The term junction spectroscopy embraces a wide range of techniques used to explore the properties of semiconductor materials and semiconductor devices. In this tutorial review we describe the most widely used junction spectroscopy approaches for characterizing deep-level defects in semiconductors and present some of the early work on which the principles of today's methodology are based. We outline ab-initio calculations of defect properties and give examples of how density functional theory in conjunction with formation energy and marker methods can be used to guide the interpretation of experimental results. We review recombination, generation and trapping of charge carriers associated with defects. We consider thermally driven emission and capture and describe the techniques of Deep Level Transient Spectroscopy (DLTS), high resolution Laplace DLTS, admittance spectroscopy and scanning DLTS. For the study of minority carrier related processes and wide gap materials we consider Minority Carrier Transient Spectroscopy (MCTS), Optical DLTS (ODLTS and DLOS) together with some of their many variants. Capacitance, current and conductance measurements enable carrier exchange processes associated with the defects to be detected. We explain how these methods are used in order to understand the behaviour of point defects, the determination of charge states and negative-U (Hubbard correlation energy) behaviour. We provide, or reference, examples from a wide range of materials including Si, SiGe, GaAs, GaP, GaN, InGaN, InAlN and ZnO.

Silicon solar cells containing boron and oxygen are one of the most rapidly growing forms of electricity generation. However, they suffer from significant degradation during the initial stages of use. This problem has been studied for 40 years resulting in over 250 research publications. Despite this, there is no consensus regarding the microscopic nature of the defect reactions responsible. In this paper, we present compelling evidence of the mechanism of degradation. We observe, using deep level transient spectroscopy and photoluminescence, under the action of light or injected carriers, the conversion of a deep boron-di-oxygen-related donor state into a shallow acceptor which correlates with the change in the lifetime of minority carriers in the silicon. Using ab initio modeling, we propose structures of the BsO2 defect which match the experimental findings. We put forward the hypothesis that the dominant recombination process associated with the degradation is trap-assisted Auger recombination. This assignment is supported by the observation of above bandgap luminescence due to hot carriers resulting from the Auger process.

Formation kinetics of oxygen-hydrogen ͑O-H͒ complexes which give rise to an infrared absorption line at 1075.1 cm Ϫ1 have been studied in Czochralski-grown silicon crystals in the temperature range of 30-150°C. Hydrogen was incorporated into the crystals by high temperature ͑1200°C͒ in diffusion from H 2 gas. It was found that the observed kinetics can be explained as being due to an interaction of mobile neutral hydrogen-related species with bond-centered oxygen atoms. The binding energy of the O-H complex was determined to be 0.28Ϯ0.02 eV. An activation energy for migration of hydrogen-related species responsible for the formation of the O-H complexes was found to be 0.78Ϯ0.05 eV. It was shown that atomic hydrogen and H 2 *, a complex containing two hydrogen atoms, one at bond-centered site and another one at antibonding site, cannot account for the hydrogen-oxygen interaction considered. Hydrogen molecules (H 2 ) located at tetrahedral interstitial site are suggested to be the species which interact with interstitial oxygen atoms and form the complex giving rise to the absorption line at 1075.1 cm Ϫ1 .

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A center from the family of "fourfold coordinated ͑FFC͒ defects", previously predicted theoretically, has been experimentally identified in crystalline silicon. It is shown that the trivacancy ͑V 3 ͒ in Si is a bistable center in the neutral charge state, with a FFC configuration lower in energy than the ͑110͒ planar one. V 3 in the planar configuration gives rise to two acceptor levels at 0.36 and 0.46 eV below the conduction band edge ͑E c ͒ in the gap, while in the FFC configuration it has trigonal symmetry and an acceptor level at E c − 0.075 eV. From annealing experiments in oxygen-rich samples, we also conclude that O atoms are efficient traps for mobile V 3 centers. Their interaction results in the formation of V 3 O complexes with the first and second acceptor levels at E c − 0.46 eV and E c − 0.34 eV. The overall picture, including structural details, relative stability, and electrical levels, is accompanied and supported by ab initio modeling studies.