Patterned growth of β-Ga2O3 thin films for solar-blind deep-ultraviolet photodetectors array and optical imaging application

doi:10.1016/j.jmst.2020.09.015

Abstract

Abstract:

Solar-blind deep-ultraviolet (DUV) photodetectors based on Ga₂O₃ have attracted great attention due to their potential applications for many military and civil purposes. However, the development of device integration for optoelectronic system applications remains a huge challenge. Herein, we report a facile method for patterned-growth of high-quality β-Ga₂O₃ thin films, which are assembled into a photodetectors array comprising 8 × 8 device units. A representative detector exhibits outstanding photoresponse performance, in terms of an ultra-low dark current of ∼0.62 pA, a large I_light/I_dark ratio exceeding 10⁴, a high responsivity of ∼0.72 A W^-1 and a decent specific detectivity of ∼4.18 × 10¹¹ Jones, upon 265 nm DUV illumination. What is more, the DUV/visible (250/400 nm) rejection ratio is as high as 10³ with a sharp response cut-off wavelength at ∼280 nm. Further optoelectronic analysis reveals that the photodetectors array has good uniformity and repeatability, endowing it the capability to serve as a reliable DUV light image sensor with a decent spatial resolution. These results suggest that the proposed technique offers an effective avenue for patterned growth of β-Ga₂O₃ thin films for multifunctional DUV optoelectronic applications.

Key words: Ultrawide-bandgap semiconductor, Solar-blind, Deep ultraviolet photodetection, Patterned growth, Image sensor

Chao Xie, Xingtong Lu, Yi Liang, Huahan Chen, Li Wang, Chunyan Wu, Di Wu, Wenhua Yang, Linbao Luo. Patterned growth of β-Ga₂O₃ thin films for solar-blind deep-ultraviolet photodetectors array and optical imaging application[J]. J. Mater. Sci. Technol., 2021, 72: 189-196.

Figures/Tables 8

Fig. 1. Schematic illustration of the procedures for fabricating patterned β-Ga2O3 thin film-based photodetectors array.

Fig. 2. FESEM images of the β-Ga2O3 thin films with the patterns of (a) periodic square array, (b) periodic round array, (c) periodic triangle array, (d) continuous 4 and 6 μm stripes and (e) “HFUT” characters. Inset in (b) shows an enlarged FESEM image of the β-Ga2O3 thin film.

Fig. 3. (a) EDS spectrum and chemical composition of both gallium and oxygen atoms, (b) XRD pattern and (c) absorption spectrum of the β-Ga2O3 thin film, the inset in (c) shows the plot of (αhν)2-hν for deducing the optical bandgap of the β-Ga2O3 thin film. (d) FESEM image of a typical β-Ga2O3 thin film-based photodetector with a MSM geometry. The elemental mapping showing the distribution of (e) Au and (f) Ga elements.

Fig. 4. (a) I-V curves of the β-Ga2O3 thin film-based photodetector in dark and under 265 nm illumination (0.952 mW cm-2). The background is a FESEM image of the photodetectors array. (b) Time-dependent photoresponse of the device under 265 nm illumination. (c) I-V curves and (d) time-dependent photoresponse of the device under 265 nm illumination with different light intensities. (e) Photocurrent and (f) responsivity and EQE of the device as functions of light intensity.

Table 1 Comparison of some key performance parameters of our device and β-Ga2O3 thin film-based DUV photodetectors in literatures.

Method	Dark current (A)	I_light/I_dark ratio	Responsivity (A W^-1)	D* (Jones)	τ_r/τ_d (s)	Ref.
PLD	1.88 × 10^-7	~10	7.1 (10 V)	-	-	[38]
magnetron sputtering	7.63 × 10^-9	1.08 × 10³	2.6 (10 V)	1.6 × 10¹²	0.26/1	[37]
magnetron sputtering	1.0 × 10^-11	~10⁵	0.89 (10 V)	-	0.3/0.25	[24]
PECVD^a	4.0 × 10^-10	37	2.0 × 10^-4 (0 V)	6.9 × 10⁹	-	[20]
PECVD	4.0 × 10^-10	~10⁵	1.2 (10 V)	1.9 × 10¹²	-	[25]
OFZ^b	2.3 × 10^-10	~10²	4 (40 V)	-	0.3/0.2	[40]
Thermal-assisted conversion	6.2 × 10^-13	6.13 × 10⁴	0.72 (10 V)	4.18 × 10¹¹	1.1/0.03	This work

Fig. 5. (a) Responsivity and EQE of the device as functions of operational bias voltage. (b) Spectral responsivity of the device in the wavelength region of 200-600 nm. (c) An enlarged photoresponse curve shows the rise (τr) and decay times (τd). (d) Time-dependent photoresponse of the device over 1000 cycles of operation (265 nm, 0.952 mW cm-2).

Fig. 6. 2D current contrast maps showing the channel currents of all the 8 × 8 devices (a) in dark and (b) upon 265 nm light illumination (0.25 μW cm-2). (c) Channel current in dark and under 265 nm light irradiation for each device unit, the dash lines represent the average values for dark current (black) and photocurrent (red). (d) 3D diagram of the Ilight/Idark ratio for each device unit.

Fig. 7. (a) Schematic illustration of the setup for DUV light imaging. (b) The 2D current contrast map of the photodetectors array under 265 nm light illumination, showing the DUV light imaging function.

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Patterned growth of β-Ga₂O₃ thin films for solar-blind deep-ultraviolet photodetectors array and optical imaging application

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