![]() In a biased photodetector the electrical field separates the carriers. 850 nm) has a 1/e penetration depth of about 16.6 im. 430 nm) is absorbed in depths up to 0.2 im while near infrared light (e.g. To give two relevant examples: blue light (e.g. The absorption coefficient a decreases strongly for increasing wavelength k. The generation rate G is dependent on the depth x from the semiconductor surface, on the wavelength k, on the photon flux U0 of the incident light and on the absorption coefficient a. Therefore for the visible light range the generation rate G of electron-hole pares in silicon can be simplified to : Nevertheless, if silicon photodetectors are used in the visible and near-infrared range (400-900 nm), literature shows, that both mentioned effects can be neglected. However, the photon can also be absorbed by free carriers without generating an electron-hole pair (free carrier absorption). Photon (corresponds to wavelengths below 375 nm). A photon can create more than one electron-hole pair only if it is a high energy Depending on the wavelength of the light, each photon can create one or more electron-hole pairs. Light within this wavelength range will penetrate into the silicon and will be absorbed in it. The physical property of silicon allows the material to be sensitive for wavelengths between 300 nm and 1100 nm. The potential to combine the photodetector together with the readout circuitry to optoelectronic integrated circuits (OEICs) introduces further advantages of integrated solutions over wire-bonded solutions, due to the absence of bonding pads and bonding wires leading to less parasitic. The main advantage of the implementation into a standard silicon process is the possibility for a cheap mass production of detector and circuitry together. Photodetectors integrated into standard silicon-based processes have several advantages over photodetectors realized in special silicon or III-V compound technologies. Nowadays photodetectors are built in silicon processes (these can also be standard CMOS or BiCMOS processes) or as III-V compound devices. By providing an additional gain, phototransistors are more suitable in some applications than photodiodes like for instance in low light scenarios. Photodiodes and phototransistors are the most commonly used photodetectors. Furthermore simulations of the electric field strength and space-charge regions were done. Due to the speed optimized design and the layer structure of the phototransistors, bandwidths up to 76.9 MHz and dynamic responsivities up to 2.89 A/W were achieved. Optical DC and AC measurements at 410 nm, 675 nm and 850 nm were done for phototransistor characterization. The three presented phototransistors were implemented in sizes of 40 x 40 im2 and 100 x 100 im2. For a further increase of the bandwidth the presented phototransistors were designed with small emitter areas resulting in a small base-emitter capacitance. This low doped p epitaxial layer leads to a thick space-charge region between base and collector and thus to a high -3 dB bandwidth at low collector-emitter voltages. The starting wafer consists of a low doped p epitaxial layer on top of the p substrate. This work reports on three speed optimized pnp bipolar phototransistors build in a standard 180 nm CMOS process using a special starting wafer. Institute of Electrodynamics, Microwave and Circuit Engineering, Vienna University of Technology, Gusshausstr. PNP PIN bipolar phototransistors for high-speed applications built in a 180 nm CMOS process Journal homepage: SOLID-STATE ELECTRONICS Contents lists available at SciVerse ScienceDirect Due to the speed optimized design and the layer structure of the phototransistors, bandwidths up to 76.9MHz and dynamic responsivities up to 2.89A/W were achieved. Optical DC and AC measurements at 410nm, 675nm and 850nm were done for phototransistor characterization. The three presented phototransistors were implemented in sizes of 40×40μm2 and 100×100μm2. This low doped p epitaxial layer leads to a thick space-charge region between base and collector and thus to a high −3dB bandwidth at low collector–emitter voltages. This work reports on three speed optimized pnp bipolar phototransistors build in a standard 180nm CMOS process using a special starting wafer. Abstract of research paper on Physical sciences, author of scientific article - P.
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