A photoelectric detector based on carrier trajectory regulation

Abstract

The application provides a photoelectric detector based on carrier trajectory regulation, and belongs to the technical field of semiconductor photoelectric devices, and comprises a semiconductor substrate layer and an absorption layer. The semiconductor substrate layer comprises a P-type doped region and an N-type doped region which are arranged transversely apart or adjacent to each other, and a junction region is formed between the two. The absorption layer is arranged on the semiconductor substrate layer and across the junction region. The lateral geometric center of the absorption layer has a lateral offset amount from the lateral geometric center of the junction region, so that the lateral overlap ranges of the bottom of the absorption layer and the P-type doped region and the N-type doped region are different, thereby making photo-generated electrons and photo-generated holes have different average drift distances, and the average drift distance of slow carriers is shorter. The application reduces the limitation of slow carriers on the overall transit time through asymmetric trajectory regulation, and can take into account higher light absorption efficiency and response speed without reducing the volume of the absorption layer, thereby breaking the bottleneck of mutual restriction between bandwidth and absorption efficiency.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronic device technology, and more specifically, relates to a photodetector based on carrier trajectory modulation. Background Technology

[0002] Silicon-based optoelectronics technology, compatible with mature CMOS (Complementary Metal-Oxide-Semiconductor) processes, boasts advantages in high integration and low cost, making it a core technology for next-generation high-speed optical communication and interconnect systems. In silicon-based optoelectronic links, waveguide-integrated silicon-based germanium photodetectors are responsible for converting optical signals into electrical signals. Their response speed (bandwidth) and light absorption efficiency (responsivity) directly determine the transmission capacity and power consumption of the entire system. One of the core physical limiting factors determining the high-frequency bandwidth of a photodetector is the carrier transit time, i.e., the time required for photogenerated electrons and holes to drift from the depletion region to the collecting electrode. The physical factor affecting responsivity is primarily the size of the absorption region.

[0003] Traditional waveguide-integrated horizontal PIN silicon-based germanium photodetectors typically employ a perfectly symmetrical design, where the germanium absorber layer is located directly above the underlying intrinsic silicon region, and the distances from the P-type and N-type doped regions to the center of the germanium absorber layer are equal. However, this symmetrical structure exposes a severe physical bottleneck when pursuing extreme high-frequency bandwidth: in germanium, the saturation drift velocity of electrons is greater than that of holes. This inherent mismatch in carrier drift velocities means that while fast electrons are rapidly collected, slow holes continue to drift slowly within the depletion region. This severe asynchrony in charge collection forces the overall carrier transit time of the device to be dominated by slow holes, leading to severe high-frequency response decay (high-frequency roll-off), becoming a fatal weakness limiting further improvements in detector bandwidth.

[0004] To overcome the transit time bottleneck dominated by slow holes, conventional improvement methods typically involve directly reducing the lateral dimensions of the device, i.e., reducing the overall width of the germanium absorber layer, thereby forcibly shortening the physical drift distance of charge carriers. However, this approach of forcibly reducing size in an asymmetric architecture faces a fatal optical bottleneck: reducing the width of the germanium absorber layer significantly weakens the waveguide device's ability to confine and absorb the light field, leading to a sharp reduction in the effective light absorption volume and a precipitous drop in light absorption efficiency, which in turn severely sacrifices the detector's responsivity.

[0005] Reference 1 (Optics Express, 2016, 24(5): 4622) discloses a typical method for realizing a horizontal high-speed germanium-silicon photodetector, which involves first etching a groove on an SOI (silicon-on-insulator) substrate, and then epitaxially growing a germanium absorption region in this groove to realize a horizontal PIN diode. Figure 1The diagram below shows the structure of the photodetector in Reference 1, which includes a P-type doped silicon layer 101, an intrinsic germanium absorption region 102, an N-type doped silicon layer 103, an intrinsic silicon layer 104, and a silicon contact electrode 105. 101, 102, 103, and 104 form a horizontal PIN junction, and 105 is the electrode for collecting photocurrent. Reference 1 reduces the transit time by decreasing the thickness of the germanium absorption region, thereby improving the device bandwidth. However, the main drawback is that reducing the thickness or width of the germanium absorption region leads to a smaller absorption region volume, which in turn reduces the responsivity. Ultimately, the product of responsivity and bandwidth remains difficult to exceed its limit.

[0006] To address this issue, Chinese patent application CN116936670A proposes a novel metal electrode design—specifically, a silicon contact electrode surrounding three sides of the germanium absorption region—to improve detector bandwidth by reducing resistance and thus RC parasitic effects, without altering the absorption region volume. However, this method is designed for vertical PIN structures. For horizontal PIN junctions, the junction capacitance is smaller, resulting in less RC parasitic effect limiting bandwidth. Therefore, this method offers only a slight bandwidth improvement for horizontal PIN photodetectors. A new mechanism to reduce transit time is still urgently needed to break this technological deadlock and achieve a win-win situation for both bandwidth and responsivity. Summary of the Invention

[0007] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a photodetector based on carrier trajectory modulation, thereby solving the technical problem that the photodetector structure is completely symmetrical in the prior art, resulting in the transit time of photogenerated holes being much longer than that of photogenerated electrons, thus causing severe signal tailing and limited bandwidth improvement.

[0008] To achieve the above objectives, according to one aspect of the present invention, a photodetector based on carrier trajectory modulation is provided, comprising a semiconductor substrate and an absorption layer, wherein the semiconductor substrate includes laterally spaced or adjacent P-type doped regions and N-type doped regions forming a junction between them. The absorption layer is disposed on the semiconductor substrate and spans the junction region; The lateral geometric center of the absorption layer is offset from the lateral geometric center of the junction region, so that the lateral overlap between the bottom of the absorption layer and the P-type doped region and the N-type doped region is different, so as to construct an asymmetric carrier physical drift path and make different types of photogenerated carriers have different average drift distances.

[0009] Preferably, the absorption layer is a germanium absorption layer.

[0010] Preferably, the semiconductor substrate layer is a silicon layer.

[0011] More preferably, for the photogenerated carriers generated in the germanium absorption layer, the asymmetric carrier physical drift path allocates a shorter physical transport distance for slow holes and a longer physical transport distance for fast electrons, thereby compensating for the difference in saturation drift velocity between electrons and holes and reducing the limitation of photogenerated holes on the overall carrier transit time.

[0012] Preferably, the length of the lateral offset is 5% to 30% of the lateral width of the absorbent layer.

[0013] Preferably, the lateral width of the absorption layer is 300 nm.

[0014] Preferably, the lateral spacing between the P-type doped region and the N-type doped region is 0 nm to 250 nm; when the lateral spacing is greater than 0 nm, an intrinsic semiconductor region is provided between the P-type doped region and the N-type doped region.

[0015] Preferably, the P-type doped region is moderately doped, with a doping concentration on the order of 10. 19 cm -3 .

[0016] Preferably, the N-type doped region is moderately doped, with a doping concentration on the order of 10. 19 cm -3 .

[0017] Preferably, the drift distance between photogenerated holes and photogenerated electrons is changed by adjusting the length of the lateral offset, thereby reducing the average transit time difference between photogenerated electrons and photogenerated holes.

[0018] More preferably, by adjusting the lateral offset, the average transit time of photogenerated electrons and photogenerated holes is made to be consistent.

[0019] Preferably, the semiconductor substrate is formed with an optical waveguide for guiding the incident light signal and coupling it into the absorption layer.

[0020] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: 1. The photodetector based on carrier trajectory modulation proposed in this invention constructs an asymmetric carrier drift trajectory by laterally offsetting the lateral geometric center of the absorption layer from that of the junction region. This results in different lateral overlaps between the bottom of the absorption layer and the P-type and N-type doped regions. This structure physically redistributes carrier paths, allowing slow carriers (such as holes) to have shorter average drift distances and fast carriers (such as electrons) to have longer average drift distances, fundamentally compensating for the inherent velocity differences between the two. This effectively alleviates the limitation of slow carriers on the high-frequency response of the device, reduces the transit time without changing the thickness or width of the absorption layer, and achieves a win-win situation for both bandwidth and responsivity.

[0021] 2. The photodetector based on carrier trajectory modulation proposed in this invention, compared with the prior art which improves bandwidth by shortening the device length to reduce the junction area and junction capacitance, or by narrowing the junction region to shorten the carrier drift distance, utilizes asymmetric path design to control the drift trajectory of electrons and holes to improve speed. It does not require a significant sacrifice of the effective light absorption volume of the absorption layer, thus achieving ultra-high bandwidth while maintaining high light absorption efficiency, and obtaining an extremely high bandwidth-efficiency product (BEP).

[0022] 3. The photodetector based on carrier trajectory modulation proposed in this invention can achieve its asymmetric bias structure simply by pre-setting a lateral offset of the geometric center of the photolithographic mask pattern, without introducing any new materials, adding extra doping steps, or complex heterogeneous integration processes. This solution has a simple structure, is fully compatible with existing standard CMOS-compatible silicon photonics manufacturing processes, and possesses extremely high engineering feasibility, mass production potential, and extremely low modification costs. Attached Figure Description

[0023] Figure 1 This is a three-dimensional schematic diagram of a horizontal photodetector structure in the prior art; Figure 2 This is a schematic diagram of the junction cross-section of a horizontal photodetector in the prior art.

[0024] Figure 3 This is a schematic diagram of the junction cross-section of a photodetector based on carrier trajectory modulation provided in an embodiment of the present invention.

[0025] Figure 4 This is a graph showing the change in carrier transit time with the offset of the horizontal PIN junction center relative to the germanium center in an embodiment of the present invention.

[0026] Figure 5 This is a graph showing the frequency response of a silicon-based germanium detector based on carrier trajectory modulation and a traditional symmetrical structure, as described in this embodiment of the invention.

[0027] In all the figures, the same reference numerals are used to denote the same elements or structures, wherein: 101-P-type doped silicon layer; 102-intrinsic germanium absorption region; 103-N-type doped silicon layer; 104-intrinsic silicon layer; 105-contact electrode on silicon; 201-P-type doped layer; 202-germanium absorption layer; 203-N-type doped layer; 204-intrinsic silicon layer; 205-photogenerated electron; 206-photogenerated hole; 207-electron drift trajectory; 208-hole drift trajectory; 301-P-type doped region; 302-absorption layer; 303-N-type doped region; 304-intrinsic semiconductor region; 305-photogenerated electron; 306-photogenerated hole; 307-electron drift trajectory; 308-hole drift trajectory; 309-lateral offset. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0029] Figure 1 This is a three-dimensional schematic diagram of the structure of a horizontal photodetector in the prior art. Figure 2 This is a schematic diagram of the junction region of the detector. (For example...) Figure 2 As shown, the photodetector includes a P-type doped layer 201, a germanium absorber layer 202, an N-type doped layer 203, and an intrinsic silicon layer 204. The P-type doped layer 201, the intrinsic silicon layer 204, and the N-type doped layer 203 together form a horizontal PIN junction, and the PIN junction is laterally symmetrically distributed with respect to the germanium absorber layer 202.

[0030] Furthermore, since the saturation drift velocity of photogenerated holes in germanium is slower than that of photogenerated electrons, under a completely symmetrical electric field and physical path, the transit time required for photogenerated holes 206 to complete collection is longer than that for photogenerated electrons 205. Therefore, photogenerated holes significantly restrict the overall carrier transit process and may cause signal tailing in the high-frequency response, thus limiting further increases in device bandwidth.

[0031] This invention proposes a photodetector based on carrier trajectory modulation, such as... Figure 3 As shown, it includes a semiconductor substrate layer and an absorption layer 302 disposed on the semiconductor substrate layer.

[0032] In a preferred embodiment of the present invention, the absorption layer 302 is a germanium absorption layer and the semiconductor substrate layer is a silicon layer.

[0033] The semiconductor substrate includes P-type doped regions 301 and N-type doped regions 303 arranged laterally spaced or adjacent to each other, forming a junction region between them. When the P-type doped regions 301 and N-type doped regions 303 are spaced apart, an intrinsic semiconductor region 304 can be disposed between them to form a horizontal PIN junction; when the P-type doped regions 301 and N-type doped regions 303 are adjacent to each other, they form a horizontal PN junction. Figure 3 The preferred embodiment shown employs a horizontal PIN junction structure.

[0034] The germanium absorber layer 302 is disposed across the junction region, covering the entire intrinsic semiconductor region 304, and extends to both sides to cover the adjacent portions of the P-type doped region 301 and the N-type doped region 303.

[0035] The lateral geometric center of the junction region has a lateral offset of 309 relative to the lateral geometric center of the germanium absorber layer 302. This lateral offset of 309 makes the contact width between the germanium absorber layer and the P-type doped region 301 greater than its contact width with the N-type doped region 303.

[0036] To further explain, the length of the lateral offset 309 is 5% to 30% of the total lateral width of the germanium absorption layer.

[0037] To further clarify, the lateral width of the germanium absorber layer 302 is 300 nm.

[0038] To further explain, the lateral width of the intrinsic semiconductor region 304 is preferably 150 nm to 250 nm.

[0039] To further clarify, the P-type doped region 301 and the N-type doped region 303 are moderately doped, with a doping concentration on the order of 10. 19 cm -3 .

[0040] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0041] In this embodiment, the core of the photodetector is a horizontal PIN diode formed by the aforementioned P-type doped region 301, intrinsic semiconductor region 304, and N-type doped region 303. An optical waveguide is formed in the semiconductor substrate layer to guide incident light waves into the germanium absorption layer 302. The germanium absorption layer 302 absorbs the incident light, thereby exciting photogenerated carriers (photogenerated electrons 305 and photogenerated holes 306). Compared to the completely symmetrical design in existing technologies, this embodiment establishes an asymmetric carrier physical drift path (ACT) by introducing a lateral offset 309. This scheme does not change the light absorption volume of the germanium absorption layer 302, effectively redistributing the carrier drift distance at a spatial geometric level without sacrificing light absorption efficiency.

[0042] Specifically, the asymmetric carrier physical drift path assigns a shorter hole drift trajectory 308 to the slow photogenerated holes 306 and a longer electron drift trajectory 307 to the fast photogenerated electrons 305, thereby compensating for the difference in saturation drift velocity between electrons and holes, achieving synchronization of their transit times, reducing the limitation of photogenerated holes on the overall carrier transit time, and thus greatly improving the radio frequency bandwidth of the detector.

[0043] According to the above embodiment, a photodetector based on carrier trajectory modulation is provided. The simulated relationship between the total carrier transit time and the lateral offset of the junction center relative to the germanium center is as follows: Figure 4 As shown in the figure, by precisely introducing a lateral offset, the total transit time of the device exhibits a trend of first decreasing and then increasing. Within a specific offset range (such as around 50 nm), the total transit time of the carrier trajectory modulation structure achieves a highly significant reduction in delay compared to the detector of the traditional zero-offset symmetry structure, with a reduction of approximately 9.3%.

[0044] Based on the two structures described above, the frequency response characteristics of the detector were actually measured and extracted, such as... Figure 5 As shown. By Figure 5 It is evident that detectors with carrier trajectory modulation structures exhibit a significant increase in normalized frequency response bandwidth (3dB) from 92 GHz to 110 GHz compared to detectors with traditional symmetrical structures. Therefore, a perfect balance of carrier transit time can be achieved through simple structural offset design, enabling ultra-high-speed silicon-based germanium photodetectors with a bandwidth of 110 GHz. Furthermore, since this structure is compatible with existing standard CMOS silicon photonics processes, it does not affect other core performance characteristics of the detector, such as responsivity.

[0045] This invention utilizes an asymmetric modulation strategy of carrier physical drift paths to construct a detector structure in which the lateral geometric center of the horizontal PIN junction is laterally offset relative to the lateral geometric center of the germanium absorption layer. This structure, without altering the original light-absorbing volume of the germanium absorption region, allocates a shorter physical transmission distance for slow-moving holes and a longer physical transmission distance for fast-moving electrons, perfectly compensating for the difference in saturation drift velocities between electrons and holes. This innovative design alleviates the technical problem of signal tailing caused by severe mismatch in carrier transit times in traditional fully symmetrical structures, breaking the technical contradiction of balancing detector bandwidth and absorption efficiency. It is beneficial to significantly improve the RF bandwidth and photoelectric conversion speed of silicon-based germanium photodetectors while maintaining high device responsivity.

[0046] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A photodetector based on carrier trajectory modulation, comprising a semiconductor substrate and an absorption layer (302), wherein the semiconductor substrate comprises laterally spaced or adjacent P-type doped regions (301) and N-type doped regions (303), forming a junction region between them, characterized in that: The absorption layer (302) is disposed on the semiconductor substrate and spans the junction region; The lateral geometric center of the absorption layer (302) is offset by a lateral amount (309) from the lateral geometric center of the junction region, so that the lateral overlap range between the bottom of the absorption layer (302) and the P-type doped region (301) and the N-type doped region (303) is different, thereby giving photogenerated electrons and photogenerated holes different average drift distances, and the average drift distance of slow carriers is shorter.

2. The photodetector based on carrier trajectory modulation according to claim 1, characterized in that, The absorption layer (302) is a germanium absorption layer; the semiconductor substrate layer is a silicon layer.

3. A photodetector based on carrier trajectory modulation according to claim 1, characterized in that, The length of the lateral offset (309) is 5% to 30% of the lateral width of the absorption layer (302).

4. A photodetector based on carrier trajectory modulation according to claim 3, characterized in that, The lateral width of the absorption layer (302) is 300 nm.

5. A photodetector based on carrier trajectory modulation according to claim 1, characterized in that, The lateral spacing between the P-type doped region (301) and the N-type doped region (303) is 0 nm to 250 nm; when the lateral spacing is greater than 0 nm, an intrinsic semiconductor region (304) is provided between the P-type doped region (301) and the N-type doped region (303).

6. A photodetector based on carrier trajectory modulation according to claim 1, characterized in that, The P-type doped region (301) is moderately doped, with a doping concentration on the order of 10. 19 cm -3 .

7. A photodetector based on carrier trajectory modulation according to claim 1, characterized in that, The N-type doped region (303) is moderately doped, with a doping concentration on the order of 10. 19 cm -3 .

8. A photodetector based on carrier trajectory modulation according to any one of claims 1-7, characterized in that, The lateral offset (309) is determined based on the drift velocity of photogenerated electrons and optical holes, so that the average transit time of photogenerated electrons is equal to the average transit time of photogenerated holes.

9. A photodetector based on carrier trajectory modulation according to claim 8, characterized in that, The semiconductor substrate is formed with an optical waveguide for guiding the incident light signal and coupling it to the absorption layer (302).

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