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The behaviour of hydrogen in crystalline semiconductors has attracted considerable interest during several decades. Due to its high diffusion rate and ability to react with a wide variety of lattice imperfections such as intrinsic point defects, impurities, interfaces and surfaces, hydrogen is an impurity of fundamental importance in semiconductor materials. It has been already evidenced in previous investigations that the most fundamental hydrogen-related defects in-group IV semiconductors are interstitial hydrogen atoms occupying the bond-centre site (BC) or the interstitial tetrahedral site (T). Using first-principles calculations Van de Walle predicted similar properties of isolated hydrogen in other II–VI and III–V semiconductors. Another interesting prediction shown in that work was the existence of a universal alignment for the hydrogen electronic (−/+) level. Until now there is no direct experimental information regarding the individual isolated hydrogen states in compound semiconductors and most reported properties have been inferred indirectly. In the present work in-situ conventional deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques are used to analyse hydrogen-related levels after low-temperature proton implantation in different II–VI and III–V semiconductors including GaAs, ZnO and CdTe. From these experimental observations the donor level of isolated hydrogen is found to keep almost a constant value in the absolute energy scale taking into account different band-offsets calculated for the whole group of semiconductors.

The first data evidencing the existence of the donor level of the interstitial hydrogen in GaAs are presented. The abundant formation of the ( 0 / + ) donor level after in situ low-temperature implantation of hydrogen into the depletion layer of GaAs Schottky diodes has been observed and the activation energy and annealing properties have been determined by Laplace DLTS. The activation energy for electron emission of this donor state is 0.14 eV. Above 100 K the hydrogen deep donor state is unstable, converting to a more stable form when there are electrons available for the capture process. A slightly perturbed form of the hydrogen donor in its neutral charge state can be recovered by illuminating the sample. This process releases twice as many electrons as the ionisation process of the hydrogen donor state itself. This fact, by analogy with the silicon case, evidences the negative-U behaviour of hydrogen in GaAs.

The stress-induced electronic level splitting pattern can provide information regarding the symmetry of a defect complex. If the components of the piezospectroscopic tensor are known it is also possible to deduce information about the lattice relaxation in the vicinity of the defect. Based on a complete piezospectroscopic analysis of the vacancy–oxygen complex in silicon we confirm that this defect has an orthorhombic symmetry in the stable configuration while in the unstable configuration of the saddle point on the reconfiguration trajectory we demonstrate that it has trigonal symmetry. The piezospectroscopic description of static defects is, in some cases, inadequate to deal with some defect complexes when they are observed at relatively high temperatures. This is often the case for the high-resolution Laplace deep level transient spectroscopy (DLTS) measurements. At very low temperatures the vacancy–oxygen–hydrogen complex has monoclinic symmetry while at the temperatures used by us for Laplace DLTS measurements the observed symmetry is orthorhombic due to fast hydrogen jumps. A similar re-orientation (position averaging) process occurs for the divacancy in silicon. However, this is true only for the divacancy in the single negative charge state while the symmetry of the complex in the double negative state is stable trigonal. We discuss how these re-orientation processes can be identified from the observed piezospectroscopic parameters for both cases.

In this study the use of the high-resolution Laplace DLTS combined with uniaxial stress has allowed us to investigate in detail the structure and electrical properties of the platinum–hydrogen-related complex PtH 2 . We correlate the defect electronic level with the results of other spectroscopic studies performed with electron paramagnetic resonance and far-infrared absorption measurements. The observed stress-induced peak splitting pattern confirms the orthorhombic-IC 2v symmetry of the complex. The re-orientation process of the defect can be observed at temperatures higher than the room temperature for all bias conditions.

We have observed the donor (Ec-0.22 eV) and acceptor (Ec-0.16 eV) levels related to hydrogen-carbon complexes in silicon. The donor level is only detected at low temperatures after proton implantat ...

The migration of monatomic hydrogen in crystalline silicon is governed by three potential energy surfaces corresponding to the three possible charges states of hydrogen. The H0 and H+ surfaces have minima at the bond-centre site (BC) and give rise to a donor state, whereas the H− surface has minimum at the interstitial tetrahedral site (T) giving rise to an acceptor state. We review the current experimental status regarding these surfaces. The BC-donor and the T-site acceptor are found to exist in two closely related forms, which we explain by a distortion of the energy surfaces when hydrogen is trapped in the silicon lattice at the nearby interstitial oxygen. We show how this oxygen distortion acts as a catalyst for the conversion from H− at T sites to H+ at BC sites and retards the migration of H+ through BC sites.

The technique of Laplace transform deep level transient spectroscopy has been used to study the acceptor levels of platinum and gold diffused into dilute (0–5% Ge) SiGe alloys. The high-resolution spectra obtained display a fine structure that we interpret as the effect of alloy splitting in terms of the relative number of silicon and germanium atoms in the immediate proximity of the transition metal. We show that Ge atoms in the first and in the second shell of atoms surrounding the impurity perturb the electronic properties of the well-known Au and Pt acceptor defects. For both defects the spectral distributions indicate an overpopulation of Ge-perturbed sites as compared to randomly occupied sites. This can be quantitatively interpreted in terms of an enthalpy difference of ∼60 meV between configurations with zero or one Ge in the first or second shell surrounding the impurity.

We identify the acceptor levels (−/0) of the VH and V 2 H defects in silicon from comparison of DLTS and EPR annealing data. The levels are very close to each other and close to the acceptor level of the PV defect (the E-center) as well. In order to separate them, we have applied the high-resolution technique of Laplace DLTS and compared the formation and annealing properties of defects generated by implantation of hydrogen or helium. We further applied Laplace DLTS in combination with uniaxial stress to study the acceptor level at E c − E t =0.31 eV previously assigned to a vacancy-hydrogen–oxygen defect. We find, in accordance with recent EPR measurements, that the defect displays orthorhombic-I symmetry and rule out that it contains two hydrogen atoms. The defect can be understood as a single hydrogen atom bound inside the A-center, the well-known VO defect of silicon, and we denote it VOH accordingly. The observed orthorhombic-I symmetry arises because the hydrogen atom (at T =160 K) swiftly jumps among two equivalent sites across the (1 1 0) plane that contains the Si–O–Si bond. Previous studies have shown that hydrogenation of oxygen-rich electron-irradiated samples leads to the formation of VOH with simultaneous depletion of the A-center. Our structural data are in accordance with this dynamic behavior.