Article

Radiation damage and substitutional chemical impurity effects in single-crystal germanium bombarded with 40-keV B+, Al+, Ga+, Ge+, P+, As+, and Sb+ ions

Canadian Science Publishing
Canadian Journal of Physics
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Abstract

Isochronal anneal studies have been made on n- and p-type germanium bombarded with germanium and several substitutional impurities, using the four-point and thermoelectric probes as means of indicating changes in sheet resistivity and majority carrier type. Electrical properties of diodes made from type converted samples were also determined. All bombardments were performed at 40 keV in a 24-in.-radius electromagnetic isotope separator at room temperature. These studies revealed the following. (1) Heavy-particle bombardment of germanium introduces acceptor states regardless of the identity of the bombarding species. (2) Annealing curves for n-type germanium indicate a two-stage process; details of the annealing process are dependent on the ion species used and the crystal orientation bombarded. (3) There is a crystallographic and mass dependence on the amount of change in sheet resistivity produced in n-type germanium. (4) Type conversion temperatures in p-type germanium were observed to occur at 450–475 °C for phosphorus, ~500 °C for arsenic, and slightly greater than 500 °C for antimony, suggesting that the ease of moving a particular species into an active lattice position is related to its atomic size. (5) Voltage–current and capacitance measurements indicate that large-area diodes of relatively good properties and reproducibility can be made by ion implantation in germanium.

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The donor properties of Na atoms introduced by ion implantation into p�Ge with the resistivity 20–40 Ω cm are established for the first time. Na profiles implanted into Ge (the energies 70 and 77 keV and the doses (0.8, 3, 30) × 1014 cm–2) are studied. The doses and annealing temperatures at which the thermo� probe detects n�type conductivity on the sample surface are established. After implantation, the profiles exhibit an extended tail. The depth of the concentration maximum is in good agreement with the calculated mean projected range of Na ions Rp. Annealing for 30 min at temperatures of 250–700°C brings about a redistribution of Na atoms with the formation of segregation peaks at a depth, which is dependent on the ion dose, and is accompanied by the diffusion of Na atoms to the surface with subsequent evaporation. After annealing at 700°C less than 7% of the implanted ions remain in the matrix. The shape of the profile tail por� tions measured after annealing at temperatures 300–400°C is indicative of the diffusion of a small fraction of Na atoms into the depth of the sample.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2004. Includes bibliographical references (p. 131-138). The development of CMOS-compatible photodetectors capable of operating throughout the entire telecommunications wavelength spectrum will aid in the integration of photodetectors with Si microelectronics, thus offering a low cost platform for high performance photoreceivers. This thesis demonstrates the first CMOS process compatible high-responsivity Ge p-i-n diodes for 1.55 [mu]m wavelengths. The thermal expansion mismatch between Ge epilayers and Si substrates was used to engineer tensile strain upon cooling from the growth temperature. This 0.2% tensile strain results in a lowering of the direct transition energy in Ge by 30 meV and extends the responsivity curve to near 1.6[mu]m. Design rules are given for high speed and high responsivity, and the advantages of waveguide integration for simultaneous achievement of high speed and high responsivity are illustrated. It is shown that waveguide integration has advantages to vertical illumination when optical saturation is considered. Optical saturation will become important as photodetector sizes shrink to the order of a few tens of microns in diameter. High Ge content SiGe could have applications for a SiGe electro-optic modulator utilizing the Franz-Keldysh effect. High Ge content SiGe films have been grown on Si substrates. The Franz-Keldysh effect has been observed in our pure Ge films as an increase in responsivity with increasing reverse bias for wavelengths longer than the bandgap energy. . by Douglas Dale Cannon. Ph.D.
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