C. Sture Petersson

Quantitative mass and energy dispersive elastic recoil spectrometry: Resolution and efficiency considerations

A time of flight-energy recoil telescope system for mass and energy dispersive recoil spectrometry has been applied to study the formation of Mg2Si layers and depth profiling of Ga1−xAlxAs quantum well structures. Measurements of the energy (depth) dependence of the mass resolution showed that the telescope could be used over the energy range from 5 to 18 MeV to distinguish between recoils of 1 amu mass difference up to mass 28 amu. The energy dependence of the detection efficiency was found to be independent of the recoil energy for 12C and 28Si recoils and no strong evidence for a recoil species dependence of the detection efficiency for recoils heavier than 16O was found.

Formation of wide and deep pores in silicon by electrochemical etching

Abstract Electrochemical etching of n-type silicon in hydrofluoric acid electrolyte is now well known as a technique for micro- or macroporous silicon formation. It is commonly admitted that the width of pores can extend over four orders of magnitude, from 2 nm to 20 μm. In this study the feasibility of using this technique to form larger pores is demonstrated. The use of a water–ethanol solvent mixture (1:1) is shown to modify the electrochemistry of silicon dissolution and pore formation. The formation of stable wide pores requires adjustment of the etching current during the pore formation as a function of the evolution of the current–voltage curve with etching time. An array of 42-μm wide pores with 2-μm wall thickness and 200-μm depth were etched using this method. The feasibility to etch pores up to 100 μm in width is also presented. The results enable to conclude that the electrochemical etching of n-type silicon could be used to form vertical structures, without restrictions concerning the wall spacing. This provides a useful tool for micro-machining.

Monte carlo simulation of electron transport in 4H-SiC using a two band model with multiple minima

A Monte Carlo study of the high‐field electron transport in 4H–SiC is presented using a new analytic band model. The band model consists of two analytical bands that include band bending at the Brillouin zone boundaries. The band bending is very important in 4H–SiC and 6H–SiC and has to be taken into account in order to have an accurate model at high electric fields. Numerical calculation of the density of states given by the new model has been used in order to model the energy dependence of the scattering mechanisms accurately. The new model predicts a lower saturation velocity in the c direction (peak velocity 1.8×107 cm/s) than in perpendicular directions (peak velocity 2.1×107 cm/s). This is directly related to the strong band bending in the c direction. This effect is also responsible for a much more pronounced velocity peak in the c direction compared to perpendicular directions. In the low‐field region the mobility is higher in the c direction (mobility ratio near 0.8), which is in agreement with e...

Thermally grown SiO2 film standards for elastic recoil detection analysis

Thin-film SiO2Si structures, prepared by wet oxidation of (111)Si wafers have been investigated as reference standards for establishment of the energy and mass scales as well as the energy dependence of the detection efficiency in elastic recoil detection analysis (ERDA). 48 MeV 81Br81+ ion incident 67.5° to the surface normal at fluences up to 2 × 1014 ions cm−2 did not lead to statistically significant oxygen loss (< 5%) from the film nor to stoichiometry changes (< 5%). Furthermore no evidence of energy broadening due to surface charging was observed. The detection efficiencies of the recoil telescope were constant within ± 5% over the energy interval 9–12.7 MeV for 16O recoils and ± 3% over the interval 13–17.5 MeV for 28 Si recoils, respectively. The detection efficiency for 12.7 MeV 16O was 72% that of 17.5 MeV 28Si recoils. This efficiency variation may be associated with the dependence of the secondary electron yield on the electronic stopping in the carbon foil.

Full band Monte Carlo simulation of electron transport in 6H-SiC

A study of electron transport in 6H-SiC is presented using a full band Monte Carlo simulation model. The Monte Carlo model uses four conduction bands obtained from a full potential band structure calculation based on the local density approximation to the density functional theory. Electron–phonon coupling constants are deduced by fitting the Monte Carlo simulation results to available experimental data for the mobility as a function of temperature. The saturation velocity perpendicular to the c axis is found to be near 2.0×107 cm/s, which is in good agreement with the experimental data available. In the c-axis direction the saturation velocity is much lower (4.5×106 cm/s). There are no direct experimental results available for the saturation velocity in the c-axis direction. A comparison between two-dimensional simulations of a 6H-SiC permeable base transistor, using transport parameters obtained from the Monte Carlo simulations, and experimental I–V characteristics confirms the low value. The physical m...

Fabrication of an integrated ΔE-E-silicon detector by wafer bonding using cobalt disilicide

Abstract The problem concerning mechanical stability of thin self-supporting ΔE detector in a ΔE-E semiconductor detector telescope, has been solved by integrating both detectors into one unit. We show here a low-cost method to integrate the detectors by wafer bonding using cobalt disilicide. The ΔE-detector has a thickness of 6.5 μm and the E detector 290 μm with an area of 24.8 mm2. The system was characterized with secondary ion mass spectroscopy (SIMS), scanning electron microscopy (SEM), electrical measurement, particle measurement and two-dimensional electrical simulation.

Electrical characterization and physical analysis of epitaxial CoSi2 grown from the Si〈100〉/Ti/Co system

The electrical and structural properties of epitaxial CoSi2 layers grown on Si by solid‐state interaction between Ti/Co bimetallic layers and Si〈100〉 substrates have been investigated. The Schottky barrier height (SBH) of the CoSi2–Si contact determined by current–voltage characteristics at room temperature varies between 0.64 and 0.71 eV on the n‐type substrates and between 0.47 and 0.43 eV on the p‐type substrates. The variation of the SBH is found to be related to the interfacial properties at the CoSi2–Si contact which is in turn determined by the heat treatment used for the CoSi2 formation. The formation of polycrystalline CoSi2 is found to be responsible for the low SBH deviated from 0.71 eV on the n‐type substrates and the high SBH deviated from 0.43 eV on the p‐type substrates. The formation of a ternary compound, identified as Co16Ti6Si7, within the epitaxial CoSi2 does not seem to affect the SBH on the n‐type substrates. A permeable base transistor (PBT) was fabricated using the epitaxial CoSi2 for self‐aligned contact metallization. The current–voltage characteristics of the PBTs are presented.

Buried Cobalt Silicide Layers in Silicon Created by Wafer Bonding

A buried conductive layer in silicon has been created using wafer bonding technique, with a cobalt interfacial layer.Co-coated silicon wafers were brought into contact with either similar or uncoated wafers at room temperature. CoSi2 wasthen formed through a solid-phase reaction, during an anneal at 700 to 900°C. A 700 A buried CoSi2-layer, with a resistivityof approximately 21 µ cm, was achieved. Good adhesion, as measured by tensile strength testing, between the wafers wasachieved. Transmission electron microscopic investigations (Co-coated wafer bonded to bare silicon) showed that thesilicide has not grown into the opposite wafer, and that an amorphous layer exists between the silicide and the siliconsurface. The presence of such a layer has been confirmed by electrical characterization.

Mass‐dispersive recoil spectrometry studies of oxygen and nitrogen redistribution in ion‐beam‐synthesized buried oxynitride layers in silicon

Mass‐dispersive recoil spectrometry has been employed to study the influence of annealing conditions in ion‐beam‐synthesized silicon oxynitride structures prepared by implantation of 1.8×1018 and 1×1017 200 keV 16O+ and 14N+ ions cm−2, respectively, at approximately 600 °C. Subsequent annealing at 1200 and 1300 °C leads to redistribution of the implanted oxygen to form a buried oxide layer with nitrogen segregation to the buried SiO2/Si interfaces. Implantation with N+ subsequent to O+ followed by annealing at 1200 °C for 2 h was found to lead to both a lower oxygen content and lower channeling detectable defect concentration in the overlying silicon film than if the order of implantation was reversed. No significant dependence on order of implantation was observed after annealing at 1300 °C for 5 h.

UV-sensitive photodetectors based on metal-semiconductor contacts on 6H-SiC

Schottky diodes on Silicon Carbide (SiC) are of interest for many applications because of the relatively simple fabrication process compared to pn diodes. In this work we have fabricated Schottky diodes by evaporation of Ti on n-type an p-type 6H-SiC. Most of the diodes show good rectifying behaviour with very low reverse current and an ideality factor below 1.20. The photo response of the diodes has been measured in the range 200-400 nm. The peak sensitivity varies in the range 250-300 nm depending mainly on substrate doping.