mid-IR LEDs Research Articles

A Miniaturised, Fully Integrated NDIR CO2 Sensor On-Chip.

In this paper, we present a fully integrated Non-dispersive Infrared (NDIR) CO2 sensor implemented on a silicon chip. The sensor is based on an integrating cylinder with access waveguides. A mid-IR LED is used as the optical source, and two mid-IR photodiodes are used as detectors. The fully integrated sensor is formed by wafer bonding of two silicon substrates. The fabricated sensor was evaluated by performing a CO2 concentration measurement, showing a limit of detection of ∼750 ppm. The cross-sensitivity of the sensor to water vapor was studied both experimentally and numerically. No notable water interference was observed in the experimental characterizations. Numerical simulations showed that the transmission change induced by water vapor absorption is much smaller than the detection limit of the sensor. A qualitative analysis on the long term stability of the sensor revealed that the long term stability of the sensor is subject to the temperature fluctuations in the laboratory. The use of relatively cheap LED and photodiodes bare chips, together with the wafer-level fabrication process of the sensor provides the potential for a low cost, highly miniaturized NDIR CO2 sensor.

Increasing the Thermostability of Optoelectronic Devices on Semiconductor Radiators

The article proposes a scheme for thermal stabilization of the radiation flux of mid-IR LEDs in the temperature range + 20 ° C + 80 ° C. It is shown that the relevance of mid-IR LEDs for solving problems of gas analysis, environmental monitoring, moisture measurement and medical diagnostics. It was revealed that the guarantee of the measurement accuracy and sensitivity of optoelectronic devices is the correct spectral matching of the photodetector, LED and absorption of the investigated substance. The disadvantages of emitting diodes associated with time and temperature instability during operation are considered. A study of the spectral characteristics of mid-IR LEDs at various temperatures showed that the wavelength at the maximum the emission spectrum increases almost linearly with increasing temperature, which leads to additional errors and lowers the measurement accuracy of optoelectronic devices. A schematic diagram is proposed for stabilizing the radiation flux of mid-IR LEDs in the temperature range + 20 ° C + 80 ° C..

High-power mid-wave infrared LED using W-superlattices and textured surfaces

Efficient mid-infrared light output has been obtained by incorporating a W-superlattice into a cascaded mid-infrared LED structure and by thinning and roughening of the emission side of the structure. At cryogenic temperatures, a radiance of ∼13.4 W/cm2-sr is achieved. Compared to the best published InAs/GaSb mid-IR LED, the maximum radiance is improved by ∼2.0×, while the wallplug efficiency improvement at the maximum radiance is improved >10×. For room temperature measurements on an un-thinned 400 μm diameter diode, the radiance (light output power) for a quasi-continuous wave and 1% duty cycle were ∼ 0.48 W/cm2-sr (2.4 mW) and ∼1.35 W/cm2-sr (6.8 mW), respectively. When compared to previous room temperature 4.2 μm LEDs, at a 1% duty cycle, this LED has optical powers that are 3× brighter. When compared to thermal emitters used in gas sensors, in the quasi-continuous wave, this LED uses ∼100× less energy per measurement.

Influence of Se on Properties of As-S-Se-I Glass for Immersion Mid-IR Leds Lenses

The study of glass components influence on the physical and chemical properties of As–S–Se–I glasses has the potential to help design glasses with the required properties. A change of certain glass properties upon the introduction of selenium into AsSI glass was demonstrated. Non-stoichiometric compounds along the As2S3-AsI3-Se diagram section were investigated by differential thermal analysis, ultrasonic measurements, dilatometric measurements. It has been shown that the introduction of selenium decreases the glass solubility in water. Change in the glass properties with the change in the short-range structure studied by Raman spectroscopy was shown. These glasses can be used for creation of immersion lenses and optical adhesives which change radiation characteristics of mid-IR LEDs.

Светодиоды средневолнового ИК диапазона на основе гетероструктур A-=SUP=-3-=/SUP=-B-=SUP=-5-=/SUP=- в газоаналитическом приборостроении. Возможности и применения 2014-2018

The paper overviews publications related to NDIR and photoacoustic sensors and NDIR gas analyzers based on A3B5 mid-IR LEDs (3-5 μm) published between 2016 and 2018 years. Capabilities of the above sensors designed for methane, CO and CO2 detection are also considered.

Prospects for 100% wall-plug efficient III-nitride LEDs.

The possibility of a III-nitride LED with 100% or greater wall-plug efficiency is examined considering recent observations of the phenomenon for smaller bandgap mid-IR LEDs under extremely low-bias operation [Phys. Rev. Lett. 108, 1 (2012)]. Thermoelectric pumping of carriers by lattice heat enables ≥ 100% WPE, but this effect is relatively weaker for the wider band gap III-nitrides. This work assesses the electrical and optical performance of several state-of-the-art nitride devices and summarizes the requirements and prospects for approaching ≥ 100% WPE for III-nitride LEDs operating at technologically relevant current densities (> 1 A/cm2).

Adhesive As-S-Se-I immersion lenses for enhancing radiation characteristics of mid-IR LEDs operating in wide temperature range

The influence of As-S-Se-I chalcogenide glass lenses on the integral and spectral power and pattern of LED radiation has been shown. Simulation of the influence of the refractive index on the integral power for two lens shapes has been performed. The wettability and adhesion force of As-S-Se-I melt has been determined for several electronic engineering materials. Mechanical stresses between chalcogenide glass and adjacent diode body materials have been calculated for −100 to 53°C temperature range. Stability of the immersion lenses against cracking has been experimentally investigated for −150 to 53°C temperature range.

MID-IR LED-based, Photoacoustic CO2 Sensor

The technology used to implement CO2 sensors depends on the requirements in terms of sensitivity, price and robustness. The most common technology for highly sensitive tasks are based on tunable diode laser spectroscopy, while so-called non-dispersive infrared (NDIR) photometers [2] are used in less demanding scenarios such as control air conditioning systems. Most NDIR systems use thermal emitters as light source which are readily available at low cost but require compensation for cross-sensitivities toward other gas species. The detector technology employed in these systems ranges from photodiodes to thermopiles and pyroelectric detectors, all of which require the use of spectral filters to avoid cross sensitivities. Here we present a low-cost photoacoustic-based detector comprised of a microphone in a hermetically sealed chamber filled with CO2. To excite sound waves a MID-IR LED emitting radiation in the strong CO2 absorption region around 4.2μm is used for the first time.

Miniature low-power IR monitor for methane detection

A portable methane gas monitor based on an infrared spectrum absorption principle has been developed using a dual-channel and dual-wavelength pyroelectric infrared detector, active filters around the overtone absorption lines of methane at 3.31 μm, reference filters around the non-absorption lines of methane at 3.93 μm, mid-IR LEDs, a miniature gold-filled cell structure, temperature sensors for gas concentration calibration and compensation, an electrical modulation source, and a highly integrated intelligent controller. A detailed investigation has been carried out to design a low-cost portable IR optical sensor for methane detection that can operate in harsh environments with temperature variations between −10 °C and 40 °C. The infrared detection optics principle used in developing this system is mainly analyzed. A prototype based on this design showed an accuracy of ±0.05%, which meets the technology requirements of lower-power consumption, reduced volume, and wide measurement range.

Portable optical water-and-oil analyzer based on a mid-IR (1.6–2.4 μm) optron consisting of an LED array and a wideband photodiode

An optical method for measuring the water and oil content using mid-IR (1.6–2.4 μm) LEDs and a wideband photodiode is suggested for the first time. This method is developed based on the absorption spectra of pure water, dewatered oil, and water—oil emulsions (cut oil) with different content of water and uses 10 types of LEDs in the spectral range 1.6–2.4 μm. It is shown that pure water heavily absorbs the LED radiation in the spectral range 1.85–2.05 μm, oil absorbs in the range 1.67–1.87 μm, and the LED radiation with a maximum at 2.20 μm is equally weakly absorbed by water and oil. An optical cell of the water-and-oil analyzer is designed on the basis of a three-element diode array with radiation maxima at 1.65 (detection of oil), 1.94 (detection of water), and 2.2 μm (reference signal) wideband photodiode covering the spectral range 1.3–2.4 μm. A calibration curve is derived that represents the dependence of the water concentration in oil on the amplitude of the reduced signal obtained by processing three signals from the LEDs. This optical method of measuring the water content in oil underlies a portable analyzer making possible online measurements directly in an oil well.

Mid-IR LEDs project dynamic scenes

Mid-IR LEDs project dynamic scenes

Towards efficient mid-IR LED operation: optical pumping, extraction or injection of carriers?

Positive and negative output power, spectral and current—voltage characteristics of the In(Ga)As and InAs(Sb) based heterostructure light-emitting diodes with the ‘episide-down’ construction grown onto heavily doped n+-InAs have been examined in the 20-200°C temperature range. Optically pumped LEDs composed from the above heterostructures or from InSb exhibited output characteristics fairly close to the conventional LEDs. Wavelength and temperature variation of the emission power in the 3.3–8 μm spectral range was compared with the phenomenological model based on the expectations of the negative luminescence power (NLP) and saturation current (I sat). The crossover of forward bias power at 1 A and negative power at I = I sat takes place at 90 and 160°C for 5.3 and 4.3 μm LEDs correspondingly.

Physics and technology of mid–infrared light emitting diodes

There is increasing interest in mid–infrared (mid–IR) light emitting diodes which operate in the 2–5 μm spectral region. Efficient LEDs operating at the characteristic absorption wavelengths of target gases, such as CH 4 , CO 2 and CO, have great potential for the next generation of optical gas sensors. The fundamental difficulties associated with realizing suitable mid–IR LEDs at different wavelengths, with high continuous wave (CW) output power at room temperature, relate principally to quantum efficiency and optical extraction of the light. Each of these will be briefly considered. Some of the different device designs and techniques used for the suppression of non–radiative Auger recombination and the reduction of Shockley–Read–Hall centres are discussed. Liquid phase epitaxy (LPE) continues to hold a strong position in mid–IR LED technology and many of the best LEDs currently available have been fabricated using this technique. In this respect, the LPE growth of associated InAs(Sb)–based epitaxial structures and their purification is briefly reported. An overview of the ‘state of the art’ is also given with respect to the application of mid–IR LEDs in practical gas sensors.