0017] The spacing is used to prevent the optical signals emitted from the four waveguide regions from directly overlapping with the germanium region, thereby preventing the uneven distribution caused by the direct absorption of the optical signals by the germanium region. During the transmission of the optical signal along the propagation direction on the side of the germanium region, multiple high-order mode states will be excited. Due to the high absorption coefficient of the germanium layer material, these multi-mode signals after interference will be gradually and evenly absorbed by the germanium layer.

[0018] The first waveguide area and the third waveguide area are symmetrical with respect to the central axis perpendicular to the bottom surface of the germanium layer, and the second waveguide area and the fourth waveguide area are symmetrical with respect to the central axis perpendicular to the bottom surface of the germanium layer. The symmetrical shape helps the germanium layer to maintain the equivalence of light absorption in the front and rear areas and the left and right areas, thereby ensuring that the optical signal of the germanium layer is uniformly absorbed.

[0019] There are two etched triangular notches on two sides of the silicon ridge waveguide and they are symmetrical about the central axis of the germanium layer, or there are four etched triangular notches on four sides of the silicon ridge waveguide and they are symmetrical about the central axis of the germanium layer. The etched notches are used to constrain the propagation direction of the optical signal so that the optical signal is transmitted to the germanium layer located at the center of the silicon ridge waveguide, which helps to improve the photoelectric conversion efficiency and the responsiveness of the photodetector.

[0020] The bottom surface of the germanium layer is rectangular, and the first waveguide region, the second waveguide region, the third waveguide region and the fourth waveguide region are all strip-shaped;

[0021] The angle between the central axis of the first waveguide region along the optical signal transmission and the long side of the bottom surface of the germanium layer is 1-45°, which is the first angle;

[0022] The angle between the central axis of the second waveguide region along the optical signal transmission and the long side of the bottom surface of the germanium layer is 1-45°, which is the second angle;

[0023] The angle between the central axis of the third waveguide region along the optical signal transmission and the long side of the bottom surface of the germanium layer is 1-45°, which is the third angle;

[0024] The angle between the central axis of the fourth waveguide region along the optical signal transmission and the long side of the bottom surface of the germanium layer is 1-45 degrees, which is the fourth angle.

[0025] The first angle, the second angle, the third angle and the fourth angle are equal. The four waveguide areas are deflected at a small angle at the same time, which can ensure that the front and rear areas of the germanium area absorb the light signal symmetrically with the action area, while making the transmission direction of the light signal deviate to the germanium area. In addition, setting a suitable angle can also make the waveguide shape correspond to the etched notch instead of dissipating in other directions, avoiding the loss of additional light signals caused by the connection between the waveguide area and the silicon ridge waveguide.

[0026] The silicon slab waveguide and the silicon ridge waveguide have the same doping type, which is the first doping type;

[0027] The doped germanium layer is of the second doping type;

[0028] The first doping type and the second doping type are opposite.

[0029] Optionally, the first doping type is P-type, and the second doping type is N-type, forming a photodetector with a PIN structure. The N-type doped germanium layer and the P-type doped region will form a built-in electric field inside the germanium layer. After the germanium layer absorbs the light signal, it will generate a large number of photogenerated carriers under the action of the built-in electric field. The P-type doped silicon ridge waveguide and silicon slab waveguide at the bottom of the germanium region can conduct electricity due to doping. The holes move in a directional manner toward a pair of contact electrodes on the silicon slab waveguide and are collected by the contact electrodes on the silicon slab waveguide. The electrons move in a directional manner toward the germanium upper electrode and are collected by the germanium upper electrode. The sum of the currents formed by the electrons and holes is the sum of the photocurrents generated by the germanium layer. The germanium silicon photoelectric detection completes the conversion of the light signal into the electrical signal.

[0030] Optionally, the first doping type is N-type, and the second doping type is P-type, forming a photodetector with a NIP type structure.

[0031] Compared with the existing technology, the design proposed by the present invention has the following advantages:

[0032] The design of the present invention aims at this problem and adopts a new coupling method. The optical signal will be evenly divided into four equal parts and incident from four strip waveguides to the silicon ridge waveguide. Since the four strip waveguides are directly connected to the four corners of the silicon ridge waveguide, and the silicon ridge waveguide is spaced a certain distance from the edge of the germanium layer, the four optical signals will be transmitted along this spacing while gradually coupling to the two sides of the germanium from the front and back through the evanescent wave, and then gradually and evenly coupled to the center of the germanium until it is completely absorbed by the germanium. Therefore, there is a very uniform light field distribution from the front end of the germanium area to the tail end of the germanium area. It avoids the problem of uneven light absorption in the germanium area caused by the use of a single waveguide input in the traditional structure, and the light transmission direction emitted by the waveguide directly overlaps with the bottom of the germanium area. The saturation power of the photodetector can be greatly improved. In addition, the design proposed by the present invention is fully compatible with existing processes, does not introduce other complex process flows, and is simple to manufacture. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the structure of a four-corner-incident germanium silicon photodetector provided by an example of the present invention;

[0034] Figure 2 A schematic diagram of the structure of a photoelectric detector of the prior art structure;

[0035] Figure 3 It is a top view of a four-corner-incident germanium silicon photodetector provided by an example of the present invention;

[0036] Figure 4 The absorption light field distribution diagram of the germanium region simulated for the photodetector with the prior art structure;

[0037] Figure 5This is a simulated germanium region absorption light field distribution diagram of a four-corner incident germanium silicon photodetector provided by an example of the present invention;

[0038] Figure 6 The figure is a comparison diagram of the output current of a four-corner-incident germanium silicon photodetector provided by an example of the present invention and a germanium silicon photodetector in the prior art with respect to the change of input light power. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings.

[0040] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0041] like Figure 1 As shown, a preferred example structure of a four-corner-incident germanium silicon photodetector includes: a strip waveguide 100, a silicon slab waveguide 121, a silicon ridge waveguide 122, a germanium layer 131, a doped germanium layer 130, a germanium upper electrode 151 and a pair of contact electrodes 141 on the silicon slab waveguide 121. Figure 3 It is a top view of the four-corner incident germanium silicon photodetector.

[0042] The silicon ridge waveguide 122 is arranged on the silicon slab waveguide 121. The strip waveguide 100 has four waveguide regions, including a first waveguide region 101, a second waveguide region 102, a third waveguide region 103 and a fourth waveguide region 104, which are respectively connected to the four vertex corners of the silicon layer ridge waveguide 122. The optical signal is divided into four equal parts, input from the four waveguide regions respectively, and coupled into the front end and the rear end of the germanium layer 131 respectively.

[0043] The germanium layer 131 is disposed on the silicon layer ridge waveguide 122, the bottom surface area of ​​the germanium layer 131 is smaller than the top surface area of ​​the silicon ridge waveguide 122, and the bottom edge of the germanium layer 131 is spaced a certain distance from the top edge of the silicon ridge waveguide 122, and the spacing is greater than the width of each waveguide area in the four waveguide areas. In this way, the germanium area can be prevented from directly butting against and overlapping with the light emitting direction of the strip waveguide 100.

[0044] The optical signal divided into four equal parts will be gradually and evenly coupled to the front and rear ends of the two side walls of the germanium region while being transmitted along the transmission direction of the strip waveguide 100. Since the refractive index of the germanium region is significantly different from that of the silicon region, the optical signal can be coupled more efficiently, and the energy of the signal will be absorbed by the germanium layer from four sides.

[0045] In this example, the first waveguide region 101 and the third waveguide region 103 are symmetrically arranged with the central axis perpendicular to the bottom surface of the germanium layer, and the second waveguide region 102 and the fourth waveguide region 104 are symmetrically arranged with the central axis perpendicular to the bottom surface of the germanium layer. In this way, a completely uniform four-equally divided optical signal enters the silicon ridge waveguide and the silicon substrate waveguide through four waveguide regions that are symmetrical and have the same shape, thereby ensuring the uniformity of the optical signal coupling to the germanium region.

[0046] The four sides of the silicon layer ridge waveguide 122 each have four etched isosceles triangle notches, and the two isosceles triangle notches on the long side of the silicon layer ridge waveguide 122 are of the same shape, symmetrical about the center point of the germanium layer 131, and the bottom of the isosceles triangle completely overlaps with the long side of the silicon layer ridge waveguide 122. The two isosceles triangle notches on the short side of the silicon layer ridge waveguide 122 are of the same shape, symmetrical about the center point of the germanium layer 131, and the bottom of the isosceles triangle completely overlaps with the short side of the silicon layer ridge waveguide 122. The four etched isosceles triangle notches can constrain the flow path of light, so that the light is transmitted to the area where the germanium 131 is located instead of escaping, which helps to improve the photoelectric conversion efficiency of the detector.

[0047] The first waveguide region 101, the second waveguide region 102, the third waveguide region 103 and the fourth waveguide region 104 are all in strip shape. The angles between the four waveguide regions and the first direction along the central axis of light transmission are all equal, and are set to 5° in this example. The simultaneous deflection of the four waveguide regions at a small angle can make the direction of the optical signal deviate to the germanium region instead of dissipating in other directions. In addition, setting a suitable angle can also make the waveguide shape correspond to the etched notch, and can also avoid the loss of additional optical signals caused by the connection between the waveguide region and the silicon ridge waveguide.

[0048] The top of the germanium layer 131 is N-doped, and the silicon slab waveguide and the silicon ridge waveguide are P-doped. The middle germanium layer is not doped and is an intrinsic layer used to absorb optical signals to generate carriers.

[0049] The germanium upper electrode 151 and the contact electrode 141 on the silicon slab waveguide will form an external electric field that is larger than the built-in electric field of the germanium layer under an external reverse bias. After the germanium layer 131 absorbs light, a large number of photons will excite electron-hole pairs inside the germanium layer. Under the action of the external electric field, the electron-hole pairs will move in a directed manner toward the corresponding electrode 151 above the germanium layer (i.e., the germanium upper electrode 151) and the contact electrode 141, forming a current.

[0050] Figure 2The figure shows a schematic diagram of a conventional photodetector structure in the prior art. It includes a strip waveguide layer 200, a silicon slab waveguide layer 222, a silicon ridge waveguide layer 221, a doped germanium layer 230, a germanium layer 231, a silicon contact electrode 241, and an electrode 251 above the germanium layer. After the light signal is transmitted through the strip waveguide layer 200, it will directly dock with the bottom of the germanium layer, and the emitted light signal will be directly absorbed by the germanium layer in the contact area of ​​the strip waveguide layer 200 and the silicon slab waveguide layer 221, resulting in a large amount of light signal accumulation at the front end of the germanium layer.

[0051] Figure 4 This is a diagram of the absorption light field distribution of the germanium region simulated in the photodetector in the prior art. Figure 5 This is a simulated distribution diagram of the germanium region absorption light field of a four-corner incident germanium silicon photodetector provided by the example of the present invention; it can be seen that the photodetector of the prior art absorbs a large amount of light power concentrated at the front end of the germanium region, and the proportion of light absorbed at the tail is very small. However, the light field of the photodetector provided by the example of the present invention is very uniformly distributed in the germanium region.

[0052] Comparison of saturation current of germanium-silicon photodetector of the present invention and existing technical structure Figure 6 shown. Figure 4 The middle circle line is the four-corner incident germanium silicon photodetector designed by the present invention. The length, width and doping of germanium are all set to be consistent to control variables. The output power of the photodetector is proportional to the square of the output photocurrent of the photodetector. Under the same conditions, it can be seen that the saturation value of the output photocurrent of the germanium silicon photodetector with a four-corner incident structure is significantly raised, indicating that the saturation power performance of the four-corner incident germanium silicon photodetector proposed by the present invention is significantly improved.

[0053] This is because the existing structure of the germanium silicon photodetector strip waveguide is directly connected to the bottom waveguide area of ​​germanium, resulting in an exponential distribution of germanium absorption of light. When the input light power is large, the light is concentrated on the front end of the germanium, the space charge effect inhibits the increase of the output current, and the tail of the germanium lacks sufficient light absorption. The photodetector reaches a saturated state. Even if the input light signal power is increased, the output current cannot continue to increase; however, for the germanium silicon photodetector with four-corner incidence, the light field distribution is very uniform. In the process of moving along the propagation direction, the light signal is gradually and evenly coupled to the germanium through the evanescent wave, forming a uniform light field absorption. The number of photogenerated carriers excited at each location in the germanium layer is almost equal, and there will be no large accumulation in a certain place. Therefore, when the same large light power is input, the photocurrent of the four-corner incident germanium silicon photodetector will not reach saturation, but will continue to increase, thereby greatly improving the saturation power of the photodetector.

[0054] The present invention proposes a four-corner-incident germanium-silicon photoelectric efficiency detector, in which the four equally divided light signals are incident from four strip waveguides into the bottom ridge waveguide on the germanium side, and then gradually and evenly coupled into the germanium along the light propagation direction, forming a uniform light field absorption, which can effectively improve the saturation power of the detector. The device manufacturing process is simple and does not add additional complexity.

Claims

1. A four-corner-incident germanium silicon photodetector, characterized in that: include: Silicon slab waveguide; A silicon ridge waveguide disposed on the silicon slab waveguide; a strip waveguide connected to the silicon ridge waveguide; a germanium layer disposed on the silicon ridge waveguide; a doped germanium layer disposed on the germanium layer; A pair of contact electrodes disposed on the silicon slab waveguide; A germanium upper electrode disposed on the doped germanium layer; The strip waveguide has four waveguide regions, including a first waveguide region, a second waveguide region, a third waveguide region and a fourth waveguide region, and the four waveguide regions are respectively connected to the four vertex corners of the silicon ridge waveguide; The bottom surface area of ​​the germanium layer is smaller than the top surface area of ​​the silicon ridge waveguide. A gap is left between the bottom surface edge of the germanium layer and the top surface edge of the silicon ridge waveguide, and the gap is greater than the width of each waveguide area in the four waveguide areas.

2. The four-corner-incident SiGe photodetector according to claim 1, characterized in that: The first waveguide region and the third waveguide region are symmetrical with respect to a central axis perpendicular to the bottom surface of the germanium layer, and the second waveguide region and the fourth waveguide region are symmetrical with respect to a central axis perpendicular to the bottom surface of the germanium layer.

3. The four-corner-incident SiGe photodetector according to claim 1, characterized in that: There are two etched triangular notches on two sides of the silicon ridge waveguide and they are symmetrical about the central axis of the germanium layer, or there are four etched triangular notches on four sides of the silicon ridge waveguide and they are symmetrical about the central axis of the germanium layer.

4. The four-corner-incident SiGe photodetector according to claim 1, characterized in that: The bottom surface of the germanium layer is rectangular, and the first waveguide region, the second waveguide region, the third waveguide region and the fourth waveguide region are all strip-shaped; The angle between the central axis of the first waveguide region along the optical signal transmission and the long side of the bottom surface of the germanium layer is 1-45°, which is the first angle; The angle between the central axis of the second waveguide region along the optical signal transmission and the long side of the bottom surface of the germanium layer is 1-45°, which is the second angle; The angle between the central axis of the third waveguide region along the optical signal transmission and the long side of the bottom surface of the germanium layer is 1-45°, which is the third angle; The angle between the central axis of the fourth waveguide region along the optical signal transmission and the long side of the bottom surface of the germanium layer is 1-45 degrees, which is the fourth angle.

5. The four-corner-incident SiGe photodetector according to claim 4, characterized in that: The first angle, the second angle, the third angle and the fourth angle are equal.

6. The four-corner-incident SiGe photodetector according to claim 1, characterized in that: The silicon slab waveguide and the silicon ridge waveguide have the same doping type, which is the first doping type; The doped germanium layer is of the second doping type; The first doping type and the second doping type are opposite.

7. The four-corner-incident SiGe photodetector according to claim 6, characterized in that: The first doping type is P type or N type, and the second doping type is P type or N type.

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