Low dimensional systems for electronic and optoelectronic devices.

Abstract

This thesis addresses two classes of ultra small devices where dimensions in all three directions approach electron de Broglie wavelength. The first class of devices are small MOSFETs while the second class is based on self assembled quantum dots. In small MOSFETs the key issues that are addressed are use of ferroelectric materials to suppress gate currents. Studies are also carried out to examine the role of polar interface charges and effects of hysteresis behaviors. We have developed formalism to address such devices and our work shows that ferroelectric MOSFETs can display enhanced inversion channel charges, memory retention in the capacitance-voltage curves and highly depressed gate leakage. In the area of self-assembled dots we examine a number of important material systems (InGaAs/GaAs; SiGe/Si, InGaN/GaN). Several issues are addressed: (i) configuration energy studies to identify the sources of size/shape non-uniformity; (ii) role of stressors to improve uniformity; and (iii) use of stressor dots to create 3D confinements in wells. Additionally we examine inter-subband optical processes in dots for applications in long wavelength detectors. Our studies show that inter-subband transitions can allow strong absorption in wavelength relevant for thermal imaging and night vision (3 mum to 20 mum wavelength). Also absorption in dots has a strong polarization dependence that can be exploited for selective detection. Our studies provide guidelines on how buried stressors can be used to create 3D confinement in quantum well regions through strain propagation.