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Abstract We present results derived from continuous and localized 35 keV55Mn+ion implantations into ZnO. Localized implantations were carried out by using self-ordered alumina membranes as masks leading to ordered arrays of implanted volumes on the substrate surfaces. Defects and vacancies in the small implantation volumes of ZnO were generated due to the implantation processes besides the creation of new phases. Rapid thermal annealing was applied in the case of continuous implantation. The samples were characterized by HRSEM, GIXRD, Raman spectroscopy and RBS/C. Magnetic characterization of the samples pointed out appreciable differences among the samples obtained by the different implantation methods. This fact was mainly attributed to the different volume/surface ratios present in the implanted zones as well as to the increase of Mn atom concentrations along the grain frontiers in the nanostructured surfaces. The samples also showed a ferromagnetic transition phase at temperature value higher than room temperature.

In the scope of supersaturated semiconductors for infrared detectors, we implanted Si samples with Ti at high doses and processed them by rapid thermal annealing (RTA) to recover the crystal quality. Also, for comparative purposes, some samples were processed by pulsed-laser melting. We measured the electronic transport properties at variable temperatures and analyzed the results. The results indicate that, for RTA samples, surface layers with a high Ti concentration have negligible conductivity due to defects. In contrast, the implantation tail region has measurable conductivity due to very high electron mobility. This region shows the activation of a very shallow donor and a deep donor level. While deep levels have been previously reported for Ti in Si, such a shallow level has never been measured, and we suggest that it originates from Ti-Si complexes. Finally, a decoupling effect between the implanted layer and the substrate seems to be present, and a bilayer model is applied to fit the measured properties. The fitted parameters follow the Meyer–Neldel rule. The role of the implantation tails in Si supersaturated with Ti is revealed in this work. [ABSTRACT FROM AUTHOR]

The energy levels created in supersaturated n-type silicon substrates with titanium implantation in the attempt to create an intermediate band in their band-gap are studied in detail. Two titanium ion implantation doses (1013cm-2 and 1014cm-2) are studied in this work by conductance transient technique and admittance spectroscopy. Conductance transients have been measured at temperatures of around 100 K. The particular shape of these transients is due to the formation of energy barriers in the conduction band, as a consequence of the band-gap narrowing induced by the high titanium concentration. Moreover, stationary admittance spectroscopy results suggest the existence of different energy level configuration, depending on the local titanium concentration. A continuum energy level band is formed when titanium concentration is over the Mott limit. On the other hand, when titanium concentration is lower than the Mott limit, but much higher than the donor impurity density, a quasi-continuum energy level distribution appears. Finally, a single deep center appears for low titanium concentration. At the n-type substrate, the experimental results obtained by means of thermal admittance spectroscopy at high reverse bias reveal the presence of single levels located at around Ec-425 and Ec-275 meV for implantation doses of 1013cm-2 and 1014cm-2, respectively. At low reverse bias voltage, quasi-continuously distributed energy levels between the minimum of the conduction bands, Ec and Ec-450 meV, are obtained for both doses. Conductance transients detected at low temperatures reveal that the high impurity concentration induces a band gap narrowing which leads to the formation of a barrier in the conduction band. Besides, the relationship between the activation energy and the capture cross section values of all the energy levels fits very well to the Meyer-Neldel rule. As it is known, the Meyer-Neldel rule typically appears in processes involving multiple excitations, like carrier capture and emission in deep levels, and it is generally observed in disordered systems. The obtained Meyer-Neldel energy value, 15.19 meV, is very close to the value obtained in multicrystalline silicon samples contaminated with iron (13.65 meV), meaning that this energy value could be associated to the phonons energy in this kind of substrates. [ABSTRACT FROM AUTHOR]

In this study, we present a structural and optoelectronic characterization of high dose Ti implanted Si subsequently pulsed-laser melted (Ti supersaturated Si). Time-of-flight secondary ion mass spectrometry analysis reveals that the theoretical Mott limit has been surpassed after the laser process and transmission electron microscopy images show a good lattice reconstruction. Optical characterization shows strong sub-band gap absorption related to the high Ti concentration. Photoconductivity measurements show that Ti supersaturated Si presents spectral response orders of magnitude higher than unimplanted Si at energies below the band gap. We conclude that the observed below band gap photoconductivity cannot be attributed to structural defects produced by the fabrication processes and suggest that both absorption coefficient of the new material and lifetime of photoexcited carriers have been enhanced due to the presence of a high Ti concentration. This remarkable result proves that Ti supersaturated Si is a promising material for both infrared detectors and high efficiency photovoltaic devices. [ABSTRACT FROM AUTHOR]

A detailed study on the resulting impurity profile in Si samples implanted with high doses of Ti and subsequently annealed by pulsed-laser melting (PLM) is reported. Two different effects are shown to rule the impurity profile redistribution during the annealing. During the melting stage, the thickness of the implanted layer increases while the maximum peak concentration decreases (box-shaped effect). On the contrary, during the solidifying stage, the thickness of the layer decreases and the maximum peak concentration increases (snow-plow effect). Both effects are more pronounced as the energy density of the annealing increases. Moreover, as a direct consequence of the snow-plow effect, part of the impurities is expelled from the sample through the surface. [ABSTRACT FROM AUTHOR]

We have analyzed the structural and optical properties of Si implanted with very high Ti doses and subsequently pulsed-laser melted (PLM). After PLM, all samples exhibit an abrupt and roughly uniform, box-shaped Ti profile, with a concentration around 2 × 1020 cm-3, which is well above the Mott limit, within a 150 nm thick layer. Samples PLM-annealed at the highest energy density (1.8 J/cm2) exhibit good lattice reconstruction. Independent of the annealing energy density, in all of the samples we observe strong sub-bandgap absorption, with absorption coefficient values between 4 × 103 and 104 cm-1. These results are explained in terms of the formation of an intermediate band (IB) originated from the Ti deep levels. [ABSTRACT FROM AUTHOR]

Si samples have been implanted with very high Ti doses (over the theoretical Mott limit) to obtain an intermediate band (IB) in the host semiconductor. The electronic transport properties of this material have been analyzed by temperature-dependent sheet resistance and Hall effect measurements in the 7-400 K range. The experimental results are successfully explained by means of an analytical two-layer model, in which the implanted layer and the substrate behave as an IB/n-Si type junction. We deduce that the IB is located at 0.38 eV below the conduction band, which is around one third of the Si bandgap, i.e., theoretically close to the optimum location for an IB. Finally, we obtain that carriers at the IB behave as holes with a mobility of 0.4-0.6 cm2 V-1 s-1. This extremely low mobility is the one expected for a semifilled, metallic band, being this metallic condition of the IB a requirement for IB solar cells. [ABSTRACT FROM AUTHOR]

The influence of the silicon nitride blocking layer thickness on the interface state densities (Dit) of HfO2/SiNx:H gate-stacks on n-type silicon have been analyzed. The blocking layer consisted of 3 to 7 nm thick silicon nitride films directly grown on the silicon substrates by electron-cyclotron-resonance assisted chemical-vapor-deposition. Afterwards, 12 nm thick hafnium oxide films were deposited by high-pressure reactive sputtering. Interface state densities were determined by deep-level transient spectroscopy (DLTS) and by the high and low frequency capacitance-voltage (HLCV) method. The HLCV measurements provide interface trap densities in the range of 1011 cm-2 eV-1 for all the samples. However, a significant increase in about two orders of magnitude was obtained by DLTS for the thinnest silicon nitride barrier layers. In this work we probe that this increase is an artifact due to the effect of traps located at the internal interface existing between the HfO2 and SiNx:H films. Because charge trapping and discharging are tunneling assisted, these traps are more easily charged or discharged as lower the distance from this interface to the substrate, that is, as thinner the SiNx:H blocking layer. The trapping/detrapping mechanisms increase the amplitude of the capacitance transient and, in consequence, the DLTS signal that have contributions not only from the insulator/substrate interface states but also from the HfO2/SiNx:H interlayer traps. [ABSTRACT FROM AUTHOR]

In this paper, we present a detailed characterization of high quality layers of Si implanted with Ti at high doses. These layers are intended to the formation of an intermediate band (IB) solar cell. The main requirement to obtain an IB material is to reach an impurity concentration beyond the Mott limit, which is, in this case, much higher than the solid solubility limit. To overcome this limit we used the combination of ion implantation and pulsed-laser melting as nonequilibrium techniques. Time-of-flight secondary ion mass spectrometry measurements confirm that Ti concentration exceeds the theoretical Mott limit in the implanted layer, and glancing incidence x-ray diffraction and transmission electron microscopy measurements prove that good crystallinity can be achieved. Sheet resistance and Hall effect mobility show uncommon characteristics that can only been explained assuming the IB existence. [ABSTRACT FROM AUTHOR]

We have studied the laser thermal annealing (LTA) effects on single crystal GaP. The samples have been analyzed by means of Raman spectroscopy, glancing incidence x-ray diffraction (GIRXD), and transmission electron microscopy (TEM) measurements. After LTA process, the Raman spectra of samples annealed with the highest energy density show a forbidden TO vibrational mode of GaP. This result suggests the formation of crystalline domains with a different orientation in the annealed region regarding the GaP unannealed wafer. This behavior has been corroborated by GIXRD measurements. TEM images show that the LTA produces a defective layer with disoriented crystalline domains in the surface. The depth of this defective layer increases with the energy density of LTA. The lack of crystallinity after LTA processes could be related with the high bond energy value of GaP. [ABSTRACT FROM AUTHOR]

Al/HfO2/SiNx:H/n-Si metal-insulator-semiconductor capacitors have been studied by electrical characterization. Films of silicon nitride were directly grown on n-type silicon substrates by electron cyclotron resonance assisted chemical vapor deposition. Silicon nitride thickness was varied from 3 to 6.6 nm. Afterwards, 12 nm thick hafnium oxide films were deposited by the high-pressure sputtering approach. Interface quality was determined by using current-voltage, capacitance-voltage, deep-level transient spectroscopy (DLTS), conductance transients, and flatband voltage transient techniques. Leakage currents followed the Poole–Frenkel emission model in all cases. According to the simultaneous measurement of the high and low frequency capacitance voltage curves, the interface trap density obtained for all the samples is in the 1011 cm-2 eV-1 range. However, a significant increase in this density of about two orders of magnitude was obtained by DLTS for the thinnest silicon nitride interfacial layers. In this work we probe that this increase is an artifact that must be attributed to traps existing at the HfO2/SiNx:H intralayer interface. These traps are more easily charged or discharged as this interface comes near to the substrate, that is, as thinner the SiNx:H interface layer is. The trapping/detrapping mechanism increases the capacitance transient and, in consequence, the DLTS measurements have contributions not only from the insulator/substrate interface but also from the HfO2/SiNx:H intralayer interface. [ABSTRACT FROM AUTHOR]

Hafnium oxide films were deposited by high pressure reactive sputtering using different deposition pressures and times. The composition, morphology, and optical properties of the films, together with the sputtering process growth kinetics were investigated using heavy ion elastic recoil detection analysis, Fourier transform infrared spectroscopy, ultraviolet-visible-near infrared spectroscopy, x-ray diffraction, and transmission electron microscopy. The films showed a monoclinic polycrystalline structure, with a grain size depending on the deposition pressure. All films were slightly oxygen rich with respect to stoichiometric HfO2 and presented a significant amount of hydrogen (up to 6 at. %), which is attributed to the high affinity for moisture of the HfO2 films. The absorption coefficient was fitted to the Tauc law, obtaining a band gap value of 5.54 eV. It was found that the growth rate of the HfO2 films depends on the deposition pressure (P) as P-1.75. This dependence is explained by a diffusion model of the thermalized atoms in high-pressure sputtering. Additionally, the formation of an interfacial silicon oxide layer when the films were grown on silicon was observed, with a minimum thickness for deposition pressures around 1.2 mbars. This interfacial layer was formed mainly during the initial stages of the deposition process, with only a slight increase in thickness afterwards. These results are explained by the oxidizing action of the oxygen plasma and the diffusion of oxygen radicals and hydroxyl groups through the polycrystalline HfO2 film. Finally, the dielectric properties of the HfO2/SiO2 stacks were studied by means of conductance and capacitance measurements on Al/HfO2/SiO2/Si devices as a function of gate voltage and ac frequency signal. [ABSTRACT FROM AUTHOR]

We have studied the effects of rapid thermal annealing at 1300 °C on GaN epilayers grown on AlN buffered Si(111) and on sapphire substrates. After annealing, the epilayers grown on Si display visible alterations with craterlike morphology scattered over the surface. The annealed GaN/Si layers were characterized by a range of experimental techniques: scanning electron microscopy, optical confocal imaging, energy dispersive x-ray microanalysis, Raman scattering, and cathodoluminescence. A substantial Si migration to the GaN epilayer was observed in the crater regions, where decomposition of GaN and formation of Si3N4 crystallites as well as metallic Ga droplets and Si nanocrystals have occurred. The average diameter of the Si nanocrystals was estimated from Raman scattering to be around 3 nm. Such annealing effects, which are not observed in GaN grown on sapphire, are a significant issue for applications of GaN grown on Si(111) substrates when subsequent high-temperature processing is required. [ABSTRACT FROM AUTHOR]

The influence of H on the composition and atomic concentrations of Si, O, and N of plasma deposited SiO x N y H z films was investigated. Those samples deposited at higher SiH 4 partial pressures show both Si-H and N-H bonds, while those deposited at lower SiH 4 partial pressures show N-H bonds only. The Si-H and N-H bond concentrations were found to be proportional to the N concentration. The deviation from H-free stoichiometric SiO x N y composition due to the presence of N-H bonds results in an effective coordination number of N to produce Si-N bonds lower than 3. By fitting the experimental composition data to a theoretical model taking into account the influence of N-H bonds, the actual concentration of N-H bonds was obtained, making evident the presence of nonbonded H. The presence of Si-H and Si-Si bonds was found to partially compensate the effect of N-H bonds, from the point of view of the relative N and Si contents. A model was developed to calculate the Si, O, and N atom concentrations taking into account the influence of N-H, Si-H, and Si-Si bonds, and was found to be in perfect agreement with the experimental data measured by HI-ERDA. [ABSTRACT FROM AUTHOR]

We have verified the accuracy of free-charge determinations from Raman scattering in doped semiconductors by comparing the results obtained from phonon-plasmon coupled-mode line-shape fits with the charge-density values extracted from the analysis of the Shubnikov-de Haas oscillations. The experiments were carried out on n-InP layers, and conduction band nonparabolicity was included both in the Lindhard-Mermin model used to fit the Raman spectra and in the Shubnikov-de Haas analysis. We find a very good agreement between Raman and magnetotransport results, which confirms the reliability of the charge-density determination from Raman-scattering measurements when the line-shape analysis is carried out using the Lindhard-Mermin model. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the lattice recovery by rapid thermal annealing of Si+-implanted InP using Raman spectroscopy. Implantation by means of Raman spectra; Alteration of free-charge coupling with the LO mode; Possible misorientation of the recrystallized material; Analysis of the first order spectrum.

Examines the deep levels present in indium phosphide junctions fabricated through ion implantation and rapid thermal annealing. Sample description; Deep level transient spectroscopy; Capacitance-voltage transient technique; Damage concentration profile; Emission coefficients.

Presents information on a study which examined the use of Kramers-Kronig transforms for the treatment of admittance spectroscopy data of junctions containing traps. Methodology; Results and discussion; Conclusion.

Presents information on a study which described current-voltage, small-signal measurements and deep-level transient spectroscopy (DLTS) spectra of p-n junctions made by magnesium implantation into undoped indium phosphate. Reverse characteristics of all junctions; Experimental details; Description of the DLTS procedure; Admittance spectroscopy.

Presents information on a study which analyzed optical properties from the point of view of Faraday effect sensors, of bulk polycrystalline Cd[sub1-x]Mn[subx]Te. Synthesis of the polycrystalline CdMnTe; Optical characterization of the polycrystalline CdMnTe; Results and discussion.

Ion implantation of Ti into Si at high doses has been performed. After laser annealing the maximum average of substitutional Ti atoms is about 1018 cm-3. Hall effect measurements show n-type samples with mobility values of about 400 cm2/V s at room temperature. These results clearly indicate that Ti solid solubility limit in Si has been exceeded by far without the formation of a titanium silicide layer. This is a promising result toward obtaining of an intermediate band into Si that allows the design of a new generation of high efficiency solar cell using Ti implanted Si wafers. [ABSTRACT FROM AUTHOR]