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Freestanding low pressure chemical vapor deposition (LPCVD) silicon nitride (SiN) membrane resonators are widely investigated as Nano-Electromechanical System (NEMS) for their outstandingly low mechanical dissipation and high mechanical quality (Q) factor. The high Q-factor brings better sensitivities to force, displacement, and temperature excitations. However, integrated actuation methods are not trivial to implement on this platform and are required to harness their high Q-factor in practical applications. The first goal of this research is to develop a recipe for fabricating large area low stress LPCVD SiN membrane since commercial membranes are relatively expensive and have limited flexibility in terms of geometries. Starting from 4 inches, 500 μm thick, (100) single crystal silicon wafers double-side coated with 100 nm LPCVD SiN, we successfully fabricate five different sizes (i.e., 1 mm, 1.5 mm, 3 mm, 6 mm and 12 mm) of square shape membrane chips. The developed recipe is universally applicable for any size (i.e., under 12 mm) of square shape SiN membrane from the same type of wafer. All recipe parameters are presented in this work, along with experienced challenges and their associated solutions. The second part of this work is to develop an on-chip actuation method for these resonators. We develop a new method for creating acoustic waves in the silicon substrate using metal – silicon nitride – silicon capacitors. Acoustic waves due to the voltage-dependent mechanical stress arising from charge attractions was already observed previously in silicon substrate p-n junction resonators but is observed here for the first time in a capacitively coupled metal-dielectric-semiconductor (MDS) assembly. In the MDS system, we model three main possible actuation regimes, i.e., depletion, accumulation, and thermal expansion. Both depletion and accumulation rely on electrostatic attraction forces in MDS capacitors when an AC electrical current flows through. The same current can also generate thermal expansion forces resulting from resistive dissipation in the silicon. This contribution, however, is found to be negligible. In experimental measurements on 1.5 mm membranes in high vacuum, the accumulation MDS is found to perform better than the depletion one in terms of membrane actuation amplitude. With 2 V drive voltage, the membrane achieves up to 10 nm displacement for fundamental mode (1, 1). The contribution of thermal expansion forces is found to be negligible, with resonator temperature changes smaller than 4 mK. A comparison of energy dissipation between a conventional external piezo actuation method and our approach is also presented, through which we find that both methods have comparable power consumption.

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The work described in this thesis investigates the effects of bandstructure modifications, brought about by Landau confinement, hydrostatic pressure and uniaxial stress, on recombination processes in narrow-gap materials and laser diodes. The effects of Landau confinement on the characteristics of InSb-based emission devices operating at a wavelength of ~5mum at 77K were studied. The change in performance due to the magnetic field applied along both the cavity and the growth direction and thereby simulating quasi-quantum wire and quasi-quantum dot structures clearly demonstrated the benefits, such as reduced threshold and temperature sensitivity, gained by the reduced dimensionality. On the other hand, suppression of LO-phonon emission due to the discrete nature of the density of states was observed, for the first time, in an interband laser device. Interband recombination dynamics were studied in In1-xGaxSb and PbSe over a range of excited carrier densities and temperatures down to 30K. Detailed analysis of the results found that the Auger-1 mechanism is reduced in In1-xGaxSb as a function of Ga-fraction due to the increased bandgap energy, in good agreement with theoretical predictions. In PbSe, the Auger-1 rate was observed to dominate at low excited carrier concentrations in spite of near-mirror bands, and was found to be approximately constant between 300K and 70K and was seen to be quenched in the low temperature regime. Stimulated emission was seen to be the most efficient recombination mechanism at high excited carrier densities at low temperatures. The Auger coefficient in PbSe was found to be one to two orders of magnitude lower than for materials with a Kane band structure (Hg1-xCdxTe) with comparable bandgap. An experimental technique was developed which enables measurements at high hydrostatic pressures and high magnetic fields at low temperatures. Hydrostatic pressures were applied to a 1.5mum laser diode at different temperatures revealing the effects of pressure on the band structure and hence the laser characteristics. A visible laser diode was measured under the simultaneous application of hydrostatic pressure and uniaxial stress. The change in performance was satisfactorily explained in terms of leakage of carriers into the X-minimum in the cladding region, the process that has been suspected of being one of the major loss mechanisms in visible laser diodes. This copy of the thesis has been supplied on the condition that anyone who consults it is understood to recognise that the copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without the prior written consent of the author or the University (as may be appropriate).

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