Energy-Band Engineering By Remote Doping of Self-Assembled Monolayers Leads to High-Performance Igzo/P-Si Heterostructure Photodetectors
Authors: Woo Gunhoo , Lee Dong Hyun , Yoo Hocheon , Kim Taesung 
Published: February 2024

Advancements in emerging technologies, such as autonomous driving, artificial intelligence, medical imaging, and augmented reality, have increased the demand for high-resolution image sensors to transmit further accurate color information. To meet the performance requirements of these applications, several research have been accelerating towards the utilization of emerging low-dimensional semiconductor materials, such as metal oxides, transition metal dichalcogenides, perovskites, and other organic materials.
Among them, metal oxide semiconductors (MOSs) are potential candidates for developing high-performance photodetectors. It can be synthesized over large areas using a simple/low-temperature process and are compatible with conventional fabrication equipment. However, MOS-based photodetectors still have several limitations, 1) the presence of charge traps and operational instability on the oxide surface, which degrade photodetection performance, and 2) the absence of an appropriate doping technique for MOS has blocked to improve photodetection performance via materials characteristic modification method.
In this study, we present a strategy to overcome these limitations and significantly enhance the performance of IGZO, which is representative of oxide semiconductor thin film, based photodetector with high operation stability and sustainability under ambient atmospheres. We utilized energy-band engineering through an octadecylphosphonic acid (ODPA) self-assembled-monolayer (SAM)-based doping treatment to enhance the photoelectric characteristics of IGZO/p-Si hetero-interfaced devices (ISH). The ODPA consists of a head group of the hydroxyl group, which forms the self-assembled covalent bond formation of R–P–O–substrate. Combining the ODPA SAM with the oxide surface of IGZO provided carrier concentration control based on their a dipole effect, and remain the performance and functionality through the surface encapsulation. As a result, under a light-emitting diode (LED) wavelength with an intensity of 3.9 mW, the proposed device exhibited remarkable photo-switching current ratio of 4.33 × 103 A/A and negative differential resistance (NDR) phenomenon. Espacially, the dark current of the ODPA treated ISH is decreased about 10 times lower than as-fabricated ISH, which shows the possibility of signal noise minimization. These performance improvement is expected to be derived from band properties modulation through IGZO layer annealing and ODPA doping. To clarify the doping effect of each treatment, we characterized the ODPA self-assembled monolayer using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Kelvin probe force microscopy (KPFM) to provide comprehensive analysis of the heterointerface effects. We also characterized the electrical properties of IGZO thin-film transistors (TFTs) based on variations of the annealing temperature to clarify the ODPA doping effect.
We evaluated 156 ODPA-treated IGZO/p-Si heterostructure photodetectors, which were scaled for fabrication on a 4 inch wafer. The devices exhibited a 100% yield, and uniform current behavior in the dark state (0.20 ± 0.06 nA) and light state (0.87 ± 0.15 µA), owing to an evenly deposited IGZO layer and a simple-to-treat ODPA doping scheme. Furthermore, consecutive sweeps of 20,000 cycles verified excellent cycle-to-cycle endurance, resulting in highly robust photoelectric behaviors without operational failure. Additionally, the performance of the ODPA-treated, IGZO/p-Si heterostructure photodetector remained unchanged for 237 days without degradation under atmospheric exposure (relative humidity (RH) = 37–53 % and 20.6–23.1 °C).

Acknowledgements

This research was supported by funding supports from the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2020R1A2C1101647) and Korea government (MEST) (NRF-2017R1A2B3011222).

Figure 1