Irradiation Of Semiconductors Research Articles

Defect dynamics in the presence of excess energetic carriers and high electric fields in wide-gap semiconductors

Irradiation of semiconductors by energetic beams generates excess electrons and holes and may cause device degradation or failure. Both gradual degradation by total ionizing radiation (TID) and sudden degradation/failure (soft/hard breakdown) by a combination of energetic heavy ions and high voltages (typically single-event effects or SEEs) are mediated by excess carriers. The role of defect dynamics in TID degradation has been adequately understood by a combination of experiments and density-functional-theory (DFT) quantum calculations, but little has been done so far to document a role for ion-induced defects in SEE. Here, we report proof-of-principle DFT calculations in a model cubic GaN system for two defect-related excess-carrier phenomena that can play a role in various forms of device degradation and failure. The first phenomenon is the existence, dynamics, and potential roles of defect-induced quasi-localized “resonant states” in the energy-band continua. These states can enhance TID-excess-carrier and hot-carrier degradation. Furthermore, they evolve and multiply during energetic-ion-induced atom recoils and defect creation (displacement damage) and can potentially serve as excess-carrier conduction paths in SEE. The second phenomenon is the conversion of isolated vacancies into nanovoids that can participate in the formation of conducting defect “nanowires” dressed by resonances or in explosive SEE hard breakdowns.

Influence of Disordered Regions on the Optoelectronic Properties of Heterostructures with Ge/Si Nanoislands Irradiated with Fast Neutrons

It is shown that the concentration оf disordered regions (radiation-induced defect clusters) formed during the irradiation of semiconductors by neutrons with a fluence of 1013–1015 cm–2 is just an order of magnitude less than the bulk concentration of Ge/Si nanoislands in modern multilayer heterostructures with their planar arrays. The elastic strain of the crystal lattice around the disordered regions is several times less than that around the Ge/Si nanoislands, which determine their optoelectronic properties. The irradiation of modern heterostructures with arrays of Ge/Si nanoislands by neutrons with a fluence of 1015 cm–2 means that up to 40% of nanoislands fall within the space charge area of many disordered regions. It is concluded that degradation of the optoelectronic properties of heterostructures with Ge/Si nanoislands irradiated with neutrons is mostly due to the influence of the energy levels of radiation-induced defects in the band gap and electric field of disordered regions on the charge carrier kinetics near nanoislands.

Contribution of Mechanical Stresses to the Surface Relief Formation Under Laser Irradiation of Semiconductors

The paper considers the effect of elastic stresses arising under pulsed laser irradiation of epitaxial layers of CdxHg1–xTe solid solutions on the formation of a periodic surface relief as a result of recrystallization of material melted by radiation.

Transient dynamics of the electronic subsystem of semiconductors irradiated with an ultrashort vacuum ultraviolet laser pulse

The irradiation of semiconductors with ultrashort laser pulses causes excitation of electrons from bound states (the valence band and deep atomic shells) to the conduction band, which produces non-equilibrium highly energetic free electrons. We apply a Monte-Carlo simulation technique to study the ionization and excitation of the electronic subsystem of a solid silicon target irradiated with a femtosecond laser pulse, obtaining the transient distribution of electrons within the conduction band. We take into account the electronic band structure and Pauli's principle for excited electrons. Secondary excitation and ionization processes induced by electrons in the conduction band and holes in the valence band were also included and simulated event by event. The temporal distributions of the density and the energy of excited electrons are calculated and discussed. We demonstrate that, due to the energy used to overcome the ionization potential, the final kinetic energy of the free electrons is significantly less than the total energy provided by the laser pulse. We extend the concept of an ‘effective energy gap’ for multiple electronic excitations, which can be applied to estimate the free-electron density after high-intensity vacuum ultraviolet (VUV) laser pulse irradiation. The effective energy gap depends on both the properties of the material and the laser pulse parameters. The concept provides a fundamental understanding of the experimentally accessible pair creation energy measured in the limit of long times.

Ion irradiation-induced disordering of semiconductors: defect structures and applications

This brief review focuses on defect and microstructural issues of importance for applications of ion irradiation of semiconductors. Ion irradiation of semiconductors can lead to a variety of disordering behaviour that depends not only on the semiconductor material but also on implantation parameters such as ion fluence, flux, energy and mass as well as the implantation temperature. In some cases, such as silicon implanted at or below room temperature, ion disorder leads readily to amorphization, whereas some other semiconductors, such as aluminium arsenide and gallium nitride, undergo very efficient dynamics annealing even at liquid nitrogen implantation temperatures and are difficult or even impossible to amorphize. In cases of efficient dynamic annealing a rich array of defects can result during implantation. This presentation gives examples of the defect structures that can arise during implantation and subsequent annealing of semiconductors and illustrates how disorder can be exploited to advantage in both electronic and optoelectronic device applications. In particular, open volume defects such as voids and cavities can be generated in silicon and these can be used to selectively remove metal impurities. In compound semiconductors such as zinc oxide, ion irradiation can be used to introduce defects that raise the resistivity of the material by more than seven orders of magnitude. Finally, disorder can be used to promote intermixing of the elemental constituents in adjacent multi-layer compound semiconductors and this process has been used to tune the wavelength of lasers.

Modification of power diode characteristics using bremsstrahlung radiation from microtron

Irradiation of semiconductors to energetic electrons/photons plays a vital role in modifying the electrical characteristics and in controlling the carrier life time effectively by creating lattice defects. Photon irradiation effects on silicon power diodes were studied by using bremsstrahlung radiation of peak energy 8 MeV from the Variable Energy Microtron. The relevant electrical characteristics of the diodes at different voltages were measured after irradiating to different doses. The present studies indicate that the bremsstrahlung irradiation modifies the characteristics of the high power diodes.

The dynamics of recrystallization and melting of implanted silicon at irradiation by powerful light pulses

One of the effects observed in the irradiation of semiconductors by powerful pulses of coherent and incoherent light sources in the range of durations from 0.2 ms to 10 s is the effect of anisotropic local melting. It allows valuable physical information on semiconductor properties and processes occurring in the sample during and after pulse irradiation to be obtained. Here the dynamics of anisotropic local melting of implanted silicon for different regimes of light pulses is investigated. The nucleation and growth of local regions of melting (LRM) during the light irradiation was detected by a high-speed camera. The time dependencies of the quantity and sizes of LRMs were dynamically observed for the first time. Diffraction gratings were formed using ion implantation and the effect of local melting. The dynamics of diffraction during and after the light pulse irradiation were studied. The results allow the specification of the mechanism of the effect of anisotropic local melting, and the optimization of the regimes of pulse annealing of implanted semiconductors and the regimes of formation of submicron dopant layers by rapid thermal diffusion from spin-on sources.

On the effect of a dopant on the formation of disordered regions in GaAs under irradiation with fast neutrons

The irradiation of semiconductors with heavy particles leads to, together with the generation of point defects ~PDs! in the volume of the semiconductor, the formation of disordered regions ~DRs!. 1 Being a collection of points defects integrated in a local volume, a DR possesses properties which are specific to the semiconductor matrix and are, as a rule, mainly responsible for the degradation of the optical and electrophysical properties of the semiconductor. 2 In this connection it is important to determine the main parameters of DRs experimentally and to study the factors determining these parameters. In the present work we investigated the effect of the type and level of doping on the effective size of DRs in the case of irradiation of gallium arsenide with fast neutrons. To this end samples of n- and p-type single-crystal GaAs, grown in the @100# direction by the Czochralski method, were selected. The n-GaAs crystals differed by the density NSn of the main donor impurity SnGa . The density n0 of equilibrium electrons in these crystals was determined by the dopant density and at T5300 K equalled 2310 16 22310 18 cm 23 . The p-type crystals were doped with zinc atoms ~ZnGa) and the hole density in the crystals was p052310 18 cm 23 at T5300 K. The dislocation density was virtually the same in the experimental n-GaAs~Sn! and p-GaAs~Zn! crystals and equalled (223)310 4 cm 22 . The samples were irradiated with fast neutrons ~average energy En52 MeV! with doses F n510 15 210 17 neutrons/cm 2 in a reactor channel with

The influence of the ion type on the anisotropic local melting of implanted silicon

One of the effects detected during the irradiation of semiconductors which include implanted layers by strong pulses of coherent and incoherent light is an anisotropic local melting. In this work systematic experimental investigations were carried out on the influence of semiconductor substrate type, light power density E 0 and pulse duration τ p, as well as dose and energy of implantation and ion type on the parameters of local melting: density, size and shape of recrystallized local molten regions. The observed local melting of implanted Si irradiated by light pulses in the duration interval of 0.1–10 s is explained by the appearance (and interaction) of recrystallization processes and thermoplastic effects, induced by light or stipulated by implantation.

Calculation of phase transition dynamics upon laser irradiation of semiconductors

Approximate expressions are obtained for calculations of the time characteristics of fusion and recrystallization, recrystallization rate, and depth to which the material fuses upon laser annealing of semiconductors. The expressions obtained may be used for selection of processing regimes.

Unique features of electrical conductivity in cadmium sulfide crystals irradiated by high-neutron dosages

Irradiation of semiconductors by high-energy heavy particles leads to the formation of defect clusters. The present study will analyze the dosage dependence of dark conductivity (σ) in high-resistance CdS single crystals upon irradiation by fast neutrons. Some parameters of defect clusters in the specimens studied are evaluated.

Semiconductor-catalyzed photooxygenation of aromatic olefins

Irradiation of semiconductors (TiO 2 and CdS) suspended in organic solvents containing 1,1-diphenylethylene and its derivatives under oxygen afforded the corresponding epoxides and benzophenone. A possible mechanism is discussed.

Ionization effects on damage yield in ion irradiation of semiconductors

Ionization effects on damage yield in ion irradiation of semiconductors