Amorphous Fermi level

The amorphous nucleation layer has the consequence that the Fermi level of the growing ZnO films reaches its equilibrium value already at very low thickness ( 2nm). This is particularly important for ZnO Al films, where the Fermi level changes by more than 1 eV upon the addition of oxygen to the sputter gas. The amorphous nucleation layer, therefore, substitutes the space charge layer, which is usually necessary for charge equilibration at the interface. This important effect is illustrated in Fig. 4.25. 

The net result is that doped a-Si H films are not very conductive (typically 10-3-10-2 Q-1 cm-1)- The Fermi level is — 0.2 eV below the conduction band in phosphorus-doped a-Si H (Spear, 1977) and is—0.5 eV above the valance band in boron-doped a-Si H (Jan et al., 1980). Since the optical gap of undoped a-Si H is typically about 1.7 eV, the built-in potential of a-Si Hp-i-n solar cells is about 1.0 eV (Williams et al., 1979). Improving the conductivity of the doped layers should lead to larger built-in potentials and consequently higher conversion efficiencies. The conductivity can be increased significantly by forming microcrystalline-doped Si H films (Mat-suda et al., 1980), but since these films contain both amorphous and crystalline phases, there is no significant increase in the built-in potential (Carlson and Smith, 1982). 

R. Schwarz, F. Wang and M. Reissner, Fermi level dependence of the ambipolar diffusion length in amorphous silicon thin film transistors, Applied Physics Letters, 63(8), 1083-1085 (1993). 

From the above example, [V ] is about 2,000 times larger than [Vx] at 823 K, which explains in part the enhanced regrowth that amorphous Si experiences when it is doped with P. As one would anticipate, the growth rate is not increased by implantation of both B and P at equal concentrations. In this case, the implanted layer has equal concentrations of donors and acceptors, and the Fermi level is near the center of the energy gap. 

We shall, therefore, be concerned with relating electronic structure of solids with chemical instability in the most general theoretical analyses, with energy transport by electronic mechanisms during detonation, with the effect of occupancy of electronic states (Fermi level) on initiation, and with the possibility of initiation by nonthermal, specifically electronic, mechanisms in both single-crystal and amorphous explosives. 

Thus P approximately equals unity if the Fermi level lies far below the centroid of the donor distribution. In a crystalline semiconductor with a low density of gap states, donor levels deliver their electrons directly into the conduction band. In an amorphous semiconductor, the situation usually is different (Spear and LeComber, 1975, 1976) Most of the electrons will condense into empty states near the Fermi level. Let Anb be the concentra-... 

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