As such, these two devices have been found to occupy different application niches. It is worth considering the avenues to high-speed diode switching that have not been explored in the main body of this thesis. For instance, other semiconductor materials might be considered for use in these devices. However, a cursory examination of the properties of other readily available semiconductors shows that silicon offers the best comprise between critical breakdown fields and hole mobility. Silicon carbide offers high breakdown voltages, but much lower mobilities.
Gallium arsenide offers comparable hole mobility, but lower breakdown fields.
No reasonable semiconductor offers both improved breakdown and mobility. However, interesting possibilities may arise from the clever use of heterostructures. For instance, one might envisage a step recovery diode band diagram like that shown in Figure 9.1. The injected charge would accumulate in the valence band pedestal next to the junction, due to the favorable energy conditions. This would ensure that the charge remains right at the junction, as is desired in a SRD, while maintaining a wide lightly-doped layer capable of withstanding a large reverse voltage.