Effects of Nanoholes Grown by Molecular Beam Droplet Epitaxy on Electrical Properties of Two Dimensional Electron Gas

The effects of nanoholes, grown by molecular beam droplet epitaxy, on the electrical properties of quantum well (QW) heterostructures are reported. To investigate how the depth of nanoholes affect the electrical properties of the QW heterostructures, the growth conditions for nanoholes were optimized with respect to their depth and density. Using the results of the optimization of the nanohole growth, three InGaAs pseudomorphic quantum wells with nanoholes were investigated with varied depth and a constant density. A QW heterostructure without nanoholes was grown as a reference structure. For all the samples, temperature dependent Hall effect measurements, noise studies as a function of both bias and temperature, and temperature dependent current-voltage (I-V) measurements have been carried out to examine the effects of nanoholes on the QW heterostructures. The Hall effect measurements revealed clear correlation between the depth of the nanoholes and the electrical characteristics of the QW systems such as Hall mobility and sheet electron density. Besides an increase in the mobility and carrier density, the nanoholes lead to a significant reduction of 1/f noise due to a decrease in the Hooge parameter, which can be advantageous for the fabrication of high performance electronic devices. In addition, it was shown that the nanoholes change the energy spectrum of the QW heterostructures which affects carrier transport in the QWs and metal-semiconductor interface. The changes of the energy spectrum were clued in by the variation of carrier activation energy, appearance of a new deep state in the band gap of an AlGaAs barrier layer that affect carrier kinetics and fluctuation phenomena in the present material system. The results of this thesis show a potential of nanoholes grown by droplet epitaxy as a promising candidate for modulation of material properties and fabrication of advanced material systems for electronic and optoelectronic application