Richard D. Harris

Displacement damage effects on the forward bias characteristics of SiC Schottky barrier power diodes

Commercial SiC Schottky barrier power diodes have been subjected to 203 MeV proton irradiation and the effects of the resultant displacement damage on the I-V characteristics have been observed. The diodes show excellent resistance to radiation damage. Changes in forward and reverse bias I-V characteristics are reported for irradiated 4H SiC commercial Schottky barrier diodes at fluences up to 2.5/spl times/10/sup 14/ p/cm/sup 2/. Small changes are seen in the reverse bias I-V characteristics with the reverse leakage actually decreasing with increasing irradiation fluence. In forward bias, the series resistance is observed to increase as the fluence increases. The changes in series resistance are interpreted as being due to changes in the effective dopant density due to carrier removal by the defects produced.

In Situ Irradiation and Measurement of Triple Junction Solar Cells at Low Intensity, Low Temperature (LILT) Conditions

The performance of triple junction InGaP/(In)GaAs/Ge space solar cells was studied following high energy electron irradiation at low temperature. Cell characterization was carried out in situ at the irradiation temperature while using low intensity illumination, and, as such, these conditions reflect those found for deep space, solar powered missions that are far from the sun. Cell characterization consisted of I-V measurements and quantum efficiency measurements. The low temperature irradiations caused substantial degradation that differs in some ways from that seen after room temperature irradiations. The short circuit current degrades more at low temperature while the open circuit voltage degrades more at room temperature. A room temperature anneal after the low temperature irradiation produced a substantial recovery in the degradation. Following irradiation at both temperatures and an extended room temperature anneal, quantum efficiency measurement suggests that the bulk of the remaining damage is in the (In)GaAs sub-cell.

Radiation Characterization of Commercial GaN Devices

Commercially available devices fabricated from GaN are beginning to appear from a number of different suppliers. In this initial study of the radiation tolerance of commercial GaN devices, several device types from several suppliers were chosen. Three different studies were performed: 1) a preliminary DDD/TID test of a variety of part types was performed by irradiating with 55 MeV protons, 2) a detailed DDD/TID study of one particular part type was performed by irradiating with 55 MeV protons, and 3) a SEB/SEGR test was performed on a variety of part types by irradiating with heavy ions. No significant degradation was observed in any of the tests performed in this study.

Proton Irradiation of Silicon Schottky Barrier Power Diodes

Commercial silicon Schottky barrier power diodes have been subjected to 203 MeV proton irradiation and the effects of the resultant displacement damage on the I-V characteristics have been observed. The diodes show excellent resistance to radiation damage. Changes in forward and reverse bias I-V characteristics are reported for irradiated commercial Schottky barrier diodes at fluences up to 4times1014 p/cm2. Small changes are seen in the reverse bias I-V characteristics with increasing irradiation fluence. In forward bias, the series resistance is observed to increase as the fluence increases. The changes in series resistance are interpreted as being due to changes in the effective dopant density due to carrier removal by the defects produced

ELDRS Characterization for a Very High Dose Mission

Evaluation of bipolar linear parts which may have Enhanced Low Dose Rate Sensitivity (ELDRS) is problematic for missions that have very high dose radiation requirements. The accepted standards for evaluating parts that display ELDRS require testing at a very low dose rate which could be prohibitively long for very high dose missions. In this work, a methodology for ELDRS characterization of bipolar parts for mission doses up to 1 Mrad(Si) is evaluated. The procedure employs an initial dose rate of 0.01 rad(Si)/s to a total dose of 50 krad(Si) and then changes to 0.04 rad(Si)/s to a total dose of 1 Mrad(Si). This procedure appears to work well. No change in rate of degradation with dose has been observed when the dose rate is changed from 0.01 to 0.04 rad(Si)/s. This is taken as an indication that the degradation due to the higher dose rate is equivalent to that at the lower dose rate at the higher dose levels, at least for the parts studied to date. In several cases, significant parameter degradation or functional failure not observed at HDR was observed at LDR at fairly high total doses (50 to 250 krad(Si)). This behavior calls into question the use of dose rate trend data and enhancement factors to predict LDR performance.

Comparison of TID Effects in Space-Like Variable Dose Rates and Constant Dose Rates

The degradation of the LM193 dual voltage comparator has been studied at different TID dose rate profiles, including several different constant dose rates and a variable dose rate that simulates the behavior of a solar flare. A comparison of results following constant dose rate vs. variable dose rates is made to explore how well the constant dose rates used for typical part testing predict the performance during a simulated space-like mission. Testing at a constant dose rate equal to the lowest dose rate seen during the simulated flare provides an extremely conservative estimate of the overall amount of degradation. A constant dose rate equal to the average dose rate is also more conservative than the variable rate. It appears that, for this part, weighting the dose rates by the amount of total dose received at each rate (rather than the amount of time at each dose rate) results in an average rate that produces an amount of degradation that is a reasonable approximation to that received by the variable rate.

Dose Rate Effects in Linear Bipolar Transistors

Dose rate effects are examined in linear bipolar transistors at high and low dose rates. At high dose rates, approximately 50% of the damage anneals at room temperature, even though these devices exhibit enhanced damage at low dose rate. The unexpected recovery of a significant fraction of the damage after tests at high dose rate requires changes in existing test standards. Tests at low temperature with a one-second radiation pulse width show that damage continues to increase for more than 3000 seconds afterward, consistent with predictions of the CTRW model for oxides with a thickness of 700 nm, the thickness of the oxide over the emitter-base junction of pnp transistors in this process.

Optocouplers: Fundamentals and Hardness Assurance for Space Applications

Operating principles and hardness assurance methods are discussed for various types of optocouplers. Radiation damage in light-emitting diodes is addressed, along with the impact of phototransistors and internal amplifiers on overall performance. Hardness assurance for optocouplers is contrasted with the approach used for conventional microelectronics. Methods of detecting abnormal devices are discussed, along with the implementation of special screening measurements.

Degradation of InP-based Geiger-mode avalanche photodiodes due to proton irradiation

Degradation of InGaAs/InP Geiger-mode avalanche photodiodes caused by proton irradiation is reported for the first time. The devices are found to be very sensitive to displacement damage. Substantial changes in the dark count rate, and the after-pulse count rate are observed following room temperature irradiation and characterization at −50°C. The device detection efficiency is unaffected by irradiation. Following 51 MeV proton fluences in the mid 109 protons/cm2 range, the dark count rate becomes so large that the devices are rendered essentially unusable. This is a very low fluence at which to observe device failure.

SiC vs. Si for High Radiation Environments

Commercial silicon carbide and silicon Schottky barrier power diodes have been subjected to 203 MeV proton irradiation and the effects of the resultant displacement damage on the I-V characteristics have been observed. Changes in forward bias I-V characteristics are reported for fluences up to 4times1014 p/cm2. For devices of both material types, the series resistance is observed to increase as the fluence increases. The changes in series resistance result from changes in the free carrier concentration due to carrier removal by the defects produced. Calculation of carrier removal rates in both materials reveals that the carrier removal rate in silicon is less than that in silicon carbide, indicating that silicon is the more radiation tolerant material.