States of hydrogen in crystalline silicon

The thermal transformation of deuterium in p-type crystalline silicon is studied with a variety of experimental techniques. It is found that D-atoms initially trapped at acceptor sites can be transferred by low temperature annealing to a different state tentatively ascribed to interstitial D₂ molecules. Diffusion of D out of the passivated sample only occurs at temperatures significantly higher than this transformation temperature. This fact allows us to produce Si samples with extremely high deuterium concentrations (several at%) by a suitable passivation-annealing sequence. With increasing D-concentration, a number of characteristic Si-D defect complexes have been observed by vibrational spectroscopy.     

Vibrational lifetime of bond-center hydrogen in crystalline silicon

The lifetime of the stretch mode of bond-center hydrogen in crystalline silicon is measured to be T1 = 7.8+/-0.2 ps with time-resolved, transient bleaching spectroscopy. The low-temperature spectral width of the absorption line due to the stretch mode converges towards its natural width for decreasing hydrogen concentration C(H), and nearly coincides with the natural width for C(H) approximately 1 ppm. The lifetimes of the Si-H stretch modes of selected hydrogen-related defects are estimated from their spectral widths and shown to range from 1.6 to more than 37 ps.     

Evidence for molecular hydrogen in single crystal silicon

Rutherford backscattering in channeling in combination with elastic recoil detection analysis has been used to study the formation and destruction of hydrogen “supermolecular” complexes (H₂)_n formed in single crystal silicon after hydrogen implantation and annealing in the range 150–800°C. Secondary ion mass spectroscopy has been used to confirm this interpretation by giving direct evidence for H₂. The supermolecular configuration can be interpreted as the nucleus for the formation of bubbles.     

Quantum state of muon and proton in crystalline silicon

Quantum state and dynamics of muon and proton in crystalline silicon have been studied by solving one‐particle Schrödinger equations for the impurities. The ground state wavefunctions and energies are determined as a function of local distortion of the host Si lattice, where the Si–H interaction we used is that parameterized by Ramírez and Herrero following the results of earlier pseudopotential‐density‐functional calculation. It is shown that quantum zero‐point motion of muon induces an effective potential barrier between the tetrahedral‐symmetry (T) site and the bond‐center (BC) site, which ensures bistability of muonium states observed in experiments. It is also shown that, if we fully consider the quantum effect with the present model potential, the BC site becomes less stable than the T site on the contrary to the experiments and former theoretical calculations.     

Theory of hydrogen-related metastability in disordered silicon

Density functional electronic structure calculations are employed to examine hydrogen for a variety of configurations in silicon. A novel complex is found for hydrogen in amorphous silicon. The complex involves the breaking of a weak silicon bond to form two Si-H bonds with both hydrogens in between the original silicon atoms. This complex provides a microscopic model for new metastable complexes observed in amorphous silicon. Mechanisms for hydrogen-related metastability are discussed for amorphous and polycrystalline silicon.     

Hydrogen diffusion and electronic metastability in amorphous silicon

Hydrogen diffusion and its role in the many electronic metastability phenomena in hydrogenated amorphous silicon (a-Si:H) is reviewed. A-Si:H contains about 10 at% hydrogen, most of which is bonded to silicon. The hydrogen diffuses at relatively low temperatures by releasing hydrogen from the Si-H bonds into interstitial sites. The reactions of hydrogen with the silicon dangling bonds and the weak bonds provide a hydrogen-mediated mechanism for electron-structural interactions, which are manifested as electronic metastability. The annealing of light-induced defects, the equilibration of defects and dopants, the stretched exponential relaxation kinetics, and the atomic structure formed during growth, are all attributed to hydrogen diffusion.     

RF hydrogen plasma influence on shallow and deep levels in crystalline silicon

Changes in charge states in c-silicon caused by hydrogen plasma treatment at temperatures from 293 to 573 K are studied by using C-V and DLTS techniques. Generation of acceptor and donor type defects is observed in the region of about 1 μm from the Si surface.     

Hexavacancies in crystalline silicon

The kinetics of disorientation of B ₈₀ ⁴ centers is studied. The reorientation energy of the centers is determined to be ～1.5 eV. Based on the fact that this value is close to the energy of hexavacancy transition from the ground state to the first metastable state, it is concluded that the B ₈₀ ⁴ center is a ring hexavacancy. The reorientation mechanism is explained by the hexavacancy transition to the metastable state and, then, to a state with a new orientation.     

On the modeling of hydrogen diffusion processes and complex formation in p-type crystalline silicon

Deuterium diffusion profiles in p-type silicon doped with boron (10¹⁷–10¹⁹ cm^-3) and aluminum (10¹⁸ cm^-3) are simulated with an improved version of a previously reported model. The new approach, based on the observation of experimental profiles, excludes H₂ molecule formation and leads to a reduced fit parameters model. The different diffusion coefficients and activation energies of H⁰ and H⁺ species are determined and discussed in the light of available data. The dissociation energies of BH and AlH complexes are also calculated and found to be in good agreement with the corresponding reported values in the literature.     

氢稀释对高速生长纳米晶硅薄膜晶化特性的影响

以SiH₄与H₂为气源,采用射频等离子体增强化学气相沉积技术,在较高的压强(230Pa)下,研究氢稀释率对纳米晶硅薄膜的生长速率和晶化特性的影响. 实验表明,薄膜的晶化率,晶粒尺寸随着氢稀释率的提高而增加,当氢稀释率为99%,薄膜的晶化率接近70%. 而沉积速率却随着氢稀释率的减小而增加,当氢稀释率从99%减小到95%时,薄膜的沉积速率由0.3nm/s 增加至0.8nm/s. 关键词： 纳米晶硅薄膜 氢稀释 晶化率 硅烷     

Hydrogen above saturation at silicon vacancies: H-pair reservoirs and metastability sites

We propose that hydrogen-passivated multivacancies which appear to be fully saturated with H can actually capture additional H in electrically inactive sites. In silicon, first-principles total energy calculations show that splitting an (m>or=2) multivacancy into a mono- and an (m-1) vacancy provides a low-strain pairing site for H, 0.4 eV per H lower than any known bulk pairing site. This monovacancy ejection mechanism is an excellent candidate for the H reservoir found both in crystalline and amorphous Si. A distinct H pairing on the fully saturated m vacancies, by forming an internal surface Si-Si dimer, provides the final state of light-induced metastable degradation of hydrogenated amorphous silicon.     

Donor-hydrogen complexes in crystalline silicon

Summary Experimental results are presented on the study of Sb-H complexes in crystalline silicon, employing¹¹⁹Sb→¹¹⁹Sn source M?ssbauer spectroscopy and a low-energy H implantation technique. In addition to a visible component, we observe a large decrease of the M?ssbauer intensity associated with the trapping of hydrogen, even at low temperatures. This is interpreted as the formation of a component with a negligible recoilless fraction. The different M?ssbauer components were studied as a function of H dose, H-implantation temperature and annealing temperature. The data show that the visible component is associated with the well-known SbH complex, whereas the invisible component is associated with the formation of SbH _n (n≥2) complexes. We show that these complexes are in thermal equilibrium with a larger hydrogen reservoir (H ₂ ^* ), which governs their thermal stability. No Sb-H complexes are observed inp-type Si after H-implantation, in agreement with the current belief that hydrogen has a deep donor level in the gap. The microscopic structure of the various Sb-H and Sn-H complexes was studied with first-principles calculations using the pseudopotentialdensity-functional approach. The structure of the Sb-H complex is found to be similar to the P-H complex, with the H in an antibonding site of a Si atom neighbouring the Sb impurity. For SbH₂ three configurations are found with energies differing by less than ≈ 0.1 eV. We find that the reaction SbH+H≠SbH₂ is exothermic. We argue that the SbH₂ complexes are shallow donors, irrespective of the structure. Therefore, the formation of SbH₂ may depassivate the sample. Paper presented at ICAME-95, Rimini, 10–16 September 1995.