INVESTIGATION OF THE ELECTROPHYSICAL PROPERTIES OF COTTON FIBERS OF THE GRADE "KAMOLOT-79" ALLOYED WITH IODINE

ABSTRACT

The main goal of the research was to study the dependence of current on voltage, temperature dependence of current, and the influence of conductivity on light of (medium thickness alloyed with iodine solution in 8% alcohol and mercerized with NaOH) The grade "Komolot-79" cotton fibers (CF)  with semiconducting properties.

The study was conducted in the temperature range (296-360 K) and voltage range (0-100 V). The sample doped with iodine is much higher than the undoped sample current was observed. It was observed that the current flowing through the sample fully obeyed Ohm's law. The value of the deep surface activation energy obtained as a result of introducing iodine into the cotton fiber was determined. It has been experimentally established that the electrical conductivity of iodine-doped cotton fibers grade "Komolot-79" increases with increasing temperature according to the law σ = σ exp (-Е_t / kТ), where Е_t = 0,74 eV.

АННОТАЦИЯ

Основной целью исследований было изучение зависимости тока от напряжения, температурной зависимости тока и влияния электропроводности на свет (средняя толщина легирована раствором йода в 8% спирте и мерсеризована NaOH). Сорта «Комолот-79» хлопковые волокна (ХВ) с полупроводниковыми свойствами.

Исследование проводилось в диапазоне температур (296-360 К) и диапазона напряжений (0-100 В). В образце, легированном йодом, ток намного выше, чем в нелегированном образце. Было замечено, что ток, протекающий через образец, полностью подчиняется закону Ома. Определено значение глубокой поверхностной энергии активации, полученной в результате введения йода в хлопковое волокно. Экспериментально установлено, что электропроводность легированных йодом хлопковых волокон  марки «Комолот-79» увеличивается с повышением температуры по закону σ = σ exp (-Е_t/kТ), где Е_t = 0,74 эВ .

Keywords: cotton fibers, natural semiconductors, doping, photoconductivity, electrical conductivity, current-voltage characteristic, activation energy.

Ключевые слова: xлопок волокон, природные полупроводники, легирование, фотопроводимость, электропроводность, вольт-амперная характеристика, энергия активации.

Introduction

The success of modern electronic technology is directly related to the development of fine technology for the production of semiconductor materials of germanium, gallium arsenide, silicon, etc., and the production of various devices based on them. At present, almost all properties of the above semiconductors have been identified. To expand the possibilities of semiconductor devices, it is necessary to identify and explore new semiconductor materials[1].

Recently, the promising scientific direction "Natural semiconductors" has begun to develop intensively [2]. Research carried out in recent years has shown that cotton fibers (CF) have semiconductor properties, their electrical conductivity increases with increasing temperature.

When doping CF with iodine, the conductivity increases by several orders of magnitude and is sensitive to light. Experiments show that the electrophysical properties of CF depend on the grade of CF. This mainly applies to the superficial area of ​​the CF - the cuticle. Apparently, the cuticles of different varieties of CF differ from each other. At present, the electrophysical properties of CF grades ATM-1, Gulbahor, Golib, Diyor doped with iodine have been studied [3–5]. However, the electrophysical properties of  "Komolot-79"  grade CF alloyed with iodine have not been studied. Expanding the scope of research in this area makes it possible to identify the physical patterns occurring in natural semiconductor materials and create various discrete semiconductor devices based on them.

The object of the study were mature CF varieties "Komolot-79". In order to dope the CF with iodine, first the CF with the seed was carefully combed with a fine comb (with a point period of 0.5 mm), then the seeds were cut out from the side. 

After washing, the CF was kept in a bath with the solution 20% NaOH in water at 15℃ for 2 minutes. After removing the CF from the bath, excess NaOH that has not formed a chemical bond is completely washed off with water and samples are dried under standard conditions[6]. Then CF cut sides were soaked in 8% alcohol solution of iodine and diffused at t=80⁰C for 7 hours. In order to create an ohmic contact and seal the cold from the external environment, we have developed an electrically conductive adhesive based on graphite and liquid glass. Crushed finely granular graphite moved with liquid glass to a thick state. After that, such an electrically conductive adhesive (R=300 Ohm at a thickness of 20 µm and a length of 0.4 sm) was applied to the end sides. This made it possible to obtain reproducible results, measurements. Thus, the samples were made in the form of a bundle of fibers, in the amount of 5000-6500 pieces laid parallel to each other, with a total weight of 4-15 mg. The current-voltage characteristics of the fabricated samples are linear. Preliminary measurements showed that after doping with iodine, the samples had n-type conductivity.

Material and Methods

The temperature dependences of the electrical conductivity of natural fibers were measured using a contact thermometer and a special heat chamber. The installation allows current measurement in the temperature range of 20 - 80⁰С. (Fig.1).

With increasing temperature, the electrical conductivity of the semiconductor increases exponentially σ = σ₀ exp (-E/kT). If there are donor or acceptor impurities in the semiconductor, at the temperature of absolute zero there will not be a single free electron (or hole) in the impurity semiconductor. As the temperature rises, impurity electrons will be the first to be released, since the activation energy of an impurity (donor or acceptor) is much less than the activation energy of semiconductor atoms.

Figure 1. Electrical circuit for measuring the temperature dependence of the electrical conductivity of natural fibers

1 - contact mercury thermometer, 2 – sample, 3 - heat chamber, 4 – heater, 5 – nanoammeter, 6 - power supply.

A further increase in temperature leads to the fact that the impurity atoms are ionized, and only then does the intrinsic electrical conductivity of the semiconductor appear. Consequently, at low temperatures, the electrical conductivity of an extrinsic semiconductor is determined by the extrinsic conductivity, and at high temperatures, by its intrinsic conductivity. The larger the band gap E_g, the more energy an electron must have in order to jump into the conduction band, i.e. the higher the temperature the semiconductor must be heated to make its own conductivity noticeable.

Results and Discussion

We have studied the temperature dependences of the electrical conductivity in samples of the "Komolot-79"  grade CF doped with iodine. In the temperature range +20÷80⁰C, the electrical conductivity grows exponentially with the activation energy E_n =0.74 eV. This is apparently due to the fact that iodine in the "Komolot-79"  variety form deep level with E_t= Ec –0.74 eV. At high temperatures in cold water, destruction can occur. If we assume that the width of the band gap CF is Eg=3.2 eV, then obviously at these temperatures we cannot measure the dependence σ=f(T) in the intrinsic conduction region.

Figure 2. Temperature dependence of electrical conductivity of a sample of "Komolot-79"  grade CF alloyed with iodine At t=80℃  for 7 hours, Arrhenius diagram of this result

Figure 2 shows the volt-amper characteristic (VAC) of the "Komolot-79"   grade CF doped with iodine 1-undoped sample (0.2 nA at 100 V), 2 - A sample doped with iodine is in the dark, 3 - sample doped with iodine under UV light. It can be seen from the figures that the VAC has a linear character. 

Measurement of the kinetics of the phase transition when illuminated with UV light with hν≈5 eV showed that the growth of the photocurrent occurs according to an exponential law with a time constant τ=656 sec. It decreases as the intensity of UV light increases. After turning off the light, the decrease in photoconductivity occurs more slowly than the exponential law.

Figure 3. VAC CF grade "Komolot-79" at T = 300K, 1-undoped sample (0.2 nA at 100 V), 2 - A sample doped with iodine is in the dark, 3 - sample doped with iodine under UV light

Conclusion

According to the conclusion, the electrophysical properties of undoped and iodine-doped "Komolot-79" cotton fiber were studied. According to the analysis of experimental results, the electrical conductivity increased by more than 1000 times when doped to the grade "Komolot-79" CF mercerized with NaOH. This result means that it is possible to control the conductance by doped an input to the CF.

A sharp increase in the conductivity of iodine-doped CF is the concentration of charge carriers in CF related to the increase. Input molecules are located in the defects of the polymer lattice and creates a deep layer in the forbidden band, resulting in free charge carriers. This ensures conductivity even at room temperature.

Thus, for the first time, the electrophysical properties of cotton fibers of the "Komolot-79" grade doped with iodine were studied. It has been established that iodine in the "Komolot-79" grade CF creates deep level with ionization energy Е_n = 0.74 eV.

References:

1. Gurusiddayya Hiremath, Mallesh N and Sunil Kumar B. A Comparative Study on Different Semiconductor Materials used for Power Devices and Its Applications. International Journal of Latest Technology in Engineering, Management & Applied Science (IJLTEMAS) Volume VII, Issue I, January 2018.
2. A.T.Mamadalimov, P.K.Khabibullaev, M.Shermatov. Some problems of modifying the physical properties of cotton fibers. UFJ, 1999 v.1. No. 6, pp. 465-479.
3. Mamadalimov A.T., Oksegendler B.L., Otazhjnov Sh.O., Turaev B.E., Usmanov T.A., Khakimova N.K., and KadIrov Zh.A. Features of the Photoconductivity of  Iodine-Doped Cotton Fibers Illuminated in the Fundamental Absorption Range. Technical Physics Letters, 2002. Vol. 28, No. 7, pp.581-583
4. A.T. Mamadalimov A new scientific direction in semiconductor physics: natural semiconductors. “Trends in the development of modern semiconductor physics: problems, achievements and prospects”. Collection of materials of the international online conference. www.e-science.uz May 28, 2020 , from 16-25.
5. N.K.Khakimova. Properties of natural semiconductor fibers. Tashkent. “KALEON PRESS”, 2021, 112 p.
6. Francis J Kolpak Mark Weih John Blackwell. Mercerization of cellulose: Determination of the structure of Mercerized cotton. Polymer Volume 19, Issue 2, February 1978, Pages 123-131. https://doi.org/10.1016/0032-3861(78)90027-7.