Jacques Bourgoin

Enhanced diffusion mechanisms

Abstract The phenomenology is reviewed for several enhanced diffusion mechanisms: the normal ionization-enhanced diffusion mechanism, the Bourgoin mechanism, the energy-release mechanism and some recoil mechanisms. Application of these mechanisms are discussed for crystalline and amorphous semiconductors, super-ionic materials and insulators in radiation damage, impurity and self-diffusion, ion-implantation, and dislocation-motion-experiments.

On amorphous layer formation in silicon by ion implantation

Abstract The introduction of disorder in silicon caused by the implantation of 70 keV argon ions has been studied using electron paramagnetic resonance and Raman scattering. It is observed that the EPR signal is not saturated when the crystalline structure (as seen by Raman scattering) has totally disappeared. The disorders measured using these two methods are compared with each other and with previously published data. It is concluded that when the saturation of the disorder is observed, it is not possible to assert that a continuous amorphous layer is formed because this saturation is not independent of the experimental technique used. It is also shown that Raman scattering can be a useful and precise technique to monitor the introduction of disorder within an implanted layer.

Study of Defects Introduced by Ion Implantation in Diamond

Natural type IIa diamonds have been implanted with 70 keV carbon, nitrogen and boron ions. The behaviour of the defects introduced is monitored using electron paramagnetic resonance, absorption, luminescence and Raman scattering measurements. We first describe and discuss the applicability of these techniques. We then present results concerning the introduction rate of the defects and their annealing; these results are briefly discussed.

Techniques for Studying Ion Implantation In Diamond

Measurements using electron paramagnetic resonance, optical absorption, Raman scattering and luminescence have been performed in ion implanted type IIa diamonds. Results are described which show how these techniques can be used to monitor the total amount of damage as well as the behaviour of point defects introduced by implantation.

Carrier Emission and Recombination

A defect whose associated energy level lies in the forbidden gap exchanges carriers with the conduction and valence bands through the emission and recombination of electrons and holes. As we discussed in [Ref.1.1, Sect. 7.3.2], the electronic transitions between level ET and the bands allow the determination of the average time a defect is occupied by a carrier, i.e., the occupancy of the level. In this chapter we consider the rates of emission of electrons or holes from the defect level to the bands and the rates of recombination. Because these rates depend on the free energy of ionization and on the cross sections for electrons and holes trapping on the defect, their study provides information from which practically all the electrical characteristics of the defect (enthalpy and entropy of ionization, trapping cross section etc.) can be deduced. Moreover, variation of the cross section versus temperature appears to be a powerful tool to get an insight into the defect-phonon interaction and consequently the correlated lattice distortion around the defect.

Atomic Configuration of Point Defects

In this first chapter, we define the objects that we shall be dealing with throughout this textbook. The defects are defined by their chemical nature and their geometrical configuration. As will be seen in [1.1], the geometrical configuration, which includes the interaction of the defect with the lattice, i.e., the lattice rearrangement around the defect, can be experimentally obtained from “spectroscopic” measurements (electron paramagnetic resonance and optical techniques). Considerations on defect geometry are necessary from the beginning for two reasons: first, atomic configurations and electronic structures are not independent, and secondly, the symmetry allows one, through the use of group theory, to simplify the treatment of electronic structures.

Lattice Distortion and the Jahn-Teller Effect

Many point defects are subject to lattice distortion, i.e., the atoms in their neighborhood are displaced with respect to their perfect crystal positions. As a consequence the point-group symmetry is often lowered and this can be observed directly in different experiments such as Electron Paramagnetic Resonance (EPR) (Chap.3) and optical absorption (Chap.4).

Other Methods of Detection

In this chapter we discuss additional information that the use of a combination of optical, paramagnetic and electrical properties provide on defect characteristics and behavior. To begin with we consider photoexcited techniques, i.e., the effect of optical excitation on conductivity, paramagnetic resonance, deep level transient spectroscopy and optical absorption. In Sect.2, we consider optical detection of EPR. Finally, in Sect.3, we group the techniques which allow direct detection of phonons, i.e., which give a direct means to observe nonradiative recombination.

Electron Paramagnetic Resonance

Electron paramagnetic resonance is the resonant absorption of electromagnetic radiation by systems composed of unpaired electrons placed in a magnetic field. The ground states of partially filled electron orbitals are spin degenerate. In a magnetic field, because there are several possible orientations for the magnetic moment associated with the total spin, the degeneracy is lifted. Energy levels associated with each orientation arise and absorption occurs when transitions are induced between them.

Defect Production by Irradiation

Defects or impurities are introduced in semiconductors, intentionally or unintentionally, during the growth process or following heat treatments. Quenching, plastic deformation and irradiation are other ways by which defects can be created. The problem with heating, quenching and plastic deformation [8.1] is that the defects produced, practically all unidentified up to now in most materials, are complexes resulting from the interaction of intrinsic defects (vacancies, interstitials, divacancies) with the various impurities present initially in the material. Moreover, the concentration of these defects is difficult, if not impossible, to control (see [Ref.1.1, Sect.6.4] for the discussion of defects resulting from quenching). On the contrary, the concentration, the distribution and (to some extent) the nature of defects produced by an irradiation can be controlled. The defect concentration is proportional to the dose of irradiation; the nature and the distribution of the defects is a function of the nature of the irradiating particle, their energy, and the impurities contained in the material which have the ability to trap the intrinsic defects originally produced by the irradiation. For this basic motivation, but also for practical reasons (knowledge of the behavior of electronic devices submitted to radiations in nuclear reactors, space, etc.) radiation effects in semiconductors have been widely studied [8.2].