Quasi‐Single‐Crystalline ZnGa₂O₄Films via Solid Phase Epitaxy for Enhancing Deep‐Ultraviolet Photoresponse

Abstract

The complex‐oxide materials are multifunctional materials, which have wide applications to the semiconductor and microelectronic fields. The ZnGa2O4 having a wide bandgap of 5.1 eV is one of the promising materials for deep‐ultraviolet photodetector (PD) applications. The ZnGa2O4 films are deposited by using conventional radio‐frequency magnetron sputtering which is extensively employed in the industry. However, the as‐deposited ZnGa2O4 films show the disordered nanocrystalline structure, resulting in the relatively poor performance. Since the Zn atoms can diffuse out of the film structure during the annealing, the ZnGa2O4 material is difficult to get the single‐crystalline structure by using the sputtering method. Here, the solid‐phase epitaxy method is used for crystallizing the ZnGa2O4 structure via rapid thermal annealing process. The disordered crystal grains as incubated seeds are obtained in the as‐deposited ZnGa2O4 film at the substrate temperature of 400 °C. Further annealing under the temperature of 700 °C in 1 min, the ZnGa2O4 film structure approaches the quasi‐single‐crystalline ZnGa2O4 structure, which is evidenced by checking the transmission electron microscopy. The responsivity of annealed ZnGa2O4 PDs can reach 2.53 A W−1 (at 240 nm and 5 V), which shows a relative enhancement of 256% compared with the as‐deposited ZnGa2O4 PDs.

Zinc Gallium Oxide—A Review from Synthesis to Applications

“…°C, then the dark current decreased, and when Ts was increased from 300 to 600 °C, the Idark showed a similar low value, as shown in Figure 23a [90]. Increasing substrate temperature could reduce defect states and as a result of this, the dark current was found to be reduced in the ZnGa2O4 PDs [90]. The substrate temperature of 400 °C is kept fixed as the optimized substrate temperature for the asdeposited ZnGa2O4 PDs.…”

“…MSM photodetectors possess low capacitance and have the potential for large-area detectors [89]. Therefore, MSM ZnGa 2 O 4 photodetectors in Reference [20,85,90,91] are taken into consideration. Their process parameters and optimized performances are listed in Tables 7 and 8, respectively.…”

“…In addition to the aforementioned methods above, post-annealing can transform the broad spectral response of the photodetector to sharp spectral response. Figure 23c exhibits that the highest responsivity of 0.71 A W −1 was achieved at T s of 400 • C in which the responsivity peak exhibited the broad spectral response due to the defects present in the ZnGa 2 O 4 PDs [90]. After post-annealing at a temperature of 700 • C, the responsivity reached 2.53 A W −1 from 0.71 A W −1 at 240 nm; then, the broad response was transformed to sharp spectral response, as shown in Figure 23d.…”

Influence of Annealing Temperature on the Properties of ZnGa2O4 Thin Films by Magnetron Sputtering

“…The photon energy gap increased from 4.7 eV for the as-deposited sample to 4.98 eV as the annealing temperature increased to 900 • C. The increase in energy gap is attributed to the decrease in the number of defect densities and grain boundaries, as well as the increase in the annealing temperature. The energy gap is narrowed because the amorphous structure usually produces excited electrons that undergo conduction in defect state [28].…”

“…The increase in energy gap is attributed to the decrease in the number of defect densities and grain boundaries, as well as the increase in the annealing temperature. The energy gap is narrowed because the amorphous structure usually produces excited electrons that undergo conduction in defect state [28]. The photoluminescence emission spectra of ZnGa2O4 thin films at various annealing temperature is shown in Figure 7a.…”