银纳米颗粒复合非晶氧化镓光电探测器的制备与研究

Preparation and Study of Ag Nanoparticles Composite Amorphous Gallium Oxide Photodetector

氧化镓(Ga_(2)O_(3))因其合适的禁带宽度(4.5~5.3 e V)在深紫外探测方面具有天然的优势。本文利用常温磁控溅射技术在非晶Ga_(2)O_(3)薄膜表面溅射银纳米颗粒,制备出简易的深紫外光电探测器。结果表明,在5 V偏压下,探测器的暗电流低至94 f A,光暗电流比高达5.9×10^(5),254 nm/365 nm波长抑制比达到1.6×10^(4),探测率为2×10^(14)Jones(探测率单位),且该探测器在不同电压和不同光强下都能快速且稳定地响应。该探测器优异的深紫外光探测表现与引入的金属银纳米颗粒密切相关。一方面,银纳米颗粒与Ga_(2)O_(3)薄膜间的肖特基势垒的形成有助于减小非晶Ga_(2)O_(3)的暗电流;另一方面,银纳米颗粒的表面等离子振动有助于增强Ga_(2)O_(3)对紫外光的吸收,且紫外光照下银纳米颗粒会产生大量的热载流子使得热电子有足够的能量克服银纳米颗粒与Ga_(2)O_(3)薄膜间的肖特基势垒,使得探测器的光电流增加。本文工作为实现具有低暗电流和高光暗电流比的深紫外光电探测器提供了一种可行的方法。

Objective Thanks to the low false alarm rate and high signal-to-noise ratio,deep ultraviolet(DUV)photodetector(PD)shows great application potential in ozone hole detection,high-voltage electric fire alarm,stealth bomber,and missile alarm.Gallium oxide(Ga_(2)O_(3))is one of the most ideal materials for DUV PDs due to its suitable and tunable bandgap(4.5-5.3 eV),simple preparation process,and high stability.Nowadays,many studies focused on crystalline Ga_(2)O_(3) film DUV PDs,but the lattice mismatch and strict growth parameters during the preparation put forward higher requirements for substrate materials and growth equipment.Compared with crystalline Ga_(2)O_(3),amorphous Ga_(2)O_(3) films have low preparation requirements and are easier to generate larger photocurrents due to the promotion of carrier separation by intrinsic defects.However,amorphous Ga_(2)O_(3) is prone to higher dark current due to more defects.It is necessary to introduce noble metal Ag nanoparticles(Ag-NPs)to improve the photodetection performance of amorphous Ga_(2)O_(3).On one hand,the formation of Schottky barriers between Ag-NPs and Ga_(2)O_(3) films helps reduce the dark current of amorphous Ga_(2)O_(3).On the other hand,the surface plasmon vibration of Ag-NPs can enhance the absorption of Ga_(2)O_(3) to UV light.Additionally,Ag-NPs can generate a large number of hot carriers under UV light to allow hot electrons with sufficient energy to overcome the Schottky barriers.We provide a feasible approach to realize DUV PDs with low dark current and high photo-to-dark current ratio(PDCR).Methods Amorphous Ga_(2)O_(3) films are grown on sapphire substrates by the facile radio frequency(RF)magnetron sputtering technology.The sputtering is carried out at room temperature for 70 min with chamber pressure and Argon flow rate of 1 Pa and 20 sccm respectively.The obtained Ga_(2)O_(3) films are cut into four parts,and three of them are continuously sputtered with Ag-NPs on the Ga_(2)O_(3) surface by direct-current(DC)magnetron sputtering.The sputtering time is 5,10,and 20 s respectively.The obtained samples are labeled as 5 s Ag-NPs/Ga_(2)O_(3),10 s Ag-NPs/Ga_(2)O_(3),and 20 s Ag-NPs/Ga_(2)O_(3).Finally,the four samples obtained previously are annealed in a tube furnace for 2 h at an annealing temperature of 200℃.The crystal structure of the sample is characterized by X-ray diffractometer(XRD),the cross-section morphology of the sample is by scanning electron microscope(SEM),and the surface morphology of the sample is by atomic force microscope(AFM).Additionally,the absorption spectrum features Q6 ultraviolet-visible(UV-Vis)spectrophotometer,and the low-pressure mercury lamps with wavelengths of 254 nm and 365 nm are employed as the ultraviolet light source.A pair of cylindrical metal indium(In)with a diameter of 1 mm and a spacing of 1 mm is pressed on the surface of samples as electrodes,and the current-voltage(I-V)characteristics and transient response curve(I-t)of the PDs are measured by a B1505A power device analyzer.Results and Discussions AFM results confirm the introduction of Ag-NPs on the surface of amorphous Ga_(2)O_(3) films,and the surface mean square root(RMS)roughness of the Ag-NPs/Ga_(2)O_(3) film after sputtering Ag nanoparticles for 20 s is significantly increased from 0.218 to 6.390 nm[Figs.1(c)and 1(d)].Meanwhile,the absorption of Ga_(2)O_(3) to UV light also increases obviously after sputtering Ag-NPs[Fig.1(e)].20 s Ag-NPs/Ga_(2)O_(3) presents a lower dark current than amorphous Ga_(2)O_(3) due to the Schottky junction formed between Ag-NPs and Ga_(2)O_(3) films,which further forms a potential barrier and reduces the dark current[Fig.2(a)].Under the irradiation of 254 nm UV light,Ag-NPs/Ga_(2)O_(3) films exhibit a higher photocurrent than amorphous Ga_(2)O_(3).In particular,the photocurrent of 20 s Ag-NPs/Ga_(2)O_(3) at 5 V is 18.8 times higher than that of amorphous Ga_(2)O_(3)[Fig.2(b)].This may be due to the enhanced scattering of UV light by the plasmonic vibrations of the Ag-NPs on the surface of Ga_(2)O_(3) films,thus leading to enhanced absorption of UV light by Ga_(2)O_(3) and an increase in the photocurrent of the Ag-NPs/Ga_(2)O_(3) PD.Additionally,the Ag-NPs vibration may generate a large number of hot carriers to have enough energy to cross the Schottky barriers between Ag-NPs and Ga_(2)O_(3) films,which leads to an increase in the photocurrent of the PD.At this point,the PDCR is as high as 5.9×10^(5),the rejection ratio(254 nm/365 nm)is 1.6×10^(4)[Fig.2(c)],and the responsivity is 36.1 mA/W[Fig.3(c)],with the detectivity of 2×10^(14) Jones and external quantum efficiency of 17.7%[Fig.3(d)].Meanwhile,both the amorphous Ga_(2)O_(3) detector and the Ag-NPs/Ga_(2)O_(3) detector have short response time(Fig.4).Conclusions In summary,the Ag-NP composite amorphous Ga_(2)O_(3) film DUV PD is prepared by a room temperature magnetron sputtering technology.The PD exhibits an excellent photodetection performance.Under 5 V voltage,the dark current of the detector is as low as 94 fA and the PDCR is as high as 5.9×10^(5),and the rejection ratio(254 nm/365 nm)is 1.6×10^(4),with the responsivity of 36.1 mA/W,detectivity of 2×10^(14) Jones,and external quantum efficiency of 17.7%.This is not only attributed to the plasmonic vibration of Ag-NPs under UV light,which scatters more incident light into the Ga_(2)O_(3) film layer to enhance the UV light absorption of the Ga_(2)O_(3) films,but also to the generation of a large number of hot carriers by Ag-NPs under UV light.These hot carriers enable the hot electrons to overcome the Schottky barriers formed by Ag-NPs and Ga_(2)O_(3) films,which brings about a significant increase in the PD photocurrent.In addition,the formation of the Schottky barriers between Ag-NPs and Ga_(2)O_(3) films helps reduce the dark current in the amorphous Ga_(2)O_(3).This study implies that the introduction of noble metal nanoparticles provides a viable solution to DUV PDs with low cost,dark current,and high PDCR.