Barrier on Doped a-Si

Whereas the Schottky barrier on undoped a-Si H is a useful configuration for experimental studies, the barrier on doped a-Si H may prove more important technologically. Because thin-film transistor action has been demonstrated, these devices may well form the basis of a new technology (Snell et al., 1981). An important aspect of this will be to form ohmic 

Following the traditional analysis of Schottky barriers, it would be anticipated that the actual barrier hei t is an intrinsic property of the materials and will not change. However, upon moderate doping, the depletion region will become very narrow because the ionized donor levels will screen the interface. The sequence is shown schematically in Fig. 19. As the semiconductor doping is increased, the Fermi energy will move toward the conduction band, and the resultant Schottky barrier will exhibit an increased built- 

The barrier height versus doping was studied by Nemanich et al. (1983). 

They correlated structural and electronic properties and examined a wider range of dopants. The barrier height versus doping was measured by J- V and internal photoemission, and the results are shown in Fig. 20. The first point to note is that good agreement was obtained between the two measurements. This was most likely due to the fact that steps were taken to ensure a uniform interface. Furthermore, the results showed very little dependence on doping up to gas-phase concentrations of 10 . After this, the effective barrier height dropped rapidly -0.3 eV for both Pd and Pt diodes. 

Although these results could be consistent with the model proposed by Viktorovitch et al. (1981), there have been no other measurements that have detected the level at 0.3 eV below the conduction band. The results are also consistent with the usual model of tunneling through a collapsed depletion region. 

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