Is HEMT operating in 2D mode?

Abstract

The complete answer to the question posed by the title of this paper requires a detailed explanation. The conceptual design of the pseudomorphic high electron mobility (p-HEMT) structure is based on 2D electron gas transport and, therefore, a HEMT is expected to manifest quantization at any point along the channel. Our main question addresses devices manufactured by a variety of semiconductor companies and research groups where a certain number of thick cap layers above the 2D channel space could work as a leakage passage for electrons out of the channel. Indeed, the measurements of output current performed by us at low temperature demonstrated limited quantization, which happens in a very small volume under the gate. In the current study, measurements of the output current of a dual-gate p-HEMT showed some control of the volume in which quantization occurs. Better control of quantization was observed in the novel HEMT we designed, where the escape of electrons from the channel was prevented. The appearance of quantization steps and the length of these steps in the output current at low temperature were dependent on the biases applied to the second gate. We tend to believe that quantization of electron energies at low temperature is responsible for the appearance of these steps in output current characteristics.