Extended Exposure of Gallium Nitride Heterostructure Devices to a Simulated Venus Environment

Abstract

Further development of harsh environment electronics capable of uncooled operation under Venus surface atmospheric conditions (~460°C, ~92 bar, corrosive) would enable future missions to the surface of Venus to operate for up to a year. Wide band-gap gallium nitride (GaN) heterostructure devices are attractive candidates for Venus lander missions due to their ability to withstand high-temperature exposure. Here, we present the first assessment of the electrical integrity of GaN-based devices subject to Venus surface atmospheric conditions. Three unique device architectures were fabricated at the Stanford Nanofabrication Facility and exposed in a Venus simulation chamber for 244 hours at the University of Arkansas Center for Space and Planetary Sciences. The three device architectures tested were InAlN/GaN high electron mobility transistors (HEMTs), InAlN/GaN Hall-effect sensors, and AlGaN/GaN UV photo detectors, which all have potential applications in the collection and readout of sensor data from Venusian landers. After exposure, HEMT threshold voltage had shifted only ~1% and gate leakage current remained on the same order of magnitude, demonstrating stability of the IrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> gate under supercritical CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ambient. Fluctuations in drain current after exposure are attributed to thermal detrapping and electrically-activated trapping processes. Measurements of the InAlN/GaN 2DEG properties in virgin and exposed Hall-effect sensors were comparable. Furthermore, the Hall-effect sensors exhibited a maximum change of only +11.4% in current-scaled sensitivity and -6.6% in voltage-scaled sensitivity post-exposure. The UV photodetectors with 362 nm peak wavelength exhibited an average decrease in responsivity of 38% after exposure, which is thought to be due to strain relaxation or ohmic contact degradation. Similar performance of the InAlN/GaN HEMTs and Hall-effect sensors before and after exposure highlights the viability of this material platform for development of Venus surface electronics, while the decrease in AlGaN/GaN UV photocurrent requires further analysis to assess whether the AlGaN/Ga heterostructure is suitable for robust, Venus-capable electronics.