Simulation And Characterization Of ZnSe/BeTe Resonant Tunneling Diode On Silicon

Abstract

ZnSe/BeTe resonant tunneling diodes were grown on silicon with a ZnxBe1-xTe buffer layer using MBE (Molecular Beam epitaxy).These devices were processed and characterized. The devices showed multiple NDR (negative differential resistance) regions at room temperature with PVR (Peak to valley ratios) between 1.01 to 1.23. Variations to the structure were made in growth and their corresponding current-voltage characteristics were studied. The ZnSe/BeTe resonant tunneling diode showed asymmetrical current voltage characteristics for positive and negative biases. The sources of asymmetry were investigated during fabrication and with the help of simulations. The Al/ZnSe contact was confirmed to be ohmic contact when the aluminum is deposited in-situ in the MBE chamber. Low temperature measurements were done on the samples and additional NDR regions were observed at 3.2K. NEMO (Nano-electronic modeling) a quantum device simulator was used to model the experimental current-voltage characteristics of the device. The sp3s* tight binding parameters which define the band structure of a material were implemented in NEMO and optimized to get the desired band offsets. The addition of no-common atom interfaces of BeSe and ZnTe to the ZnSe/BeTe hetero-structure were found to qualitatively model the experimental characteristics. The other sources of asymmetry in current-voltage characteristics such as non-equivalent interfaces, asymmetric doping and asymmetric thickness were studied using NEMO.The most important factor contributing to the asymmetry in NEMO current-voltage simulations were found to be the alternating interfaces of BeSe and ZnTe. Thermally assisted tunneling and the effect of Fermi-level raising on PVR were studied using NEMO.