Abstract
Extending and controlling the spectral range of light detectors is very appealing for several sensing and imaging applications. Here we report on a normal incidence dual band photodetector operating in the visible and near infrared with a bias tunable spectral response. The device architecture is a germanium on silicon epitaxial structure made of two back-to-back connected photodiodes. The photodetectors show a broad photoresponse extending from 390nm to 1600nm with the capability to electronically select the shorter (400-1100 nm) or the longer (1000-1600 nm) portion with a relatively low applied voltage. Devices exhibit peak VIS and NIR responsivities of 0.33 and 0.63 A/W, respectively, a low optical crosstalk (<-30dB), a wide dynamic range (>120dB) and, thanks to their low voltage operation, maximum specific detectivities of 7·1011cmHz1/2/W and 2·1010cmHz1/2/W in the VIS and NIR, respectively.
Highlights
Photodetectors are consolidated key components of most optoelectronic systems
While the market of near infrared (NIR) photodetectors is largely dominated by III-V semiconductor compounds (InGaAs, InGaAsP), the past two decades have seen a fast progress of germanium on silicon (Ge/Si) photodiodes
In this work we propose to exploit the Ge/Si technology combining the Ge and Si optical properties in order to obtain dual band photodetectors to allow sensitivity in both the visible and the near infrared
Summary
Photodetectors are consolidated key components of most optoelectronic systems. fast developing applications such as optical communications, self-driving cars, virtual/augmented reality and medical diagnostics are stimulating an increasing demand for innovation towards performance improvement in terms of sensitivity and speed and of spectral response. Its compatibility with silicon promoted significant research efforts towards NIR optoelectronics integrated circuits able to combine optics and electronics functions to improve compactness, reliability and scalability while reducing the overall cost [4] Such development was triggered by the ability to obtain high quality Ge epitaxially grown on Si, despite their relatively large (4%) lattice mismatch [5]. The principle underlying the voltage tunable dual band operation is quite simple and relies on the combination of two effects: the spectral splitting operated by the different optical absorption of the two semiconductors and the bias dependent photoresponse of the photodiodes This approach has been originally proposed for WDM optical communication to simultaneously detect and demultiplex two wavelengths, avoiding additional optical components. The device structure is illustrated along with its fabrication details
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