Materials Design for the Low-Resistivity in p-Type ZnO and Transparent Ferromagnet With Transition Metal Atom Doped ZnO:
- PDF / 628,483 Bytes
- 11 Pages / 391.5 x 607.5 pts Page_size
- 42 Downloads / 197 Views
acceptor-donor complex
S
Acceptor
0 Donor
isolated acceptor
(b)
A --attractive
D C isolated donor
VBM
repulsive attractive
Figure 1: Codoping forms (a) acceptor donor complex with (b) attractive acceptor-donor interactions and repulsive acceptor-acceptor interactions. In order to make p-type semiconductors, we should make imbalance between the acceptor and donor vapor pressure during the crystal growth. (c) Acceptor (A) level is lowered and donor (D) levels is raised with formation of acceptor and donor complex upon codoping.
to reduce "the formation energy" of the dopant due to the reduction of the lattice relaxation energy and Madelung energies in the kinetics of the thermal non-equilibrium crystal growth conditions [see Fig. 1 -(b)]. (ii) The codoping method contributes to increase the carrier mobility due to the short-range dipole scattering or screened short-range scattering (a longrange Coulomb interaction is dominant in the case of simple doping). (iii) The codoping also contributes to reduce the energy level of acceptors due to the formation of donor and acceptor complex (a donor level is raised and an acceptor levels is lowered with forming donor and acceptor complex [see Fig. 1 -(c)]. By the way, if p-type ZnO become available, a ZnO based magnetic semiconductor will be most promising candidate for a ferromagnetic semiconductor. Diluted magnetic semiconductors (DMS) are semiconductors which contain some magnetic atoms as impurities, and they have possibility to bring new ideas to create a functional material with making use of the carrier control techniques in semiconductors, e.g. its magnetic property is controllable by changing the carrier density. Such a trial had already become realistic owing to the first fabrication of (In, Mn)As [6] and the following intensive investigations on III-V DMS [7 9], and it was successful for these compounds to control their magnetic behavior by using hetrojunctions [8] or light irradiation [9]. However, the Curie temperature (T,) of the III-V based DMS is as low as about 100 K, and the low solubility of Mn in them prevents us 2to realize a large magnetization. In the II-VI compound ZnO it is plausible that the Mn +
66
SN
*
III (=A], Ga or In)
(a)
(b)
Figure 2: Crysta.l structure of supercells for (a) ZnO:2N and (b) codoped p-type ZnO with N acceptors and the reactive donors, Al, Ga. or In species. with d5 high spill configuration is realized. Moreover, high solubility of Mn in ZnO matrix is expected, becaluse it is in the same transition metal series as Zn. Taking these into account, in this pa.per, we also propose a ZnO based magnetic semiconductor as a cafndidate to realize a high T, a.nd a large magnetization magnetic semiconductor. Jo search another ca~ndidate of a functional1 magnetic material, the magnetism of 3d transition metal impurities in ZnO was also investigated within the same framework. CALCULATIONS LOW-RESISTIVITY p-TYPE ZnO:[Gaz
11+2No,
AIZn1 +2No, InZn+2No]
In the cases of materils design for the low-resistivity p-type ZnO, our ca
Data Loading...
