Scaling of GaSb/InAs Vertical Nanowire Esaki Diodes Down to Sub-10-nm Diameter

This work studies the diameter scaling behavior of broken-band GaSb/InAs vertical nanowire (VNW) Esaki diodes. A top-down fabrication process involving precise reactive-ion etching and alcohol-based digital etch has yielded devices with a tunneling junction diameter below 10 nm. Clear Esaki peaks are observed with an average peak current density of 1 MA/cm2 and ideal areal scaling over two orders of magnitude in diameter. In the non-Esaki branch, an average current density of 4 MA/cm2 is demonstrated at 0.3 V. This suggests a great potential for the broken-band GaSb/InAs system for ultralow power VNW tunnel FET (TFET) applications. Toward evaluating the ultimate TFET potential of this material system, we have extracted the series resistance of our diodes and developed a model for it. We find that the main contribution to the series resistance comes from the GaSb body. Comparatively, the contact resistance at the top of the VNW has a minor impact in spite of the tiny Ni/InAs contact area. Self-consistent quantum transport simulations based on non-equilibrium Green's function (NEGF) formalism are carried out. We simulate two devices with different dimensions, that is, one with strong quantum confinement and one with bulk-like behavior. Inelastic tunneling due to phonon emission is found to both widen the Esaki peak and to suppress tunneling in the non-Esaki branch.