The Features of Electronic Conduction in InAs

DOI: http://dx.doi.org/10.24018/ejers.2021.6.3.2401 Vol 6 | Issue 3 | April 2021 75 Abstract — The electrical properties of n-type crystals of InAs compound, grown from stoichiometric melt by the horizontal zone melting method, have been investigated in the temperature range of 4.2 K-300 K before and after fast neutron irradiation up to high integral fluences of 2×10n∙cm. At a fixed temperature electrons concentration (n) increases almost by one order during irradiation, and practically does not change with increasing of temperature. n increases only slightly by increasing of temperature near 300 K, both before and after irradiation. When n0 ≥ 4×10 cm the change of n during irradiation is negligible. Comparison of experimental data of mobility with theory shows that the privileged scattering mechanism of electrons at 300 K is scattering on optical phonons in InAs with n~ 10-10 cm and scattering on ions of impurity in InAs with n10-10 cm. The analysis shows that during irradiation point type scattering centers of donor-type structural defects with shallow levels in the forbidden zone appear. Consequently, the mobility decreases during irradiation. At 300 K in n − InAs sample with electrons concentration of n0 =3×10 16 cm the mobility decreases by 5 times after irradiation, which is equivalent to the formation of 1.5×10cm charged point scattering centers.

I. INTRODUCTION 1 InAs is one of the semiconductors, that is currently widely used in modern electronics, namely in high speed transistors, integrated circuits, IR photodetectors, injection lasers, nanowire, nanostructures, structures with quantum dots and etc. Therefore, InAs is an interesting material and needed component in semiconductor solid solutions. Papers dedicated to InAs research are become classical nowadays. However, the most interesting thing that distinguishes having high electrons mobility InAs from all elementary semiconductors and other III-V compounds is the different and unusual behavior of its electrical properties during irradiation [1]- [6]. Aukerman [1] first pointed out that the concentration of electrons in InAs crystals increases during irradiation. Kekelidze et al. [2], [3] showed that this phenomenon is unique features of InAs and, unlike of all other semiconductors, in InAs mainly donor-type radiation defects appear when it is exposed by any type and any dose of hard radiation. Submitted  Despite much scientific attention to InAs, the nature of its amazing radiation properties is still far from being solved. Due to the great importance of this issue, the electrical properties of the InAs compound are the subject of our study.

II. EXPERIMENT
Experimental samples of InAs were grown from stoichiometric melt by the horizontal zone melting method. The data of electrical properties are obtained by the measurements of Hall effect and electric conductivity with compensation circuit at the direct current in the interval of 4.2 K-300 K. The obtained samples were n-doped by Te. High degree of homogeneity of InAs crystals was confirmed by several methods, among which the most important are X-ray micro and microstructure analyses. The typical microstructure of experimental samples is shown in Fig. 1, which does not change during irradiation. The crystals were irradiated with fast neutrons up to fluencies of Ф = 2×10 18 n/cm 2 .

III. RESULTS AND DISCUSSION
The mobility of current carriers is a key parameter in semiconductor devices to characterize the transfer of charged particles and the output of current. Current carriers have the ability to move quickly at high mobility values in materials. For this reason, the main task of semiconductor material science is to achieve the maximal possible value of I. Kalandadze, Georgian technical University, Georgia. the current carriers mobility of the material [7]. It is especially advanced the problem of mobility of current carriers during operation of the device in an irradiated environment. The mobility itself is determined by the velocity of the current carriers, which scatter on the lattice vibrations, impurities of ions, defects in the semiconductor crystal structure. The velocity of the charge carriers is 1/τ (the inverse value of the relaxation time τ of between electrons scattering). The values of mobility (µ) depend on the mean relaxation time (͞͞ ͞͞ τ) between scattering as follows: where q is the elementary charge, m*-the effective mass of the charge carriers, ̅ -the mean time between scattering of charge carriers. Fig. 2 and 3 show the mobility dependences on the current carriers concentration (at 300 K and 77 K) and temperature respectively for the different current carriers concentration of InAs before irradiation. The temperature dependencies of the mobility at the fixed current carriers concentration are determined by the different scattering mechanisms and changing of the contribution of the various components of the scattering mechanisms in total scattering when temperature is changing (Fig. 3). Existing theories allow to identify the main mechanisms of the scattering of the current carriers [8]- [12]. The total mobility depends on the mobility components, associated with the different scattering mechanisms, as the sum of the inverse values of the mobility components. Comparison of the experimental data of the mobility with the theory in InAs, where the impurity concentration is varying in the area of 10 16 -10 19 cm -3 , shows that from all possible scattering mechanisms, electrons mobility in InAs mainly is determined by the combination of current carriers scattering on the optical phonons and ions of impurities in the temperature interval of 150 K -300 K.

A. Unirradiated Crystals
The contribution of these scattering mechanisms is different at various temperatures and electrons concentration. Calculations have shown that the privileged scattering mechanism of electrons at 300 K is scattering on optical phonons in InAs with n10 16 -10 17 cm -3 . In InAs with charge carriers of n10 18 -10 19 cm -3 scattering on ions of impurity predominates. When the temperature decreases the scattering on the optical phonons decreases and the scattering on the ions of the impurities begins to dominate when T<150 K. The existence of the maximum in the temperature dependence of the mobility is related to the changes of the contribution of the electrons scattering on the optical phonons and the ions of the impurities into the total scattering during the changes of temperature. It is seen that the observed maximum disappears at the carriers concentration of n ~ 10 18 cm -3 .

B. Crystals Irradiated with
Fast Neutrons (Φ=2•10 18 n·cm -2 ) Fig. 4 and 5 show the temperature dependences of the concentration of current carriers and mobility of InAs before and after irradiation respectively. Fig. 4 shows that at a fixed temperature is increasing significantly, almost by one order during irradiation, and practically does not change with increasing of temperature.  n increases only slightly by increasing of temperature near 300 K, both before and after irradiation. When 0 ≥ 4×10 18 cm -3 the changes of during irradiation is negligible. The analysis shows that the observed phenomenon is related to the occurrence of donor-type structural defects during irradiation, which form shallow levels in the forbidden zone. Consequently, the mobility (Fig. 5) decreases during irradiation. The mobility at 300 K in n-InAs sample with concentration of 0 =3×10 16 cm -3 decreases by 5 times after irradiation, which is equivalent to the formation of 1.5×10 19 cm -3 charged point centers. The observed regularity in electrons concentration and mobility temperature dependences of InAs preserved in doped by 10at%P crystals of InAs ( Fig. 4 and 5, curves 3 and 4).

IV. CONCLUSION
Electrical properties in InAs with a concentration range of current carriers of 10 16 -10 19 cm -3 were studied before irradiation and during the irradiation at a temperature range of 4.2 K-300 K. According to the temperature dependencies of the mobility of current carriers in InAs and on the base of existing theories, the main mechanisms of scattering of electrons have been revealed.
The phenomena observed during irradiation are related to the occurrence of donor-type structural defects which is equivalent to the formation of 1.5×10 19 cm -3 charged point scattering centers with shallow levels of forbidden zone. The observed regularity of temperature dependences of electrical properties of InAs preserved in doped by 10at%P crystals of InAs.