Band structure engineering for electron tunneling devices

Negative differential resistance devices based on electron tunneling have potential applications in the frequency range above 200 GHz, where conventional field-effect and bipolar transistors have not yet been able to operate. High-speed performance depends primarily on increasing the peak current density and reducing the parasitic resistance. The room temperature peak-to-valley current ratio also must be maximized and the peak voltage should be reduced to reduce the power dissipated in the device. Two-terminal negative differential resistance devices are also stepping stones in the development of three-terminal devices based on coherent electron transport. In the future, these novel devices may offer the prospect of continued downscaling of integrated circuit components to nanometer dimensions, where conventional device concepts apparently fail.; We apply standard techniques of molecular beam epitaxy to the growth of novel semiconductor heterostructures for electron tunneling devices. The samples are characterized by current and conductance values, measured as a function of device bias and temperature. The observed electrical characteristics are interpreted in terms of the energy band alignments of the heterojunctions and the energy levels and elastic tunneling current flows predicted by calculations based on a two-band model of the bulk band structures of the constituent materials.; Such experiments have yielded nine new results that bear on the development of quantum-effect devices: observation of intervalley coupling at a GaAs/AlAs heterointerface, the crystallographic orientation dependence of the excess valley current in AlAs tunneling barriers, negative differential resistance at room temperature in single tunneling barriers of AlGaSb, the longest coherence distance (24 nm) of any resonant tunneling device (InAs/AlSb) resonant tunneling of holes in GaSb/AlSb quantum wells, interband tunneling in polytype InAs/AlSb/GaSb heterostructures, resonant interband tunneling in this system with low-temperature peak-to-valley current ratios greater than 60:1, substantial negative differential conductance in polytype quantum wells wider than 100 nm, and resonant interband coupling in a single-barrier InAs/GaSb/InAs structure. The achievement of large peak-to-valley ratios in wide InAs quantum wells suggests the possibility of high-speed three-terminal tunneling devices.