P-type β-MoO2 nanostructures on n-Si by hydrogenation process: synthesis and application towards self-biased UV-visible photodetection

Abstract

We report on the synthesis and UV–vis photodetection application of p-type MoO2 nanostructures (NSs) on Si substrate. β-MoO2 NSs have been synthesized from previously grown α-MoO3 structures/n-type Si via a hydrogenation process at 450 °C. After hydrogenation, the α-MoO3 structures were completely converted into β-MoO2 NSs without the presence of sub-oxidized phases of molybdenum oxide. The as-grown NSs exhibited very good p-type electrical conductivity of ≈2.02 × 103 S–cm−1 with hole mobility of ≈7.8 ± 1.3 cm2–V−1–Sec−1. To explore optoelectronic properties of p-type β-MoO2 NSs, we have fabricated a p-MoO2/n-Si heterojunction photodetector device with Au as the top and Al as the bottom contacts. The device exhibits peak photoresponsivity of ≈0.155 A W−1 with maximum detectivity ≈1.28 × 1011 cm–Hz1/2–W−1 and 44% external quantum efficiency around ≈436 nm, following the highest photoresponse (Iph/Id ≈ 6.4 × 102) and good response speed (rise time ∼29 ms and decay time ∼38 ms) at −1.5 V. Importantly, this device also shows good self-powered high-speed (rise time ∼47 ms and decay time ∼70 ms) photodetection performance with peak responsivity and detectivity of ≈45 mA W−1 and ≈4.05 × 1010 cm–Hz1/2–W−1, respectively. This broadband UV-visible light detection feature can be attributed to the coordinated effects of MoO2 band-edge absorption, interfacial defects and self absorption in Si. The photodetection behavior of the device has been understood by proposed energy-band diagrams with the help of an experimentally derived work function, band gap and valence band maximum position of MoO2 NSs.