We present a modular microfluidic chip, containing a microreactor and mixing channels, hyphenated with ATR-FTIR for real-time online analysis.
Optical characterization of PureGaB germanium-on-silicon (Ge-on-Si) photodiodes was performed for wavelengths between 255 nm and 1550 nm. In PureGaB technology, chemical vapor deposition is used to grow germanium islands in oxide windows to the silicon substrate and then cap them in-situ with nm-thin layers of first gallium and then boron, thus forming nm-shallow p + n diodes. These PureGaB Ge-on-Si photodiodes are CMOS compatible and characterized by low leakage currents. Here they are shown to have high responsivity in the whole ultraviolet (UV) to near infrared (NIR) wavelength range. Particularly, two sets of diodes were studied with respect to possible detrimental effects of the Al metallization/alloying process steps on the responsivity. Al-mediated transport of the Ge and underlying Si was observed if the PureGaB layer, which forms a barrier to metal layers, did not cover all surfaces of the Ge islands. A simulation study was performed confirming that the presence of acceptor traps at the Ge/Si interface could decrease the otherwise high theoretically attainable responsivity of PureGaB Ge-on-Si photodiodes in the whole UV to NIR range. A modification of the device structure is proposed where the PureGaB layer covers not only the top surface of the Ge-islands, but also the sidewalls. It was found that to mitigate premature breakdown, it would be necessary to add p-doped guard rings in Si around the perimeter of Ge islands, but this PureGaB-all-around structure would not compromise the optical performance.
An overview is given of the many applications that nm-thin pure boron (PureB) layers can have when deposited on semiconductors such as Si, Ge, and GaN. The application that has been researched in most detail is the fabrication of nm-shallow p+n-like Si diode junctions that are both electrically and chemically very robust. They are presently used commercially in photodiode detectors for extremeultraviolet (EUV) lithography and scanning-electron-microscopy (SEM) systems. By using chemicalvapor deposition (CVD) or molecular beam epitaxy (MBE) to deposit the B, PureB diodes have been fabricated at temperatures from an optimal 700 °C to as low as 50 °C, making them both front- and back-end-of-line CMOS compatible. On Ge, near-ideal p+n-like diodes were fabricated by covering a wetting layer of Ga with a PureB capping layer (PureGaB). For GaN high electron mobility transistors (HEMTs), an Al-on-PureB gate stack was developed that promises to be a robust alternative to the conventional Ni-Au gates. In MEMS processing, PureB is a resilient nm-thin masking layer for Si micromachining with tetramethyl ammonium hydroxide (TMAH) or potassium hydroxide (KOH), and low-stress PureB membranes have also been demonstrated.
Avalanche-mode visual light emission in Si diodes is shown to be useful for rapid assessment of the origin of non-ideal currents. In the test structure design, it was important to consider the breakdown-voltage distribution, diode size and contact positioning to obtain light-spot appearances at positions related to bulk defect distributions.
The relationship between light-emission patterns from silicon avalanche-mode light-emitting diodes (AMLEDs), and avalanche breakdown was investigated using photodiodes fabricated in pure boron (PureB) technology. The quality of the diodes ranged from highquality, low dark-current devices with abrupt breakdown characteristics that were suitable for operation as singlephoton avalanche diodes (SPADs), to diodes with gradually increasing reverse currents before actual breakdown. The reverse I-V characteristics were measured and correlated to light-emission data obtained simultaneously using a PureB photodetector, and inspected using a camera with which distinct emission patterns could be identified. When increasing the voltage far past breakdown, light emission invariably becomes dominant at the photodiode periphery. Based on the examination of a large variety of anode geometries, it is concluded that the most efficient light emission per consumed power is achieved with defect-free narrow-anode diodes that also are applicable as low-darkcount-rate SPADs.
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