Search

Electrical and structural changes in GaAs are monitored using electron beam induced current (EBIC) and transmission electron microscopy (TEM) measurements after irradiation by protons and silicon ions. It has been determined that higher energy protons (E [greater than or equal to] 10 MeV) and silicon ions disordered regions that are electrically and structurally different than those produced by lower energy protons. The data suggest that these disordered regions are responsible for causing the deviations between experimental data and NIEL. From analyses of the recoil spectra, high energy recoils appear to be responsible for the formation of these disordered regions. Index Terms--Defect formation, disordered regions, displacement damage, EBIC, GaAs, heavy ion, irradiation, NIEL, recoil spectrum, recombination centers, TEM.

We characterize radiation induced defects in n-type GaAs following electron, proton, and silicon ion irradiations using Deep Level Transient Spectroscopy (DLTS) and Electron Beam Induced Current (EBIC) measurements. EBIC micrographs show the existence of radiation induced recombination centers following high energy proton (E > 50 MeV) or 22 MeV silicon ion irradiations, which were not observed following 1 MeV electron or 2 MeV proton irradiations. The evolution of the U-band defect as determined by DLTS seems to occur when active recombination centers are observed in the EBIC images and therefore, appears to be produced by high energy recoils probably creating defect clusters. Index Terms--Displacement damage, DLTS, EBIC, GaAs, heavy ion, irradiation, NIEL, photovoltaic, recoil spectrum, recombination center.

An analysis of the effects of low energy proton irradiation on the electrical performance of triple junction (3J) InGa[P.sub.2]/GaAs/Ge solar cells is presented. The Monte Carlo ion transport code SRIM is used to simulate the damage profile induced in a 3J solar cell under the conditions of typical ground testing and that of the omnidirectional space environment. The results are used to present a quantitative analysis of the defect, and hence damage, distribution induced in the cell active region by the different radiation conditions. The modeling results show that, in the space environment where the incident radiation is omnidirectional, the solar cell will experience a uniform damage distribution through the active region of the cell. The cases of directional spectrum irradiation and omnidirectional irradiation through very thin shielding are also considered. Through an application of the displacement damage dose analysis methodology, the implications of this result on mission performance predictions are investigated. Index Terms--Displacement damage, nonionizing energy loss, radiation effects, solar cells.

Abstract--GaAs solar cells with different structures and polarities were irradiated with 1 and 5 MeV electrons. The energy dependence of the electron damage coefficients for the photocurrent, photovoltage, and maximum power were found to vary approximately linearly with NIEL in contrast to what has been found for other GaAs cells. Index Terms--Damage correlation, displacement damage, electron displacement damage, GaAs solar cells, nonionizing energy loss (NIEL), radiation damage.

We present results of displacement damage correlation between 2 MeV protons and 22 MeV silicon ion irradiation damage in [p.sup.+] n GaAs solar cells. The radiation induced degradation of the photovoltaic response correlates well in terms of displacement damage dose. Index Terms--Damage correlation, displacement damage, GaAs solar cells, ion irradiation, nonionizing energy loss (NIEL), proton irradiation, radiation damage, SRIM.

An index that would reliably rank the relative radiation hardness of semiconductors would be very helpful for selecting materials for many applications. The concept of 'concentration of primary defects' (CPD) has been proposed as such an index. Here we show that for the GaAs-InP family of semiconductors used in solar cells, CPD yields results that do not agree with experiment. The long-established concept of damage constants for various semiconductor properties is a more reliable index. For solar cells the relevant damage constant is that for the degradation of minority carrier lifetime. Although the damage constants reported for different semiconductors are specific to a particular type and energy of radiation, we show they can be extended beyond the type and particle energy for which they were originally determined by using nonionizing energy loss (NIEL), thereby greatly extending their possible application. Index Terms--Displacement damage, nonionizing energy loss (NIEL).

The effect of incident particle range, straggling, primary recoil atom range and target volume on the expected applicability of nonionizing energy loss (NIEL) as a basis for correlating displacement damage effects are quantified. Examples are given for protons and alpha particles incident on both silicon and gallium arsenide. Index Terms--Displacement damage, nonionizing energy loss (NIEL).

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 ( Index Terms--MCNPX, nonionizing energy loss (NIEL), Ziegler-Biersack-Littmark (ZBL) screened potential.

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. Index Terms--Displacement damage, nonionizing energy loss (NIEL), nuclear stopping power.

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.

A longstanding discrepancy between proton nonionizing energy loss (NIEL) calculations and experimental measurements in GaAs devices for E > 20 MeV is explored. The various calculations of proton NIEL in GaAs are consistent. The experimental results and calculations can be made to agree by various methods that restrict the effect of high-energy recoils, such as the neutron 'damage efficiency function.' However, it should be noted that some damage coefficients track the total NIEL and further work is clearly required. Index Terms--GaAs, nonionizing energy loss (NIEL), proton damage.

The effect of proton irradiation of InGaAs/GaAs quantum-well (QW) light-emitting diodes (LEDs) has been studied at energies ranging from 1 to 500 MeV in order to determine device damage mechanisms. The data are analyzed in terms of the theory of Rose and Barnes, and complete correlation of the data over the entire proton energy range was achieved. This degradation data, along with data from other GaAs-based optoelectronic devices, are discussed in terms of the nonionizing energy loss (NIEL). The energy dependences of the various damage coefficients for proton energies greater than about 10 MeV are bounded by the total NIEL and the elastic NIEL. Index Terms--Displacement damage, nonionizing energy loss, optoelectronic.