Tunneling Based Electronic Devices

This thesis concerns different kinds of tunneling based devices all showing negative differential resistance. The thesis is divided in three parts, resonant tunneling transistors, Esaki diodes and coupled zero dimensional systems.

The resonant tunneling transistors are GaAs-based vertical field effects transistors, based on a combination of overgrown tungsten gates and double barrier heterostructures. The gate is placed in direct vicinity of the heterostructure, and due to Schottky depletion around the gate the effective conducting area of the heterostructure can be controlled. Transistors based on two different double barriers have been investigated, GaAs0.3P0.7 and Al0.8Ga0.2As/GaAs/In0.2Ga0.8As. The GaAsP-system were used for low temperature operation, whereas the AlGaAs was optimized for room temperature functionality. For resonant tunneling diode structures, a peak current density of 70 kA/cm2, a peak-to-valley ratio of 4 with a peak voltage of 0.3V was obtained, all at room temperature. The transistors has a simultaneously a maximum transconductance gm=120 mS/mm, and a peak-to-valley ratio of 2.5. Further on, a transistor based on three dimensional integration of two resonant tunnel diodes and a single metallic gate has been demonstrated.

The same technology has also been used to fabricate structures for coupled low dimensional systems. Studies of transport between a single impurity and an electrostatically defined quantum dot were preformed at a temperature T=0.3 K and B-fields up to 12 T. The resulting data shows that the angular momentum of the electrons are conserved during the tunneling event.

SiGe Esaki Tunnel Diodes has been fabricated using a combined approach of ultra high vacuum chemical vapor deposition epitaxial growth and proximity rapid thermal diffusion. This process is suitable for integration of tunnel diodes with mainstream SiGe-technology. The diodes shows a peak current density of 0.18 kA/cm2 and a peak-to-valley ratio of 2.6 at room temperature.