S. U. Campisano

Room‐temperature luminescence from Er‐implanted semi‐insulating polycrystalline silicon

Semi‐insulating polycrystalline silicon films with oxygen concentrations in the range 4–27 at. % were deposited by low‐pressure chemical vapor deposition of SiH4 and N2O onto silicon substrates, annealed at 920 °C, and then implanted with 2×1015 500 keV Er ions/cm2. After annealing at temperatures in the range 300–900 °C, the samples show intense room‐temperature luminescence around 1.54 μm, characteristic of intra‐4f emission from Er3+, upon excitation using an Ar ion laser. The luminescence intensity increases with increasing oxygen concentration in the film. The luminescence is attributed to Er3+ ions in oxygen‐rich shells around Si nanograins, excited by a photocarrier‐mediated process.

Erbium in oxygen-doped silicon: Optical excitation

The photoluminescence of erbium‐doped semi‐insulating polycrystalline and amorphous silicon containing 30 at. % oxygen is studied. The films were deposited on single‐crystal Si substrates by chemical vapor deposition, implanted with 500 keV Er to fluences ranging from 0.05 to 6×1015 ions/cm2, and annealed at 300–1000 °C. Upon optical pumping near 500 nm, the samples show room‐temperature luminescence around 1.54 μm due to intra‐4f transitions in Er3+, excited by photogenerated carriers. The strongest luminescence is obtained after 400 °C annealing. Two classes of Er3+ can be distinguished, characterized by luminescence lifetimes of 170 and 800 μs. The classes are attributed to Er3+ in Si‐rich and in O‐rich environments. Photoluminescence excitation spectroscopy on a sample with 1×1015 Er/cm2 shows that ∼2% of the implanted Er is optically active. No quenching of the Er luminescence efficiency is observed between 77 K and room temperature in this Si‐based semiconductor. The internal quantum efficiency for ...

Mechanisms of amorphization in ion implanted crystalline silicon

Abstract The process of ion beam amorphization of crystalline silicon is reviewed in order to elucidate the underlying mechanisms. The role of dopants on this process is also explored studying amorphization of undoped and highly doped crystalline Si in the temperature range 77–423 K and by using Ge ion irradiation at an energy of 400 keV or 1 MeV. At each temperature the amorphous fraction increases more than linearly with the fluence and, at temperatures higher than 300 K, is strongly dependent on dopants. In particular amorphization is retarded by B and enhanced by As doping at concentrations of ∼ 1020/cm3. These processes are shown to mirror closely ion beam induced amorphization of pre-existing amorphous clusters. The amorphization is modelled in terms of three dimensional nucleation and growth of amorphous Si clusters under ion irradiation. The defects which are not quenched into amorphous regions during the early stages following the collision cascade are long living and interact with the existing amorphous islands inducing their growth. In the presence of B the amorphization rate is reduced while the nucleation rate is unaffected. The As effect is discussed in terms of its strong interaction with point defects.

Erbium in oxygen‐doped silicon: Electroluminescence

Room‐temperature electroluminescence at 1.54 μm is demonstrated in erbium‐implanted oxygen‐doped silicon (27 at. % O), due to intra‐4f transitions of the Er3+. The luminescence is electrically stimulated by biasing metal‐(Si:O, Er)‐p+ silicon diodes. The 30‐nm‐thick Si:O, Er films are amorphous layers deposited onto silicon substrates by chemical‐vapor deposition of SiH4 and N2O, doped by ion implantation with Er to a concentration up to ≊1.5 at. %, and annealed in a rapid thermal annealing furnace. The most intense electroluminescence is obtained in samples annealed at 400 °C in reverse bias under breakdown conditions and it is attributed to impact excitation of erbium by hot carriers injected from the Si into the Si:O, Er layer. The electrical characteristics of the diode are studied in detail and related to the electroluminescence characteristics. A lower limit for the impact excitation cross section of ≊6×10−16 cm2 is obtained.

Reduction of secondary defect density by C and B implants in GexSi1−x layers formed by high dose Ge implantation in (100) Si

(100) oriented Si substrates were implanted with 70 keV Ge ions at a dose of 3×1016 cm−2, corresponding to a Ge peak concentration of ≊15 at. %. Annealing at 1100 °C for 10 s forms a large density of secondary defects (dislocation loops). A 30 keV C implant at a dose of 3×1015 cm−2 on the Ge implanted samples suppresses the formation of secondary defects after the annealing. In GexSi1−x layers implanted with 30 keV B at a dose of 2.5×1015 cm−2, a dense dislocation network after annealing is present. Therefore C is much more effective in the suppression of secondary defects than B. In addition, it is shown that good epitaxial quality can be obtained in the heavily B doped GexSi1−x layers amorphizing a 2 μm thick surface layer by high energy Si implants prior to annealing.

Optimization of the tradeoff between switching speed of the internal diode and on-resistance in gold- and platinum-implanted power metal-oxide-semiconductor devices

Diffusion of platinum and gold has been used to reduce minority-carrier lifetime in power metal-oxide-semiconductor devices in order to improve the switching characteristics of the internal diode. Gold thin-film deposition and gold- or platinum-ion implantation techniques have been adopted to realize the prediffusion source. For a given reduction in lifetime, the concomitant increase in the on-resistance of the device, as determined by the forward characteristics, is smaller in gold-implanted than in gold-deposited devices; an even smaller increase in on-resistance is obtained by using platinum implantation. Therefore, ion implantation of platinum in power MOS devices fabrication provides a better tradeoff between static characteristics of the devices and switching speed of their internal diodes. >

Diffusion and lifetime engineering in silicon

Diffusion mechanisms in crystalline silicon are reviewed emphasizing the role played by the structural defects like vacancies and self-interstitials. These defects control the diffusion process of some transition metals, such as Au and Pt, which undergo fast long-range diffusion as interstitials and become substitutional by replacing a Si atom in a kick-out reaction. The influence of boundary conditions and sample surfaces on the concentration profiles of these metals are analysed in detail. These profiles can be precisely tailored using ion-implantation to achieve a low fluence diffusion source. Fine tuning of the metal profiles is shown to improve greatly the trade-off between dynamic and static characteristics of some silicon power devices like metal-oxide-semiconductor field effect transistors. Moreover, the possibility to obtain a preferential reduction of lifetime by metal doping in a selected area of a semiconductor device is demonstrated.

Two‐dimensional junction profiling by selective chemical etching: Applications to electron device characterization

We present recent developments of the sample preparation technique used to obtain the delineation of a two‐dimensional junction profile by transmission electron microscopy analysis. The technique is based on the selective chemical etching of doped regions in silicon by a HF:HNO3 chemical mixture. The role of crystallographic defects and the influence of the substrate doping (n or p type) is explained by taking into account the free carriers present at the solid/solution interface during the silicon dissolution process. This information allows us to identify some crucial aspects of the sample preparation method, and two‐dimensional junction profiles can also be obtained in the case of samples doped with boron. The high spatial resolution of the technique allows us to resolve several features of the doping profiles which are not detectable with other techniques and to characterize a wide range of electron devices.

Grain growth kinetics during ion beam irradiation of chemical vapor deposited amorphous silicon

The amorphous to polycrystal transition during Kr ion beam irradiation of chemical vapor deposited silicon layers has been studied in the temperature range 320–480 °C. At each irradiation temperature the average grain diameter increases linearly with the Kr dose, while the grain density remains constant within the experimental accuracy. The growth rate follows a complex behavior which can be described by dynamic defect generation and annihilation. The absolute value of the grain growth rate is equal to that of the ion‐assisted epitaxial layer by layer crystallization in the silicon (111) orientation. This result can be related to the crystal grain structure and morphology.

The damage recovery and electrical activation of shallow boron implants in silicon: The effects of high energy implants

Abstract A study of the interaction between shallow implanted boron junctions and high-energy silicon implants is presented. The implantation induced damage structure and its evolution with annealing temperature was followed by transmission electron microscopy. The electrically active boron depth profiles have been measured using spreading resistance profiling. The results show that the boron secondary defect formation is greatly suppressed by a high-energy silicon implant. A reduction by more than 50% has been observed. Moreover, the electrical activation is affected, and is found to be very sensitive to the initial damage structure, which depends on the implant conditions and subsequent thermal processes. The interaction between the damage structure of the low energy and high energy implants has been simulated by solving the appropriate set of fully coupled diffusion equations for interaction and diffusion of point defects. A comparison of the experimental findings with the results of the simulations is presented and discussed.