Effects of Coulomb Impurity in Semiconductor Nanowire

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Effects of Coulomb Impurity in Semiconductor Nanowire Tamar Tchelidze, Tamaz Kereselidze and Teimuraz Nadareishvili Ivane Javakhishvili Tbilisi State University, Faculty of Exact and Natural Science, 0179 3 Chavchavadze Ave. Tbilisi, ABSTRACT We present calculation of electronic structure of impurity in nanowire. Ionization energy of impurities are calculated in dependence on nanowire radius. Direct Hamiltonian matrix diagonalization method with the physically reasonable approximate potential is employed for finding the exact solution of Schrödinger equation in the effective-mass approximation. It is shown that shallow donors are strongly influences by space confinement, which is expressed in sharp increase of ionization energy. Calculations show that effect of space confinement on deep impurities is less pronounced. The obtained results give hope that by selecting optimal value of nanowire radius compensation processes can be suppressed. INTRODUCTION Semiconductor nanowires, are believed to act as key elements in future nanoscaled optoelectronic devices, as they offer intriguing electrical and optoelectronic properties. However, the future of any semiconductor nanowire technology will essentially rely on their doping capability. The availability of both n- and p-type semiconductors is important for the realization of nanowire-based electronics. Wide band gap semiconductors, such as ZnO, suffer from doping polarity. They can be easily doped n- (or p-type) to the expense of difficulties for doping of opposite type. Space confinement changes donor and acceptor ionization energies. The main factor that makes difficult to obtain n- or p-conductivity is formation of compensating defects. Compensating processes is strongly affected by electronic structure of system: band gap, ionization energies of donors, acceptors and their compensating centers. Therefore, the understanding of the dependence of electronic structure of Coulomb impurity on geometrical sizes of system in ZnO is crucial for its technological applications. There is especially growing interest in the study of Coulomb impurity in nanosized semiconductor structures of various shapes. A significant number of works has been devoted to the study of the behavior of Coulomb impurity in semiconductor nanoobjects, such as quantum dots, nanorods and nanowires. Obviously, the first attempt to study impurity states in a quantum well was made in [1]. In this work a variational calculation is carried out and the binding energy of donor (acceptor) has been calculated as a function of layer thickness and impurity position. This work, presumably, stimulated activity of theoreticians and in the following works the binding energies of hydrogen impurity in quantum dots [2,3], quantum wells [4,5] and quantumwell wires [6-9] were calculated. The effect of applied electric and magnetic fields on binding energy was the subject of investigation in [10,11]. The common method that was employed in these works was a variational method. The calculations were carried out for both finite an