Investigation of vertical current-voltage characteristics of Al(Ga)N/GaN RTD-like heterostructures

Abstract

Vertical double heterostructures based on GaN were prepared and investigated for their current voltage characteristics and compared to theory. In our quest to observe negative differential resistance (NDR) phenomenon based on quantum mechanical tunneling to, we fabricated resonant tunneling diode (RTD) like structures grown on low defect density and high quality templates prepared by metal organic chemical vapor deposition using in situ SiN nanonetwork induced epitaxial lateral overgrowth. The measured threading dislocation density of the template was in the range of 10⁷ cm^-2. Inductively coupled plasma reactive ion etching (ICP-RIE) where in enhanced chemical etching mode was used for reducing the detrimental surface defects on the mesa walls which otherwise contribute to current. Double barrier structures with varying barrier and quantum well thicknesses as well as doping profiles were tested for their I-V characteristics. The rectifying phenomenon occurred as a result of depletion region in GaN above the top Al(Ga)N layer and asymmetric barrier shape of GaN RTD-like structure due to polarization. With the aid of calculated band structure and resultant doping profile optimization, we now observe what appears to be resonant increase in current, the source of which is not yet clear, at quantum states of the well.