Current Directions In Resonant Tunneling Research

Resonant tunneling through double-barrier heterostructures has attracted increasing interest recently, largely because of the fast charge transport1 it provides. In addition, the negative differential resistance regions that exist in the current-voltage (I-V) curve (peak-to-valley ratios of 3.5:l at room tem~erature~-~ and nearly 1O:l at 77 K have been measured) suggest that high-speed devices based on the unique character of the I-V curve should be possible. For example, the negative differential resistance region is capable of providing the gain necessary for high-frequency o~cillations.~ In our laboratory we have been attempting to increase the frequency and power of these oscillators,6 and to demonstrate several different highfrequency devices. Others have worked toward a better understanding of the equivalent circuit of the device7 and the underlying processes responsible for the frequency Many three-terminal devices using resonant tunneling in various ways have also been proposed and fabricated.11-20 In this paper we will summarize the work at Lincoln Laboratory on microwave and millimeter-wave devices, discuss the possibility of applications of resonant tunneling to digital logic, and then review some three-terminal devices that have been proposed, and in some cases tested.