Schottky-junction photodiodes with quantum-tunneling barriers

Abstract

Silicon (Si) photodiodes play a crucial role in complementary metal-oxide-semiconductor (CMOS) image sensors, particularly in visible cameras, and are increasingly in demand for infrared or short-wavelength (SWIR) cameras in modern autonomous vehicles operating under various weather conditions. However, the bandgap energy of 1.12 eV in Si limits its capability to detect light in the infrared range, only allowing visible light detection. In this study, we propose transparent, quantum-thickness, Schottky-junction photodiodes on Si for light detection from visible to SWIR wavelengths. We employ an atomically thin TiO2 interfacial layer between an n-type Si substrate and a nanometer-thick metallic layer, which is positioned beneath a transparent conductive oxide (TCO) layer, to create n-Si/TiO2/TiN/ITO multilayered Schottkyjunction photodiodes. Without the typical p-n junction in Si, we observed photocurrents through interband transitions by incident photons in the wavelength range of 400 ~ 1,100 nm. Additionally, small but noticeable amounts of photocurrent were also measured by internal photoemission (IPE) via hot carrier generation even at the wavelength of 1,310 nm. The embedded TiO2 layer significantly reduced dark current by two orders of magnitude with little change in photocurrent or quantum efficiency. This can be attributed to the low conduction band offset of the TiO2 semiconductor, which contributes to a quantum tunneling barrier without changing the Schottky barrier height and disturbing the internal photoemission process.