A Schottky diode based on a heterojunction of three-dimensional (3D) nanohybrid materials, formed by hybridizing reduced graphene oxide (RGO) with epitaxial vertical zinc oxide nanorods (ZnO NRs) and AlGaN(∼25 nm)/GaN is presented as a new class of high-performance chemical sensors. The RGO nanosheet layer coated on the ZnO NRs enables the formation of a direct Schottky contact with the AlGaN layer. The sensing results of the Schottky diode with respect to NO, SO, and HCHO gases exhibit high sensitivity (0.88-1.88 ppm), fast response (∼2 min), and good reproducibility down to 120 ppb concentration levels at room temperature. The sensing mechanism of the Schottky diode can be explained by the effective modulation of the reverse saturation current due to the change in thermionic emission carrier transport caused by ultrasensitive changes in the Schottky barrier of a van der Waals heterostructure between RGO and AlGaN layers upon interaction with gas molecules. Advances in the design of a Schottky diode gas sensor based on the heterojunction of high-mobility two-dimensional electron gas channel and highly responsive 3D-engineered sensing nanomaterials have potential not only for the enhancement of sensitivity and selectivity but also for improving operation capability at room temperature.

No abstract

No abstract

Excellent surface passivation and anti-reflection properties of double-stack layers is a prerequisite for high efficiency of n-type c-Si solar cells. The high positive fixed charge (Q f ) density of N-rich hydrogenated amorphous silicon nitride (a-SiN x :H) films plays a poor role in boron emitter passivation. The more the refractive index (n) of a-SiN x :H is decreased, the more the positive Q f of a-SiN x :H is increased. Hydrogenated amorphous silicon oxynitride (SiON) films possess the properties of amorphous silicon oxide (a-SiO x ) and a-SiN x :H with variable n and less positive Q f compared with a-SiN x :H. In this study, we investigated the passivation and anti-reflection properties of Al 2 O 3 /SiON stacks. Initially, a SiON layer was deposited by plasma enhanced chemical vapor deposition with variable n and its chemical composition was analyzed by Fourier transform infrared spectroscopy. Then, the SiON layer was deposited as a capping layer on a 10 nm thick Al 2 O 3 layer, and the electrical and optical properties were analyzed. The SiON capping layer with n=1.47 and a thickness of 70 nm resulted in an interface trap density of 4.74=10 10 cm −2 eV −1 and Q f of −2.59=10 12 cm −2 with a substantial improvement in lifetime of 1.52 ms after industrial firing. The incorporation of an Al 2 O 3 /SiON stack on the front side of the n-type solar cells results in an energy conversion efficiency of 18.34% compared to the one with Al 2 O 3 /a-SiN x :H showing 17.55% efficiency. The short circuit current density and open circuit voltage increase by up to 0.83 mA cm −2 and 12 mV, respectively, compared to the Al 2 O 3 /a-SiN x :H stack on the front side of the n-type solar cells due to the good anti-reflection and front side surface passivation.

No abstract