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利用超快瞬态吸收光谱, 针对氧化镓(β-Ga2O3)晶体中本征缺陷诱导的载流子俘获和复合等动力学进行研究. 实验发现, 由本征缺陷诱导的宽带吸收光谱具有很强的偏振依赖性, 特别是从不同探测偏振下的瞬态吸收光谱中可以提取出两个缺陷态吸收响应. 该缺陷诱导的吸收响应归因于从价带到本征缺陷(镓空位)不同电荷态的光学跃迁, 利用基于单缺陷的多能级载流子俘获模型拟合得到缺陷俘获空穴的速率远快于俘获电子, 且缺陷态的吸收截面相较于自由载流子吸收截面大至少一个数量级. 本文的研究结果不仅能明确本征缺陷与光生载流子动力学之间的关系, 而且为β-Ga2O3在超快宽带光电子器件中的应用提供科学指导.The ultra-wide bandgap semiconductor gallium oxide β-Ga2O3 with enhanced resistance to the irradiation and temperature is favorable for high-power and high-temperature optoelectronic devices. β-Ga2O3 also exhibits great potential applications in the field of integrated photonics because of its compatibility with the CMOS technique. However, a variety of intrinsic and extrinsic defects and trap states coexist in β-Ga2O3, including vacancies, interstitials, and impurity atoms. The defect-related carrier dynamics in β-Ga2O3 not only adversely affect the optical and electrical properties, but also directly limit the performance of β-Ga2O3 based devices. Therefore, a comprehensive understanding of the carrier transportation and relaxation dynamics induced by intrinsic defects is very important. Supercontinuum-probe spectroscopy can provide a fruitful information about the carrier relaxation processes in different recombination mechanisms, and thus becomes an effective way to study the defect dynamics. In this work, we study the dynamics of carrier trapping and recombination induced by intrinsic defects in pristine β-Ga2O3 crystal by using wavelength-tunable ultrafast transient absorption spectroscopy. The broadband absorption spectra induced by the intrinsic defects are strongly dependent on the polarization of pump pulse and probe pulse. Particularly, two absorption peaks induced by the two defect states can be extracted from the transient absorption spectra by subtracting the absorption transients under two probe polarizations. The observed defect-induced absorption features are attributed to the optical transitions from the valence band to the different charge states of the intrinsic defects (such as gallium vacancy). The data are well explained by a proposed carrier capture model based on multi-level energies. Moreover, the hole capture rate is found to be much greater than that of the electron, and the absorption cross-section of the defect state is at least 10 times larger than that of free carrier. Our findings not only clarify the relationship between intrinsic defects and photogenerated carrier dynamics, but also show the importance in the application of β-Ga2O3 crystals in ultrafast and broadband photonics.
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Keywords:
- β-Ga2O3 /
- transient absorption /
- defect dynamics /
- carrier trapping
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图 1 (a) UID和Sn掺杂β-Ga2O3的透射光谱, 箭头表示泵浦光波长; (b)不同入射光强下β-Ga2O3的开孔Z扫描曲线, 实线为理论拟合曲线
Fig. 1. (a) Optical transmission spectra of UID and Sn-doped β-Ga2O3, where the arrow denotes the pump wavelength; (b) open-aperture Z-scan data of β-Ga2O3 at different incident light intensities, where the solid lines are theoretical fitting curves.
图 2 在不同的延迟时间下, 沿(a) [010]和(b) [102]晶轴探测下UID β-Ga2O3晶体的瞬态吸收光谱; 沿(c) [010]和(d) [102]轴探测下提取的不同波长吸收衰减动力学. 泵浦脉冲固定为沿[102]轴偏振
Fig. 2. Transient absorption spectra of the UID β-Ga2O3 crystal probed at different delay times for different probe polarizations with respect to the (a) [010] and (b) [102] crystal axes. Extracted decay dynamics of absorption under different probe wavelengths for probe polarization along the (c) [010] and (d) [102] axes. The pump pulse is fixed to be polarized along the [102] axis.
图 3 在td = 2 ps处沿(a) [010]和(b) [102]晶轴探测偏振下的缺陷吸收光谱(数据点); (c)两个探测偏振方向的差分瞬态吸收ΔmOD*. 所有的缺陷吸收光谱都可以用两个高斯函数(虚线)进行拟合
Fig. 3. Defect absorption spectra (dots) as a function of probe photon energy for polarization along the (a) [010] and (b) [102] crystal axes at td = 2 ps; (c) the difference transients ΔmOD* between two probe polarization directions. All the defect absorption spectra can be fitted using two Gaussian functions (dashed lines).
图 4 双光子激发(2PE)载流子俘获和本征缺陷吸收图, VGa相关缺陷的多电荷态(
$ {2{\rm{V}}}_{{\rm{G}}{\rm{a}}}^{1}{\text{-}}{{\rm{G}}{\rm{a}}}_{{\rm{i}}}^{{\rm{c}}} $ )可以被泵浦脉冲激发并允许载流子俘获和光学跃迁(探测脉冲所经历的瞬态吸收)Fig. 4. Diagram of two-photon excited (2PE) carrier capture and the intrinsic defect absorption, the multiple charge states of the VGa-related defects (
$ {2{\rm{V}}}_{{\rm{G}}{\rm{a}}}^{1}{\text{-}}{{\rm{G}}{\rm{a}}}_{{\rm{i}}}^{{\rm{c}}} $ is for consideration) can be excited by pump pulses and allow carrier trapping (black arrows) and optical transitions (transient absorption experienced by the probe pulses).
图 5 (a)—(c)泵浦光沿[102]轴偏振时, 测量和拟合得到的不同探测偏振和波长下UID β-Ga2O3的吸收动力学
Fig. 5. (a)–(c) Measured and computed absorption kinetics in UID β-Ga2O3 for different probe polarizations and wavelengths when pumped along the [102] axis.
表 1 提取的瞬态吸收动力学模型参数
Table 1. Extracted parameters to model the transient absorption kinetics.
参数 数值 Nd/cm3 (1.7±0.2)×1016 $C_{\text{p}}^{ - 2}$/(cm3·s) (1.6±0.3)×10–6 $C_{\text{p}}^{ - 1}$/(cm3·s) (1.3±0.2)×10–6 σ–1 |max// [010]/cm2 (1.4±0.4)×10–17 σ–1 |max// [102]/cm2 (2.3±0.5)×10–17 σ0 |max// [102]/cm2 (2.2±0.6)×10–17 
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[1] Pearton S J, Yang J C, Cary P H, Ren F, Kim J, Tadjer M J, Mastro M A 2018 Appl. Phys. Rev. 5 011301
Google Scholar
[2] Higashiwaki M, Kaplar R, Pernot J, Zhao H P 2021 Appl. Phys. Lett. 118 200401
Google Scholar
[3] Higashiwaki M, Sasaki K, Kuramata A, Masui T, Yamakoshi S 2012 Appl. Phys. Lett. 100 013504
Google Scholar
[4] Chen X H, Ren F F, Gu S L, Ye 2019 Photonics Res. 7 381
Google Scholar
[5] Guo D Y, Guo Q, Chen Z, Wu Z, Li P, Tang W H 2019 Mater. Today Phys. 11 100157
Google Scholar
[6] Tadjer M J, Lyons J L, Nepal N, Freitas Jr J A, Koehler A D, Foster G M 2019 ECS J. Solid State Sci. Technol. 8 Q3187
Google Scholar
[7] McCluskey M D 2020 J. Appl. Phys. 127 101101
Google Scholar
[8] Zhang J, Shi J, Qi D C, Chen L, Zhang K H L 2020 APL Mater. 8 020906
Google Scholar
[9] Koksal Q, Tanen N, Jena D, Xing H G, Rana F 2018 Appl. Phys. Lett. 113 252102
Google Scholar
[10] Varley J B, Weber J R, Janotti A, Van de Walle C G 2010 Appl. Phys. Lett. 97 142106
Google Scholar
[11] Kananen B E, Halliburton L E, Scherrer E M, et al. 2017 Appl. Phys. Lett. 111 072102
Google Scholar
[12] Feng Z, Bhuiyan A F M, Kalarickal N K, Rajan S, Zhao H 2020 Appl. Phys. Lett. 117 222106
Google Scholar
[13] Sun Y F, Li Z G, Fang Y, Wu X Z, Zhou W F, Jia Z T, Yang J Y, Song Y L 2022 Appl. Phys. Lett. 120 032101
Google Scholar
[14] Zhang Z, Farzana E, Arehart A R, Ringel S A 2016 Appl. Phys. Lett. 108 052105
Google Scholar
[15] Islam M M, Rana D, Hernandez A, Haseman M, Selim F A 2019 J. Appl. Phys. 125 055701
Google Scholar
[16] Islam M M, Adhikari N, Hernandez A, et al. 2020 J. Appl. Phys. 127 145701
Google Scholar
[17] Yamaoka S, Furukawa Y, Nakayama M 2017 Phys. Rev. B 95 094304
Google Scholar
[18] Gao H, Muralidharan S, Pronin N, et al. 2018 Appl. Phys. Lett. 112 242102
Google Scholar
[19] Skachkov W R L, Lambrecht H J, von Bardeleben U 2019 J. Appl. Phys. 125 185701
Google Scholar
[20] Montes J, Kopas C, Chen H, et al. 2020 J. Appl. Phys. 128 205701
Google Scholar
[21] Othonos A, Zervos M, Christofides C 2010 J. Appl. Phys. 108 124302
Google Scholar
[22] Singh A, Koksal O, Tanen N, McCandless J, Jena D, Xing H G, Peelaers H, Rana F 2021 Phys. Rev. Res. 3 023154
Google Scholar
[23] Cho J B, Jung G, Kim K, Kim J, Hong S K, Song J H, Jang J I 2021 J. Phys. Chem. C 125 1432
Google Scholar
[24] 方宇, 吴幸智, 陈永强, 杨俊义, 宋瑛林 2020 物理学报 69 168701
Google Scholar
Fang Y, Wu X Z, Chen Y Q, Yang J Y, Song Y L 2020 Acta Phys. Sin. 69 168701
Google Scholar
[25] Fang Y, Wu X Z, Yang J Y, Wang J P, Wu Q Y, Song Y L 2021 Appl. Phys. Lett. 118 112105
Google Scholar
[26] Fang Y, Yang J Y, Yang Y, Wu X Z, Xiao Z G, Zhou F, Song Y L 2015 Journal of Phys. D: Appl. Phys. 49 045105
Google Scholar
[27] 王建苹, 吴幸智, 杨俊义, 陈永强, 吴泉英, 宋瑛林, 方宇 2022 光学学报 42 2219001
Google Scholar
Wang J P, Wu X Z, Yang J Y, Chen Y Q, Wu Q Y, Song Y L, Fang Y 2022 Acta Opt. Sin. 42 2219001
Google Scholar
[28] Singh A, Koksal O, Tanen N, McCandless J, Jena D, Xing H L, Peelaers H, Rana F 2020 Appl. Phys. Lett. 117 072103
Google Scholar
[29] Chen H, Fu H, Huang X, Montes J A, Yang T H, Baranowski I, Zhao Y 2018 Opt. Express 26 3938
Google Scholar
[30] Sun Y F, Fang Y, Li Z G, Yang J Y, Zhou W F, Liu K, Song Y L 2021 J. Phys. D: Appl. Phys. 54 495105
Google Scholar
[31] Kuramata A, Koshi K, Watanabe S, Yamaoka Y, Masui T, Yamakoshi S 2016 J. Appl. Phys. 55 1202A2
Google Scholar
[32] Luchechko A, Vasyltsiv V, Zhydachevskyy Y, et al. 2020 J. Phys. D: Appl. Phys. 53 354001
Google Scholar
[33] Galazka Z, Ganschow S, Fiedler A, et al. 2018 J. Cryst. Growth 486 82
Google Scholar
[34] Peelaers H, Van de Walle C G 2019 Phys. Rev. B 100 081202
Google Scholar
[35] Varley J B, Peelaers H, Janotti A, Van de Walle C G 2011 J. Phys. Condens. Matter 23 334212
Google Scholar
[36] Deák P, Ho Q D, Seemann F, Aradi B, Lorke M, Frauenheim T 2017 Phys. Rev. B 95 075208
Google Scholar
[37] Ingebrigtsen M E, Kuznetsov A Y, Svensson B G, Alfieri G, Mihaila A, Badstübner U, Perron A, Vines L, Varley J B 2019 APL Mater. 7 022510
Google Scholar
[38] Johnson J M, Chen Z, Varley J B, et al. 2019 Phys. Rev. X 9 041027
Google Scholar
[39] Nie Y Y, Jiao S J, Li S F, et al. 2022 J. Alloys Compd. 900 163431
Google Scholar
[40] Farzana E, Ahmadi E, Speck J S, Arehart A R, Ringel S A 2018 J. Appl. Phys. 123 161410
Google Scholar
[41] Zimmermann C, Rønning V, Frodason Y K, Bobal V, Vines L, Varley J B 2020 Phys. Rev. Mater. 4 074605
Google Scholar
[42] Fang Y, Wu X Z, Yang J Y, Xiao Z G, Yang Y, Zhou F, Song Y L 2015 Appl. Phys. Lett. 107 051901
Google Scholar
[43] Ščajev P, Jarašiūnas K, Leach J 2020 J. Appl. Phys. 127 245705
Google Scholar
[44] Reshchikov M A, Vorobiov M, Demchenko D O, et al. 2018 Phys. Rev. B 98 125207
Google Scholar
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