Room-temperature-operated fast and reversible vertical-heterostructure-diode gas sensor composed of reduced graphene oxide and AlGaN/GaN

A vertical heterostructure diode (VHD) based on a van der Waals heterojunction between reduced graphene oxide (rGO) and AlGaN/GaN for toxic gas sensing. The Schottky diodes based on the 2D rGO nanosheets and a 3D AlGaN/GaN semiconductor have been utilized for chemical sensing since the rGO nanosheets can actively interact with the target gas species and result in doping/de-doping of the rGO by reducing/oxidizing gases. As a result, Schottky barrier height between rGO and AlGaN/GaN changes and, in turn, the current flowing through the VHD gas sensor under forward bias can be modulated upon adsorption of both oxidizing and reducing gases. [Display omitted] •A vertical heterostructure diode for toxic gas sensing is demonstrated.•Heterojunction between reduced graphene oxide and AlGaN/GaN is formed.•The sensor showed fast response, and ppb-level detection at room temperature.•Variation of the SBH upon gas exposure is the primary sensing mechanism. A vertical heterostructure diode (VHD) based on a van der Waals heterojunction between reduced graphene oxide (rGO) and Al0.3Ga0.7N/GaN/sapphire was fabricated for use in the chemical sensing of toxic gases. Target gases interacted with the atomically thin rGO layer, which served as a contact and sensing material; this interaction induced a change in the forward bias current of the VHD through modulation of the effective Schottky barrier height (SBH). The VHD gas sensor showed fast, repeatable, reproducible, recoverable, and stable room-temperature (RT)-operable gas-sensing performance for toxic gases, including nitrogen dioxide, sulfur dioxide, and ammonia. The variations of the SBH, ideality factor and series resistance of the VHD gas sensor upon gas exposure were systematically analyzed by studying the changes in the current transport mechanism through the vertical junction due to the presence of various gases. The analysis revealed that the variation of the SBH upon gas exposure is the primary sensing mechanism of the VHD gas sensor. The VHD device has great promise as the fundamental structure of simple, low-power, low-noise, and RT-operable chemical sensors.