Indium nitride humidity sensing devices with microwave resonant property

Abstract

An effective microstructure indium nitride (InN) humidity sensing (INHUSE) device has been developed after InN compound was appropriately annealed with nitrogen source compensation. An X-ray diffraction spectrum of the as-synthesised structure shows one strong peak at 30.5° corresponding to the (0002) atomic plane of the InN hexagonal compound. The InN compound of p-type is exhibited to reach an average Hall coefficient of 2.270 × 107 m2/C, which can be conjugated with the n-type substrate to construct the p–n sensing device with a resonant tunnelling property. The Raman spectrum reveals the longitudinal optical phonon mode A1(LO) (polar mode), transverse optical phonon mode A1(TO) (polar mode) and transverse optical phonon mode E1(TO) of the InN-based INHUSE device in 582, 437 and 473 cm−1, respectively. The negative differential resistance effect of the INHUSE device with an excellent peak current density in 13.2 kA/cm2 and an outstanding peak to valley current ratio of about 3.36 is exhibited. Experimental moisture examination of the INHUSE device from RH30 to 90% in accordance with the calculation of the microwave resonant property up to GHz is completed. The linear region of relative humidity measurement is from RH40 to 70% in resistance value, reached as the measured resistance value at about 31 Ω. The sensitivity of the INHUSE device is about 50 kHz/RH% for the self-resonant frequency and 2.5 MHz/RH% for the resistive cutoff frequency.