Ultra-high-performance of Self-Powered

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1 Ultra-high-performance of Self-Powered β-ga 2 Thin Film Solar-blind Photodetector Grown on Cost-Effective Si Substrate using High-Temperature Seed Layer Kanika Arora, Neeraj Goel #, Mahesh Kumar # and Mukesh Kumar * Functional and Renewable Energy Materials Laboratory, Indian Institute of Technology Ropar, Punjab, , India # Department of Electrical Engineering, Indian Institute of Technology Jodhpur, India * Corresponding author: mkumar@iitrpr.ac.in S1

2 Figure S1 (a). Schematic of the experimental set-up for measuring spectral response on gallium oxide photodetector, (b) Schematic diagram of β-ga2o3 thin film based MSM-DUV photodetector with details of interdigitated electrodes. S2

3 TABLE S1 Comparison of β-ga 2 thin film photodetector at moderate bias on different substrates with our work. Substrate Responsivity (A/W) EQE (%) Photocurrent (A) Ref. Ga 2 wafer 39.3 (20V) [1] c-plane sapphire 3.3 (16 V) µa [2] c-plane sapphire 54.9 (10V) µa [3] c-plane sapphire 26.1 (10V) [4] c-plane sapphire 0.77 (10V) µa [5] Ga 2 wafer 1.8 (3.8 V) na [6] Si-doped GaAs wafer (20V) µa [7] 4H-SiC 0.18 (-5 V) µa [8] Hetero-β-Ga 2 /p-si (100) 370 (10 V) [9] Sapphire 9.66 (10V) - - [10] 2-D β-ga 2 nanosheet Si/SiO (10V) na [11] Ga 2 nanobelt Si/SiO (30V) [12] Ga 2 /SnO 2 :Ga core shell nanowire (sapphire) (5 V) µa [13] Quartz 0.19 (20V) µa [14] Sapphire (10V) - - [15] ZnO (0001) 0.35 (-5V) µa [16] S3

4 MSM-β-Ga 2 Si (100)-with HSL (5 V) µa This work S4

5 The optical bandgap (E g ) of gallium oxide thin film deposited with and without high-temperature seed-layer are estimated using a formula (hυ EQE) 2 =A(hυ-E g ) [17], where EQE is the external quantum efficiency, A is proportional constant, and hυ is the incident photon energy. The band gap was calculated by extrapolating the linear fit of the curve on energy-axis. The optical bandgap of sample without HSL is found to be 4.66 ev while with HSL it is 4.68 ev, which is in the good agreement with the reported value of optical band gap for Ga 2 thin film lying in the range of ev for β-ga 2 [18]. Figure S2. (hυ EQE) 2 vs. hυ for β-ga 2 film deposited without HSL and with HSL on a silicon substrate. The optical bandgap is observed around 4.66 and 4.68 ev for β-ga 2 film deposited with and without high-temperature seed layer, respectively. S5

6 Figure S3 Fitting of dark I-V curve of Ga2O3 thin film grown without and with high-temperature seed layer. S6

7 Figure S4. (a), (b) Time-dependent photoresponse of the sample without HSL and with HSL respectively and (c), (d) the corresponding exponential fitting of under 254 nm illumination at - 5V bias. We have performed transient response measurements with 254 nm DUV source at -5 V bias for both the samples. The results are shown in Figure S4 (a-d). Figure S4 (a-b) shows the transient response for the sample without HSL and with HSL conditions with a remnant photoconductive behaviour. The rise time/decay time at -5 V bias for the sample without HSL and with HSL conditions are shown in Figure S4 (c-d). For device without HSL rise time/ decay time estimated to be 2.5 s/ s and 2.7 s/ 31.7 s, respectively. For a sample with HSL, the rise time and decay time at -5 V bias shown in Figure S4 (d) are estimated to be 0.58 s and 0.45 s, respectively. As indicated in Figure S4 (b) it shows that for a fixed applied bias, a sample with HSL exhibit an I photo /I dark ratio of ~ under a 254 nm light illumination. The decrease in the on/off gain is attributed to the increment in the dark current at higher bias caused to release more carriers from the traps and move with swift drift velocity which increases recombination S7

8 probability and charge carrier scattering respectively. The slow rise/decay time indicates the carrier trapping/release process is extremely slow, resulting in the existence of a slow-response component at -5 V bias. S8

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