We report a vertically stacked graphene tunnel junction with an atomically thin insulating layer for novel function devices. The insulating water layer sandwiched between graphene samples as a tunnel barrier which is fabricated through deionized (DI) water treatment of epitaxial graphene. Two graphene samples fabricated by SiC thermal decomposition are directly bonded to each other in a face-to-face manner. Vertically stacked graphene samples without DI water treated formed an ohmic junction. By inserting the structured water layer as tunnel barrier, the stacked junction exhibits Direct tunneling characteristics in a low-electric-field regime and Fowler-Nordheim tunneling (FNT) characteristics in a high-electric-field regime. The thickness of the structured water layer is estimated to be 0.28 nm by fitting the FNT formula. The very thin structured water layer is stable as tunnel barrier on epitaxial graphene for diode devices, which will have a widely application in electronic devices.

Band alignment between NiO x and nonpolar GaN plane and between NiO x and semipolar GaN plane are measured by x-ray photoelectron spectroscopy. They demonstrate that the maximum value of the valence band in the unintentional-doped a-plane, m-plane, and r-plane GaN are comparable to each other, which means that all the substrates are of n-type with similar background carrier concentrations. However, the band offset at the NiO x /GaN interface presents obvious crystalline plane dependency although they are coated with the same NiO x films. By fitting the Ga 3d spectrum obtained from the NiO x /GaN interface, we find that relatively high Ga–O content at the interface corresponds to a small band offset. On the one hand, the high Ga–O content on the GaN surface will change the growth mode of NiO x . On the other hand, the affinity difference between Ga and O forms a dipole which will introduce an extra energy band bending.

DBR lasers are attractive light sources due to their narrow linewidth, well stability frequency and large side-mode suppression. In the design, a 3 mm long active gain section and a 1 mm long passive 6th order surface Bragg grating consist of a 4 mm device. The wide of ridge waveguide is 3-4 m. The rear facets (grating side) are not coated and the front facets are coated to a reflectivity of 30%. For reducing the difficulty of grating fabrication, we choose 6th order surface grating which period is a round 960nm. The effective reflection coefficient of DBR-section is approximately 55%. Based on the ridge-waveguide structure, we use holographic lithography and dry etching to fabricate Bragg gating on ridge-waveguide.

Effect of anode area on temperature sensing ability is investigated for a vertical GaN Schottky-barrier-diode sensor. The current-voltage-temperature characteristics are comparable to each other for Schottky barrier diodes with different anode areas, excepting the series resistance. In the sub-threshold region, the contribution of series resistance on the sensitivity can be ignored due to the relatively small current. The sensitivity is dominated by the current density. A large anode area is helpful for enhancing the sensitivity at the same current level. In the fully turn-on region, the contribution of series resistance dominates the sensitivity. Unfortunately, a large series resistance degrades the temperature error and linearity, implying that a larger anode area will help to decrease the series resistance and to improve the sensing ability.