G.P. Summers

Correlation of Particle-Induced Displacement Damage in Silicon

Correlation is made between the effects of displacement damage caused in several types of silicon bipolar transistors by protons, deuterons, helium ions, and by 1 MeV equivalent neutrons. These measurements are compared to calculations of the nonionizing energy deposition in silicon as a function of particle type and energy. Measurements were made of displacement damage factors for 2N2222A and 2N2907A switching transistors, and for 2N3055, 2N6678, and 2N6547 power transistors, as a function of collector current using 3.7 - 175 MeV protons, 4.3 - 37 MeV deuterons, and 16.8 - 65 MeV helium ions. Long term ionization effects on the value of the displacement damage factors were taken into account. In calculating the energy dependence of the nonionizing energy deposition, Rutherford, nuclear elastic, and nuclear inelastic interactions, and Lindhard energy partition were considered. The main conclusions of the work are as follows: 1) The ratio of the displacement damage factors for a given charged particle to the 1 MeV equivalent neutron damage factor, as a function of energy, falls on a common curve which is independent of collector current. 2) Deuterons of a given energy are about twice as damaging as protons and helium ions are about eighteen times as damaging as protons.

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.

High energy electron induced displacement damage in silicon

New measurements of displacement damage factors for electron-irradiated (4 to 53 MeV) bipolar silicon transistors have extended the correlation between nonionizing energy loss and damage factors reported previously another three orders of magnitude downward, to cover a total of six decades. To first order, the correlation remains linear for both n- and p-type silicon, but deviations are observed and explained in terms of differences in the fraction of initial vacancy interstitial pairs that recombines. These differences correlate linearly with the low-energy component of the PKA spectrum. Deep level transient spectroscopy measurements show oxygen- and dopant-related defect levels as well as divacancies. Defect concentrations scaled linearly with gain degradation, and no differences were seen between electron and proton plus neutron irradiated material. The results are consistent with a damage mechanism involving migration of vacancies to form well-separated stable defects. >

Displacement damage in GaAs structures

High-energy knock-on atoms produced by incident protons are much more important in determining the total nonionizing energy deposited in GaAs than in Si, due to the relative size of the Lindhard correction for partitioning the recoil energy. High-energy recoils are mainly produced by inelastic nuclear interactions between the incident protons and the target atoms. A review of previous calculations indicates that both the fast cascade and the evaporation phases of the elastic interaction contribute to the average energy of the recoiling ion. New calculations are presented for the energy dependence of the nonionizing energy deposited in GaAs as a result of inelastic interaction with protons over the energy range 10-1000 MeV. These calculations are combined with the previously determined contribution from elastic interactions to obtain the energy dependence of the total nonionizing energy deposited in GaAs by protons. The calculation is compared with both new and earlier experimental data for ion-implanted GaAs resistors irradiated with protons over the energy range 40-188 MeV, in order to form a basis whereby proton displacement effects in GaAs structures can be predicted. It is shown that results obtained for 10 MeV protons, for example, can be used to predict results to be expected at much higher energies. >

Probability model for cumulative solar proton event fluences

A new model of cumulative solar proton event fluences is presented. It allows the expected total fluence to be calculated for a given confidence level and for time periods corresponding to space missions. The new model is in reasonable agreement with the JPL91 model over their common proton energy range of >1 to >60 MeV. The current model extends this energy range to >300 MeV. It also incorporates more recent data which tends to make predicted fluences slightly higher than JPL91. For the first time, an analytic solution is obtained for this problem of accumulated fluence over a mission. Several techniques are used, including Maximum Entropy, to show the solution is well represented as a lognormal probability distribution of the total fluence. The advantages are that it is relatively easy to work with and. To update as more solar proton event data become available.

Displacement damage extremes in silicon depletion regions

Measurements of proton-induced dark current increases in a Si CID (charge injection device) imager have been made following displacement damage by 12- and 63-MeV protons. Populations of 61504 pixels optimize statistics and make possible the first detailed study of rare events. To this end, extreme value statistics allow a quantitative treatment and lead to characterization of a rare device-dependent mechanism. Data comparing the response of two similar CID structures suggest that electric-field-enhanced emission is responsible for the largest dark current increases in the CID structure with the higher electric fields. Comparisons between observations and estimates based on new calculations of the recoil spectrum parameters demonstrate that the largest dark current increases can be predicted in the absence of high fields. In this case the inelastic recoil component of the recoil spectrum plays a dominant role in determining the large dark current increases. Implications for other materials are discussed. >

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.

Probability model for worst case solar proton event fluences

A predictive model of worst case solar proton event fluences is presented. It allows the expected worst case event fluence to be calculated for a given confidence level and for periods of time corresponding to space missions. The proton energy range is from >1 to >300 MeV, so that the model is useful for a variety of radiation effects applications. For each proton energy threshold, the maximum entropy principle is used to select the initial distribution of solar proton event fluences. This turns out to be a truncated power law, i.e., a power law for smaller event fluences that smoothly approaches zero at a maximum fluence. The strong agreement of the distribution with satellite data for the last three solar cycles indicates this description captures the essential features of a solar proton event fluence distribution. Extreme value theory is then applied to the initial distribution of events to obtain the model of worst case fluences.

Energy Dependence of Proton-Induced Displacement Damage in Gallium Arsenide

Nonionizing energy deposition in gallium arsenide has been calculated for protons with energies ranging from 1 to 1000 MeV. The calculations are compared with new experimental results for ion implanted gallium arsenide resistors and Hall samples irradiated with protons in the energy range 1 to 60 MeV. Results are also compared with recent studies of proton induced displacement damage in silicon.