Jeffrey H. Warner

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.

Correlation of Electron Radiation Induced-Damage in GaAs Solar Cells

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.

W-structured type-II superlattice-based long- and very long wavelength infrared photodiodes

W-structured type-II superlattices (W-SLs) were initially developed to increase the gain of mid-wave infrared (MWIR) lasers. The design addressed the reduced optical transition matrix elements due to the spatial displacement between valence and conduction band wavefunctions in the type-II superlattice (T2SL), and further improved the differential optical gain by providing a mostly two-dimensional density of states. As a result, W-SL and W interband cascade lasers have lower thresholds and higher pulsed and cw operating temperatures than any other III-V interband MWIR lasers. These same features give W-SLs desirable properties for IR detectors, and here we report for the first time on characteristics of W-SLs used for long-wave and very long-wave IR photodiodes. IR transmission measurements of W and conventional T2SL photodiodes revealed absorption characteristics that are well described by theory, including line shape and peak absorption coefficient values which are about a factor of 2 greater in the W-SLs. Similarly, the low temperature photoluminescence shows much higher and sharper emission intensity in the W-SLs. While the W-SLs have demonstrated superior optical properties, as predicted, additional work is needed to achieve higher detector quantum efficiency. Results suggest that the excess carrier collection in the W-structures is reduced with respect to similar T2SL structures, especially for the lowest energy state. Possible mechanisms of excess carrier loss, as well as new designs to improve charge collection, in the W-SL, will be discussed.

Proton energy dependence of the light output in gallium nitride light-emitting diodes

Gallium nitride (GaN)-based blue-emitting diodes (CREE Model C430-DH85) were irradiated at room temperature with protons in the energy range 2 to 115 MeV at fluences varying from 1/spl times/10/sup 11/ to 1/spl times/10/sup 15/ cm/sup -2/. Light output degradation curves were obtained for each energy and the damage constant (A) associated with these curves was determined according to the theory of Rose and Barnes. For proton energies less than 10 MeV, A varies inversely with the proton energy (E). At higher energies, A is consistently above the 1/E relationship. The change in nature of the energy dependence is attributed to nuclear interactions. Nonionizing energy loss calculations for the case of protons on GaN are presented. Good agreement between theory and experiment is obtained.

Displacement damage correlation of proton and silicon ion radiation in GaAs

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.

Displacement Damage Evolution in GaAs Following Electron, Proton and Silicon Ion Irradiation

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 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.

Effect of Omnidirectional Proton Irradiation On Shielded Solar Cells

An analysis of the effects of low energy proton irradiation on the electrical performance of triple junction (3J) InGaP2/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

Design of Radiation-Hardened RF Low-Noise Amplifiers Using Inverse-Mode SiGe HBTs

A SiGe RF low-noise amplifier (LNA) with built-in tolerance to single-event transients is proposed. The LNA utilizes an inverse-mode SiGe HBT for the common-base transistor in a cascode core. This new cascode configuration exhibits reduced transient peaks and shorter transient durations compared to the conventional cascode one. The improved SET response was verified with through-wafer two-photon absorption pulsed-laser experiments and supported via mixed-mode TCAD simulations. In addition, analysis of the RF performance and the reliability issues associated with the inverse-mode operation further suggests this new cascode structure can be a strong contender for space-based applications. The LNA with the inverse-mode-based cascode core was fabricated in a 130 nm SiGe BiCMOS platform and has similar RF performance to the conventional schematic-based LNA, further validating the proposed approach.

An Investigation of Single-Event Effects and Potential SEU Mitigation Strategies in Fourth-Generation, 90 nm SiGe BiCMOS

The single-event effect sensitivity of fourth-generation, 90 nm SiGe HBTs is investigated. Inverse-mode, ≥1.0 Gbps SiGe digital logic using standard, unoptimized, fourth-generation SiGe HBTs is demonstrated and the inverse-mode shift register exhibited a reduction in bit-error cross section across all ion-strike LETs. Ion-strike simulations on dc calibrated, 3-D TCAD SiGe HBT models show a reduction in peak current transient magnitude and a reduction in overall transient duration for bulk SiGe HBTs operating in inverse mode. These improvements in device-level SETs are attributed to the electrical isolation of the physical emitter from the subcollector-substrate junction and the high doping in the SiGe HBT base and emitter, suggesting that SiGe BiCMOS technology scaling will drive further improvements in inverse-mode device and circuit-level SEE. Two-photon absorption experiments at NRL support the transient mechanisms described in the device-level TCAD simulations. Fully-coupled mixed-mode simulations predict large improvements in circuit-level SEU for inverse-mode SiGe HBTs in multi-Gbps, inverse-mode digital logic.

Deep level defects in proton radiated GaAs grown on metamorphic SiGe/Si substrates

The effect of 2MeV proton radiation on the introduction of deep levels in GaAs grown on compositionally graded SiGe∕Si substrates was investigated using deep level transient spectroscopy (DLTS). Systematic comparisons were made with identical layers grown on both GaAs and Ge substrates to directly assess the influence of threading dislocations on radiation-related deep levels for both n-type and p-type GaAs. DLTS revealed that for p+n structures, proton irradiation generates electron traps at Ec−0.14eV, Ec−0.25eV, Ec−0.54eV, and Ec−0.72eV in the n‐GaAs base, and, for n+p structures, radiation-induced hole traps appear at Ev+0.18eV, Ev+0.23eV, Ev+0.27eV, and Ev+0.77eV in the p-type GaAs base, irrespective of substrate choice for both polarities. The primary influence of substituting SiGe∕Si substrates for conventional GaAs and Ge substrates is on the introduction rates of the individual traps as a function of proton radiation fluence. Substantially reduced concentrations are found for each radiation-induce...