Reversible H2 passivation of Si ≡ Si3 interface defects in (1 1 1)Si/SiO2

K-band electron spin resonance (ESR) at 4.3 K has revealed the dipole-dipole (DD) interaction effects between [1 1 1]P_b centers (^*Si ≡ Si₃ defects with unpaired sp³ hybrid [1 1 1]) at the 2 dimensional (1 1 1)Si/SiO₂ interface. This has been enabled by the perfectly reversible H₂ passivation of P_b, which affects the defect's spin state. Sequential hydrogenation at 253–353°C and degassing treatments in high vacuum at 743–835°C allowed to vary the P_b density in the range 5 × 10¹⁰ < [P_b] (1.14 ± 0.06) × 10¹³ cm^-2. With increasing [P_b] fine structure doublets are clearly resolved. It is found that (1 1 1)Si/SiO₂ interfaces, dry thermally grown at ≈920°C, naturally comprise a ^*Si ≡ Si₃ defect density — passivated or not — of 1.14 × 10¹³ cm^-2.     

The effects of hydrogen dose and thermal treatment on the formation of microsplits in hydrogen implanted GaAs

Transmission electron microscopy has been used to study the effect of thermal treatment on the formation of microsplits and damage rafts in hydrogen implanted (1 × 10¹⁶ and 5 × 10¹⁶ H⁺ cm^-2) and annealed (700 and 800°C) GaAs. The results show that microsplit and damage raft formation in implanted samples may be prevented if the samples are first given a pre-anneal heat treatment for 15 minute intervals at 300, 350, 400 and 450°C, during which the hydrogen concentration is reduced without allowing vacancy coalescence to take place.     

EXAFS analysis of Er sites in Er–O and Er–F co-doped crystalline Si

We present extended X-ray absorption fine structure (EXAFS) and photoluminescence (PL) analyses of Er–O and Er–F co-doped Si. Samples were prepared by multiple implants at 77 K of Er and co-dopant (O or F) ions resulting in the formation of a2 μm thick amorphous layer uniformly doped with 1×10¹⁹ Er/cm³ and 3×10¹⁹ O/cm³, 1×10²⁰ O/cm³ or 1×10²⁰ F/cm³. EXAFS measurements show that the local environment of the Er sites in the amorphous layers consists of 6 Si first neighbors. After epitaxial regrowth at 620°C for 3 h, Er is fully coordinated with 8 F ions in the Er–F samples, while Si and O ions are concomitantly present in the first shell of O co-doped samples. Post regrowth thermal treatments at 900°C leave the coordination unchanged in the Er+F, while the Er+O (ratio 1 : 10) doped samples present Er sites with a fully O coordinated shell with an average of 5 O atoms and 4 O atoms after 30 s and 12 h, respectively. We have also found that the fine structure and intensity of the high-resolution PL spectra are strongly dependent on the Er-impurity ratio and on thermal process parameters in the Er–O co-doped samples, while this is not observed for the F-doped samples. The most intense PL response at 15 K was obtained for the 1 : 3 E : O ratio, suggesting that an incomplete O shell around Er is particularly suitable for optical excitation.     

Incorporation of hydrogen in CdTe and HgTe epitaxial layers grown by MOCVD

The incorporation of hydrogen into MOCVD-grown layers of CdTe, HgTe and CdHgTe using H₂ as the vector gas has been studied. Concentrations of incorporated H going from 6.5 × 10¹⁷ cm^-3 to 5 × 10¹⁸ cm^-3 have been found by SIMS in CdTe layers. This concentration decreases with increasing growth temperature and decreasing bond strength of the host material.     

A new method to determine Si/SiO2 interface recombination parameters using a gate-controlled point-junction diode under illumination

A new method is presented to determine Si/SiO₂ interface recombination parameters. The device employed is constituted by a polysilicon-oxide-semiconductor capacitor with a microscale central junction (a gate-controlled point-junction diode). The excess minority carriers are photo-generated rather than being injected, which results in a one-dimensional current flow normal to the Si/SiO₂interface. The minority carrier quasi-Fermi level is probed at the Si/SiO₂ interface by means of the point junction. The one-dimensionality of the current flow and the exact knowledge of the minority carrier quasi-Fermi level permit an accurate measurement of the recombination rate. The method has been applied to characterize p-type 100 Si/SiO₂ interfaces with boron dopant concentrations ranging from 2.2×10¹⁵ to 2.0×10¹⁷ cm^-3. Data analysis has been performed using a numerical scheme to find a quasi-exact solution for the current recombining at the interface. It was found that the interface recombination parameters (trap density and capture cross-sections) depend only weakly on trap energy in a wide range around midgap. The cross-section for capturing electrons (σ_n) was found to greatly exceed (by a factor of 10² to 10³) the cross-section for capturing holes (σ_p).     

Interface states and impurities in MOS structures with very thin tunneling barriers

Electron tunneling spectroscopy was used to investigate MOS junctions with very thin silicon oxide or silicon oxynitride layers (2–5 nm) as tunneling barriers. For the tunneling measurements at 4.2 K highly degenerate P-doped (3×10²⁰ cm^-3) Si substrates, oxidized in dry oxygen at 600°C were used. Silicon oxynitride layers were prepared by plasma nitridation in an NH₃ discharge. As gate electrodes evaporated films of Al, Au or Pb were utilized. Changes in the tunneling conductivity were attributed to changes in the density of interface states, caused by hydrogen annealing or by high field stress. The results indicate a correlation between the generation of interface states and the removal of Si-H configurations. Vibrational modes of phonons, dopants and impurities were detected by inelastic electron tunneling spectroscopy.     

Structure and properties of molybdenum implanted with high-flux carbon ion

High purity molybdenum was implanted by C ion in a metal vapour vacuum arc (MEVVA) implanter. The influence of implantation parameters was studied by varying ion fluence and ion current density. The samples were implanted by 45 keV C ion with fluences from 1×10¹⁵ to 1×10¹⁸ ions/cm², respectively. The as-implanted samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and nanoindenter. Different morphologies were observed on the surfaces of the as-implanted samples due to irradiation damage, and clearly related to implantation parameters. XRD spectra confirm formation of β-Mo₂C with ion fluences equal to or larger than 1×10¹⁶ ions/cm², and formation of -Mo₂C with ion fluence of 1×10¹⁸ ions/cm². The maximum nanohardness and maximum modulus of the as-implanted samples increased gradually with increasing ion fluence, and reached the corresponding maximum values with ion fluence of 1×10¹⁸ ions/cm². The experimental results suggest that the structure and properties of the as-implanted Mo samples exhibited strong dependence on implantation parameters.     

Time-dependent response of interface states determined by using differential isothermal transient spectroscopy

A method based on the differential analysis of the isothermal transients is proposed to study the dynamical properties of the charging and discharging of interface states, and several possibilities of using this method are shown. The results obtained in SiO₂/Si and Si₃N₄/SiO₂/Si samples are in agreement with the existence of a spatial and energy distribution of interface states within the insulator. From the experimental data, the concentration of traps within the insulator at 35 Å is estimated to be 5×10⁹ cm^-2 eV^-1, with a tunneling cross section 10^-19 cm², at E_c-E ≈ 0.2 eV.     

Effect of boron ion implantation on the structural, optical and electrical properties of ZnSe thin films

Zinc Selenide (ZnSe) thin films were deposited onto well cleaned glass substrates using vacuum evaporation technique under a vacuum of 3×10⁻⁵ mbar. The prepared ZnSe samples were implanted with mass analyzed 75 keV B⁺ ions at different doses ranging from 10¹² to 10¹⁶ ions cm⁻². The composition, thickness, microstructures, surface roughness and optical band gap of the as-deposited and boron-implanted films were studied by Rutherford backscattering (RBS), grazing incidence X-ray diffraction, Atomic force microscopy, Raman scattering and transmittance measurements. The RBS analysis indicates that the composition of the as-deposited and boron-implanted films is nearly stoichiometric. The thickness of the as-deposited film is calculated as 230 nm. The structure of the as-deposited and boron-implanted thin films is cubic. It is found that the surface roughness increases on increasing the dose of boron ions. In the optical studies, the optical band gap value decreases with an increase of boron concentration. In the electrical studies, the prepared device gave a very good response in the blue wavelength region.     

Defect versus nanocrystal luminescence emitted from room temperature and hot-implanted SiO2 layers

Silicon nanocrystals have been synthesized in SiO₂ matrix using Si ion implantation. Si ions were implanted into 300-nm-thick SiO₂ films grown on crystalline Si at energies of 30–55 keV, and with doses of 5×10¹⁵, 3×10¹⁶, and 1×10¹⁷ cm⁻². Implanted samples were subsequently annealed in an N₂ ambient at 500–1100°C during various periods. Photoluminescence spectra for the sample implanted with 1×10¹⁷ cm⁻² at 55 keV show that red luminescence (750 nm) related to Si-nanocrystals clearly increases with annealing temperature and time in intensity, and that weak orange luminescence (600 nm) is observed after annealing at low temperatures of 500°C and 800°C. The luminescence around 600 nm becomes very intense when a thin SiO₂ sample is implanted at a substrate temperature of 400°C with an energy of 30 keV and a low dose of 5×10¹⁵ cm⁻². It vanishes after annealing at 800°C for 30 min. We conclude that this luminescence observed around 600 nm is caused by some radiative defects formed in Si-implanted SiO₂.     

Structure and luminescence of a-plane GaN on r-plane sapphire substrate modified by Si implantation

We show the structural and optical properties of non-polar a-plane GaN epitaxial films modified by Si ion implantation. Upon gradually raising Si fluences from 5×10¹³ cm^-2 to 5×10¹⁵ cm^-2, the n-type dopant concentration gradually increases from 4.6×10¹⁸ cm^-2 to 4.5×10²⁰ cm^-2, while the generated vacancy density accordingly raises from 3.7×10¹³ cm^-2 to 3.8×10¹⁵ cm^-2. Moreover, despite that the implantation enhances structural disorder, the epitaxial structure of the implanted region is still well preserved which is confirmed by Rutherford backscattering channeling spectrometry measurements. The monotonical uniaxial lattice expansion along the a direction (out-of-plane direction) is observed as a function of fluences till 1×10¹⁵ cm^-2, which ceases at the overdose of 5×10¹⁵ cm^-2 due to the partial amorphization in the surface region. Upon raising irradiation dose, a yellow emission in the as-grown sample is gradually quenched, probably due to the irradiation-induced generation of non-radiative recombination centers.     

Ohmic and Schottky contacts of hydrogenated and oxygenated boron-doped single-crystal diamond with hill-like polycrystalline grains

Hill-like polycrystalline diamond grains(HPDGs) randomly emerged on a heavy boron-doped p~+ single-crystal diamond(SCD) film by prolonging the growth duration of the chemical vapor deposition process.The Raman spectral results confirm that a relatively higher boron concentration(～1.1 × 10~(21) cm~(-3)) is detected on the HPDG with respect to the SCD region(～5.4 × 10~(20) cm~(-3)).It demonstrates that the Au/SCD interface can be modulated from ohmic to Schottky contact by varying the surface from hydrogen to oxygen termination.The current-voltage curve between two HPDGs is nearly linear with either oxygen or hydrogen termination,which means that the HPDGs provide a leakage path to form an ohmic contact.There are obvious rectification characteristics between oxygen-terminated HPDGs and SCD based on the difference in boron doping levels in those regions.The results reveal that the highly boron-doped HPDGs grown in SCD can be adopted as ohmic electrodes for Hall measurement and electronic devices.     

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.     

Erbium in silicon–germanium quantum wells

Strained Si_1−xGe_x/Si quantum wells have been doped with erbium by implantation. A comparison is made with strained Si_1−xGe_x/Si quantum wells and relaxed Si_1−xGe_x, with x between 10% and 25%, doped with erbium during MBE growth. The erbium concentration was between 1×10¹⁸ and 5×10¹⁸ cm⁻³ throughout the active regions. Transmission electron microscopy, X-ray diffraction, and photoluminescence studies indicate that good regrowth can been achieved after full amorphisation by implantation of the strained quantum wells. The erbium luminescence is more intense in the Si_1−xGe_x/Si layers, but erbium-implanted samples containing Si_1−xGe_x exhibit defect luminescence in the region of 0.9–1.0 eV. These defects are also present when Si_1−xGe_x/Si quantum wells are implanted with an amorphising dose of silicon, and then regrown. They are attributed to small germanium-rich platelets, rather than to erbium-related defects. Electroluminescence is presented from a forward biased erbium-implanted Si_0.87Ge_0.13/Si structure at a drive current density of only 1.8 mA/cm².     

A two-component model for the electron distribution function in ahigh-current pseudospark or back-lighted thyratron

Temperature, energy, and densities of two electron distribution function components, including an isotropic bulk part and an anisotropic beam, are analyzed for a hydrogen pseudospark and/or back-lighted thyratron switch plasma with a peak electron density of 1-3×10¹⁵ cm^-3 and peak current density of ≈10⁴ A/cm². Estimates of a very small cathode-fall width during the conduction phase and high electric field strengths lead to the injection of an electron beam with energies ⩾100 eV and density of 10¹³-10¹⁴ cm^-3 into a Maxwellian bulk plasma. Collisional and radiative processes of monoenergetic beam electrons, bulk plasma electrons and ions, and atomic hydrogen are modeled by a set of rate equations, and line intensity ratios are compared with measurements. Under these high-current conditions, for an initial density n_H2=10¹⁶ cm^-3 and electron temperature of 0.8-1 eV, the estimated beam density is ≈10¹³ -10¹⁴ cm^-3. These results suggest the possibility of producing in a simple way a very high-density electron beam     

Hydrogen diffusion in crystalline semiconductors

The diffusion of hydrogen in semiconductors is complicated by the existence of several charge states (notably H⁺ in p-type material and H^- or H⁰ in n-type material, at least for Si) and also that hydrogen is present in a number of different forms, namely atomic, molecular or bound to a defect or impurity. Since the probability of formation of these different states is dependent on the defect or impurity type and concentration in the material and on the hydrogen concentration itself, then the apparent hydrogen diffusivity is a function of the sample conductivity and type and of the method of hydrogen insertion. Under conditions of low H⁺ concentration in p-type Si, for example, the diffusivity is of the order of 10^-10 cm² · s^-1 at 300 K and is consistent with the value expected from an extrapolation of the Van Wieringen and Warmoltz expression D_H = 9.4 × 10^-3 exp[-0.48 eV/kT] cm² · s^-1. The characteristics of hydrogen diffusion in n- and p-type Si and GaAs are reviewed in this paper, and the retardation of hydrogen permeation by molecular formation and impurity trapping is discussed. The measurement of several key parameters, including the energy levels for the hydrogen donor and acceptor in Si and the diffusivity of the H⁰ and H^- species, would allow a more quantitative treatment of hydrogen diffusion in semiconductors.     

Field emission from quantum size GaN structures

Whisker structures and quantum dots fabricated by photoelectrochemical (PEC) etching of undoped and doped metalorganic chemical vapor deposition (MOCVD)-grown GaN (2×10¹⁷ or 3×10¹⁸ cm⁻³) are investigated in relation with their field-emission characteristics. Different surface morphologies, corresponding to different etching time and photocurrent, results in different field-emission characteristics with low turn-on voltage down to 4 V/μm and the appearance of quantum-size effect in the I–V curves.     

Hydrogen depth profile measurement in a-Si1-xCx:H films by elastic recoil detection

The hydrogen content and depth profile in a-Si_1-xC_x:H films were measured by the elastic recoil detection (ERD) technique. It is shown that the hydrogen content changes from 15 to 50 at% with increasing carbon content x. For x<0.4 the hydrogen content increases mainly due to the increase of the Si-CH₃ contribution and for x > 0.4 due to C-H bonds. By combining the ERD and IR results, the proportionality between the number of Si-CH₃ bonds and the intensity of IR absorption due to the Si-CH₃ rocking mode vibration is ascertained. The proportionality constant is found to be A^roc_Si-CH3 = 5 × 10¹⁹ cm^-2.     

INFLUENCE OF C+-IMPLANTATION DOSE ON BLUE EMISSION AND MICROSTRUCTURES OF Si-BASED POROUS β-SIC

Crystal Si were implanted with different doses of C⁺ from 10¹¹ to 10¹⁷ cm^-2 at an energy of 50 keV. β-SiC precipitates were formed by thermal annealing at 1050 ℃ for 1 h and porous structures were prepared by electrochemical anodization. Under the excitation of ultraviolet, the samples, with C⁺ dose ≥10¹⁵ cm^-2 have intense blue emission which is stronger than the photoluminescence (PL) intensity of reference porous silicon (PS), and increases as C⁺ dose increases; the samples with C⁺ dose ≤10¹⁴ cm^-2 show similar PL spectra to those of PS. The blue peak intensity in PL spectra is correlated with the TO phonon absorption strength of β-SiC in infrared absorption spectra. The transmission electron microscopy study shows that the blue peak is also correlated with the microstructures. Because porous β-SiC is nanometer in size, it is suggested that the quantum confinement effect be responsible for the blue light emission.     

The influence of oxygen on the lattice sites of rare earths in silicon

We have used conversion electron emission channeling to investigate the lattice sites of ^167mEr following implantation of the radioactive isotope ¹⁶⁷Tm into CZ Si and FZ Si at varying doses (6×10¹² – 5×10¹³ cm⁻²). In all cases isothermal annealing at 900°C caused Er to leave its preferred near-tetrahedral sites in favour of random lattice sites, but this process occurred by orders of magnitude faster in CZ Si. Furthermore, in CZ Si the incorporation of Er on random lattice sites was fastest in samples implanted with low doses of Tm+Er. We compare our experimental results to a simple numerical model which accounts for the diffusion of Er and O and the formation of Er_nO_m complexes. On the basis of this model, our experimental data indicate that only a few (probably between 1 and 2) O atoms are required in order to remove an Er atom from its tetrahedral site.