C. Cytermann

Damage threshold for ion‐beam induced graphitization of diamond

The critical dose for graphitization of diamond as a result of ion implantation induced damage (boron and arsenic) and subsequent thermal annealing is determined by combining secondary ion mass spectroscopy measurements, chemical etching of the graphitized layer, and TRIM simulations. Li ions are implanted as a deep marker to accurately determine the position of the graphite/diamond interface. The damage density threshold, beyond which graphitization occurs upon annealing, is found to be 1022 vacancies/cm3. This value is checked against published data and is shown to be of general nature, independent of ion species or implantation energy.

Dependence of the superconducting transition temperature on the doping level in single crystalline diamond films.

Homoepitaxial diamond layers doped with boron in the 10(20)-10(21) cm(-3) range are shown to be type II superconductors with sharp transitions (approximately 0.2 K) at temperatures increasing from 0 to 2.1 K with boron contents. The critical concentration for the onset of superconductivity in those 001-oriented single-crystalline films is about 5-7 10(20) cm(-3). The H-T phase diagram has been obtained from transport and ac-susceptibility measurements down to 300 mK.

Is sulfur a donor in diamond

Homoepitaxial diamond layers grown by chemical-vapor deposition in the presence of H2S, which were published to exhibit n-type conductivity, are carefully analyzed both electrically and structurally. Hall-effect measurements as a function of temperature clearly show the samples to exhibit p-type conduction, with an activation energy, carrier concentrations, and mobilities which very much resemble those of B-doped p-type diamond. Secondary-ion-mass spectroscopy confirms that indeed the samples, previously claimed to be n type due to a donor state attributed to sulfur, contain enough unintentional boron to explain the observed p-type features.

CoSi2 and TiSi2 for SiSiGe heterodevices

Abstract Novel Si SiGe heterodevices with enhanced performance demand low thermal budget contact formation. CoSi2 and TiSi2 can meet this requirement. The investigation of self-aligned rapid thermal processes for the formation of CoSi2 (at 600–650 °C) and TiSi2 (at 650–750 °C) and their application to n-channel hetero field effect transistors and heterobipolar transistors (HBTs) is described and effects on the device performance are presented. Specific resistances of around 20 μΩ cm for CoSi2 and 17 μΩ cm for TiSi2 could be confirmed for the Si/SiGe heterosystem. Contact resistances on n+-phosphorous implanted layers below 6 μΩ cm2 have been derived from TLM structures. The silicide formation is severely affected by SiGe. Therefore the compound formation of CoSi2 in the Co Si and the Co Si 1 − x Ge x system has been investigated and compared as a function of annealing time in a temperature range from 400 to 600 °C. X-ray diffraction measurements on SiGe layers confirmed the formation of a mixture of CoSi and Co germanides with higher resistivity due to the interfacial reaction and the accumulation of Ge at the interface, which may act as a diffusion barrier. The choice of a Si cap above SiGe, whose thickness was properly adjusted to the material consumption correlated with the resulting silicide thickness, is proposed. The process and the performance of SiGe HBTs could be improved by the introduction of a Ti salicide process: base resistances yield values around 20 Ω (for an emitter area of 0.8 × 5 μm2). Nearly ideal Gummel plots confirm the advantage of using TiSi2.

Hydrogen diffusion in B-ion-implanted and B-doped homo-epitaxial diamond: passivation of defects vs. passivation of B acceptors

Drastic differences in diffusion of H (deuterium) in diamond, B-doped by ion implantation and during homo-epitaxial film growth, and its influence on electrical properties are found by SIMS depth profiling, and by electrical (Hall effect) measurements. Type IIa natural diamond, B-doped by ion implantation and high quality homo-epitaxial B-doped diamond films were subjected to D plasma treatment under similar conditions. The results of SIMS measurements clearly show a huge difference in D diffusion profile for these two samples. While the sample doped during growth was totally deuterated, the implanted one showed only minor D penetration. Electrical measurements indicated that while the homo-epitaxial samples became insulating or showed strong decrease in their free hole concentration following deuteration, the identical treatment to the B-ion implanted sample caused only slight changes in electrical properties. The electrical properties and their dependence on annealing are correlated with the deuterium diffusion into diamond. A possible mechanism of (B, H) and (defect, H) pair formation is suggested as a possible explanation of the observed differences.

Nitrogen implantation into glassy carbon as an attempt to grow a carbon nitride thin film

Abstract The current interest in carbon nitride comes from the recent theoretical prediction that this material could have superior structural, thermal and electronic properties to those of diamond. Over the last few years considerable efforts have been made in an attempt to grow thin films of the β-C 3 N 4 phase by employing various deposition techniques. In the present work, the possibility of carbon nitride formation by ion implantation of nitrogen into glassy carbon was investigated with particular attention to the effect of the implantation parameters and post-annealing processes. The distribution and bonding states of the implanted nitrogen as well as the composition and the structure of the modified layer have been studied by AES, XPS and Raman techniques. Highenergy, up to 50 keV, and high-dose, up to 1 × 10 18 cm −2 , nitrogen ion implantations into glassy carbon were performed as an attempt to form a continuous carbon nitride layer. Low-energy (0.5 keV) nitrogen implantation was performed as a model study of possible chemical bond formation between nitrogen and carbon atoms. In this work we present experimental data demonstrating the predominant formation of an almost unpolarized carbon-nitrogen bond during hot nitrogen implantation. Such bonds are expected to be present in the elusive carbon nitride β-phase.

Diamond processing by focused ion beam—surface damage and recovery

The nitrogen vacancy color center (NV−) in diamond is of great interest for photonic applications. Diamond nano-photonic structures are often implemented using focused-ion-beam (FIB) processing, leaving a damaged surface which has a detrimental effect on the color center luminescence. The FIB processing effect on single crystal diamond surfaces and their photonic properties is studied by time of flight secondary ion mass spectrometry and photoluminescence. Exposing the processed surface to hydrogen plasma, followed by chemical etching, drastically decreases implanted Ga concentration, resulting in a recovery of the NV− photo-emission and in a significant increase of the NV−/NV0 ratio.

Diffusion of hydrogen in undoped, p-type and n-type doped diamonds

Hydrogen is a key impurity in diamond since it is unintentionally incorporated in all chemical vapor deposition (CVD) grown diamond layers.Its presence in the material can grossly affect its electrical and optical properties.Theoretically, hydrogen has been predicted to be present in diamond in one of the three charge states, H , H and H .Moreover it may form complexes q 0 y with impurities, native defects or with other hydrogen atoms.This paper is comprised of two parts: (a) a review of previous results of studies investigating different aspects of the diffusion of hydrogen (deuterium) in various kinds of diamonds.The diamonds studied are: undoped type IIa diamonds, undoped CVD diamond layers containing growth defects only, p-type B-doped homoepitaxially CVD grown diamond layers or B ion implanted type IIa diamonds and n-type P doped homoepitaxially CVD grown diamond or N-doped type Ib natural diamonds.Hydrogen is introduced in diamond by exposing the diamond surface to hydrogen plasma or by using hydrogen ion implantation.The following issues are discussed: (1) the influence of the interaction between H and the dopants and defects on the hydrogen diffusion. (2) The kinetic of (B, H), (P, H ) and (N, H) pair formation and dissociation. (3) The modification of the optical and electrical properties as a result of hydrogen incorporation and annealing. It is found that, under certain conditions, H diffuses into the B containing layer and it passivates B acceptors.In contrast, no H diffusion could be observed in n-type diamonds, up to 1000 8C. (b) Recent results of our group regarding other aspects related to the diffusion of H in diamond are presented.These include results on: (i) the influence of ion implantation related defects on the diffusion of deuterium.For this study type IIa samples implanted with B or non-dopant ions are used. (ii) The determination of the charge state of H or Hydefects complex as a function of diamond type.For that, annealing under bias is applied to deuterated diamond layers.We show that the presence of implantation defects retards the deuterium diffusion in a B-implantation doped diamond, demonstrating that D strongly interacts with defects, thus inhibiting diffusion.The new-formed complexes deteriorate the electrical properties of the diamonds and are very stable up to high temperatures.We confirm that, as expected, in highly B-doped CVD diamond layers, H diffuses as a positive ion.In lightly B-doped homoepitaxial layers, however, D is incorporated in complexes which seem to be negatively charged. � 2003 Elsevier Science B.V. All rights reserved.

Crystallization in fluorinated and hydrogenated amorphous silicon thin films

The amorphous‐to‐crystalline (AC) transition of amorphous Si thin films containing fluorine or hydrogen is studied by transmission electron microscopy. The AC transition can be described quantitatively by the incubation time prior to the onset of crystallization t0. This parameter is found to decrease exponentially with temperature with an activation energy of 1.7 eV for a‐Si:F and 3.1 eV for a‐Si:H:D. It is found that during the crystallization process in a‐Si:F the crystallites organize as dendrite single crystals oriented along the 〈110〉 axis perpendicularly to the film surface. a‐Si samples that had been covered by Pd or Al crystallize at appreciably lower temperatures. In the case of Al lower activation energies of 0.7 eV for hydrogenated and 0.4 eV for fluorinated a‐Si are measured. In the case of Pd/a‐Si:H,F for both kinds of a‐Si an activation energy of 1.7 eV is found.

Conversion of p-type to n-type diamond by exposure to a deuterium plasma

The lack of a shallow donor in diamond with reasonable room temperature conductivity has been a major obstacle, until now, for the realization of many diamond based electronic devices. Most recently it has been shown that exposure of p-type (B doped) homoepitaxial diamond layers to a deuterium plasma can result in the formation of n-type diamond with a shallow donor state (Ea=0.34eV) and high room temperature mobility (430cm2∕Vs) [Z. Teukam et al., Nat. Mater. 2, 482 (2003); C. Saguy et al., Diamond Relat. Mater. 13, 700 (2004)]. Experimental results, based on the comparison of secondary ion mass spectrometry profiles of B and D and Hall effect measurements at different temperatures are presented. They confirm the previous speculation that some deuterium related complex is responsible for the donor activity in diamond. These donors are shown to be formed in a two-step process. First, deuterium diffuses into the entire B containing layer rather slowly, being trapped by the boron acceptors and passivating t...