Abstract:
In this thesis, we present theoretical studies of the structural, optoelectronic
and magnetic properties of metals doped III-V semiconductors in the zinc
blende phase. For the calculation of the physical properties of the com-
pounds, we used the full potential linearized augmented plane waves (FP-
LAPW) method within the density functional theory.
In the Al1−x Gax N and Al1−x Inx N crystals, Al is replaced by Ga and In
respectively in the step of 0.25 from 0 to 1. In In1−x Bx N, In is replaced
by B for the entire range. We calculate the variation in the bandgap with
the variation in the doping concentration. Frequency dependent optical pa-
rameters such as complex dielectric function, refractive index, reflectivity,
absorption coefficient, and optical conductivity of these materials are also
calculated and are found to be concentration dependent. It is further no-
ticed from the optical spectra that the refractive index drops below 1 for
higher energy photons. In this energy range the group velocity of photon is
larger than the vacuum velocity of light. This astonishing result shows that
at higher energies the optical properties of these materials shift from linear
to non-linear. This comprehensive theoretical study of the optoelectronic
properties of these materials predicts that they can be effectively used in the
optical devices working in the major parts of the spectrum.
The magnetic nature, half-metallicity and robustness of half metallicity
of transition metals doped III-V semiconductors in the zinc blende crystal
structure are investigated. The calculated ground state spin polarized band
structures and density of states of Al0.75 Cr0.25 N, Ga0.75 Cr0.25 N, Al0.75 Co0.25 N
and Al0.75 Ni0.25 N reveal that these compounds are semiconductor for spin up
state and conductor for spin down state. For the majority spin-channels the
electronic cloud of the N-2p states overlaps with the TM-3d and 2s states
and causes spd-hybridization, which is the origin of half metallicity in these
compounds. The calculated spin-polarized band structure of In0.75 Cr0.25 N
shows that it is conductor for both spin channels.
The electronic structure and magnetic properties of Ga1−x Mnx P and
Ga1−x Mnx As (x=0.125) are calculated and the feasibility of the growth of
these compounds on different substrates on the basis of the variation in the
lattice constants is discussed. The results show that, both the compounds
hold their half-metallic nature (conductor for spin-up state and semiconduc-
tor for spin-down state) with their lattice compressions up to certain critical
lattice constants.