| InGaAs/AlAs/InAs Resonant tunneling diode structure was designed, processed and characterized. The design was implemented using a quantum device simulator, NEMO or NanoElectronic Modeling tool. This tool enables the user to simulate different quantum structures. A lattice matched InGaAs layer was grown on InP substrate, above which the RTD structure was fabricated. For obtaining a lattice matched composition X-ray diffraction was used. The main goal was to design and characterize an RTD which would give a high peak to valley ratio at room temperature. The material system chosen was due to the fact that these materials are radiation resistant and exhibit better properties as far as carrier transport is concerned.; Molecular Beam Epitaxy was used to fabricate the device. The device consisted of a 11 ml AlAs barrier, 7 ml InGaAs on either side of a 2 ml InAs subwell. The InAs subwell allows for the first resonance to occur at a lower bias even though the well is not wide and also it aids in reducing alloy disorder scattering which exists in ternary alloys like InGaAs. The measured devices exhibited peak to valley ratios ranging from 1.95 to 2.05. The structure was simulated in NEMO using a Thomas Fermi with quasi Fermi level potential model. The simulations were multiband with numerical integration over the transverse momentum which considers the transmission probability varying with the transverse momentum.; The results obtained were compared to experimental data and it seemed that the structure was asymmetric. Also a higher valley current was obtained in experiment in comparison to the simulation, this could be attributed to various carrier transport phenomenon which have not been included in the simulations. There could also be scattering effects as the InGaAs layer which was not perfectly lattice matched to the InP substrate. The devices fabricated showed repeatable NDR and not much hysteresis was seen. This could be due to very thin barriers, which do not hold the well in the charged state for a long enough duration.; In conclusion, the InGaAs/AlAs/InAs RTD structure was studied. A design was proposed for obtaining high peak to valley ratio under room temperature conditions. Fabrication and processing was done and results obtained were compared to simulation to determine the precise model for the RTD. |
