Fig. 1. Schematic drawing of the tunable perfect absorber structure. GST phase-change thin film is sandwiched between the Au disk array and the SiO2 insulating layer. Broadband plane wave polarized in x-axis is normally incident on the Au disk array. Au disks have a diameter of 300 nm and a thickness of 20 nm. GST layer is 20 nm thick.

Fig. 2. Absorption spectra of the tunable perfect absorber in a variety of crystallization levels between the amorphous phase (0%) and crystalline phase (100%).

Fig. 3. (a) Enhancement of electric field intensity at the second peak in the xy cross section at 10 nm above the GST layer; (b) enhancement of electric field intensity at the second peak in the xz cross section along the diameter of the disk; (c) enhancement of magnetic field intensity at the second peak in the xz cross section along the diameter of the disk. Main panels are extracted from the structure with 0% crystallized GST. Insets, corresponding near-field enhancements at the first peak.

Fig. 4. Maximum absorption at the second peak and the quality factor of the second peak as functions of crystallization level.

Fig. 5. 2D color maps present the absorption at the plasmonic resonance as functions of lattice constant (x-axis) and the thickness of SiO2 layer (y-axis) for the following; (a) amorphous GST; (b) crystalline GST.