We report here on the fabrication of a guided-mode resonant III-nitride grating reflector on a silicon substrate. In addition to compensating the residual stress of III-nitride layers, hafnium oxide (HfO2) film also serves as a hard mask during inductively coupled plasma reactive ion etching of III-nitride layers. The silicon substrate underneath the III-nitride gratings is etched and thus the III-nitride gratings are released and freely suspended with air as low refractive index materials on the top and bottom. The guided-mode resonances that are affected by the grating period, duty ratio, polarization and effective refractive index are experimentally characterized in the reflectance measurements. These works open the possibility of fabricating resonant III-nitride structures on the silicon substrate for further tunable III-nitride optical devices and integrated optics.

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Ultra-small electromechanical comb-drive actuators made of GaN crystal were studied in order to apply them to optical micro-electromechanical systems. Using GaN crystals grown on Si substrates by metal-organic chemical vapor deposition, two kinds of electrostatic comb-drive actuators were designed and fabricated. In the fabrication, due to a residual stress of the grown crystal, the movable part of the actuator suffered considerable deformation depending on the growth conditions. The strain-stress issue of the grown crystal layer is discussed on the basis of lattice misfit and thermal expansion. To compensate for a convex deformation, crystallization tension of a thin HfO2 film deposited on a GaN layer was investigated. The displacement of the actuator having dimensions of 52.2 μm in width and 105.4 μm in length was 1.3 μm at 70 V. Several variable systems will be feasible by combining the actuators monolithically with GaN opt-electronic devices. Future applications are also briefly discussed.

Micro-electro-mechanical comb-drive actuators made of GaN crystal are studied for an integrated a tunable GaN optical device. The GaN crystal was grown on a Si substrate by metal-organic chemical vapor deposition (MOCVD) with a low-temperature buffer layer. Selectively etching the Si substrate by XeF2 gas, the GaN thin crystal layers are self-supported in air. Due to the residual stress by the crystal growth, the freestanding GaN layer of actuator suffers from the considerable deformation depending on the growth conditions. To compensate the convex deformation, the crystallization tension of thin HfD2 film deposited on the GaN layer is used. The displacement is 1.3 �m at 70V. The fabricated GaN actuator can be useful for the monolithic integration for tunable GaN light sources.