The Possibility of Negative Resistance Effects in Semiconductors

The possibility of obtaining negative resistance effects in a new way in semiconductors is discussed. The principle of the method is to heat carriers in a high mobility sub-band with an electric field so that they transfer when they have a high enough `temperature' to a higher energy low mobility sub-band. The conditions required for negative resistance are discussed generally and more specific conditions are obtained for some simple cases of spherical and ellipsoidal bands by solving the Boltzmann equation. It is shown that the most favourable case is when the sub-bands are sufficiently separated in energy for the emission of optical phonons to be the dominant mechanism for energy relaxation in both sub-bands. Ge-Si alloys and some III-V compounds may have suitable sub-band structures in the conduction bands. The case of p-type uniaxially strained silicon appears to be marginal in the region where the current is proportional to the square root of the electric field. The electrical instability of a crystal with a differential negative resistance is briefly discussed and it is pointed out that some sort of `electrical domain' formation may establish itself and inhibit the observation of negative resistance. Side effects which can influence the condition for negative resistance such as specimen heating, which is advantageous, and impact ionization, which is deleterious, are also discussed.