A. Carnera

Room‐temperature electroluminescence from Er‐doped crystalline Si

We have obtained room‐temperature electroluminescence (EL) at ∼1.54 μm from Er and O co‐doped crystalline p‐n Si diodes fabricated by ion implantation, under both forward and reverse bias conditions. Under forward bias, the EL intensity decreases by a factor of ∼15 on going from 110 to 300 K, where a weak peak is still visible. In contrast, we report the first sharp luminescence peak obtained under reverse bias conditions in the breakdown regime. In this case the EL intensity decreases only by a factor of 4 on going from 110 to 300 K and the room‐temperature yield is more than one order of magnitude higher than under forward bias. The data suggest that Er excitation occurs through electron‐hole mediated processes under forward bias and through impact excitation under reverse bias.

On the mechanisms of strain release in molecular‐beam‐epitaxy‐grown InxGa1−xAs/GaAs single heterostructures

Inx Ga1−x As/GaAs single heterostructures have been grown by molecular‐beam epitaxy with different growing rates and In molar fractions. Indium composition, layer thickness, and residual strain have been measured mainly by Rutherford backscattering/channeling spectrometry and the results on selected samples compared with the results of other techniques like Auger electron spectroscopy and single‐ and double‐crystal x‐ray diffraction. Cathodoluminescence, x‐ray topography, transmission electron microscopy, and ion dechanneling have been employed to observe dislocations and to characterize their nature and density. While the onset of misfit dislocations has been found to agree with the predictions of the equilibrium theory, the strain release has been found to be much lower than predicted and the results are compared with the available metastability or nucleation models. Present results are in best agreement with nucleation models. Moreover, annealing experiments show that these heterostructures are at (or ...

Electrical and optical characterization of Er‐implanted Si: The role of impurities and defects

The electrical and optical properties of Er‐implanted Si are shown to be critically dependent on the presence of impurities and defects. A large enhancement in the electrical activation of Er (up to three orders of magnitude) is obtained by coimplanting Er with O or C at 300 °C. The use of C also allows one to obtain a good quality crystal after implantation and annealing. This is shown to be crucial in the photoluminescence process. In fact, in spite of the large amount of active Er atoms, photoluminescence is inhibited in the presence of the high concentration of precipitates and crystallographic defects which are left after annealing of the Er and O coimplants. The photoluminescence intensity is, on the other hand, enhanced by the high concentration of active Er atoms in the defect‐free crystal which is left after annealing of the Er and C coimplants. Moreover, a clear shift in the main photoluminescence peaks is observed in Er‐ and C‐coimplanted samples as a result of the different surroundings experi...

Strain relaxation in graded composition InxGa1-xAs/GaAs buffer layers

A model to compute the strain relaxation rate in InxGa1−xAs/GaAs single layers has been tested on several compositionally graded buffer layers. The existence of a critical elastic energy has been assumed as a criterion for the generation of new misfit dislocations. The surface strain accuracy results are within 2.5×10−4. The influence of different grading laws and growth conditions on residual strain, threading dislocation density, misfit dislocation confinement, and surface morphology has been studied. The probability of dislocation interaction and work hardening has been shown to strongly influence the mobility and the generation rate of the dislocations. Optimization of the growth conditions removes residual strain asymmetries and smoothes the surface roughness.

Structural characterization of proton exchanged LiNbO3 optical waveguides

This paper reports the results of structural analysis of proton‐exchanged lithium niobate optical waveguides fabricated in Z‐, X‐, and Y‐cut substrates immersed in pure benzoic acid. Rutherford backscattering spectrometry, nuclear reactions, secondary ion mass spectrometry, scanning electron microscopy, and x‐ray diffraction were used to measure atomic composition profiles and the marked lattice distortion induced by the proton exchange process in the waveguiding layer. H and Li concentration measurements indicate an exchange of about 70% of the Li atoms are present in the virgin LiNbO3 crystal.

Dissolution kinetics of boron-interstitial clusters in silicon

In this work, we have investigated the stoichiometry of boron-interstitial clusters (BICs) produced in a molecular-beam-epitaxy-grown B box by Si implantation and annealing, and their dissolution during further prolonged annealing cycles. Low-concentration B delta doping was used to quantitatively monitor the interstitial (I) flux. A stoichiometric ratio of about 1.2 between I and B was found for the BICs formed at 815 °C. The BIC dissolution kinetics was investigated by analyzing the concentration profiles at different times and temperatures (in the range 815–950 °C) with a simulation code able to deconvolve the processes of B diffusion and B release from clusters. We found that the main mechanism for cluster dissolution is the release of interstitial boron atoms, with a thermal activation energy of 3.2±0.4 eV. These data are discussed and compared with existing literature data.

Role of fluorine in suppressing boron transient enhanced diffusion in preamorphized Si

We have explained the role of fluorine in the reduction of the self-interstitial population in a preamorphized Si layer under thermal treatment. For this purpose, we have employed a B spike layer grown by molecular-beam epitaxy as a marker for the self-interstitial local concentration. The amorphized samples were implanted with 7×1012, 7×1013, or 4×1014 F/cm2 at 100 keV, and afterwards recrystallized by solid phase epitaxy. Thermal anneals at 750 or 850 °C were performed in order to induce the release of self-interstitials from the end-of-range (EOR) defects and thus provoke the transient enhanced diffusion of B atoms. We have shown that the incorporation of F reduces the B enhanced diffusion in a controlled way, up to its complete suppression. It is seen that no direct interaction between B and F occurs, whereas the suppression of B enhanced diffusion is related to the F ability in reducing the excess of silicon self-interstitials emitted by the EOR source. These results are reported and discussed.

Ion implantation induced swelling in 6H-SiC

Ion implantation induced surface expansion (swelling) of 6H-SiC was investigated through the measurement of the step height between implanted and unimplanted areas. The samples were irradiated at room temperature with 500 keV Al+ ions in the dose range 1.25×1014–3×1015 ions cm−2. Swelling was related to dose and the area density of ion-induced damage measured by Rutherford backscattering channeling technique. The observed trend is consistent with the hypothesis that the volume expansion of the ion damaged crystal is proportional to the area density of displaced atoms, plus an additional relaxation occurring at the onset of the crystalline to amorphous transition.

Electrical behavior of ultra-low energy implanted boron in silicon

In this paper an extensive characterization of the electrical activation of ultra-low energy implanted boron in silicon is reported. The Spreading Resistance Profiling technique has been used, in a suitable configuration, for measuring doped layers shallower than 100 nm, in order to extract the carrier concentration profiles. The dependence on the implant energy, dose, and annealing temperature allowed us to gain more insight into the mechanisms responsible for the electrical activation at implant energies below 1 keV. By measuring the electrical activation as a function of time for several annealing temperatures, the thermal activation energy for the electrical activation of the dopant was achieved. It slightly depends on the implant dose and it is in the range of 2–3 eV. In particular, for an implant dose of 1×1014/cm2 it is 2.0 eV, close therefore to the 1.7 eV activation energy found [Napolitani et al., Appl. Phys. Lett. 75, 1869 (1999)] for the enhanced diffusion of ultra-low energy implanted boron. ...

Complete suppression of the transient enhanced diffusion of B implanted in preamorphized Si by interstitial trapping in a spatially separated C-rich layer

A method for completely suppressing the transient enhanced diffusion (TED) of boron implanted in preamorphized silicon is demonstrated. Boron is implanted in a molecular beam epitaxy (MBE) grown silicon sample that has been previously amorphized by silicon implantation. The sample is then annealed in order to epitaxially regrow the amorphous layer and electrically activate the dopant. The backflow of silicon interstitials released by the preamorphization end-of-range (EOR) damage is completely trapped by a carbon-rich silicon layer interposed by MBE between the damage and the implanted boron. No appreciable TED is observed in the samples up to complete dissolution of the EOR damage, and complete electrical activation is obtained. The method might be considered for the realization of ultrashallow junctions for the far future complementary metal–oxide–semiconductor technology nodes.