Xingzhao Liu

The solar-blind ultraviolet photodetectors are alternative for confidential communications and missile track due to its low false alarm rate. Amorphous multi-component oxide semiconductors have become excellent choices for solar-blind ultraviolet detectors due to their tunable bandgap and large-area uniformity. In this work, we fabricated amorphous In_0.2Ga_1.8ZnO₄/In_0.2Ga_1.8MgO₄ (IGZO/IGMO) heterojunction. The band alignment reveals the effective separation and transport of photogenerated carriers at the interface, which makes recombination more challenging. As expected, IGZO/IGMO phototransistor shows a high responsivity of 499.3 A/W, a high external quantum efficiency of 2.4 × 10⁵%, a high detectivity of 3.7 × 10¹⁴ Jones, which demonstrates a significant ultraviolet sensitivity improvement compared to single-layer-film phototransistor. Furthermore, a rise/decay time of 1.4/2.7 ms, linear photoresponse characteristic and high visible-blind rejection ratio R_255nm/R_400nm of 1.5 × 10⁴ show the superiority of IGZO/IGMO phototransistor in high-performance solar-blind ultraviolet detection. We believe that the IGZO/IGMO phototransistor demonstrates great potential for next-generation advanced optoelectronic devices.

Amorphous indium–gallium–zinc–oxide (IGZO) has attracted much attention due to its great potential for high-performance optoelectronic devices. In this work, the optimized atomic composition in $\text{In}_{{0}.{2}}$ $\text{Ga}_{{1}.{8}}$ ZnO₄ films enhances their ability to absorb solar-blind ultraviolet light. By controlling the oxygen flux during sputtering, two typical IGZO thin films with different oxygen vacancy distributions were obtained, and corresponding phototransistors were fabricated. The detailed performance investigations of both phototransistors reveal the contradictory effect of oxygen vacancy on promoting the solar-blind ultraviolet sensitivity and deteriorating the response time and stability. Moreover, the phototransistor made from IGZO film with low oxygen vacancy concentration exhibits a responsivity of 215 A/W and detectivity of 6.0 × 10¹⁵ Jones together with a rise time of 2.9 ms and a decay time of 1.2 ms under solar-blind ultraviolet illumination. Meanwhile, this phototransistor also demonstrates a high visible-blind rejection ratio ( ${R}_{{255}{\,}\text {nm}}$ / ${R}_{{400}{\,}\text {nm}}\text {)}$ of $4.1\times 10^{{5}}$ and good stability. Anyway, our IGZO phototransistor is on the same level or even better than many photodetectors, which demonstrates the great potential for next-generation advanced optoelectronic devices.

The performance of photodetectors can be improved by constructing a metal nanoparticle/semiconductor hybrid structure based on the localized surface-plasmon-resonance effect generated by the surface metal nanoparticles. However, an unexpected increase in dark current will be introduced, thus degrading the ability of photodetectors to respond to weak light signals. To avoid this problem, γ-In ₂ Se ₃ /Au-nanoparticles (Au-NPs) heterostructures are prepared, with the Au layer below the γ-In ₂ Se ₃ thin film. Benefiting from the depletion of the γ-In ₂ Se ₃ thin film and the photogenerated carrier trapping by Au-NPs, the optimized γ-In ₂ Se ₃ / Au-NPs structure exhibits suppressed dark current and enhanced light current. Compared to the single γ-In ₂ Se ₃ layer photodetector, its responsivity improves several times, and the detectivity increases by more than an order of magnitude.

An In₂Se₃/Ge heterojunction is fabricated via molecular beam epitaxy. The p–n junction device features a broadened photosensitive spectrum ranging from a visible (VIS) to short-wave infrared (SWIR) region (400–1700 nm). Notably, self-powered high responsivity of 0.32 A/W@450 nm and 0.52 A/W@1550 nm, decent specific detectivity of 3.2 × 10¹¹ Jones@450 nm, and 5.2 × 10¹¹ Jones@1550 nm at zero bias are achieved. Moreover, our photodetector exhibits a fast response speed with a sub-millisecond response time. These results can be attributed to the high quality of the In₂Se₃–Ge interface. Benefiting from the superposable dual-band photoresponse, the potential of the device for encrypted optical communication has been demonstrated.

Amorphous indium-gallium-zinc-oxide (a-IGZO) thin film was deposited by radio frequency sputtering in an oxygen-free atmosphere. The composition of the a-IGZO thin film was adjusted to be In0.2Ga1.8ZnO4 so that the bandgap of the a-IGZO thin film was 4.5 eV for solar-blind ultraviolet photodetectors. Then, the bottom-gate IGZO phototransistor was fabricated with a high-k gate dielectric layer of hafnium oxide (HfO2) to enhance the gate controllability. The phototransistor showed excellent performance with an on/off ratio of $10^{{9}}$ and field-effect mobility of 5.4 cm $^{{2}}\cdot \text {V}^{-{1}}\cdot \text {s}^{-{1}}$ . Under the 255 nm illumination, the phototransistor presented a gate voltage-controlled ultraviolet response. With zero voltage gate bias, a responsivity of $3.2\times 10^{{5}}$ AW $^{-{1}}$ and a detectivity of $1.4\times 10^{{16}}$ Jones was obtained. As a phototransistor made from amorphous semiconductors, the response speed is very low. The rise time and decay time are estimated at about 12 s and over 1800 s, respectively. However, the response time was tremendously improved to be less than $25~\mu $ s by interleaving both positive and negative gate voltage pulses synchronized with the UV illumination. The synchronous gate voltage pulses can be easily realized in readout integrated circuits (ROICs). Therefore, a-IGZO thin-film phototransistor should be a good candidate for flexible solar-blind ultraviolet photodetector with excellent performance.

We report a dual-junction strategy for fabricating a high-performance In2SexOy/In2Se3/Si heterojunction photodiode by oxidizing the epitaxial In2Se3 thin films. The device exhibits a suppressed dark current (4.2 × 10−11 A) and enhanced photocurrent at zero bias, benefiting from the double built-in electric fields. Consequently, it demonstrates excellent and uniform self-powered broadband (255–1050 nm) photodetection performance with the typical responsivity of several hundred mA/W, and detectivity of over 5 × 1011 Jones. Moreover, a fast response speed with a response time of 0.20 ms is achieved. Our investigation offers a potential route to construct full-spectrum photodetectors.

The phase and stoichiometry diversity of indium selenides provides the potential for several novel applications, especially for enhancing optoelectronic performance. Therefore, the epitaxial growth of single-phase indium selenides (In ₂ Se ₃ and InSe) is of particular interest, which however, is still a challenge. Herein, the controllable growth of γ-In ₂ Se ₃ and β-InSe thin films is realized via molecular beam epitaxy on c-plane Al ₂ O ₃ substrates. The growth mode is tuned by the incorporation or not of the Se source during the deposition process. The fabricated metal-semiconductor-metal structured γ-In ₂ Se ₃ photodetector (PD) exhibits superior performance with a high responsivity of 44.6 A/W and a high detectivity of 1.69 × 10 ¹³ Jones under blue light illumination, which are 2-3 times larger than those of β-InSe PD. Besides, the γ-In ₂ Se ₃ PD has an ultrafast photoresponse (i.e., τ _r /τ _d of 0.18/0.20 ms). While β-InSe PD is sensitive to broader-spectrum from ultraviolet to near-infrared range. Both devices possess the potential for situation-specific photodetection. Moreover, the uniform and reliable properties of the devices dispersed on the same substrate have been demonstrated, which are crucial for practical applications. This work provides an alternative route for the development of high-performance PDs based on large-area indium selenide thin films.