A double-tweezer setup is used to induce mechanical stress in systems of molecular biology. A double strand of DNA is first stretched and the data is compared to precedent experiments to check the experimental setup. Then a short foldable fragment of RNA is probed; the typical unfolding/refolding hysteresis behaviour of this kind of construction is shown and followed by a study of its elasticity and a comparison to a worm-like chain model. Eventually, we describe the unfolding of a larger RNA structure, which unfolds by multiple steps. We show that this unfolding is not reversible and that it presents numerous unfolding pathways.

The dc electrical conductivity of double stranded DNA is investigated experimentally. Single DNA molecules are manipulated with subpiconewton force and deposited on gold nanoelectrodes by optical traps. The DNA is modified at its ends for specific bead attachments and along the chain to favor charge transfer between the DNA base pair stack and the electrodes. For an electrode separation of 70 nm we find, in aqueous environment, electrical resistances above 100 G Omega indicating that even for weak stretching the double helix is almost insulating at this length scale.

An integrated array of field-effect transistor structures is used to detect two oppositely charged biopolymers: poly(L-lysine) and DNA. Local deposition of polymer solutions on part of the array induces sizeable variations in the dc current-voltage characteristics of the transistors exposed to the molecular charge. The whole transistor array is measured in the presence of a common electrolyte. Differential signals are studied as a function of electrolyte salt and polymer concentrations. The measurements provide information on the interface electrostatic potentials of the (semiconductor/biopolymer/electrolyte) system and the experimental data are compared to an analytical model which accounts for screening of the adsorbed charge by mobile ions.

An integrated array of silicon field-effect transistor structures is used for electronic detection of label-free DNA. Measurements of the dc current–voltage characteristics of the transistors gives us access to reproducible detection of single- and double-stranded DNA, locally adsorbed on the surface of the device. We combine this approach with allele-specific polymerase chain reaction, to test for the 35delG mutation, a frequent mutation related to prelingual nonsyndromic deafness.

In LEC‐grown GaP doped with silicon, two vibrational absorption lines are measured at 2175.1 and 2190.3 cm–1 (T = 7 K). These lines are due to H stretching modes where hydrogen passivates SiGa donors. Uniaxial stress experiments show that the SiGa complex responsible for the 2175.1 cm–1 line has trigonal symmetry and is the isolated passivated SiGa. The complex creating the 2190.3 cm–1 line has the symmetry Cs and contains additionally a BGa with the four constituents located in an {110} mirror plane. Therefore, also the structure of the group‐IV donohydrogen complexes is in GaP different from that observed in GaAs.

Comprehensive studies of the electrical properties of Mg-doped bulk GaN crystals, grown by high-pressure synthesis, were performed as a function of temperature up to 750 °C. Annealing of the samples in nitrogen ambient modifies qualitatively their resistivity values ρ and the ρ(T) variation. It was found that our material is characterized by a high concentration of oxygen-related donors and that the charge transport in the studied samples is determined by two types of states, one of shallow character (Mg-related state, EA≈0.15 eV), and the second one much more deep, E2≈0.95 eV (above the valence band). Depending on the effective concentration of either states, different resistivities ρ can be observed: lower resistivity (ρ<104 Ω cm at ambient temperature) in samples with dominant EA states and very high resistivity (ρ>106 Ω cm at ambient temperature) in samples with dominant E2 states. For the first type of samples, annealing at Tann<500 °C leads to a decrease of their resistivity and is associated with an increase of the effective concentration of the shallow Mg acceptors. Annealing of both types of samples at temperatures between 600 and 750 °C leads to an increase of the deep state concentration. The presence of hydrogen ambient during annealing of the low-resistivity samples strongly influences their properties. The increase of the sample resistivity and an appearance of a local vibrational mode of hydrogen at 3125 cm−1 were observed. These effects can be removed by annealing in hydrogen-free ambient.

Several local vibrational modes (LVMs), observed in magnesium-doped high-pressure grown bulk samples, are attributed to two types of magnesium–oxygen complexes. The equivalent high-energy modes for beryllium–oxygen complexes are also observed in GaN:Be samples. Therefore, oxygen plays two roles for p-type doping of GaN: it compensates the acceptors and makes complexes with them. In addition to the well known LVM at 3125cm−1 resulting from the passivation of the magnesium acceptor by hydrogen, two new modes at 4090 and 4110cm−1 (at 6K) are observed in as-grown OMVPE layers. We interpret them as originating from rotating hydrogen molecules in interstitial sites of the GaN lattice. Therefore, hydrogen passivates the acceptors and is also present in molecular form.

A local-vibrational-mode absorption line is measured at 1006.8cm−1 (T=7K) in GaP and identified as due to the antisymmetric stretching mode of interstitial oxygen (Ga–16Oi–P). The line due to 18Oi is found at 981.9cm−1. Uniaxial stress experiments indicate that the centre has a Cs(C1h) symmetry. For stress applied parallel to 〈001〉 direction, a low-temperature dichroism I||/I⊥>1 is observed. This is due to a low-temperature reorientation of the centre among its three equivalent configurations around a trigonal axis.

Local vibrational modes due to complexes of hydrogen with sulfur, selenium and tellurium in gallium phosphide are reported together with the corresponding mode due to the deuterium–sulfur complex. The wave numbers of these modes indicate that hydrogen or deuterium binds to one of the host phosphorus atoms which are next-nearest neighbors of the group-VI donor. Experiments under uniaxial stress show that the complexes have Cs (C1h) symmetry, the mirror planes being {110} planes. The orientation of the mode-induced electric dipole moment is determined for each of the complexes. The structure of the complexes of group-VI donors with hydrogen in GaP is different from the one determined previously in other III–V compounds such as GaAs or AlSb.

One of the major problems encountered for the elaboration of blue light emitting devices processed with either nitrides or II-VI compounds is the difficulty for p-type doping of the materials. It is shown that the unintentional introduction of hydrogen, issued for instance from the organometallic precursors during the process is responsible for at least part of the problem. Various experimental techniques for investigating hydrogen in semiconductors are reviewed. They show unambiguously that hydrogen forms complexes with the accepters and neutralises them. The microscopic structure of the complexes is discussed. The processes which allow to reactivate the neutralised accepters are discussed; their limitations are outlined.

The kinetics of electrical activation of hydrogenated arsenic accepters in MOVPE grown cadmium telluride layers was studied for arsenic doping in the range 8 x 10(16) to 10(20) cm(-3). Thermal annealings were performed in the temperature interval 150-550 degrees C with a duration from 1 s to 1 h. The hole concentration in the annealed samples was determined by the van der Pauw method and As-H pair concentration was deduced from the intensity of the LVM absorption line at 2022 cm(-1), detected by Fourier transform spectrometry. Short annealing experiments (<1 min) showed a continuous increase in hole concentration with time and temperature, limited to about (1-2) x 10(17) cm(-3) at a temperature of 500 degrees C. The concentration of As-H pairs concurrently decreased but at a higher rate. Longer annealings usually led to a decrease in hole concentration while the As-H pair concentration either continued to drop or recovered depending on the value of arsenic doping. These results were interpreted in the framework of a theoretical analysis which took into account several processes: dissociation-recombination of impurity-hydrogen pairs, electronic ionization of arsenic impurities and electrical compensation due to the formation of arsenic-vacancy complexes. It was proposed that arsenic ionization takes place in two steps, the first one corresponding to a thermally activated conversion process and the second one to hole emission. The microscopic nature of the intermediary neutral impurity state is not known at present.

Because of the great electronegativity of nitrogen, hydrogen is expected to behave differently in GaN and in the more conventional III-V semiconductors GaP and GaAs. In order to check this point, we have performed a spectroscopic investigation of nitrogen and hydrogen doped GaP and GaAs. In GaP, three different states of a nitrogen-hydrogen complex have been observed; two of these states, which correspond to two different charge states of the complex, are observed at equilibrium whereas the third one is metastable. The complex involves two hydrogen atoms; its structure is discussed. In GaAs, only two states of the complex are observed: a stable one and a metastable one.

Niobium doped GaAs has been investigated by photoluminescence, absorption and photoluminescence excitation spectroscopy. Photoluminescence and absorption experiments reveal only a sharp transition at 6416.4 cm(-1) whereas photoluminescence excitation spectroscopy evidences a broad triple peak band around 9000 cm(-1). Experiments under uniaxial stress on the 6416.4 cm(-1) transition are reported. All the results are discussed in the frame of neutral niobium energy levels diagram.

Short thermal treatments (5 and 30 s) have been performed on MOVPE grown CdTe layers doped with arsenic in the concentration range 8 × 1016 to 7 × 1018cm−3. In the as-grown state most of the As atoms form with hydrogen neutral AsH pairs characterized by a local vibrational mode (LVM) at 2022 cm−1. The hole concentration increases with annealing temperature and reaches a maximum for an annealing temperature of 500–550°C where the LVM intensity comes to zero. Almost full activation of the arsenic is obtained in the lowest doped layer. However the maximum hole concentration is limited to (1.5–2) × 1017cm−3 in the more doped layers, well below the concentration of As atoms involved in the pairs in the original state. Possible explanations are presented which imply short range precipitation or existence of a relaxed inactive As state.

Detailed infrared studies performed on GaP samples weakly doped with nitrogen and hydrogen have been performed. A trigonal defect involving nitrogen and a pair of nonequivalent hydrogen has been identified, with local vibrational modes at 2885.5, 2054.1, and 1049.8 cm(-1) for the N-14 related complex. N-14-N-15 isotopic shifts have been observed for the two high wave number modes. All of these modes are attributed to a defect with one hydrogen in bond centered and the other one in antibonding positions around nitrogen. The two hydrogen atoms are bonded mainly to the same nitrogen atom.

A study of the behavior under uniaxial stress of the local vibrational mode due to the manganese-hydrogen complex has been performed. It shows that the complex is trigonal and that its structure is the same as the one of group II shallow acceptor-hydrogen complexes. The local vibrational mode of the complex has a strongly non linear behavior under uniaxial stress without direct evidence of additional structure.

It is shown that the incorporation of unintentional hydrogen, during the growth by organometallic vapour phase epitaxy of cadmium telluride layers, is higher in arsenic doped layers than in undoped ones. Arsenic-hydrogen pairs are directly evidenced through the observation of the arsenic-hydrogen stretching local vibrational mode.