Semiconductors are present periodic table of group II-VI, in this paper, impurities doped with Be-series, Zn-series and Cd-series such as BeS, BeSe, BeTe, ZnS, ZnSe, ZnTe and CdS, CdSe, CdTe. The value of distorted bond length found corresponds with orbital parameter, covalence, empirical parameter and hybrid energy used as input data.
We have investigated bonding properties such as bond length distortion of atomic substitution in Be-series, Zn-series and Cd-series of II-VI group of semiconductors. Using bond orbital parameters based on tight binding theory with universal parameters. We have studied schematic behaviour of lattice distortion with respect to some of chemical parameters such as covalency difference and electro-negativity difference between the impurity atom and host atom and the change in covalent energy of the bond when the impurity replaces the host has been attempted.
The optoelectronic properties of II-VI group of semiconductors compounds V.K. Singh et al. [1-3] and Bond length distortion in III-V group of semiconductor compounds Kalyan Singh et al. . The ideas of simple force constant model suggested by Kraut and Harrison [5-8] have also described a method to estimate the local relaxation around impurities in semiconductors using just the natural bond length. In this model the second neighbour relaxation of the nearest neighbours. Thus the bond length distortion ?d due to the size difference between the impurity and host atom in any defect system is given as three fourths the difference of the natural bond length of impurity-host and host-host bond.
?d = 3/4 (dimpurity-host – dhost-host) …. (1)
The positive distortion + ?d corresponds to the nearest neighbours relaxing outwards and the negative distortion - ?d corresponds to the nearest neighbour relaxing inwards.
To study bond length distortion of atomic substitutions in semiconductors we have taken Be-series, Zn-series and Cd-series from II-VI group of semiconductors. In every compound semiconductors system the cationic substitutions of group II and VI impurities is followed by the anionic substitutions of groups V and VI impurities. We studied dependence of the sign and extent of bond length distortion of various impurities in different host system.
(i) Change in covalent energy of the host impurity bond with respect to that of host-host bond. The covalent energy V2, which is the potential parameter in related with the bond length by the following equation.
III. RESULT AND DISCUSSION
We have also studied the bond length distortion of atomic substitutions in III-V group of semiconductors . Again we have studied bond length and bond length distortion of atomic substitutions in II-VI group of semiconductors. In every compound semi-conducting system the cationic substitution of groups II and III impurities is followed by the anionic substitution of groups V and VI impurities. We have studied the dependence of the sign and extent of bond length distortion of Cd cation and Te anion impurities in Zn-series as host system. We have calculated and reported the value of bond length (impurity-host system), bond length distortion and the ratio of bond length distortion to the host bond length in Table-3. It is found that the dependence of bond length and bond length distortion on bond orbital parameter V2 is same as on the hybrid energy [9-11]. The sense of distortion is decided by the sign of the difference in electro-negativity between the host and the impurity atom. An impurity with a high electro-negativity than the host atom it is replacing, results in a contraction and vice-versa. This is an agreement with the suggestions made by Scheffler et al. [12, 13]. It is also suggested that when an impurity outer a semiconductor substitutionally, the resulting bond length distortion is a function of above parameters and not just decided by the difference in size between the impurity and host atoms.
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