【Domestic Papers】Integrating photodetection and neuromorphic vision in ALD-grown amorphous Ga₂O₃ thin films via bias-voltage modulation

      Researchers from the Nanjing University of Science and Technology have published a dissertation titled "Integrating photodetection and neuromorphic vision in ALD-grown amorphous Ga₂O₃ thin films via bias-voltage modulation" in Optics Express.

Project Support

      Fundamental Research Funds for the Central Universities (30923011002).

Background

      Gallium oxide (Ga₂O₃), an ultra-wide-bandgap semiconductor (UWBG) material, has attracted significant research interest due to its exceptional properties, including an ultra-wide bandgap, high refractive index, and superior mechanical hardness. These characteristics make it highly suitable for diverse applications such as sensing systems, memory devices, power electronics, and photodetectors. Recently, Ga₂O₃ based optoelectronic artificial synapses have attracted widespread attentions, which can be utilized in the fields of image recognition and information encryption. In particular, Ga₂O₃ is an excellent candidate for deep ultraviolet (DUV) photodetection, owing to its tunable bandgap (4.5-5.3 eV) . This wide bandgap ensures high transparency in the visible spectrum while enabling strong absorption of deep ultraviolet radiation.

Abstract

      We demonstrate what we believe to be a new atomic layer deposition (ALD) process utilizing gallium chloride (GaCl₃) and water vapor as complementary precursors for synthesizing high-quality Ga₂O₃ thin films. The developed process enables the growth of ultrasmooth amorphous Ga₂O₃ layers with sub-nanometer surface roughness and an ultrawide bandgap of 5.29 eV, ideal for deep-ultraviolet (DUV) photonic applications. Metal-semiconductor-metal (MSM) photodetectors employing the Au/ Ga₂O₃/Au architecture achieve exceptional performance metrics, including an outstanding photocurrent ratio of 98.36 under 254 nm illumination and ultrafast response characteristics (0.23 s rise/0.25 s decay times). The devices exhibit unique bias-tunable dual-mode operation: low-voltage operation enables conventional fast-response photodetection, while high bias conditions induce persistent photoconductivity effects. This voltage-dependent reconfigurability allows effective emulation of neurobiological functions, particularly demonstrating paired-pulse facilitation and replicating sophisticated learning-forgetting-relearning cognitive processes. Our findings establish ALD-grown Ga₂O₃ as a versatile platform for developing multifunctional optoelectronic systems that synergistically integrate high-performance DUV detection with neuromorphic computing capabilities, paving the way for next-generation reconfigurable optical memory devices and bio-inspired visual processing architectures.

Conclusion

      In this work, we demonstrate the growth of high-quality Ga₂O₃ thin films via thermal ALD using GaCl₃ and H₂O as a new precursor combination. The self-limiting, layer-by-layer growth characteristics of ALD enable precise thickness control and yield films with excellent uniformity and low surface roughness. Optical characterization reveals strong deep-ultraviolet absorption with a tunable bandgap ranging from 4.5 to 5.5 eV. Fabricated MSM photodetectors exhibit outstanding performance metrics under 1 V bias, including a high PDCR of 98.36 and fast response characteristics (rise time τ_r1 = 0.23 s; decay time τ_d1 = 0.25 s). Notably, the device demonstrates bias-voltage-tunable multifunctionality, enabling reversible switching between conventional photodetection and neuromorphic visual sensing modes. At high bias voltage, biological synaptic behaviors such as paired-pulse facilitation and learning-forgetting-relearning processes can be realized. These results highlight the significant potential of ALD-derived Ga₂O₃ thin films for developing next-generation reconfigurable optoelectronic devices with integrated functionalities.

Fig. 1. The schematic of ALD process for Ga₂O₃ using GaCl₃ and H₂O.

Fig. 2. GPC of Ga₂O₃ film plotted as a function of (a) GaCl₃ pulse time, (b) H₂O pulse time, and (c) growth temperature. (d) Plot of film thickness versus the number of ALD cycles at 300 °C.

 

DOI：

doi.org/10.1364/OE.564628