Abnormal Photocurrent in Semiconductor p-n Heterojunctions: Toward Multifunctional Photoelectrochemical-Type Photonic Devices and Beyond

Semiconductor p-n heterojunctions are important building blocks for modern electronic and photonic devices. Further combining semiconductor p-n heterojunctions with light and electrolyte environment, interesting photoelectrochemical (PEC) phenomena can occur, which enriches the design principles of multifunctional devices. In fact, recent years have witnessed the emergence of PEC-type photonic devices. For PEC-type photonic devices, a key to realize multifunctionality is to control the photocurrent polarity of the photoelectrode. In this study, an abnormal photocurrent is reported from p-InGaN/n-GaN nanowire heterojunctions under a blue light illumination: although n-GaN is transparent to the blue light (and thus optical absorption mainly occurs in p-InGaN) and p-InGaN in principle can only give negative PEC photocurrent, the detailed experiments show that positive PEC photocurrent can be generated from the p-InGaN segment due to the existence of the built-in electric field at the p-n junction. This study shows a new route to control the photocurrent polarity in a semiconductor p-n heterojunction photoelectrode. This unveiled role of the built-in electric field is expected to impact the design of emerging PEC-type photonic devices, as well as other novel photonic and electronic devices based on semiconductor nanowire p-n heterojunctions. Abnormal positive photocurrent is measured from p-InGaN/n-GaN nanowire heterojunction photoelectrode, when light absorption only occurs in p-InGaN and in principle p-InGaN only supports negative photocurrent. This manifests the role of the built-in electric field at the p-n junction on photocarrier dynamics and could facilitate the design of novel photonic and electronic devices using semiconductor nanowire p-n heterojunctions.image