Observation of negative differential conductivity in a FET with structured gate

Using electron beam lithography, we have fabricated a novel quantum device in which a lateral surface superlattice (LSSL) replaces the gate of a high electron mobility transistor (HEMT). We have observed strong negative differential conductivity (NDC) which we believe could be due to the onset of Bloch oscillations. Other devices, identical in all ways except that the gates are solid instead of grid-like as in the BlochFET, did not show NDC. Alternative explanations for the NDC are discussed and discounted for various reasons.Dedicated to Professor Karlheinz Seeger on the occasion of his 60th birthday