First-prinicples Study Of Doped Cubic Boron Nitride

Diluted magnetic semiconductors are the based materials of spintronic devices in science area. CubicBN is a direct band gap semiconductor material, belongs to Ⅲ-V group. It’s band-gap is 6.4eV. This article calculated electronic structures and formation energies of intrinsicBN, BN（Li） system, BN（Na） system, BN（K） system, BN（Li, O） system, BN（Na, O）system and BN（K, O） system. This article used density functional theory based on first-principles plane wave ultrasoft pseudopotential method and general gradient approximation. The results are as follows.The calculation of intrinsicBN materials shows the intrinsicBN is a direct band gap semiconductor. Eigen BN does not exist magnetism. Firstly, Li-doped, Na-doped and k-doped BN systems of 96 Super lattice of atoms were geometry optimizated, then the energy structures, electron densities and formation energies of doped super lattice were calculated respectively. The analysis of spin-up and spin-down energy band diagrams of doped systems shows: partially filled valence bands across the Fermi level in spin-up and spin-down systems,which results in the metallic nature. Bandgaps of B₄₇KN₄₈, B₄₇ NaN₄₈ and B₄₇ LiN₄₈ become narrow than bandgap of Eigen BN. The order of bandgaps from small to large is B₄₇KN₄₈,B₄₇ NaN₄₈, and B₄₇ LiN₄₈. Hybridization phenomenon between dopant atoms and systems becomes obvious gradually, which means that the hybridization phenomenon of K is more complex than Na in the system. Li electronic contribution is not obvious. The main reason is the complexity of the outer electrons of the nucleus. The order of formation enegies by calculating from large to small is B₄₇ NaN₄₈, B₄₇KN₄₈ and B₄₇ LiN₄₈. The stability of system is on the contrary with the formation energy, so the order of stability from high to low is,B₄₇ LiN₄₈, B₄₇KN₄₈, B₄₇ NaN₄₈.The energy band structures, electronic densities and formation energies of Li-O doped BN system, Na-O doped system and K-O doped BN system were analyzed. Results show that the spin-up energy band diagram and the spin-down energy band diagram exist bandgap,which proves the system did not affect complete semiconductor property of BN. The bandgaps of Li-O doped BN system, Na-O doped system and K-O doped BN system are4.08 eV, 3.25 eV, 2.44 eV. There are partially filled valence bands on the Fermi level in the three systems, resulting in the whole half-metallic quality. The valence bands near the Fermi level can theoretically achieve perfect injection of carriers like electron hole. The bandgaps of three systems become smaller. The analysis of spin-density of Li-O doped BN system, Na-O doped BN system and K-O doped BN system shows: spin-up and spin-down electrondensities near the Fermi level split obviously. Spin-up electron does not cross the Fermi level,performing the nature of semiconductor material. Spin-down electron crosses the Fermi level,showing complete metallic property. Through comparing the electron number of Fermi level occupied states by integrating, there are differences which leads to ferromagnetic property.Differences between spin-up state and spin-down state are 0.43%, 0.58% and 0.80%. Doping system of Oxygen results in the semimetal property; The formation enegy of codoped system is lower than the metal-sheet doping system. So the doping of Oxygen contributes to the stability of system.Through comparison between the first main group metals（Li, Na, K） doped BN systems and the first main group metals（Li, Na, K） with O elements doped BN systems we can know that: O element makes the system have the semimetal property and contributes to the stability of system. The K-O doped BN system is the best system in making spintronic devices in the three systems. The systemic stability of K-O is poor, so it is the question that we should continue to explore.