Effect of structural parameters on resonant tunneling diode performance

The influence of structural parameters on resonant tunneling diode (RTD) performance is described in this thesis. Al{dollar}sb{lcub}rm x{rcub}{dollar}Ga{dollar}sb{lcub}rm 1-x{rcub}{dollar}As/In{dollar}sb{lcub}rm y{rcub}{dollar}Ga{dollar}sb{lcub}rm 1-y{rcub}{dollar}As resonant tunneling diodes grown by molecular beam epitaxy (MBE) with a symmetric and asymmetric spacer layer have been fabricated and tested via electric and high magnetic field measurements.; The device performance (peak current, peak to valley current ratio and valley width) improves as the spacer layer thickness increases for lattice matched AlGaAs/GaAs RTDs because of reduced ionized impurity scattering in the tunneling region of the diode, and it does not show any further improvement once the layer thickness is greater than a certain critical value. This is due to the formation of a spacer barrier which reduces the number of carriers available for the conduction process.; Spacer layers on pseudomorphic AlGaAs/InGaAs RTDs produce quite different features when the lowest allowed state in the well lies below the spacer barrier height. A thick spacer layer at the leading edge of the diode forms an accumulation layer while one at the trailing edge acts as an effective tunnel barrier. Pseudomorphic AlGaAs/InGaAs RTDs with asymmetric spacer layer thicknesses provide very strong evidence that the spacer layer is playing a different role which depends on the bias configuration. Tunnel injection is through the ground state of the InGaAs well when the thick spacer layer is located at the leading edge of the device while it is through the first excited state of the InGaAs well when the thick spacer layer is at the trailing edge of the diode. Evidence is also provided which suggests that silicon impurity outdiffusion occurs during MBE growth.; RTDs subjected to a strong magnetic field exhibit magneto-quantum assisted tunneling features which become larger with increasing applied magnetic field. These features are distinguished between phonon assisted tunneling or successive Landau level tunneling by the peak position dependence on the magnetic field, as well as by Shubnikov-de Haas oscillations obtained from the RTDs.