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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. [ABSTRACT FROM AUTHOR]

Gallium oxide is an emerging wide-bandgap semiconductor with promise for applications in space systems that may be exposed to energetic particles. We use molecular dynamics simulations, based on first principles density-functional methods, to determine the nature and stability of the defects generated by atoms knocked-out by particle irradiation at near threshold energies (found to be 28 ± 1 eV for Ga and 14 ± 1 eV for O). For Ga atoms, several types of low energy knock-out events result in defect complexes, but the final structures depend critically on the initial displacement direction. In contrast, a vacancy plus a peroxide linkage occurs in all types of low energy knock-out events of O atoms. Based on energy-barrier calculations, there is a low (high) probability for Ga (O) defect recombination. The electronic structure of residual, relaxed defects generated by Ga knock-outs reveals defect levels near the band edges. [ABSTRACT FROM AUTHOR]

Energetic carriers in semiconductors thermalize by impact-ionization, which generates electron–hole pairs (EHPs), and by energy losses to phonons. The average EHP creation energy is typically about three times the energy gap. In 1960, Shockley derived a simple equation for the average EHP creation energy with a single free parameter that fits experimental values for a wide range of materials, but the underlying assumptions, as stated, have been widely criticized as lacking justification. Modified expressions derived by improved approximations have been proposed but do not fare better. Here, we revisit the foundations of Shockley's equation and provide a robust justification for the kinetic-energy component as a model averaging procedure and then apply a similar procedure to the phonon component of the equation. The phonon result retains Shockley's form, but the interpretation and justification are now on par with those of the kinetic-energy term. The single-parameter fit to the data remains unchanged, i.e., the present analysis accounts for the exceptional applicability of Shockley's equation. [ABSTRACT FROM AUTHOR]

This paper discusses two different modes of breakdown in the reverse-biased I–V characteristics observed generically in bipolar junction transistors (BJTs) with the base emitter shorted, showing an erratic behavior, in the presence of large displacement currents. Experimental observations related to reverse-biased collector junctions of BJTs, that exhibit two different states of breakdown when a fast voltage ramp is applied are presented. Numerical simulations of the transient behavior of avalanche injection in p/n-/n+ structures show that two very close breakdown states coexist. The mechanisms leading to the erratic behavior of the second breakdown are discussed. The jittery nature of the breakdown is attributed to the delay associated with the buildup of the electric field across the n-/n+ junction. [ABSTRACT FROM AUTHOR]

We report on the measurement and analysis of energetic heavy ion radiation effects on the mechanical properties of silicon carbide (SiC) crystals, by exploiting a vertical stack of micromachined vibrating SiC thin diaphragms integrated in a three-dimensional (3D) fashion. The diaphragms are 1 mm × 1 mm in lateral dimensions and 2 μm in thickness, vibrating at their multiple flexural modes in the range of 200 to 800 kHz. Upon 10.25 MeV oxygen ion irradiation, the 4 devices in the 3D stack exhibit saliently different changes in their multimode resonance frequencies. The device that is intended to capture most ions shows the largest frequency downshifts (∼6.6%–11.3%), corresponding to the extracted tension release from 382 MPa to 306 MPa, which can be explained by the maximum displacement damage in this device. The design of 3D integration not only scientifically enables probing different radiation effects in multiple devices simultaneously with clear controls but also economically evades very expensive, repetitive tests on individual devices, thus proving to be a powerful platform for analyzing and understanding radiation damage in micro/nanoelectromechanical systems and other micro/nanosystems. [ABSTRACT FROM AUTHOR]

Presents information on a study which derived theoretical expressions which relate to the terminal characteristics of photoconductive switches to the incident light. General relations from energy considerations useful for computation of the efficiency of a variety of switching devices; Measurement of the spatial photosensitivity of a high-resistivity intrinsic substrate with blocking and injecting contacts; Experimental arrangement.

We find that atomic-scale mechanisms for bias-temperature instabilities (BTIs) in SiC/SiO2 structures can differ significantly from those in Si/SiO2 structures. The measured effective-activation energies for BTI in 4H-SiC metal-oxide-semiconductor capacitors, 0.23±0.02 eV for p-type and 0.12±0.02 eV for n-type, are essentially identical to the respective dopant ionization energies, which are much larger than in Si. This suggests a key role for carrier release from deep dopants for BTI in SiC. In addition, asymmetric degradation is observed under switched-bias stress in p-type and n-type SiC, as a result of the reconfiguration of O vacancies in SiO2 layer after hole capture. [ABSTRACT FROM AUTHOR]