The detection of biological species using microarrays and lab-on-a-chip systems is a powerful diagnostic tool that enables the acquisition of genetic, proteomic, and cellular information. Such approaches allow massively parallel, highly sensitive and rapid analysis for disease diagnostics, drug discovery, or food and environmental analysis. Several techniques currently in use to detect diagnostic analytes involve the detection of fluorescence, chemiluminescence, or use colorimetric assays. Hydrogenated amorphous silicon (a-Si:H) photodetectors, which exhibit low dark current and high quantum efficiency in the visible range, are promising candidates to be used in such integrated bioarrays.
Design of optical filters
In the fluorescence detection of biological analytes, efficient optical filtering is required in order to suppress the excitation light and allow only the emission light to be detected by the photodetector. Two types of optical filters are being investigated for this application:
- Absorbing high-pass filters based on hydrogenated amorphous silicon carbide (a-SiC:H) can be tuned by changing the amount of carbon content during the deposition. The percentage of carbon in the filter affects the refractive index, the optical bandgap, and consequently the cut-off wavelength of the transmission characteristics.
- Interference filters consist of a stack of two interchanging materials with a sufficient difference in the refractive indices. By trimming the thicknesses of the individual layers in the stack, either a constructive or a destructive interference in either reflection or transmission can be achieved at certain wavelengths. Numerical modelling and simulations are crucial for accurate design and optimisation of interference filters.