Scott R. Messenger

Damage correlations in semiconductors exposed to gamma, electron and proton radiations

The use of nonionizing energy loss (NIEL) in predicting the effect of gamma, electron, and proton irradiations on Si, GaAs, and InP devices is discussed. The NIEL for electrons and protons has been calculated from the displacement threshold to 200 MeV. Convoluting the electron NIEL with the slowed down Compton secondary electron spectrum gives an effective NIEL for CO/sup 60/ gammas, enabling gamma-induced displacement damage to be correlated with particle results. The fluences of 1 MeV electrons equivalent to irradiation with 1 Mrad(Si) for Si, GaAs, and InP are given. Analytic proton NIEL calculations and results derived from the Monte Carlo TRIM agree exactly, as long as straggling is not significant. The NIEL calculations are compared with experimental proton and electron damage coefficients using solar cells as examples. A linear relationship is found between the NIEL and proton damage coefficients for Si, GaAs, and InP devices. For electrons, there appears to be a linear dependence for n-Si and n-GaAs, but for p-Si there is a quadratic relationship which decreases the damage coefficient at 1 MeV by a factor of approximately 10 below the value for n-Si. >

Nonionizing energy loss (NIEL) for heavy ions

The concept of nonionizing energy loss (NIEL) has been found useful for characterizing displacement damage effects in materials and devices. Published tabulations, however, are limited with respect to target materials, particle types and energies. In this paper we show how the NIEL database can be significantly expanded to include heavy ions in the coulombic limit by using the Monte Carlo code SRIM. The methodology used to extract NIEL from SRIM is described. This greatly adds to the number of materials and incident particles for which the NIEL concept can be applied. To show that values so derived are consistent with previous calculations, we compare alpha particle NIEL for GaAs derived from SRIM with a direct analytical calculation. The SRIM code is limited in that only coulombic interactions are considered. General rules of thumb are also described which permit prediction of NIEL for any target material over a large energy range. Tabulated values of NIEL for alpha particles incident on Si, GaAs and InP are presented.

Proton nonionizing energy loss (NIEL) for device applications

The proton-induced nonionizing energy loss (NIEL) for representative device materials are presented for the energy range between the displacement damage threshold to 1 GeV. All interaction mechanisms (Coulomb and nuclear elastic/nonelastic) are fully accounted for in the present NIEL calculations. For Coulomb interactions, the Ziegler-Biersack-Littmark (ZBL) screened potential was used in the lower energy range (<50 MeV) and the relativistic formulation was used in the higher energy range (/spl ges/50 MeV). A charged particle transport code, MCNPX, was used to compute the NIEL due to nuclear interactions.

Characterizing solar proton energy spectra for radiation effects applications

The Weibull distribution for smallest values is shown to be a useful description for solar proton event energy spectra. One advantage is its compact analytic expression, which allows easy conversion between differential and integral spectra. Another is its versatility, which is necessary for describing the highly variable spectra of concern. Furthermore, the Weibull distribution appears to be appropriate for use over broad energy ranges extending out to GeV. Examples are shown and comparisons to previously used distributions are made. An especially useful consequence of this approach for radiation effects applications is that it allows both predictive model spectra and observed spectra to be described by the same distribution. This allows spectra to be systematically ranked by severity of radiation damage caused in microelectronics. It further allows observed spectra to be related to predictive model parameters such as confidence levels. These points are demonstrated by evaluating the ionization dose deposited by various spectra in silicon behind aluminum shielding appropriate for spacecraft.

NIEL for heavy ions: an analytical approach

We describe an analytical model for calculating nonionizing energy loss (NIEL) for heavy ions based on screened Coulomb potentials in the nonrelativistic limit. The model applies to any incident ion on any target material where the Coulomb interaction is primarily responsible for atomic displacement. Results are compared with previous methods of extracting NIEL from Monte Carlo SRIM runs. Examples of NIEL calculations are given for incident ions having energies ranging from the threshold for atomic displacement to 1 GeV. The incident ions include H, He, B, Si, Fe, Xe, and Au. Example targets include Si, GaAs, InP, and SiC.

Proton displacement damage and ionizing dose for shielded devices in space

The sensitivity of displacement damage and ionizing dose calculations to both the incident proton energy spectrum and that transmitted through shields is calculated down to 100 eV for a solar proton event. The method is also applicable to trapped proton environments.

High-energy proton irradiation effects in GaAs devices

In this paper, we compare the energy dependences (53 and 115 MeV) of proton displacement damage coefficients for p/sup +/n GaAs solar cells with previously reported calculations of nonionizing energy loss (NIEL). Deep level transient spectroscopy (DLTS) was used to generate damage coefficients from the introduction rates of defects. New damage coefficients generated from GaAs bulk LEDs light output (1-530 MeV) are also reported. The damage coefficients from these devices for proton energies E>10 MeV vary but are bounded by the total and Coulombic NIEL.

Application of displacement damage dose analysis to low-energy protons on silicon devices

Past work has shown that the degradation of GaAs solar cells in space radiation environments can be described with a single curve for all incident particle energies. This greatly simplifies the prediction of the performance of solar cells exposed to complex particle spectra. A similar approach has not been applied to silicon solar cells because the large diffusion length in silicon means that protons with relatively high energies lose a significant fraction of their energy in the active region of the cell. The proton energies are, therefore, not well defined in the device. In this paper, we show how the Monte Carlo code SRIM can be used to extend the displacement damage dose concept to cases where this occurs. The approach described can be used to analyze the response of complex device structures in the space environment.

Radiation effects in single-walled carbon nanotube papers

The effects of ionizing radiation on the temperature-dependent conductivity of single-walled carbon nanotube (SWCNT) papers have been investigated in situ in a high vacuum environment. Irradiation of the SWCNT papers with 4.2MeV alpha particles results in a steady decrease in the SWCNT paper conductivity, resulting in a 25% reduction in room temperature conductivity after a fluence of 3×1012 alpha particles/cm2. The radiation-induced temperature-dependent conductivity modification indicates that radiation damage causes an increase in the effective activation barrier for tunneling-like conductivity and a concomitant increase in wavefunction localization of charge carriers within individual SWCNTs. The spatial defect generation within the SWCNT paper was modeled and confirms that a uniform displacement damage dose was imparted to the paper. This allows the damage coefficient (i.e., differential change in conductivity with fluence) for alpha particles, carbon ions, and protons to be compared with the corresp...

Deep level transient spectroscopy of irradiated p-type InP grown by metalorganic chemical vapor deposition

Results are presented of a deep level transient spectroscopy study of radiation‐induced defects in p‐type (Zn‐doped) InP grown by metalorganic chemical vapor deposition. Three major hole traps (H3, H4, and H5) and two electron traps (EA and EB) were observed. The electron trap structure in particular is significantly different from that reported in the literature for p‐type InP grown by other methods. Activation energies of 0.22 eV (EA) and 0.76 eV (EB) have been measured, and capture cross sections (σ∞) of 4.4×10−15 cm2 (EA), and 1.4×10−12 cm−2 (EB) have been determined. The H5 center has a thermally activated capture cross section with an energy barrier of 0.35 eV. The measured injection annealing rate of the primary hole trap (H4) was different than previously observed.