The selection of appropriate characterisation methodologies is vital for analysing and comprehending the sources of defects and their influence on the properties of heteroepitaxially grown III-V layers. In this work we investigate the structural properties of GaAs layers grown by Metal-Organic Vapour Phase Epitaxy (MOVPE) on Ge substrates -(100) with 6⁰ offset towards <111> -under various growth conditions. Synchrotron X-ray topography (SXRT) is employed to investigate the nature of extended linear defects formed in GaAs epilayers. Other X-ray techniques, such as reciprocal space mapping (RSM) and triple axis ω-scans of (00l)-reflections (l = 2, 4, 6) are used to quantify the degree of relaxation and presence of antiphase domains (APDs) in the GaAs crystals. The surface roughness is found to be closely related to the size of APDs formed at the GaAs/Ge heterointerface, as confirmed by X-ray diffraction (XRD), as well as atomic force microscopy (AFM), and transmission electron microscopy (TEM).
We present a reliable dry-etch process for patterning deep-submicron structures in ultrathin (16 nm) HfO2 layers deposited on GaAs substrates. Plasma chemistries based on BCl3/O2 and SF6/Ar have been investigated using an inductively-coupled plasma reactive ion etch (ICP-RIE) reactor. The process reliability has been examined in terms of etch rate selectivity, etch time control, anisotropy, and surface roughness of the underlying GaAs substrate for potential application to gate nanopatterning in next-generation field-effect transistor fabrication. We show that a SF6/Ar plasma process provides excellent prospects as a nanopatterning method for subsequent re-growth of GaAs in novel device architectures.
Nanostructuring of ultrathin HfO2 films deposited on GaAs (001) substrates by high-resolution Lloyd's mirror laser interference nanolithography is described. Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas. A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition. We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm. The exposed GaAs trenches were found to be residue-free and atomically smooth with a root-mean-square line roughness of 0.18 nm after plasma etching.PACS: Dielectric oxides 77.84.Bw, Nanoscale pattern formation 81.16.Rf, Plasma etching 52.77.Bn, Fabrication of III-V semiconductors 81.05.Ea
We report on the nanopatterning by electron beam lithography (EBL) and reactive ion etching (RIE) in a SF6/Ar+ plasma of ultra-thin HfO2 films deposited on GaAs (001) substrates for gate oxide application in next generation III-V metal-oxide-semiconductor field effect transistors (MOSFETs). Characterization of the HfO2/GaAs nanostructured samples by atomic force microscopy (AFM), high-resolution scanning electron microscopy (HRSEM), energy-dispersive X-ray spectroscopy microanalysis (EDX) and transmission electron microscopy (TEM) has shown the formation of well defined HfO2 patterns with nanometre-scale linewidth control and anisotropic profiles. In addition, atomically smooth, stoichiometric and residue-free bottom GaAs etched lines with a lateral dimension of approximately 50 nm have been demonstrated.
We have evaluated the effect of thermal annealing on the morphology, crystalline phase and elemental composition of high-k dielectric HfO(2)-on-GaAs nanopatterns at 500-620 °C by using atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS). While the HfO(2)-GaAs interface continues to be atomically abrupt at 620 °C, we have found a gradual shrinkage in the pattern linewidth and period with increasing temperature. Facet formation triggered by a nanoscale-modulated sequence of tensile and compressive stresses on the GaAs substrate, observed at 620 °C, has been attributed to a volumetric expansion of the HfO(2) nanostructures, caused by the tetragonal/cubic to monoclinic HfO(2) phase transformation and, to a lesser extent, by solid-state diffusion of As into HfO(2).
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