无电荷层InGaAs/Si雪崩光电探测器的优化设计
InGaAs/Si avalanche photodiode (APD) employs Si materials with extremely low electron hole ionization coefficients as the multiplication layer, which to some extent solves the problem of high equivalent noise. However, its manufacturing involves ion implantation of Si charge layer and high-temperature annealing activation, which features a complex process, uneven impurities distribution, and high cost. We propose the utilization of etching technology to prepare groove rings in the Si multiplication layer and fill different media in the groove rings to modulate the electric field in the InGaAs layer and Si layer, thus building a charge-free layer InGaAs/Si APD device model. The results indicate that filling the groove ring with air or SiO2 can achieve high-performance InGaAs/Si APD. Finally, theoretical guidance can be provided for the subsequent development of InGaAs/Si APD with simple processes, stable performance, and low noise.
We propose to adopt etching technology to prepare a groove ring within the Si multiplication layer and fill different media inside the groove ring to modulate the electric field in the InGaAs layer and Si layer, which helps build a charge-free layer InGaAs/Si APD device model. Firstly, the changes in APD optical and dark current with different media are simulated. The changes in recombination rate and carrier concentration are simulated to explore the reasons for the changes in optical current. Secondly, the energy band changes of the APD are simulated to further understand the reasons for electron concentration changes. Thirdly, the changes of charge concentration, impact ionization rate, electric field, and other parameters with different media are simulated. Finally, the gain, bandwidth, and gain-bandwidth product of APD are simulated, and a comparison of different media shows that filling with the air can yield the best device performance.
The overall trend of optical current and dark current decreases with the increasing dielectric constant of the medium (Fig. 2). As the dielectric constant of the medium rises, the recombination rate decreases in the InGaAs absorption layer, Si multiplication layer, and Si substrate, consistent with the trend of optical current variation (Fig. 3). The conduction band of APD has no band order at the bonding interface, while the valence band at the interface has obvious band orders, making it difficult for carriers to transport at the interface and a large number of holes to accumulate at the interface (Fig. 5). The ionization coefficients of electrons and holes in the absorption layer slowly increase, while the ionization coefficients of electrons and holes in the multiplication layer further decrease, which is consistent with the trend of electric field changes (Fig. 7). As the dielectric constant increases, the electric field strength in the multiplication region gradually reduces, which weakens the carrier impact ionization effect and decreases the gain (Fig. 8). When the bias voltage is 35 V, the gain-bandwidth product basically shows a downward trend with the increasing dielectric constant of the medium. Additionally, when the medium inside the groove ring is air and the reverse bias voltage is equal to the avalanche voltage (35.2 V), the gain-bandwidth product reaches 100 GHz (Fig. 11).
We investigate the effect of filling different media in the Si multiplication layer groove ring on the charge-free layer InGaAs/Si APD. The results show that as the dielectric constant of different media increases, both optical current and dark current present a decreasing trend under the same bias voltage. The InGaAs/Si APD with air or SiO2 as the dielectric materials finally overlaps with the optical current and dark current after reaching the avalanche voltage, exhibiting the best current characteristics. As the dielectric constant of the medium rises, the gain-bandwidth product shows a downward trend under the same bias voltage. After the device avalanche, the gain-bandwidth product exhibits a trend of first increasing and then decreasing. When the medium inside the groove ring is air and the reverse bias voltage is 35.2 V, the gain-bandwidth product reaches 100 GHz. In summary, replacing the charge layer with a groove ring to construct a charge-free layer InGaAs/Si APD does not require ion implantation, and the process is simple. Meanwhile, filling the groove ring with air can yield the best device performance, and this new configuration provides a new idea for designing high-performance InGaAs/Si APD with simple processes.
1 引言
雪崩光电二极管(APD)是一种常见的半导体光电探测器件,它利用载流子碰撞雪崩倍增效应放大光电信号,实现对极微弱光信号的探测[1]。与传统光电探测器相比,APD具有功耗低、体积小、工作频谱范围宽和工作电压低等优势,被广泛运用于激光雷达[2-4]、量子通信[5-8]、生物发光及深空探测等领域[9-11]。近些年,一些新型探测器(如有机光电探测器、二维材料探测器)得到了迅速发展,其中,有机光电探测器具有制备简单、可调性好、轻量化、柔性、生物相容性等优点,因此在柔性电子学、可穿戴设备和环境探测等应用方面具有极大的发展潜力[12-13]。目前,以Si、Ge、GaN、InGaAs为代表的无机半导体光电探测器仍占主导地位,故本文主要研究无机光电探测器。
近年来,关于Ⅲ-Ⅴ族半导体APD的研究已经取得了较大进展,例如InGaAs/InP、InGaAs/InAlAs APD等已经被广泛应用于近红外波段光子信号的探测。由于InGaAs为直接带隙半导体材料,其带隙为0.74 eV,在近红外波段具有极高的吸收系数,吸收峰值出现在1.65 μm左右,故常被用作近红外APD的吸收层材料。InGaAs材料与雪崩倍增材料InP的晶格匹配较好[14],因此采用外延技术可以在InP上直接生长出高质量的InGaAs薄膜[15-17],从而构建吸收-渐变-电荷-倍增分离结构的InGaAs/InP APD[18-21],以抑制吸收层中的隧穿,降低暗电流。InGaAs/InP APD的应用波段是900~1700 nm,且在1550 nm通信窗口具有较大的优势,并且具有工作温度低、体积小、稳定性高等优点。外延的InP倍增材料存在高密度、深能级的缺陷[22-24],且其电子与空穴的离化系数之比(k值)高达0.3~0.5,导致InGaAs/InP APD有较大的等效噪声,难以进一步提升器件性能。
提升InGaAs/InP APD性能的最直接方法是使用比InP的k值更小的材料作为倍增层,从而降低器件的等效噪声并提高器件的增益带宽积。Si是一种间接带隙半导体材料,其k值小,对雪崩击穿的温度依赖性非常低,但是其禁带宽度(1.12 eV)不适用于近红外波段的吸收探测,因此需要结合其他半导体材料如Ge、InGaAs等制备APD[25]。以Si为倍增区的器件等效噪声较小,故InGaAs/Si APD成为近红外探测的理想选择之一。InGaAs和Si的晶格失配度[26-28]高达7.7%,导致器件暗电流较大,雪崩倍增受到限制,增益带宽积难以进一步提高,因此采用外延技术难以获得低穿透位错密度的InGaAs/Si界面。采用低温键合技术[29-32]可以有效降低InGaAs和Si间失配晶格对器件性能的影响,获得更大的增益带宽积、更低的噪声和更好的温度特性,但是InGaAs/Si APD中用于调制电场的电荷层的制备涉及离子注入和高温退火激活[33-36],工艺繁琐、杂质分布不均匀、成本高。
本文提出一种无电荷层InGaAs/Si APD器件结构,即利用刻蚀技术在Si倍增层内制备凹槽环并填充不同的介质,以调制 InGaAs层与Si层的内部电场,使得InGaAs处于低电场状态,而Si倍增层处于高电场状态。重点仿真分析了APD键合界面凹槽环内不同介质对APD暗电流、光电流、载流子复合率、载流子浓度、碰撞电离率、增益、3 dB带宽、载流子速率以及增益带宽积等的影响。
2 结构模型与模拟软件
图 1. 无电荷层InGaAs/Si APD的三维结构图
Fig. 1. 3D structural diagram of charge-free layer InGaAs/Si APD
表 1. 凹槽环填充材料参数
Table 1. Parameters of groove ring filling materials
|
InGaAs/Si APD涉及载流子的输运,因此需要引入泊松方程[
泊松方程表示为
式中:
电流连续方程表示为
式中:
依赖于平行电场的载流子迁移模型表示为
式中:
俄歇复合模型表示为
式中:
由浓度决定的SRH复合模型表示为
式中:
光学辐射复合模型表示为
式中:
缺陷辅助俄歇复合模型表示为
式中:
标准能带跃迁模型表示为
式中:
Trap-Assisted跃迁模型表示为
式中:
库仑势阱Poole-Frenkel势垒降低模型表示为
式中:
3 结果与讨论
首先,模拟了InGaAs/Si APD电流随键合界面凹槽环内不同介质的变化,结果如
图 2. 凹槽环内不同介质对无电荷层InGaAs/Si APD的影响。(a)电流;(b)95%Vb下的电流;(c)雪崩电压
Fig. 2. Effect of different dielectric materials in the grooved ring on the charge-free layer InGaAs/Si APD. (a) Current; (b) current at 95%Vb; (c) avalanche voltage
为探究电流变化的原因,模拟了无电荷层InGaAs/Si APD复合率随键合界面凹槽环内不同介质的变化,结果如
图 3. 无电荷层InGaAs/Si APD复合率随介质的变化。(a)复合率结构切面图;(b)在X=16.229处截取的复合率曲线
Fig. 3. Changes of recombination rate of charge-free layer InGaAs/Si APD with media. (a) Section diagram of recombination rate structure; (b) recombination rate curves taken at X=16.229
其次,模拟了APD中载流子浓度随键合界面凹槽环内不同介质的变化,结果如
图 4. 无电荷层 InGaAs/Si APD电子浓度和空穴浓度随介质的变化。(a)结构切面的电子浓度;(b)结构切面的空穴浓度;(c)在X=16.229处的电子浓度;(d)在X=16.229处的空穴浓度
Fig. 4. Changes of electron and hole concentrations of charge-free layer InGaAs/Si APD with media. (a) Electron concentration in structural section; (b) hole concentration in structural section; (c) electron concentration at X=16.229; (d) hole concentration at X=16.229
再次,模拟了InGaAs/Si APD在结构切面X=16.229处的能带随键合界面凹槽环内介质的变化,结果如
图 5. 凹槽环内不同介质对无电荷层InGaAs/Si APD的影响。(a)键合界面导带;(b)键合界面价带;(c)电荷浓度
Fig. 5. Effect of different dielectric materials in the grooved ring on the charge-free layer InGaAs/Si APD. (a) Conduction band of bonding interface; (b) valence band of bonding interface; (c) charge concentration
然后,模拟了APD中碰撞电离率随键合界面凹槽环内介质的变化,结果如
图 6. 凹槽环内不同介质对无电荷层InGaAs/Si APD的影响。(a)结构切面的碰撞电离率(RIIR);(b)在X=16.229处的碰撞电离率;(c)在X=16.229处的电子离化系数;(d)在X=16.229处的空穴离化系数
Fig. 6. Effect of different dielectric materials in the grooved ring on the charge-free layer InGaAs/Si APD. (a) Impact ionization rate (RIIR) of structural section; (b) impact ionization rate at X=16.229; (c) electron ionization coefficient at X=16.229; (d) hole ionization coefficient at X=16.229
载流子的碰撞电离系数为单位距离内载流子发生碰撞电离的次数,可以用来表征碰撞电离的难易程度,与电场强度有关。本实验模拟了电子和空穴的离化系数随键合界面凹槽环内不同介质的变化,结果如
图 7. 无电荷层InGaAs/Si APD电场随介质的变化。(a)结构切面的电场;(b)在X=16.229处的电场
Fig. 7. Variation of electric field in the charge-free layer InGaAs/Si APD with media. (a) Electric field of structural section; (b) electric field at X=16.229
最后,提取了APD的增益随键合界面凹槽环内介质的变化,结果如
图 8. 无电荷层InGaAs/Si APD增益随介质的变化。(a)增益曲线;(b)95%Vb下的增益
Fig. 8. Variation of InGaAs/Si APD gain with media. (a) Gain curves; (b) gain at 95%Vb
带宽是表征APD性能的重要参数之一,
图 9. 无电荷层InGaAs/Si APD 3 dB带宽曲线
Fig. 9. 3 dB bandwidth curves of InGaAs/Si APD without charge layer
为了探索带宽变化的原因,模拟了载流子速率随键合界面凹槽环内介质的变化,结果如
图 10. X=16.229处的无电荷层InGaAs/Si APD电子速率和空穴速率随介质的变化。(a)电子速率;(b)空穴速率
Fig. 10. Variation of electron and hole rates in the charge-free layer InGaAs/Si APD at X=16.229 with media. (a) Electron rate; (b) hole rate
此外,还模拟了键合界面凹槽环内不同介质对无电荷层InGaAs/Si APD增益带宽积的影响,结果如
图 11. 无电荷层InGaAs/Si APD 增益带宽积
Fig. 11. Gain-bandwidth product of charge-free layer InGaAs/Si APD
4 结论
分析Si倍增层凹槽环内填充的介质对无电荷层InGaAs/Si APD的影响。研究表明,随着不同介质介电常数的增加,在同一偏压下,光电流和暗电流均呈下降趋势。其中介质材料为空气或SiO2的InGaAs/Si APD在达到雪崩电压后,光电流和暗电流最终重合,具有最优良的电流特性。随着介质介电常数的增加,在同一偏压下,增益带宽积基本呈下降趋势;器件雪崩后,增益带宽积呈现先增加后减小的趋势;当凹槽环内介质为空气且反向偏压为35.2 V时,增益带宽积达到100 GHz。综上,采用凹槽环替代电荷层,构造无电荷层InGaAs/Si APD,不需要注入离子,工艺简单,同时在凹槽环内填充空气可获得最佳的器件性能,这一新构型为设计工艺简单的高性能InGaAs/Si APD提供了新思路。
[1] Kim H, Jung Y, Doh I J, et al. Smartphone-based low light detection for bioluminescence application[J]. Science Letter, 2017, 7: 40203.
[2] Li C, Wu K, Cao X Y, et al. Monolithic coherent LABS lidar based on an integrated transceiver array[J]. Optics Letters, 2022, 47(11): 2907-2910.
[3] Li Z H, Bao Z Y, Shi Y F, et al. Photon-counting chirped amplitude modulation lidar with 1.5-GHz gated InGaAs/InP APD[J]. IEEE Photonics Technology Letters, 2015, 27(6): 616-619.
[4] Li Z J, Lai J C, Wu Z X, et al. Dead-time-based sequence coding method for single-photon lidar ranging[J]. Optics Communications, 2022, 517: 128260.
[5] Koehler-Sidki A, Dynes J F, Lucamarini M, et al. Best-practice criteria for practical security of self-differencing avalanche photodiode detectors in quantum key distribution[J]. Physical Review Applied, 2018, 9(4): 044027.
[6] Piveteau A, Pauwels J, Håkansson E, et al. Entanglement-assisted quantum communication with simple measurements[J]. Nature Communications, 2022, 13: 7878.
[7] Couteau C, Barz S, Durt T, et al. Applications of single photons to quantum communication and computing[J]. Nature Reviews Physics, 2023, 5: 326-338.
[8] Brambila E, Gómez R, Fazili R, et al. Ultrabright polarization-entangled photon pair source for frequency-multiplexed quantum communication in free-space[J]. Optics Express, 2023, 31(10): 16107-16117.
[9] Gao H T, Muralidharan S, Karim M R, et al. Neutron irradiation and forming gas anneal impact on β-Ga2O3 deep level defects[J]. Journal of Physics D, 2020, 53(46): 465102.
[10] Love A C, Caldwell D R, Kolbaba-Kartchner B, et al. Red-shifted coumarin luciferins for improved bioluminescence imaging[J]. Journal of the American Chemical Society, 2023, 145(6): 3335-3345.
[11] 万超, 郝浩, 赵清源, 等. 单光子探测在无线光通信收发技术中的应用[J]. 激光与光电子学进展, 2022, 59(5): 0500001.
[12] Lv T R, Zhang W H, Yang Y Q, et al. Micro/nano-fabrication of flexible poly (3, 4-ethylenedioxythiophene)-based conductive films for high-performance microdevices[J]. Small, 2023, 19(30): 2301071.
[13] 柯宇轩, 岑颖乾, 綦殿禹, 等. 基于二维材料的光通信波段光电探测器[J]. 中国激光, 2023, 50(1): 0113008.
[14] Bai X, Li Y F, Fang X W, et al. Innovative strategy to optimize the temperature-dependent lattice misfit and coherency of iridium-based γ/γ′ interfaces[J]. Applied Surface Science, 2023, 609: 155369.
[15] Fan Y B, Shi T T, Ji W J, et al. Ultra-narrowband interference circuits enable low-noise and high-rate photon counting for InGaAs/InP avalanche photodiodes[J]. Optics Express, 2023, 31(5): 7515-7522.
[16] Tian Y, Lin Z B, Zhao Y L. The excess noise characteristics of InGaAs/InP APD in consideration of nonlinearity effect[J]. Proceedings of SPIE, 2022, 12154: 121540T.
[17] Li X Z, Zhang J Y, Yue C, et al. High performance visible-SWIR flexible photodetector based on large-area InGaAs/InP PIN structure[J]. Scientific Reports, 2022, 12: 7681.
[18] Wu W, Shan X, Long Y Q, et al. Free-running single-photon detection via GHz gated InGaAs/InP APD for high time resolution and count rate up to 500 mcount/s[J]. Micromachines, 2023, 14(2): 437.
[20] Karnik T S, Dao K P, Du Q Y, et al. High-efficiency mid-infrared InGaAs/InP arrayed waveguide gratings[J]. Optics Express, 2023, 31(3): 5056-5068.
[21] Braga O M, Delfino C A, Kawabata R M S, et al. Investigation of InGaAs/InP photodiode surface passivation using epitaxial regrowth of InP via photoluminescence and photocurrent[J]. Materials Science in Semiconductor Processing, 2023, 154: 107200.
[22] Zhu X, Zhang Y W, Zhang S N, et al. Defect energy levels in monoclinic β-Ga2O3[J]. Journal of Luminescence, 2022, 246: 118801.
[23] Lian W T, Jiang C H, Yin Y W, et al. Revealing composition and structure dependent deep-level defect in antimony trisulfide photovoltaics[J]. Nature Communications, 2021, 12: 3260.
[24] Zhou X Q, Ning L X, Qiao J W, et al. Interplay of defect levels and rare earth emission centers in multimode luminescent phosphors[J]. Nature Communications, 2022, 13: 7589.
[25] 仵欣杰, 叶海福, 艾杰, 等. 硅光电倍增管在辐射探测领域中的应用进展[J]. 激光与光电子学进展, 2022, 59(21): 2100004.
[26] Yun J, Bae M S, Baek J S, et al. Modeling of optimized lattice mismatch by carbon-dioxide laser annealing on (In, Ga) Co-doped ZnO multi-deposition thin films introducing designed bottom layers[J]. Nanomaterials, 2022, 13(1): 45.
[27] Li S C, Liang H Y, Li C, et al. Lattice mismatch in Ni3Al-based alloy for efficient oxygen evolution[J]. Journal of Materials Science & Technology, 2022, 106: 19-27.
[28] Tian Y, Feng P, Zhu C Q, et al. Nearly lattice-matched GaN distributed Bragg reflectors with enhanced performance[J]. Materials, 2022, 15(10): 3536.
[29] Ke S Y, Zhou J R, Huang D L, et al. Polycrystalline Ge intermediate layer for Ge/Si wafer bonding and defect elimination in Si (SOI)-based exfoliated Ge film[J]. Vacuum, 2020, 172: 109047.
[30] Ke S Y, Ye Y J, Lin S M, et al. Low-temperature oxide-free silicon and germanium wafer bonding based on a sputtered amorphous Ge[J]. Applied Physics Letters, 2018, 112(4): 041601.
[31] Ke S Y, Lin S M, Ye Y J, et al. Temperature-dependent interface characteristic of silicon wafer bonding based on an amorphous germanium layer deposited by DC-magnetron sputtering[J]. Applied Surface Science, 2018, 434: 433-439.
[32] Huang Z W, Mao Y C, Lin G Y, et al. Low dark current broadband 360-1650 nm ITO/Ag/n-Si Schottky photodetectors[J]. Optics Express, 2018, 26(5): 5827-5834.
[33] Liu C X, Lu Y, Ding W J, et al. One-dimensional and two-dimensional Er3+-doped germanate glass waveguides by combination of He+ ion implantation and precise diamond blade dicing[J]. Vacuum, 2023, 209: 111743.
[34] Harada S, Sakane H, Mii T, et al. Suppression of partial dislocation glide motion during contraction of stacking faults in SiC epitaxial layers by hydrogen ion implantation[J]. Applied Physics Express, 2023, 16(2): 021001.
[35] 鲍诗仪, 母浩龙, 周锦荣, 等. 不同晶态Ge薄膜键合层对InGaAs/Si雪崩光电二极管性能的影响研究[J]. 中国激光, 2023, 50(14): 1403001.
[36] 周锦荣, 鲍诗仪, 佘实现, 等. 不同Ge组分a-Si1-xGex键合层对InGaAs/Si雪崩光电二极管性能的影响(英文)[J]. 光子学报, 2022, 51(9): 0951611.
Zhou J R, Bao S Y, She S X, et al. Effect of a-Si1-xGex bonding layer with different Ge components on the performance of InGaAs/Si avalanche photodiode[J]. Acta Photonica Sinica, 2022, 51(9): 0951611.
Article Outline
张娟, 姚儿, 柯少颖. 无电荷层InGaAs/Si雪崩光电探测器的优化设计[J]. 光学学报, 2024, 44(5): 0504001. Juan Zhang, Er Yao, Shaoying Ke. Optimal Design of Charge-Free Layer InGaAs/Si Avalanche Photodetector[J]. Acta Optica Sinica, 2024, 44(5): 0504001.