G. A. Gavrilov

Low Voltage CO

This study presents a comparative analysis of parameters of infrared radiation source and detector hardware that are most important for the creation of portable optical nondispersive infrared (NDIR) gas sensors. An analytical model of the optical gas sensor is proposed. The notions of an instrument and transfer functions of the sensor as a measurement device are introduced. Capabilities of the model have been demonstrated by the example of carbon dioxide sensor based on immersion diode optopairs. Validity of the model is proved by good coincidence of calculated and experimental data. Analytical description of the transfer function of a NDIR carbon dioxide sensor allowed us to carry out the comparative analysis of potential sensitivity of sensors based on different hardware produced by basic fabricators of IR components.

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Abstract Mid-infrared LEDs based on InGaAs, InAsSb(P) and InGaAsSb alloys with an emission band of 0.3–0.5 μm, output power in the 10–50 μW range and long-term operation up to 20 000 h have been fabricated and tested. The LED-based analyser prototypes with PbSe photoresistors as detecting elements have been made and characterized with respect to CO, CO2 and H2O detection. A first attempt to make a qualitative analysis of hydrocarbons at 3.3 μm using transmission spectra recorded by an LED array spectrometer module has been undertaken.

-Gas Sensor Based on III–V Mid-IR Immersion Lens Diode Optopairs: Where we Are and How Far we Can Go?

The noise of photodetectors based on mid-IR A3B5 photodiodes (PhDs) implemented in a transimpedance amplifier scheme is analyzed. Recommendations concerning the choice of amplifier elements depending on the dynamic resistance of PhDs are given. It is shown that, using modern low-noise amplifiers, it is possible to reach a potential limiting threshold sensitivity of photodetectors only using PhDs with dynamic resistances above 50 Ω.

Mid-infrared (3-5 μm) LEDs as sources for gas and liquid sensors

Mid-infrared immersion lens photodiodes developed at the Ioffe Institute have high spectral selectivity (λmax/▵λ≈0.1...0.15) at different wavelengths -2.9, 3.3, 4.2 and 4.7 microns, the response time (up to 10-9s) and detectivity (D* ≈ 109-1011, (cm√Hz)/W) being significantly higher than those of currently known detectors of thermal radiation[1].The analysis of the transfer function of the temperature sensors based on A3B5 photodiodes has shown that they permit implementing the methods of color and two-color pyrometry providing a significant decrease of the methodical error in optical temperature measurements associated with unknown values of object surface emissivity and uncontrollable changes in the environment transmission.

Limiting sensitivity of photodetectors based on A3B5 photodiodes for middle infrared range

This work presents a pyrometer for measurement of temperature of a substrate surface during the MBE growth of semiconductor heterostructures. The pyrometer sensor is based on a high-sensitivity low-noise photodiode sensor representing a microassemblage of a Si p-i-n photodiode with an electronic signal processing scheme using time-pulse modulation. The basic advantage of the proposed pyrometer is its high sensitivity, accuracy (not worse than 1.5oC ) and reproducibility within the temperature interval 450-1200 oC for the operation speed 0.001-1 s under the condition of changing transmission of a vacuum chamber observation (pyrometric) window by up to 10 times. High accuracy and reproducibility of results has been achieved due to implementing the calibration principle against characteristic temperature points inherent in an object and received in situ on indirect measurements.

A3B5 photodiode sensors for low-temperature pyrometry

The dielectric and pyroelectric properties of a typical relaxer ferroelectric, 0.9PbMg1/3Nb2/3O3-0.1PbTiO3 (PMN-PT), are studied experimentally. Based on the results obtained, the pyroelectric constant and figure of merit of the material when used in IR detectors are calculated. These parameters are presented as a function of temperature and external electric field. The current and voltage sensitivities and the detectivity of PMN-PT-based IR detectors are evaluated. They are compared with the same properties of pyroelectric detectors and dielectric bolometers that use traditional pyroelectric materials as the active element and also of other uncooled photodetectors.

High-sensitivity temperature sensor with calibration against temperature of a real object

An optical pyrometer designed for precision measurement of the GaAs substrate temperature during MBE growth is considered. The pyrometer can be calibrated against a certain characteristic absolute temperature that is visually determined from a change in the RHEED pattern. This enables one to calculate the absolute temperature of the substrate with regard to its radiant emissivity and minimize the inaccuracy of radiation temperature measurement. The inaccuracy is associated with the deposition of growth products on the pyrometer window.

Relaxer ferroelectrics as promising materials for IR detectors

Low-frequency noise of a photodiode-based photodetector (PD) implementing a transimpedance amplifier scheme has been analyzed. It is found that the low-frequency (drift) noise component in the input chains of modern operational amplifiers makes a decisive contribution to resultant noises of PDs based on A3B5 photodiodes at frequencies up to several hundred kilohertz. An illustrative “vector” method of description of the noise characteristics of PD elements is proposed for selecting the optimum type of operational amplifier so as to achieve the final sensitivity and accuracy characteristics at a given response speed.

Pyrometer unit for GaAs substrate temperature control in an MBE system

An analytic model is proposed for an optical gas sensor based on diode optopairs, which takes into account the line spectral structure of gases being analyzed, as well as peculiarities of spectral characteristics of immersion-type light-emitting diodes and photodiodes operating in the mid-IR spectral range. The model makes it possible to calculate the transfer characteristic of the sensor and to estimate the measurement error for gas analyzers operating on the basis of these sensors. The experiments demonstrate bright prospects of application of sensors based on immersion-type diode optopairs in small-size gas analyzers; the expected values of the threshold sensitivity of a CO2 sensor at a level of 10 ppm and the absolute error of measurements below 0.1% (reduced error is 1%) in a range of up to 10 vol % at a speed of up to 10 counts per second exceed the parameters of available portable CO2 gas analyzers. The validity of the model is confirmed by conformity between the calculated data and the experimental results obtained on a prototype of a CO2 diode sensor.

Effect of low-frequency noise on the threshold sensitivity of middle-IR photodetectors in a broad frequency range

A simple method for determining heat-transfer coefficients of solid objects is proposed that is based on direct measurement of the sample surface temperature dynamics. The object is probed by a laser beam with preset temporal variation of the radiation power, and the thermal response is detected by photodiodes operating in the mid-IR spectral range without forced cooling.