Epitaxial growth and characterization of semiconductor devices for SWIR and MIR applications and of the heavy fermion compound YbRh2Si2

Abstract

This dissertation focuses on the design, epitaxial growth, and characterization of detectors and lasers for short-wavelength infrared (SWIR) and mid-infrared (MIR) applications, as well as on the epitaxial growth of the heavy fermion compound YbRh2Si2.MIR and SWIR sources and detectors are essential for numerous applications. While quantum cascade detectors (QCDs) reached pioneering steps in the MIR range, the SWIR range is still marginal due to the limit imposed by the conduction band offset (CBO) of the materials. In this thesis, the functionalities of QCDs are expanded to the SWIR region of the electromagnetic spectrum by implementing a new type of detector that uses the inter band (IB) transitions in the extractor region of QCDs. The design, realization, and characterization of this new type of detector are shown. The IB transitions are analyzed in four different type-II InAs/AlSb QCD structures on GaSb substrates, addressing wavelengths between 1.83 μm and 2.33 μm. The methods employed here are universal in nature and can be applied to optimize the dual-wavelength functionality of detectors and advance research in the field of IB detectors. Inter band cascade lasers (ICLs) are the preferred MIR lasers in terms of low operating power, efficiency, and portability. This is attributed to their low threshold current densities, which are an order of magnitude lower compared to those of MIR quantum cascade lasers. Here, the growth of ICLs on GaSb substrates by molecular beam epitaxy (MBE)is investigated for the first time in the group. The optimal parameters in terms of growth temperature, strain-balance, shutter sequences, and doping are discussed. Moreover, the relationship between the size and performance metrics of ICL ring waveguides is determined by comparing the modes simulation with the device characterization results. Finally, strongly correlated electron materials exhibit a wide range of interesting phenomena, from strange metal behavior to unconventional superconductivity. The epitaxial thin films of the heavy fermion compound YbRh2Si2 have opened new possibilities in the investigation of the strange metal state, including terahertz transmission spectroscopy and shot noise. To further explore this potential, advancements in film quality are necessary for experiments conducted at lower temperatures and energies. YbRh2Si2 thin films have not yet demonstrated bulk-like transport quality due to challenges in achieving precise control over elemental growth rates and obtaining homogeneous surfaces. Here, growth recipes and programs are developed to accurately control the growth parameters. Various strategies are implemented to improve the quality of the films. The improvement in crystallinity and surface smoothness of YbRh2Si2 thin films grown by MBE using Knudsen cells and electron-beam evaporation sources are demonstrated.