R.L. Maltez

Synthesis of GaN by N ion implantation in GaAs (001)

Both the hexagonal and cubic GaN phases were synthesized in GaAs (001) by 50 keV N ion implantation at 380 °C and subsequent furnace annealing at 850–950 °C for 10 min–2 h. For a fluence of 1.5×1017 cm−2, transmission electron microscopy revealed that cubic GaN epitaxially crystallizes as precipitates in the GaAs matrix. A cubic‐to‐hexagonal GaN phase transition was observed for extended thermal anneals. By increasing the N fluence to 3×1017 cm−2, a continuous buried layer of randomly oriented hexagonal‐GaN nanocrystals was produced.

Sequential phase formation by ion‐induced epitaxy in Fe‐implanted Si(001). Study of their properties and thermal behavior

The epitaxial growth of FeSi2 silicides was studied by using ion‐beam epitaxial crystallization (IBIEC) of Fe‐implanted Si(001) samples. By employing Rutherford backscattering/channeling spectrometry and transmission electron microscopy it was possible to determine that the IBIEC process produces a γ‐, α‐, and β‐FeSi2 phase sequence, with increasing Fe concentration along the implantation profile. The critical concentrations for γ→α and α→β phase transitions are 11 and 21 at. %, respectively. A study of the thermal behavior of these phases shows that the γ‐ and α‐FeSi2 are metastable with respect to the β‐FeSi2 phase. The γ to β‐FeSi2 transition starts at 700 °C via an Ostwald ripening process. In addition a 800 °C, 1 h anneal of high Fe concentration samples produces a complete α and γ to β‐FeSi2 transformation. Finally, it is demonstrated that a regular or a rapid thermal annealing on Fe‐implanted Si samples induces only the formation of a β‐FeSi2 phase.

Hafnium diffusion in α-Ti

Abstract The diffusion of Hf in α-Ti has been studied in the temperature range 823–1023 K for the first time using the Rutherford backscattering technique on films 150 A thick deposited on α-Ti samples. The results show that the diffusion coefficients follow a non-regular Arrhenius plot. This behaviour, which has already been observed for α-Zr, is discussed in terms of possible intrinsic and extrinsic diffusional mechanisms.

Optical and structural properties of InAsP ternary self-assembled quantum dots embedded in GaAs

We report on the growth of self-assembled ternary InAsP quantum dots embedded into GaAs. A comparison between average sizes and recombination energies for different dot species (InAs, InAsP, and InP) confirms the formation of the ternary alloy islands. By carefully changing the growth conditions, we determined a global growth map for InAs, InAsP, and InP dots, showing that it is possible to tailor the optical characteristics of the InAsP species, thus covering the energy range between InAs and InP quantum dot emission.

Sequential phase formation by ion-induced epitaxy in fe-implanted si(001)

Ion‐beam‐induced epitaxial crystallization (IBIEC) of Fe‐implanted Si(001) was studied by transmission electron microscopy and Rutherford backscattering spectrometry. For sufficiently high Fe doses, it was found that IBIEC at 320 °C results in sequential epitaxy of Fe silicide phases in Si, with a sequence of γ‐FeSi2, α‐FeSi2, and β‐FeSi2 with increasing Fe concentration along the implantation profile. The critical concentrations for the γ‐α and α‐β phase transitions were determined as ≊11 and 21 at. % Fe, respectively. The observed sequential phase formation can be correlated to the degree of lattice mismatch with the Si matrix and the stoichiometry of the silicide phases.

Ion beam synthesis of cubic-SiC layer on Si(111) substrate

We have investigated SiC layers produced by ion beam synthesis on Si(111) substrates using different procedures. Bare Si(111) and SiO2∕Si(111) structures were implanted with carbon at 40keV up to a fluence of 4×1017cm−2 at a temperature of 600°C. Postimplantation annealing was carried out at 1250°C for 2h in pure O2 or Ar (with 1% of O2). A SiC layer was synthesized for all the procedures involving annealing under Ar. However, for the samples annealed under pure O2 flux, only that employing implantation into the bare Si(111) resulted in SiC synthesis. Rutherford backscattering spectrometry shows that, after annealing, the stoichiometric composition is obtained. Transmission electron microscopy measurements demonstrate the synthesis of cubic-SiC layers that are completely epitaxial to the Si(111) substrate. However, there is a high density of nanometric twins, stacking faults, and also narrow amorphous inclusions of laminar shape between the crystalline regions. The procedure based on high temperature impl...

Controlling alloy composition of InAsP self-assembled quantum dots embedded in GaAs

We report on the growth of quantum dot (QD) layers of InAsP alloys buried in GaAs by low-pressure metalorganic chemical vapor deposition. Ternary QDs were obtained by the addition of a PH3 flux during the InAs QD growth, exhibiting recombination energies lying between those of InAs and InP QDs. The electronic properties of these QDs, as evaluated by photoluminescence spectroscopy, could be tailored by varying both the growth rate and the PH3 flux for a constant AsH3 flux. The morphology of these QDs was investigated by transmission electron microscopy from which the formation of an InAsP ternary alloy QDs was inferred. Based on electron microscopy results, the fundamental role of As incorporation on the morphology of and on the defect nucleation associated to InAsP QDs could be then evaluated. From this optical–structural combined analysis, we were able to identify the growth conditions that produce good quality InAsP QDs embedded in GaAs.

Ion-beam induced sequential epitaxy of α, β and γ-FeSi2 in Si (100) at 320°C

Abstract Ion-beam induced epitaxial crystallization (IBIEC) of Fe implanted Si(001) was studied by transmission electron microscopy and Rutherford and channeling backscattering spectrometry. For sufficiently high Fe fluences it was found that IBIEC at 320°C results in a sequential epitaxial formation of γ, α and β-FeSi2 phases with increasing Fe concentration. The critical concentrations for γ → α and α → β transitions were found to be ∼ 11 and 21 at.% Fe respectively.

Thermal behavior study of Sn and Ag implanted into photoresist film

Abstract The thermal stability of Sn and Ag implanted AZ1350 photoresist films has been investigated via Rutherford backscattering technique. We find that a shallow Sn implantation increases the temperature at which the photoresist starts to decompose. This feature is not observed when Ag is implanted under the same conditions. These results indicate that chemical effects play an important role in the improvement of the photoresist thermal stability. We have also studied the thermal behavior of the implanted Sn and Ag ions. It was found that Sn diffuses regularly while Ag segregates toward the surface.

Thermal behavior study of Sb implanted into photoresist film

Abstract The thermal stability of Sb implanted AZ1350 photoresist films has been investigated via the Rutherford backscattering technique. We find that a shallow Sb implantation raises the temperature at which the photoresist starts to decompose considerably. Comparison of the present results with those of Ag, Sn and Bi into the same photoresist indicates that not only radiation but also chemical effects have to be considered in order to explain the improvement of the photoresist thermal stability.