High-temperature deep-level transient spectroscopy system for defect studies in wide-bandgap semiconductors

Full investigation of deep defect states and impurities in wide-bandgap materials by employing commercial transient capacitance spectroscopy is a challenge, demanding very high temperatures. Therefore, a high-temperature deep-level transient spectroscopy (HT-DLTS) system was developed for measurements up to 1100 K. The upper limit of the temperature range allows for the study of deep defects and trap centers in the bandgap, deeper than previously reported by DLTS characterization in any material. Performance of the system was tested by conducting measurements on the well-known intrinsic defects in n-type 4H-SiC in the temperature range 300-950 K. Experimental observations performed on 4H-SiC Schottky diodes were in good agreement with the literatures. However, the DLTS measurements were restricted by the operation and quality of the electrodes

DLTS and FTIR study of quenching induced defects in germanium

Due to the high carrier mobility in Ge, it is more and more used as active semiconducting layer in advanced electronic devices on Si substrates [1]. Successful growth, doping and further processing of Ge requires however a good understanding of the intrinsic point defect properties that are unfortunately not well known. The present paper reports on the progress of an effort to determine the formation energy and diffusivity of the vacancy in Ge using thermal quenching techniques [2]. Experimental data on the thermal equilibrium concentration and diffusivity of vacancies in Ge are scarce and most are more than 40 years old. Most of the experimental data were obtained based on thermal quenching experiments assuming that the formed acceptors are due to quenched-in vacancies so that their concentration and formation energy can be determined from measured resistivity changes. The formation energy of the vacancy in its different charge states has recently also been calculated using ab initio calculations which showed that the (double) negatively charged vacancy has the lowest formation energy of about 2 eV in good agreement with the acceptor formation energy determined from the quenching experiments. Based on vacancy mediated dopant diffusion studies, Brotzmann et al [3] also concluded that the double negatively charged vacancy is the most probable charge state of the vacancy. In this contribution, the quenched-in acceptors are studied using deep-level transient spectroscopy. As Cu is known as contaminant which is difficult to avoid when quenching Ge, the electric properties of the quenched-in acceptors are carefully compared with those of substitutional Cu. Although at first glance similarities are striking, remarkable differences are also observed and discussed. [1] J. Vanhellemont and E. Simoen, J. Electrochem. Soc. 154 (2007), p. H572. [2] J. Vanhellemont, J. Lauwaert, A. Witecka, P. Spiewak, I. Romandic and P. Clauws, Physica B 404 (2009), p. 4529. [3] S. Brotzmann and H. Bracht, J. Appl. Phys. 103 (2008), p. 033508

Bisimulations over DLTS in O(m.log n)-time

The well known Hopcroft's algorithm to minimize deterministic complete automata runs in $O(kn\log n)$-time, where $k$ is the size of the alphabet and $n$ the number of states. The main part of this algorithm corresponds to the computation of a coarsest bisimulation over a finite Deterministic Labelled Transition System (DLTS). By applying techniques we have developed in the case of simulations, we design a new algorithm which computes the coarsest bisimulation over a finite DLTS in $O(m\log n)$-time and $O(k+m+n)$-space, with $m$ the number of transitions. The underlying DLTS does not need to be complete and thus: $m\leq kn$. This new algorithm is much simpler than the two others found in the literature.Comment: Submitted to DLT'1

THE SPECTROSCOPY OF CRYSTAL DEFECTS - A COMPENDIUM OF DEFECT NOMENCLATURE

The authors bring together tables of current defect nomenclature and a summary of the rules actually practised (rather than idealised schemes) in choosing such labels for signals obtained with a range of spectroscopies. As well as providing a source of reference for the user lost in a maze of labels, the compilation also indicates parallels between similar defect species in very different systems (e.g. ice and quartz), even though the relationships may be far from obvious from the labels. The systems considered are all non-metals, namely ionic crystals (including oxides), silica, semiconductors (e.g. III-V and tetrahedrally coordinated II-VI), valence crystals (e.g. diamond, c-Si, a-Si) and other special hosts like ice and conducting polymers

Optical and electrical activity of defects in rare earth implanted Si

A common technique for introducing rare earth atoms into Si and related materials for photonic applications is ion implantation. It is compatible with standard Si processing, and also allows high, non-equilibrium concentrations of rare earths to be introduced. However, the high energies often employed mean that there are collision cascades and potentially severe end-of-range damage. This paper reports on studies of this damage, and the competition it may present to the optical activity of the rare earths. Er-, Si, and Yb-implanted Si samples have been investigated, before and after anneals designed to restore the sample crystallinity. The electrical activity of defects in as-implanted Er, Si, and Yb doped Si has been studied by Deep Level Transient Spectroscopy (DTLS) and the related, high resolution technique, Laplace DLTS (LDLTS), as a function of annealing. Er-implanted Si, regrown by solid phase epitaxy at 600degrees C and then subject to a rapid thermal anneal, has also been studied by time-resolved photoluminescence (PL). The LDLTS studies reveal that there are clear differences in the defect population as a function of depth from the surface, and this is attributed to different defects in the vacancy-rich and interstitial-rich regions. Defects in the interstitial-rich region have electrical characteristics typical of small extended defects, and these may provide the precursors for larger structural defects in annealed layers. The time-resolved PL of the annealed layers, in combination with electron microscopy, shows that the Er emission at 1.54microns contains a fast component attributed to non-radiative recombination at deep states due to small dislocations. It is concluded that there can be measurable competition to the radiative efficiency in rare-earth implanted Si that is due to the implantation and is not specific to Er.</p

Point defects in silicon after zinc diffusion - a deep level transient spectroscopy and spreading-resistance profiling study

We present results from spreading-resistance profiling and deep level transient spectroscopy on Si after Zn diffusion at 1294 K. Concentration profiles of substitutional in dislocation-free and highly dislocated Si are described by a diffusion mechanism involving interstitial-substitutional exchange. Additional annealing at 873 K following quenching from the diffusion temperature is required in the case of dislocation-free Si to electrically activate . The formation of complexes of with unwanted impurities upon quenching is discussed. Additional Ni diffusion experiments as well as total energy calculations suggest that Ni is a likely candidate for the passivation of Zns. From total energy calculations we find that the formation of complexes involving Zn and Ni depends on the position of the Fermi level. This explains differences in results from spreading-resistance profiling and deep level transient spectroscopy on near-intrinsic and p-type Si, respectively