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We investigate differential evolution optimization to fit Rutherford backscattering data. The algorithm helps to find, with very high precision, the sample composition profile that best fits the experimental spectra. The capabilities of the algorithm are first demonstrated with the analysis of synthetic Rutherford backscattering spectra. The use of synthetic spectra highlights the achievable precision, through which it becomes possible to differentiate between the counting statistical uncertainty of the spectra and the fitting error. Finally, the capability of the algorithm to analyze large sets of experimental spectra is demonstrated with the analysis of the position-dependent composition of a Sr x Ti y O z layer on a 200 mm silicon wafer. It is shown that the counting statistical uncertainty as well as the fitting error can be determined, and the reported total analysis uncertainty must cover both. [ABSTRACT FROM AUTHOR]

Barium titanate (BaTiO3 or BTO) is a perovskite structure material with interesting intrinsic properties, such as spontaneous ferroelectricity or electro-optical behavior, which strongly depend on thin film crystallinity. For such functional oxide systems, the pulsed-laser deposition (PLD) approach is one promising growth technique due to its precise stoichiometry control of the metals composing the perovskite crystal and higher oxygen environment compared to the classically used molecular beam epitaxy (MBE) approach. In this article, we demonstrate a BTO epitaxial layer by PLD onto an Si(001) substrate thanks to a thin pseudomorphic SrTiO3 buffer layer grown by MBE. In our study, the various investigated PLD parameters show strong impacts on the BTO polarization orientation. Hence, adjusting the growth conditions allows control of the polarization orientation, which is crucial for both electronic and optical applications. In addition, lattice parameter changes of BTO layers are investigated using x-ray diffraction and cross-sectional transmission electron microscopy, which evidenced a correlation between mismatch relaxation and oxygen growth pressure. Finally, with the analysis of BTO C–V curves, the polarization direction transition is demonstrated electrically. [ABSTRACT FROM AUTHOR]

In0.53Ga0.47As p + n diodes with different densities of extended defects have been analyzed by detailed structural and electrical characterization. The defects have been introduced during Metal-Organic Vapor Phase Epitaxy (MOVPE) growth by using a lattice-mismatched layer on a semi-insulating InP or GaAs substrate. The residual strain and indium content in the n-type In0.53Ga0.47As layer have been determined by high-resolution X-ray diffraction, showing nearly zero strain and a fixed indium ratio of 0.53. The deep levels in the layer have been characterized by Deep Level Transient Spectroscopy. The mean value of electron traps at 0.17 ± 0.03 eV below the conduction band minimum EC is assigned to the "localized" states of α 60° misfit dislocations; another broad electron trap with mean activation energies between EC− 0.17 ± 0.01 and 0.39 ± 0.04 eV, is identified as threading dislocation segments with "band-like" states. A high variation of the pre-exponential factor KT by 7 orders of magnitude is found for the latter when changing the filling pulse time, which can be explained by the coexistence of acceptor-like and donor-like states in the core of split dislocations in III-V materials. Furthermore, two hole traps at EV+ 0.42 ± 0.01 and EV+ 0.26 ± 0.13 eV are related to the double acceptor of the Ga(In) vacancy (VGa/In3-/2-) and 60° β misfit dislocations, respectively. Finally, the dislocation climbing mechanism and the evolution of the antisite defects AsGa/In are discussed for n-type In0.53Ga0.47As. [ABSTRACT FROM AUTHOR]

In this work, we present a systematic study of the effect of the stoichiometry of BaTiO3 (BTO) films grown on the Ge(001) substrate by molecular-beam-epitaxy using different characterization methods relying on beam diffraction, including reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and selected-area electron diffraction in transmission electron microscopy. Surprisingly, over a wide range of [Ba]/[Ti] ratios, as measured by the Rutherford backscattering spectrometry, all the BTO layers exhibit the same epitaxial relationship h100iBTO(001)// 〈110〉Ge(001) with the substrate, describing a 45° lattice rotation of the BTO lattice with respect to the Ge lattice. However, varying the [Ba]/[Ti] ratio does change the diffraction behavior. From RHEED patterns, we can derive that excessive [Ba] and [Ti] generate twinning planes and a rougher surface in the non-stoichiometric BTO layers. XRD allows us to follow the evolution of the lattice constants as a function of the [Ba]/[Ti] ratio, providing an option for tuning the tetragonality of the BTO layer. In addition, we found that the intensity ratio of the 3 lowest-order Bragg peaks I(001)/ I(002), I(101)/I(002), and I(111)/I(002) derived from ω-2θ scans characteristically depend on the BTO stoichiometry. To explain the relation between observed diffraction patterns and the stoichiometry of the BTO films, we propose a model based on diffraction theory explaining how excess [Ba] or [Ti] in the layer influences the diffraction response. [ABSTRACT FROM AUTHOR]

Metrology for structural and electrical analyses at device level has been identified as one of the major challenges to be resolved for the sub-14 nm technology nodes. In these advanced nodes, new high mobility semiconductors, such as III–V compounds, are grown in narrow trenches on a Si substrate. Probing the nature of the defects, the defect density, and the role of processing steps on the surface of such structures are prime metrology requirements. In order to enable defect analysis on a (III–V) surface, a proper sample preparation for oxide removal is of primary importance. In this work, the effectiveness of different chemical cleanings and thermal annealing procedures is investigated on both blanket InP and oxide embedded InP trenches by means of scanning probe microscopy techniques. It is found that the most effective approach is a combination of an HCl-based chemical cleaning combined with a low-temperature thermal annealing leading to an oxide free surface with atomically flat areas. Scanning tunneling microscopy (STM) has been the preferred method for such investigations on blanket films due to its intrinsic sub-nm spatial resolution. However, its application on oxide embedded structures is non-trivial. To perform STM on the trenches of interest (generally <20 nm wide), we propose a combination of non-contact atomic force microscopy and STM using the same conductive atomic force microscopy tip Our results prove that with these procedures, it is possible to perform STM in narrow InP trenches showing stacking faults and surface reconstruction. Significant differences in terms of roughness and terrace formation are also observed between the blanket and the oxide embedded InP. [ABSTRACT FROM AUTHOR]

We use an improved AC conductance method and a modified Gray-Brown method to study fast interface traps and slow border traps in Ge-based MOS capacitors. The combined methods provide the corrected Fermi energy level (E) versus gate voltage (Vg) relationship, even in samples with high densities of traps that cause significant C-V distortion, the energy distribution of interface traps, their capture cross sections (σ), as well as slow border traps. A wide range of σ's in p-type Ge is found, indicating that there is more than one type of interface trap near the Ge valence band edge. In contrast, a constant σ near the Ge conduction band edge is observed in n-type Ge. XPS results indicate that Ge suboxides near the interface are accountable for the detected slow border traps. [ABSTRACT FROM AUTHOR]