Mid-gap optical absorption and electron spin resonance (ESR) attributed to optically induced localized paramagnetic states have been studied in several chalcogenide glasses amorphous arsenic for $T\ensuremath{\le}80$ K. The observation of these metastable centers provides the most direct evidence yet obtained existence gap semiconductors. Irradiation with light whose energy corresponds Urbach tail edge ($\ensuremath{\alpha}\ensuremath{\simeq}100$ ${\mathrm{cm}}^{\ensuremath{-}1}$) excites...

Optically induced ESR and absorption due to localized paramagnetic states in the forbidden gap have been observed several semiconducting chalcogenide glasses below \ensuremath{\sim}15 K. Analysis of spectra indicates that these centers are holes on chalcogens not directly associated with impurities.

A new extended x-ray-absorption fine structure spectroscopy study of local bonding identifies for the first time significant concentrations Ge-Ge bonds in amorphous Ge2Sb2Te5. The provides a understanding molecular this phase-change material. Application bond constraint theory indicates that phase is an ideal network which average number constraints per atom equals dimensionality. Analysis within framework imparts and insights concerning nature reversible optically driven...

Microwave and far-infrared absorption have been studied in several chalcogenide oxide glasses (${\mathrm{As}}_{2}$${\mathrm{Se}}_{3}$, ${\mathrm{Tl}}_{2}$Se${\mathrm{As}}_{2}$${\mathrm{Te}}_{3}$, 3Si${\mathrm{O}}_{2}$ \ifmmode\cdot\else\textperiodcentered\fi{} ${\mathrm{Na}}_{2}$O) at frequencies between 0.1 100 ${\mathrm{cm}}^{\ensuremath{-}1}$ 300 K 0.8 10 K. In addition, previously published data for Si${\mathrm{O}}_{2}$ other amorphous materials are analyzed. The results exhibit...

Five glasses and four polycrystalline compounds of the lithium borate system have been subjected to γ irradiation at 77°K subsequently examined by ESR techniques 9.1 35 GHz while maintaining this low temperature. The familiar “five-line-plus-a-shoulder” spectrum is observed X band for both Li2O·4B2O3 compound containing ≲25 mole % Li2O. However, previously unreported structure noted on low-field shoulder compound. This new structure, like “five-line” part, due a hyperfine interaction with...

The pure ${\mathrm{As}}^{75}$ nuclear quadrupole resonances (NQR) of crystalline and amorphous ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ have been investigated compared. temperature dependence the resonance frequencies, asymmetry parameters $\ensuremath{\eta}$, orientation principal axes electric field grandient with respect to crystal obtained for (orpiment). We obtain ${\ensuremath{\eta}}_{\mathrm{I}}=0.343$ ${\ensuremath{\eta}}_{\mathrm{II}}=0.374$, where I II refer two inequivalent As sites...

We report the first observation of absence photodarkening (PD) effect in bulk chalcogenide glasses. In prototype systems ${\mathrm{Cu}}_{\mathrm{x}}$(${\mathrm{As}}_{0.4}$${\mathrm{S}}_{0.6}$${)}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ and ${\mathrm{Cu}}_{\mathrm{x}}$(${\mathrm{As}}_{0.4}$${\mathrm{Se}}_{0.6}$${)}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ PD is essentially destroyed for x\ensuremath{\ge}0.01 0.05 S Se systems, respectively. A structural model Cu-As-Se Cu-As-S proposed, which based...

In previous work we have identified a near-gap photoluminescence in Ga0.52In0.48P which exhibits strong dependence of emission energy on excitation intensity (‘‘moving emission’’) and correlated its presence strength to conditions growth. this extend our investigations the rise decay lifetimes associated with moving nonmoving components emission. The two processes proceed simultaneously at same energy. For emission, time constants scale approximately linearly intensity. Decaying luminescence...

Recently Conradi and Norberg have proposed that a small density of molecular hydrogen in $a$-Si: H films provides the relaxation mechanism which is responsible for minimum proton spin-lattice time ${T}_{1}$ at about 30 K. Although we are unable to observe an NMR line attributable ${\mathrm{H}}_{2}$, able conversion ${\mathrm{H}}_{2}$ molecules from ortho state para 4.2 The process bimolecular with rate constant 0.010 ${\mathrm{h}}^{\ensuremath{-}1}$. existence large number sites trap such...

The excitation intensity dependence of the photoluminescence (PL) from Ga0.52In0.48P grown by organometallic vapor phase epitaxy on GaAs substrates has been investigated as a function epitaxial layer growth temperature and substrate orientation. It is well known that degree ordering band-gap energy this material are functions conditions. We report here PL emission which shifts rapidly with intensity. rate shift also conditions including There is, however, no significant correlation between...

In addition to the previously reported paramagnetic hole center localized on chalcogen, a conjugate optically induced electron an As atom is observed in glassy ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ and ${\mathrm{As}}_{2}$${\mathrm{Se}}_{3}$. The chalcogen further identified as nonbonding $p$ orbital. These centers are unique amorphous phase, their density saturates at or below ${10}^{17}$ spins/${\mathrm{cm}}^{3}$.

NMR spin-lattice relaxation rates ${{T}_{1}}^{\ensuremath{-}1}$ of $^{1}\mathrm{H}$ in $a$-Si:H films exhibit a maximum near 40 K. Both the magnitude, temperature, and frequency dependences ${T}_{1}$ are well described by model which assumes coupling to disorder modes associated with some hydrogen atoms. Results suggest that sites may contribute electronic states within gap.

A systematic study of tin-catalyzed vapor−liquid−solid (VLS) growth silicon nanowires by plasma-enhanced chemical vapor deposition at temperatures ranging from 300 to 400 °C is presented. Wire structure, morphology, and rate are characterized as a function process variables. The observed have crystalline core with polycrystalline shell due simultaneous VLS axial vapor−solid radial growth. Axial rates controllable through hydrogen dilution the plasma which affects concentration silane...

Phase selective synthesis of type II silicon clathrates from thermal decomposition NaSi has previously been limited to small quantities due the simultaneous formation competing phases. In this work we show that local sodium vapor pressure during precursor is a critical parameter for controlling phase selection. We demonstrate techniques allow us tune Na pressure, yielding I or clathrate products are ≥90 wt.% pure. The "cold plate" reactor design discussed in maintains low NaSi, thus large...

While numerous crystalline Si allotropes have been predicted in recent years and, several instances, synthesized under high pressure, the exploration of phases with a lower density than conventional diamond (d-Si) is still its infancy. Theoretical calculations on electronic properties these expanded forms suggest that, unlike most stable d-Si structure, many may possess direct or quasi-direct bandgaps and only exhibit slightly higher formation energies d-Si. The few that already display...

Ordering in the CuPt structure is known to significantly reduce band gap of Ga0.52In0.48P as well induce a number unusual details its optical properties, including long, excitation-intensity-dependent lifetimes and an emission energy. We report photoluminescence (PL), excitation (PLE), resonant Raman measurements performed on ordered disordered Ga0.52In0.48P. The dominant high energy process at low temperature established be excitonic, but exciton trapping not unique. PLE from shows...

Amorphous films of GeTe, Sb2Te3, and Ge2Sb2Te5 were grown to thicknesses 0.3–3μm using rf sputtering. The optical properties these are influenced by the presence oxygen impurities. absorption edge in glasses is sometimes broader than “standard” chalcogenide glasses, such as GeSe2 or As2Se3. This result implies either that valance band consists highly strained bonds large densities defects exist. In some samples, there exists an electron paramagnetic resonance signal absence any excitation,...

Several paramagnetic centers have been observed in doped and undoped $a$-Si:H after x irradiation at 77 K. The responses nominally include (1) an increase the Si "dangling-bond" line, (2) trapped N${\mathrm{O}}_{2}$ molecules. In O- N-doped hydrogenated $a$-Si [$a$-Si:(H,O,N)] least four are observed: oxygen-associated hole center which is probably a singly coordinated oxygen bonded either to silicon or another oxygen, (3) $s{p}^{3}$-hybridized dangling bond on three oxygens...

Numerous glasses were prepared from mixtures of alkali halides and boron oxide subjected to 60Co γ rays at room temperature; these examined by ESR techniques 9.1 35 GHz. The induced spectra can be divided into two categories: (1) a resonance due boron–oxygen centers previously studied in borate glasses, (2) certain new resonances which are shown V-type (halogen2− molecule ions). Cl2− species is stable its spin-Hamiltonian parameters determined means computer simulation the spectrum are: g‖ =...

The kinetics of a metastable, optically induced increase in the ESR a-Si:H have been examined between 77 and \ensuremath{\sim}500 K. Isothermal annealing (decay) inducing (growth) curves indicate that decay is bimolecular thermally activated with an activation energy \ensuremath{\sim}1 eV, growth relatively temperature independent. These are more easily explained through optical rearrangement charge existing dimagnetic (negative-U) defects less terms creation additional, paramagnetic...

Thallium in $a$-${\mathrm{As}}_{2}$${\mathrm{Se}}_{3}$ reduces transient hole transport but has no effect upon the photoluminescence and photoinduced ESR. The results are discussed terms of recent models charged defects chalcogenides.