EXPERIMENTAL AND THEORETICAL INVESTIGATION OF THE DC AND HIGH-FREQUENCY CHARACTERISTICS OF THE NEGATIVE DIFFERENTIAL RESISTANCE IN PSEUDOMORPHIC ALGAAS/INGAAS/GAAS MODFETS

We report a detailed investigation of the negative differential resistance (NDR) in the I-V characteristics of pseudomorphic AlGaAs/InGaAs/GaAs MODFET's with gate lengths of 0.3-mu-m. We experimentally verify the existence of abrupt multiple NDR in both the input circuit (I(gs) versus V(gs)) and the output circuit (I(gs) versus V(gs)). The NDR occurs over a short range of drain voltage (less than 200 mV) and gate voltage (less then 5 mV) in contrast to a smooth and broader bias range (greater then 1 V) for NDR induced by thermionic emission. We provide a general interpretation of the measured dc results based on tunneling real-space transfer (TRST) which occurs because of the formation of hybrid excited states across the InGaAs channel and AlGaAs donor layer. We verify the existence of stable reflection gain in both the input and output circuits with stable broad-band frequency response in the output circuit to at least 49 GHz. These results show that NDR via TRST in pseudomorphic MODFET's can provide wide-band frequency response not limited by the electron transit time from source to drain.