Nanocavity Enhanced Absorption of Ultra-thin Films

Mid-to-far infrared tunable perfect absorption by a sub - λ/100 nanofilm in a fractal phasor resonant cavity

“…When a perfect absorber acts as active medium in a photodetector, it must be nanoscale-thick to ease photocarrier extraction. 5 In general in any device, nanoscale-thick absorbers are also beneficial for the performance since it is easier to grow defect-free absorbing materials with good physico-chemical properties as thin layers than as thick ones. Another requirement for a perfect absorber to be fully efficient is angleinsensitivity: it must effectively absorb the light impinging from any angle of incidence.…”

“…For this reason, efforts have been made for developing thin films with valuable optical properties by more accessible lithography-free deposition processes. 5,[14][15][16][17][18][19][20][21][22][23][24][25][26][27] To achieve nanoscale perfect absorption at a selected wavelength, the most practical approach consists in integrating an absorbing thin film into a simple resonant cavity. Perfect absorption in this film is achieved by destructive optical interference at the cavity resonance wavelength, which can be tuned by changing the component materials and/or tailoring the cavity structure, for instance the absorbing film thickness.…”

“…However, this restriction is overcome by an improved design that introduces a transparent spacer between the absorbing film and the mirror, 5 i.e. with the fractal phasor resonant cavity.…”