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Spectral response of the PC-QWIP (solid line), absorption (chain-dotted line), and refractive index (dashed line) of . Absorption and refractive index were taken from literature (Ref. 22) The inset shows a scanning electron microscopy image of the etched PC.
(a) PC resonance shift: photocurrent spectra were measured for various deposition thicknesses, data points were Lorentzian fitted. (b) Effective hole refractive index: each data point (small circles) corresponds to the measured peak resonance for a certain deposition thickness. From Eq. (1) the hole refractive index was calculated without (, chain-dotted line) and with (, dashed line) anisotropic sidewall-deposition effects. (c) Top-view SEM pictures of the same device before (upper image) and after 780 nm surface deposition (lower image).
The QWIP peak responsivity (triangles) experiences only small changes in magnitude from the resonance tuning. In contrast, the PC peak resonance (open circles) experiences a significant increase with increasing layer thickness. The most likely explanation is the formation of an antireflective coating by the surface layer. The data points of the PC peak were fitted with a cosine-type function (dashed line).
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