Black silicon induced junction photodiodes have nearly ideal responsivity across a wide range of wavelengths between 175-1100 nm, with external quantum efficiency over 99 % at visible wavelengths, when a single spot is measured using light beam between 1 to 2mm in diameter. The spatial uniformity of responsivity is also an important characteristic of a high-quality photodiode, when considering its usage as a reference in photometry. We study here the spatial uniformity of responsivity of large area (8mmx8mm) black silicon photodiodes at 405 nm wavelength. Our results show that the spatial non-uniformity is less than 0.5 % over 90 % of the surface area, and thus the photodiodes meet the thigh criteria typically set for reference standards and are hence suitable for such application.
Black silicon induced junction photodiodes have been shown to have nearly ideal responsivity across a wide range of wavelengths. Another important characteristic of a high-quality photodiode is rise time which can be used to approximate bandwidth of the photodiode. We show experimentally that the rise time of black silicon photodiodes is shorter than in planar photodiodes when alumina layer with similar charge is used to make an induced junction in both. Additionally, we show that the rise time can be rather well approximated using an analytical equation, which combines Elmore delay from equivalent circuit with standard RC-delay arising from series and load resistances.
A high-quality photodiode has high signal-to-noise ratio (SNR), which is ultimately defined by the responsivity and dark current of the photodiode. Black silicon induced junction photodiodes have been shown to have nearly ideal responsivity across a wide range of wavelengths between 175-1100 nm at room temperature (RT). Here we present their spectral responsivity stability and dark current at different temperatures. Both quantities show temperature dependencies similar to conventional pn-junction photodiodes, proving that black silicon photodiodes maintain their improved SNR also at temperatures other than RT.
There is an increasing demand for highly sensitive near infrared (NIR) detectors due to many rapidly growing application areas, such as LiDAR and optical communications. Despite the limited NIR absorption, silicon is a common substrate material in NIR detectors due to low cost and maturity of the technology. To boost the NIR performance of silicon devices, one option is texturizing the front and/or back surface to reduce reflectance and extend the optical path by scattering. Here we demonstrate silicon photodiodes with nanostructured front surface (i.e. black silicon fabricated with reactive ion etching (RIE) that exhibit significantly enhanced external quantum efficiency (EQE) at NIR wavelengths compared to typical state-of-the-art silicon photodiodes. The detectors exhibit over 90% EQE with wavelengths up to 1040 nm and above 60% at 1100 nm. Identical detectors with a planar surface are also investigated revealing that the enhancement from black silicon effectively corresponds to increasing the substrate thickness up to 43% at 1100 nm depending on the thickness of the active layer and back surface structure. This confirms that in addition to reduced reflectance, scattering of transmitted light induced by black silicon plays a key role in the EQE enhancement which benefits especially devices such as backside illuminated photodetectors where very thin substrates are required. We also demonstrate that the high EQE of the black silicon detectors is maintained at incidence angles up to 60 degrees allowing excellent performance in applications where the light is not always perpendicular.
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