LITMIR.BIZ

      Scientific Research Institute "Physics of Semiconductors and Microelectronics" at the National University of Uzbekistan

      Annotation. The article proposes a humidity meter based on semiconductor emitters. The spectral characteristics of humidity and LED are given. A block diagram of a humidity meter on semiconductor emitters is given.

      In the humidity meter on semiconductor emitters, LEDs based on GaAlAsSb/GaInAsSb/GaAlAsSb (2.2 microns) are used as a emitting diode at the reference wavelength, and LEDs based on GaAlAsSb/GaInAsSb/GaAlAsSb (1.94 microns) are used as a emitting diode at the measuring wavelength.

      Keywords: optoelectronics, spectra, absorption, LEDs, photodiodes, device, mathematical model, block diagram, microprocessor unit.

      Аннотация. В статье предложен измеритель влажности на полупроводниковых излучателях. Приведены спектральные характеристики влажности и светодиода. Приведена блок схема измерителя влажности на полупроводниковых излучателях.

      В измерителе влажности на полупроводниковых излучателях использованы в качестве излучающего диода на опорной длине волне светодиоды на основе GaAlAsSb/GaInAsSb/GaAlAsSb (2.2 мкм), а излучающего диода на измерительной длине волны светодиоды на основе GaAlAsSb/GaInAsSb/GaAlAsSb (1.94 мкм).

      Ключевые слова: оптоэлектроника, спектры, поглощение, светодиоды, фотодиоды, устройство, математическая модель, блок схема, микропроцессорный блок.

      Introduction

      The basis of optoelectronic methods and devices are emitters and photodetectors. The widespread use of optoelectronic methods was hindered by the lack of simple reliable radiation sources. The appearance of semiconductor radiation sources has significantly expanded the scope of application of optoelectronic methods and devices [1].

      At present, semiconductor emitters with a radiation spectrum ranging from the ultraviolet section to the near infrared section of the optical spectrum have been developed and are being mass-produced. Practically at present, it is possible to develop emitters in the range from 210 to 4000 microns with spectral characteristics close to monochromatic (with quasi-monochromatic spectral characteristics). The features of semiconductor emitters are high speed, the ability to control the radiation flow by current, monochromaticity, sufficient radiation power and small overall dimensions. The presence of such advantages in semiconductor emitters creates prerequisites for the research and development of various monitoring, measurement and conversion devices for various fields of science and technology. Hence follows a wide range of work in the field of creating devices and systems based on semiconductor emitters [2].

      The basis of optical methods and devices is the presence of an emitter and an optically connected photodetector through the medium. The radiation generated by the emitter, passing through the medium (air, substance, etc.), is perceived by the photodetector. In these methods and devices, optical radiation is used as a data carrier that does not create electromagnetic interference and is not affected by these interference. The presence of such a feature and the simplicity of the instrument implementation create prerequisites for the research and development of various devices based on the use of optical radiation [3].

      The main part

      To build a moisture meter on semiconductor emitters, the property of water to absorb IR radiation of a certain wavelength is important [4]. All substances and materials have a certain hygroscopicity and, therefore, absorb moisture from the external environment. The analysis of spectral characteristics showed that the absorption bands lie in the range of 0.76…0.97 and 1.19…1.94 microns [5].

      Table 1 shows the absorption spectra of water and their affiliation.

      From the different spectral characteristics of dry matter (Fig. 1, curve 1) and at a humidity of 9% H2O (curve 2), it follows that at a wavelength of 1.94 microns, water has significant absorption [6]. In the humidity meter on semiconductor emitters, LEDs with radiation spectra of 2.2 microns are used as a reference channel, and LEDs with radiation spectra of 1.94 microns are used as a measuring channel).

      Fig. 1. Emission spectra of LED1, LED2 LEDs and spectral sensitivity of PD24 photodiode.

      LEDs based on the semiconductor compound GaSb and its solid solutions GaInAsSb and AlGaAsSb have been developed to measure the moisture content of raw cotton. LED structures are manufactured by the FEF method and grown on Gaas n-type conductivity substrates doped with Te to an electron concentration of 8·1017 cm-3. The emitters for measuring the moisture content of raw cotton consisted of an active layer of n – GaInAsSb (Eg = 0.51 eV) 2—3 microns thick and grown on n – GaSb substrates and doped with Te to a charge carrier concentration of 9·1017 cm—3, the wide-band emitter p – AlGaAsSb, doped with germanium to a concentration of 5·1018 cm-3 (fig.2).

      Fig.2. GaSb-based LED for humidity measurement.

      LEDs based on the GaSb semiconductor compound for measuring the humidity of raw cotton at a temperature of 24 0C had an external quantum photon output of 5.9 – 6.5% and an optical power of 3.9 MW in direct current.

      To maximize the output of optical radiation, the TO-18 housing with a parabolic reflector is used, which allows collimating radiation at an angle of 10—11o. Figure 3 shows the design of the IR LED:

      Fig. 3. LED with a parabolic reflector: a) design, b) radiation spectra, c) VAC (where: 1 – LED chip (1.94 microns), 2 – thermal cooler, 3 – LED chip (2.2 microns), 4 – parabolic reflector)

      LEDs based on the GaAlAsSb/GaInAsSb/ GaAlAsSb double heterostructure had a quantum yield of 5.8%, a radiation wavelength of 1.94 microns for measuring the moisture content of raw cotton, its main parameters are shown in Table 2.

      The proposed design provides equal conditions for two LED crystals, thus eliminating the time and temperature instabilities of their main parameters.

      Fig. 3 shows a block diagram of a digital humidity meter, which consists of the following elements: a master generator – ZG; trigger – T; frequency divider – DC; differentiating devices – DU1, DU2; exponent modulator – ME; emitter repeater – EP; pulse amplifier – IU; radiation receiver – AF; low – noise amplifier – MSU; matching circuit – SS; counter – SCH; decoder – DS; indicator – IN; reference LED – ID1; measuring LED – ID2.

      Fig.4. Block diagram of a humidity meter on semiconductor emitters

      The

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