USTC team demonstrates ε- and α-gallium oxide UV-photodetector
Researchers claim very high performance with record low dark current and record high photo-to-dark-current ratio
Solar-blind photodetectors (PDs) have attracted a lot of attention in recent years for their applications in deep space exploration, space communication and solar-blind imaging. Ga2O3 is intrinsically suitable for solar-blind photodetection with its wide band-gap of 4.7−5.2 eV.
Ga2O3 has five isomorphic structures, and so far, extensive research has been carried out on studying monoclinic β-Ga2O3 film which is relative thermodynamically stable. However, other phases, including α-, γ-, δ- and ε- Ga2O3 are less studied.
Recently, there has been increasing interest in the investigation of ε-Ga2O3 which possesses highly symmetric hexagonal structure close to the conventional wide bandgap III-nitrides. It is possible to integrate nitrides with ε-Ga2O3 to form III-oxide/III-nitride heterojunction device for optoelectronic applications.
Additionally, α-Ga2O3 has corundum-like structure: the same as α-Al2O3, which is a promising substrate candidate that can be produced in large diameters. Hence, α-Ga2O3 is of particular interest since it can be hetero-epitaxially grown on cheap sapphire substrates in large scale.
University of Science and Technology of China (USTC) led by Haiding Sun, Shibing Long, Ming Liu and Structured Materials Industries in USA, have made high-quality single crystal epsilon-phase Ga2O3 (ε-Ga2O3) and alpha-phase-dominated(α-phase-dominated) Ga2O3 films. These were hetero-epitaxially-grown on c-plane sapphire substrate by MOCVD to create UV photodetectors (PDs) with lateral Schottky photodiode (LSPD) based on ε-Ga2O3 film and metal-semiconductor-metal (MSM) structure based on α-Ga2O3 film.
The researchers claim very high performance for their PDs with record low dark current of 81 fA, record high photo-to-dark-current ratio exceeding 107, an ultrahigh detectivity of 1.0×1015 Jones, high external quantum efficiency (EQE) of 4.1×104 percent and high responsivity of 84 A/W with fast response time under 254 nm light illumination.
The four graphs (above) show the ε-Ga2O3 Schottky photodiode performance: (a) Semi-log and linear I-V curves of the ε-Ga2O3 Schottky photodiode in the dark and under 254 nm light illumination with a light density (P λ) of 87µW/cm, (b) semi-log and linear I-V curves of the device in the dark and under 254 nm light illumination with different light intensities, (c) photocurrent and photo-to-dark-current ratio ( PDCR ) and (d) responsivity ( R ) and detectivity ( D ∗) as a function of light intensity.
The ε-Ga2O3 Schottky photodiode shows a rectification ratio of∼102 with low dark current of 25 pA at V = 6V. It has a high photo-to-dark-current ratio of 5.7×104 under 254nm light illumination. Furthermore, the PD exhibits an ultrahigh detectivity and external quantum efficiency of 4.2×1014 Jones and 4.1× 104 percent, respectively. The diode also has an ultrahigh responsivity of 84 A/W with a fast response. Such high performance of the ε-Ga2O3 PD was attributed to the high crystal quality of the film with low defects such as oxygen vacancies which, to some extent, might improve the carrier mobility and carrier collection efficiency indirectly.
Fig. 2 above shows (a) I-V curves of α-DGO PD in the dark and under 254nm illumination with a light density of 520 µW/cm2. The inset shows I-V curves in a semi-log scale. (b) Responsivity (R) and gain (G) as a function of the bias voltage. (c) Photocurrent and photo-to-dark-current ratio (PDCR) under UV light illumination with different intensities at V = 12 V. (d) Detectivity (D∗) and R as a function of light intensity at V =12 V.
'High-Performance Metal-Organic Chemical Vapor Deposition Grown -Ga2O3 Solar-Blind Photodetector With Asymmetric Schottky Electrodes' by Yuan Qin et al; IEEE Electron Device Letters, Vol. 40, No. 9, September 2019
'Ultrahigh-Performance Solar-Blind Photodetector Based on -Phase- Dominated Ga2O3 Film With Record Low Dark Current of 81 fA' by Xiaohu Hou et al; IEEE Electron Device Letters, Vol. 40, No. 9, September 2019
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