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We report deuteron and proton nuclear magnetic resonance (NMR) measurements on high quality plasma enhanced chemical vapor deposition amorphous silicon films containing from 5 to 15 at.% hydrogen (H and/or D). Our results show that from 2% to 40% of the hydrogen in these samples is not atomically bonded by the Si–H chemical bond. We present conclusive evidence that in highest quality films nearly all of this non-bonded hydrogen is present as isolated hydrogen molecules. These molecules are located in centers of atomic dimensions, perhaps in the analogue of T-sites in crystalline Si. In high quality films these molecules are not the small population of densely packed molecules in the occasional microvoids. The photoelectronic quality of the films (as measured by the ημτ photoresponse product) increases as the fraction of non-bonded hydrogen increases. Our results are consistent with IR spectral measures of hydrogen. Our experiments also suggest that the non-bonded hydrogen is in the vicinity of light induced defects. Finally by comparing successive annealings and other studies it appears that the molecular hydrogen can be identified with the less-clustered proton narrow NMR line.

Amorphous hydrogenated/deuterated silicon nitride (a-SiN:H,D) thin films were studied by deuteron magnetic resonance (DMR). DMR spectra show two quadrupolar broadened Pake-type doublets with splittings of 65.4 kHz for SiD, and 154 kHz for ND bonds; the ratio of these DMR doublet cusp-splittings ( Δ ND Δ SiD = 2.35 ) is, to within experimental error, equal to the ratio of the squares of the respective bond-stretching frequencies (( ω ND ω SiD ) 2 = 2.36 ), as determined by analysis of Fourier transform infrared spectra. The center frequencies of the SiD and ND DMR doublets are not coincident, but rather are shifted by ∼ 2 kHz, indicating that the SiD and ND groups are interacting, and must therefore be near-neighbors in the amorphous network. This explanation consistent with an interpretation of the shifts in bond-stretching frequencies of IR modes that occur when Si(H)D and N(H)D modes are found in the same film.

Proton NMR studies on hydrogen in numerous plasma deposited a-Si:H thin film samples over many years have established that there are primarily two dipolar broadened lines, representing different distinct degrees of proton clustering involving most of the contained hydrogen. In addition, both of these configurations were thought to be hydrogen tightly bonded to silicon. However, deuteron magnetic resonance established long ago that a substantial fraction of the hydrogen (deuterium) population was a weakly bonded species, very different than the silicon bonded hydrogen typically seen in infrared measurements. Deuteron magnetic resonance can easily distinguish bond strength because deuterons have spin, an electric quadrupole moment, and are sensitive to electric field gradients. The much weaker deuteron dipolar coupling results in NMR line shapes and widths that are determined by distributions of electric field gradients and angular averages about the applied magnetic field direction. The primary features of the deuteron line shape are a sharp powder-pattern Pake doublet attributed to the tightly silicon bonded species and a broad central Gaussian component originally interpreted as a weakly bound component, but now recognized as molecular deuterium and HD trapped in the amorphous equivalent of T-sites. This latter result is confirmed by spin-echo double resonance experiments using 1H and 29Si nuclides, which reveal a very appreciable population of molecular hydrogen in T-like sites. NMR line shape subtractions also indicate that the majority of this species resides in the less-clustered hydrogen phase. Also a comparison of the T-site molecular hydrogen fraction with measured photoresponse, combined with light-induced changes in the DMR line shape, indicate that this species is in regions of a-Si:H that control the optoelectronic properties of the material.

New NMR measurements show that interstitial T site-trapped molecular hydrogen can amount to more than one third of the contained hydrogen in high quality PECVD amorphous silicon. Microvoid-contained dense molecular hydrogen is negligible in these good films. Experiments on a sequence of hydrogenated and/or deuterated a-Si films have characterized individually-trapped molecular HD and D2 in films deposited from SiD4, and from SiH4+D2. The T site-trapped molecular hydrogen fraction observed here is larger than previously reported because of recent efforts to measure very slowly relaxing molecular components and the employment of radiofrequency pulse sequences to detect ortho-D2 with nuclear spin I=2. The population of interstitially trapped molecular hydrogen increases with increasing photovoltaic quality over a range of an order of magnitude in photoresponse product ημτ. Above 200 K, hopping transport of molecular hydrogen among the amorphous equivalent of interstitial T sites occurs with an activation energy near 50 meV.

Deuteron magnetic resonance (DMR) has been used to further examine hydrogen (deuteron) populations in amorphous-silicon (a-Si) and in n-type crystalline silicon (x-Si). In both a-Si and x-Si DMR shows central components arising at least in part from isolated molecular deuterium and sharp doublet features from Si-bonded hydrogen (D). Our new results include the observation in x-Si of molecule-specific DMR multiple echoes from trapped ortho-D2. A second new result is the observation in x-Si of a substantialn Si-bonded D population with splittings between 46 and 80 kHz and perhaps arising from (deuterated) hydrogen bond-centered and antibonding configurations.

We report deuteron magnetic resonance (DMR) measurements on aged deuterium-implanted single crystal n-type silicon and comparisons with amorphous silicon spectra. The sample film was prepared six years ago by deuteration from a-D2 plasma and evaluated by a variety of experimental methods. Deuterium has been evolving with time and the present DMR signal shows a smaller deuteron population. A doublet from Si-D configurations along 〈111〉 has decreased more than have central molecular DMR components, which include 47 and 12 kHz FWHM gaussiane. Transient DMR magnetization recoveries indicate spin lattice relaxation to para-D2 relaxation centers.

Proton NMR and deuteron NMR (DMR) have been used to measure hydrogen populations in a series of PECVD a-Si:H,D films. The sharp DMR doublet from Si-D is fitted and subtracted out. The residual spectra then show specific signatures for molecular D2 and HD. The fitting procedures yield quantitative measures of Si-bonded and molecular species. A particular comparison is made between a pair of films prepared as the powered and unpowered electrodes in the same plasma deposition. Both silicon-bonded and molecular populations axe significantly different in the two films and correlate with photoresponse products ημT and with IR as well as other materials characterizations.

Proton and deuteron NMR in hydrogenated amorphous silicon yield quantitative measures of species-specific structural configurations and their dynamics. Populations of silicon-bonded and molecular hydrogens correlate with photovoltaic quality, doping, illumination/dark anneal sequences, and with infrared and other characterizations. High quality films contain substantial populations of nanovoid-trapped molecular hydrogen.

Light-induced rearrangements in a-Si:H,D during and after illumination have been studied by deuteron magnetic resonance (DMR). A film sample was deposited on a 230°C Al substrate by plasma decomposition of S1H4 and D2. The high quality film contained 4 at.% H and 4 at. % D. DMR spectra of fast-relaxing components were examined at 700 msec or less after radio frequency saturation. At 30 K these showed a broad central signal (primarily nanovoid-trapped HD and D2), part of which shifted paramagnetically during illumination. No comparable shifts were shown by spectral components from Si-bonded hydrogen or from microvoid-contained dense fluid hydrogen. The observed post-illumination shifts vanished upon 150°C dark anneal and reflected light-induced metastable magnetic changes in the surroundings of hydrogen trapped in nanovoids.

A systematic study of both proton and deuteron NMR in hydrogenated amorphous silicon films has revealed significant resonance shifts among various resolved components. The shifts include both paramagnetic and diamagnetic displacements of resolved spectral features from trapped molecular hydrogens. The shifts depend on film quality and deposition conditions. Some of the shifts vary as 1/T and reflect Curie susceptibilities characteristic of local regions of differing dangling bond densities. Spectra from relatively immobile hydrogen molecules trapped in nanovoids are shifted diamagnetically and broadened as temperature decreases. Hydrogens tightly bound to Si do not show similar changes and thus are more remote from dangling bonds and other magnetic defects. Similar spectrally-resol ved shifts have been observed in a-Ge and a-SiGe films and are correlated with film photovoltaic quality as measured by mobility-lifetime products.

Nuclear spin relaxation times and resonance line shapes have been measured at 30 MHz for deuterons in a-Ge:H, D plasma-deposited from a 10% GeH 4 /D 2 gas mixture. The molecular D 2 component of the resonance is relatively much larger, in comparison to the lattice-bound D components, than has been observed for similarly prepared a-Si:H, D samples. The increased D 2 /D ratio is interpreted to reflect a larger fractional void volume in a-Ge. The lattice-bound D in a-Ge shows a resolved quadrupolar doublet splitting in good agreement with infra red stretching mode absorptions. The deuteron spin-lattice relaxation shows a component dominated by relaxation via effectively dilute p-D 2 relaxation center molecules located in microvoids. Another deuteron T 1 component, associated with the resolved doublet, shows a distribution of relaxation times over five orders of magnitude and reflects the distribution of bonded D with respect to microvoid locations.

A plasma-deposited sample of a-Si:D,H was incrementally annealed in a series of 30′ heatings at temperatures between 250 and 600°C. Subsequent deuteron magnetic resonance measurements resolve changes in various 2D components. A weakly bound deuterium fraction vanishes after a 350°C anneal. Reduced, but detectable, strongly bound deuterium and molecular deuterium signals persist after progressive anneals to 600°C. The magnetic resonance line shapes of the weakly bound deuterium and the strongly bound deuterium show that they reside in very different local environments. Several characteristics of these environments can be deduced.

Nuclear resonance line shapes and spin relaxation rates have been measured for deuterons and protons in five a-Si samples plasma-deposited from SiH4/D2 and SiD4/Ar gas mixtures. Some samples show spin-lattice relaxation rates which increase exponentially with temperature above 50 K to sharp maxima near 400 K. In all five samples one component of the nuclear spin-lattice relaxation proceeds via dilute molecular D2 and H2 relaxation centers. The corresponding temperature variations of molecular electronic relaxation rates are given by CE★T★2 where C varies systematically with sample preparation conditions.

Progressive annealing of a-Si:D and a-Si:DH samples between 250 and 600°C is found to eliminate the broad central deuteron magnetic resonance (DMR) spectral component associated with weakly bonded D. The well-resolved doublet arising from tightly bound D diminishes in intensity. The narrow central line associated with microvoid-contained molecular D2 and HD increases and then decreases for the warmest anneals. DMR relaxation times, line shapes, and hole-burning spectra reflect changes in sample morphology upon annealing.

Deuteron magnetic resonance (DMR) measurements have been made on plasma-deposited samples of a-Ge: D, H; a-Si:D,F; and a-SiGe:D,F. The experiments were performed at 30.7 MHz with a Bruker CXP 200 spectrometer and a probe constructed to permit operation at high rf power down to temperatures near 4 K. The 50 to 100 mg samples comprise less than 1 mm flakes in Kel-F containers of 5 mm diameter.

Deuteron magnetic resonance line shapes and spin lattice relaxation times are presented for a-Si:D, F and a-SiGe:D, F. These parameters differ from those for typical a-Si:D, H samples, but in some respects are similar to those for an annealed a-Si:D, H sample. The a-SiGe:D, F spectra display an unusually large broad central weakly bound D resonance component and a barely-resolved Ge-D quadrupolar doublet. Comparisons indicate substantial differences in void morphology between the a-Si:D, F and a-SiGe:D, F.