13:30 〜 15:30
▲ [22p-P03-8] Fabrication of Quadrupole Topological Photonic Crystal Slabs
キーワード：photonic crystals, topological photonics
Quadrupole topological insulators, which can host corner states robust against defects and fabrication induced errors, have demonstrated in plenty of platforms, including phononic systems, electrical circuits, and microwave photonic crystals (PhCs), in the past few years. However, no demonstration has been reported in a slab-type PhC platform, which can operate in optical communication wavelengths and is suitable for photonic integration. We have previously reported a design of slab-type PhC structures that exhibit quadrupole phases. Here, we report the fabrication of the structure.
We use InGaAsP slab containing multiple quantum wells (MQWs) (total thickness of 250 nm) grown on (001)-InP substrate following a 2-mm-thichkn InP sacrificial layer and a 90-nm-thick InGaAs etch stop layer. Our designed structure is a square-lattice PhC consisting of a unit cell with four holes. The PhC pattern is first transferred to a SiO2 hard mask, then to the InGaAsP slab layer by ICP-RIE. Finally, the sacrificial layer is wet etched by a HCl solution. To tune the resonant wavelength at around 1,550 nm, the lattice constant and the diameter of holes are set to be around 850nm, and 280 nm respectively. We found that the undercutting process is sometimes prevented due to slow etching in (111) InP surface, resulting the etch cross-section in a (110) plane becomes overcut V-shaped. Once the grooves below neighboring holes don't overlap, the etching process almost stops at this step. We overcome this issue by etching the holes deeply down to the sacrificial layer. Deeper holes allow the grooves to merge and the formation of a new surface other than (111), resulting in the successful removal of the sacrificial layer.
We use InGaAsP slab containing multiple quantum wells (MQWs) (total thickness of 250 nm) grown on (001)-InP substrate following a 2-mm-thichkn InP sacrificial layer and a 90-nm-thick InGaAs etch stop layer. Our designed structure is a square-lattice PhC consisting of a unit cell with four holes. The PhC pattern is first transferred to a SiO2 hard mask, then to the InGaAsP slab layer by ICP-RIE. Finally, the sacrificial layer is wet etched by a HCl solution. To tune the resonant wavelength at around 1,550 nm, the lattice constant and the diameter of holes are set to be around 850nm, and 280 nm respectively. We found that the undercutting process is sometimes prevented due to slow etching in (111) InP surface, resulting the etch cross-section in a (110) plane becomes overcut V-shaped. Once the grooves below neighboring holes don't overlap, the etching process almost stops at this step. We overcome this issue by etching the holes deeply down to the sacrificial layer. Deeper holes allow the grooves to merge and the formation of a new surface other than (111), resulting in the successful removal of the sacrificial layer.