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本文采用射频磁控溅射在蓝宝石衬底上室温下制备了非晶掺锡氧化镓薄膜, 而后在氮气氛围下进行不同温度(400—800 ℃)退火, 并基于退火前后薄膜制备了相应的日盲光电探测器, 探究退火温度对薄膜特性及器件性能的影响规律. 研究结果表明: 非晶掺锡氧化镓薄膜在700 ℃退火后开始出现氧化镓β相结晶, 且薄膜中晶格氧以及Sn4+离子比例随退火温度的升高而增大, 说明薄膜质量升高, 导电性增强. 然而, 随着退火温度升高至800 ℃时, 晶格氧以及Sn4+离子比例下降, 薄膜的质量及导电特性变差, 这可能归因于薄膜中Sn表面偏析以及Al从衬底中扩散进入薄膜. 综上, 薄膜的质量及其导电特性对掺锡氧化镓日盲探测器性能起到调控作用, 当退火温度为700 ℃, 器件获得最优的光电性能: 暗电流低至89.97 pA、响应度为18.4 mA/W、光暗电流比可达1264以及上升/下降时间低至0.93 s/0.87 s.In this study, Sn-doped Ga2O3 thin films are prepared on sapphire substrate by RF magnetron sputtering at ambient temperature, and then annealed at different temperatures (400–800 ℃) in nitrogen atmosphere. The corresponding metal-semiconductor-metal (MSM) solar blind photodetectors (PDs) are prepared based on those films before and after annealing to explore the influence of annealing temperature on the characteristics of the films and device properties. The results show that the as-deposited Sn-doped Ga2O3 film displays amorphous structure. With the increase of annealing temperature, the proportion of OL, Ga3+ and Sn4+ ions in the film increase, and the band gap of the film decreases slightly, indicating that the conductivity of the film is enhanced and the quality of the film is improved. When the annealing temperature increases to 700 ℃, the β-Ga2O3 ($\overline {402} $) crystal surface diffraction peak appeares, indicating that the film begins to crystallize. As the annealing temperature increases to 800 ℃, the proportion of OL, Ga3+ and Sn4+ decreases, and the quality and conductive properties of the film deteriorate, which may be attributed to Sn surface segregation and Al diffusion into the film from the substrate. In addition, the average particle size and surface roughness of the film surface increase with annealing temperature increasing, which is consistent with the changing trend of film characteristics. Then, based on Sn-doped Ga2O3 thin films before and after annealing, the MSM solar blind PDs are prepared to explore the influence of annealing temperature on device performance. The quality of the film and its conductive characteristics play a role in regulating the performance of Sn-doped Ga2O3 solar blind PD. The optimal device performance can be obtained when the annealing temperature is 700 ℃, with a low dark current of 89.97 pA, a responsivity of 18.4 mA/W, a light-dark current up to 1264, and the rise/fall time of 0.93 s/0.87 s. In summary, the annealing temperature has an important effect on the characteristics of Sn-doped Ga2O3 films and the performance of solar blind PDs, which has certain guiding significance for the preparation of high-quality Sn-doped Ga2O3 films and high-performance solar blind PDs.
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Keywords:
- radio frequency magnetron sputtering /
- Sn-doped Ga2O3 film /
- annealing temperature /
- solar-blind photodetector
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图 1 Sn掺杂Ga2O3薄膜退火前后X射线衍射图
Fig. 1. XRD diffraction property of Sn-doped Ga2O3 films annealed at various temperatures.
图 2 退火前后Sn掺杂Ga2O3薄膜的XPS图谱 (a) 全谱图; (b) 元素比例
Fig. 2. (a) XPS survey spectrum, (b) atomic percent of O, Ga, C, and Sn of Sn-doped Ga2O3 films annealed at various temperatures.
图 3 Sn掺杂Ga2O3薄膜退火前后的XPS核心能谱图 (a) O 1s, (b) Ga 3d, (c) Sn 3d; (d)晶格氧OL/(OL+ONL)的比例; (e) Ga3+/(Ga3++Ga+)比例; (f) Sn4+/(Sn4++Sn2+)比例
Fig. 3. High-resolution XPS spectra and its fitting spectra of (a) O 1s, (b) Ga 3d, and (c) Sn 3d; the OL proportion (d), Ga3+ ratio (e) and Sn4+ percentage (f) of the films annealed at various temperatures.
图 4 Sn掺杂Ga2O3薄膜的SIMS图 (a) 未退火; (b) 800 ℃退火后
Fig. 4. SIMS data of the Sn-doped Ga2O3 films: (a) before and (b) after 800 ℃ annealing.
图 5 退火前后Sn掺杂Ga2O3薄膜的FESEM, AFM及颗粒尺寸统计图 (a) 未退火; (b)—(f) 400—800 ℃退火后
Fig. 5. The FESEM, AFM, and cluster size distribution pictures of the Sn-doped Ga2O3 films annealed at different temperatures: (a) As-dep; (b)–(f) after 400–800 ℃ annealing.
图 6 退火前后Sn掺杂Ga2O3薄膜 (a)透射光谱, 插图为(αhν)2和hν的Tauc图; (b)光学带隙随退火温度变化曲线
Fig. 6. (a) The transmittance as well as Tauc plot of (αhν)2 versus hν (inset) spectra and (b) optical bandgap of the Sn-doped Ga2O3 films for varying annealing temperatures.
图 7 不同退火温度下Sn掺杂Ga2O3薄膜的载流子浓度、电阻率和迁移率
Fig. 7. Carrier concentration, resistivity, and hall mobility of Sn-doped Ga2O3 films with different annealing temperatures.
图 8 不同退火温度下Sn掺杂Ga2O3日盲光电探测器 (a) 暗电流, 插图为光学显微镜下器件的俯视图; (b) 光电流; (c) 瞬态响应
Fig. 8. (a) The dark current–voltage curves, the inset is the physical top-view of photodetectors; (b) the photocurrent–voltage curves; (c) the transient response (I–t) curves of photodetectors under different annealing temperature.
表 1 磁控溅射Sn掺杂Ga2O3薄膜工艺及退火参数
Table 1. Growth and annealing parameters of the sputtered Sn-doped Ga2O3 films.
参数 值 背景压力/Torr 5×10–7 工作压力/Torr 9×10–3 溅射功率/W 500 气体总流量/sccm 40 [O2/(O2+Ar)]/% 1.0 沉积温度/℃ 室温 薄膜厚度/nm ~102 退火气氛和时间 N2气体和2 h 退火温度/℃ As-dep., 400, 500, 600, 700, 800 
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表 2 退火前后Sn掺杂Ga2O3探测器的性能参数
Table 2. Performance of the Sn-doped Ga2O photodetectors before and after annealing.
退火温度/℃ 暗电流/pA 光电流/nA 光暗
电流比响应度/
(mA·W–1)上升时
间/s下降时
间/sAs-dep. 1.10 0.94 854.5 0.15 1.61 1.02 400 23.33 22.05 945.14 3.57 2.28 3.54 500 63.85 66.73 1045.11 10.8 1.43 1.34 600 80.28 89.65 1116.72 14.5 1.03 0.98 700 89.97 113.74 1264.20 18.4 0.93 0.87 800 1.14 0.09 82.46 0.02 1.12 17.36
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