It can be seen from Figure 5(c) that the acceptor level in the valence band maximum of GaN:[V.sub.Ga] is mainly contributed by N2p electron states.
Ga vacancy will introduce a deep acceptor level near the Fermi level.
This suggests however that acceptor behavior via Sb-doping is not necessarily simple formation of an isolated acceptor level but involves defect complexes within the material, which we believe to be the relevant mechanism for appreciable room temperature hole conduction.
An understanding of the reaction pathways and specific model to explain the acceptor level is the key to stable and reproducible p-type ZnO.
The result shows that N-doped ZnS is promised to be p-type, but the ionization energy is calculated to be 144 meV, which is still deep acceptor level.
This suggests that N doping generates a deep acceptor level above the valence band.
Based on the literature data [20-22], levels of the background nitrogen impurity, the acceptor levels of boron and aluminum, and the vacancy levels and traps in 4H silicon carbide are presented in Figure 1.
As one can see from the diagram, transitions from the valence band to the conduction band (beginning at 3.23 eV), transitions of electrons through acceptor levels of boron to the conduction band (from 2.6 to 2.9 eV), and transitions from the valence band to boron levels (from 0.35 to 0.65 eV) should be observed.
For p-type metal oxide semiconductors, the adsorbed oxygen will form
acceptor levels near the valence band at the surface, resulting in the upward band bending and formation of an accumulation layer of holes.
Given the optical absorption bandgap and the need to set the
acceptor levels sufficiently below the polymer's LUMO for efficient exciton separation, increasing the Voc in a single-layer bulk heterojunction device can be challenging.
Hence, the
acceptor levels located apart about 0.1 and 0.2 eV higher of the edge of the CISCuT valence band make a contribution to the barrier formation at a free surface of the CISCuT layers studied.
One exciting discovery is that substituting tin oxide ([SnO.sub.2]) for [TiO.sub.2] sufficiently chang es the
acceptor levels and electronic coupling efficiencies to produce cells with absorbed photon-to-current efficiencies approaching 40 %, constant across the visible spectrum.