Diode sensors

The development of SiC Schottky diode sensors was of interest due to their simple associated electronic circuitry. A Schottky diode usually consists of a metal contact on top of a low-doped semiconductor (Figure 2.6). These devices were pioneered by... 

Schottky diode sensors based on other wide bandgap materials have also been investigated, as previously mentioned. GaN Schottky diodes processed on either the Ga or N face have been examined by Schalwig et al. [11,21]. A Pt/GaN Schottky diode with a barrier height of 1-eV has been shown to reversibly transform into an ohmic contact through exposure to [94]. Kokobun et al. have also investigated Pt-GaN Schottky diodes as hydrogen sensors up to 600°C [15]. 

The mechanisms of detection and the functions of the conductor layer and of the semiconductor are the same in a C-I-S diode sensor as they are in a C-S diode sensor. The only difference between these two structures is the presence of the purposefully inserted interfacial layer (I-layer) between the conductor and the semiconductor in the C-I-S devices. In general, this I-layer is employed in the C-I-S sensor configuration for one of two reasons (1) either it is used to block chemical reactions between the conductor and the semiconductor or (2) it is used to augment or reduce the role of the interface in establishing the double layer or controlling transport. 

If a conductor material undergoes a work function change when exposed to a certain chemical species, then clearly one has the foundations of a C-S diode sensor. However, this sensor cannot be made to function if the conductor chemically reacts with the semiconductor. This loss of sensitivity occurs because the new material resulting from the reaction, in general, will not have the same work function sensitivity to the chemical species as the conductor has. The C-I-S configuration solves this problem since a properly chosen I-layer, capable of supporting an electrical current, can be inserted between the conductor and semiconductor to prevent their reaction. The resultant C-I-S structure is able to respond to the effects of the gas species on the conductor. 

We note that, in the case of both C-S and C-I-S diode sensors, the current density J passed at a bias voltage V by these devices is given by (1, 2)... 

A chemical species in the environment of a C-I-S capacitor sensor structure can interact with the device and thereby modify its double layer in the same four ways it can interact with the double layer of a C-S or C-I-S diode sensor. These four mechanisms need to... 

Figure 9 shows the typical result that higher temperatures generally give faster C-S and C-I-S diode sensor response. However, as... 

The influence of elevated operating temperatures on the interference to hydrogen detection arising from water vapor is generally advantageous. That is, water vapor does not have a detrimental effect on SiOx-based C-I-S devices for T > 100°C. This is apparently due to water leaving the sensor surface for T > 100°C. We also note that, as at room temperature, CO does not interfere with hydrogen detection in diode sensors at elevated temperatures (14). 

Hiac 8012 liquid particle counting system analyzes viscous, dark, dirty fluids without dilution. The system includes the Hiac SDS (syringe driven sampler), 8000A counter and an HRLD (Hiac/Royco laser diode) sensor. 

Hiac/Royco also offer the Dynacomt laser diode sensors for sizing particles in liquids with a dynamic range of greater than 150 1 at number concentration levels up to 12000 mh. HRLD-150 covers the size range of 1 to 150 pm at particle concentrations up to 12,000 ml and flow rates from 10 to 75 ml min. HRLD-400 covers the size range of 2 to 40 pm at particle concentrations up to 8,000 ml and flow rates between 10 and 200 ml min. ... 

An example of a solid state detector is the Reticon self-scanning photodiode array, which was specifically designed for spectroscopic applications [104]. These diode arrays contain 512 or 1024 silicon diode sensor elements on 25 jum centers corresponding to a density of 40 diodes mm" . Each diode is 2.5 mm high giving each element a slit-like geometry with a 100 1 aspect ratio. Beam registration problems do not apply to the diode array since the channel dimensions are defined by a photomask and hence the detector element size and position are completely reproducible. Solid state detectors do not suffer from lag [105] and althou they will bloom, the effect is much less severe than in a vidicon. 

One IC-based sensor array approaching commercialization is the Wide Range Ha Sensor [63, 64], which combined CMOS-compatible metal-insulated semiconductor (MIS) diode sensors and resistive sensors (Pd-Ni alloy) with on-chip control electronics. The wide-range claim relies on the MIS sensor for sensitivity to low concentrations of hydrogen gas (0.1%), and the resistive sensor for higher concentrations (1-100%). Non-standard IC processes for deposition of the Pd-based structures were devised at the Sandia foundry. Tests indicated little variability among sensors, e.g. 1-2% error. It was found that sensor exposures... 

Temperature sensors for providing closed-loop feedback for APFC are being developed by Stanford University for the measurement of combustion species and temperature. Laser-diode sensors offer nonintrusive measurements of the combustion exit plane temperature pattern. A detailed description of the sensor measurement methodology can be found in the literature [1, 2]. There is... 

Also for CO sensing, the present sensors are available only for the field of security not for environmental use because of the insufficient sensitivity and selectivity to monitor CO in the atmosphere. Examples of CO sensor which have been improved their sensitivity and selectivity are, for example, SnO semiconductor sensors operated under periodic temperature cycle[85-87], a electrochemical sensor using nafion membrane[88], a catalytic combustion sensor composed of catalysts and hydrophobic pol uner[89], a SnOj diode sensor doped with Pd[90] and an optical fiber catalytic sensor with Au/CogO as combustion catalyst[91]. 

Field test results over a one-month period for differential diode sensors with boride-based ohmic contacts. 

Remote sensing system for hydrogen using GaN Schottky diodes . Sensors and Actuators B-Chemical, 105(2), 329-333. 

Silicon-based materials with unique (opto)electronic properties photoluminescent materials for flat panel technology, displays, light-emitting diodes, sensors electroluminescence, nonmetallic conductors, e.g. siloles, polysilanes, 2,3-diphenyl-1-silacyclobutene chemistry design and application of liquid crystals. 

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