AlGaAs/GaAs heterojunction bipolar transistors irradiated with 10/sup 15/ neutrons/cm/sup 2/ demonstrated superior performance to silicon bipolar transistors. The postneutron current gain was dominated by recombination in the emitter-base depletion region. The base current exhibited an ideality factor n>2 after irradiation, which was attributed to two possible recombination mechanisms associated with neutron-induced traps: tunneling-assisted trapping and recombination arising from a nonuniform distribution of Shockley-Read-Hall centers within the depletion region. The emitter-base heterojunction was degraded more than the collector-base homojunction after irradiation. >

Neutron irradiation effects on AlGaAs/GaAs heterojunction bipolar transistors

The application of fiber optic links in both commercial and military space systems, as well as other hostile environments, will mean that these links must be able to withstand exposure to radiation of various types. In this paper, we summarize our work on the effects of radiation on typical emitters and detectors employed in fiber optic links.

The Effects Of Radiation On Optoelectronic Devices

A review is given of the effects of radiation on various photonic modulator materials and devices including polymer-based structures, insulator-based devices, semiconductor-based devices, and spatial light modulators. We conclude by providing recommendations for further work in the area of radiation effects in photonic modulators.

Radiation effects in photonic modulator structures

The rapidly expanding field of optoelectronics includes a wide variety of both military and non-military applications in which the systems must meet radiation exposure requirements. Herein, we review the work on radiation effects on sources and detectors for such optoelectronic systems. For sources the principal problem is permanent damage-induced light output degradation, while for detectors it is ionizing radiation-induced photocurrents.

Radiation Effects On Light Sources And Detectors

Radiation tolerance up to 1015 1-MeV neq/cm2 is required for the silicon microstrip sensors to be operated at the Super LHC experiment. As a candidate for such sensors, we are investigating non-inverting n+-on-p sensors. We manufactured sample sensors of 1 times 1 cm in 4" and 6" processes with implementing different interstrip electrical isolation structures. Industrial high resistive p-type wafers from FZ and MCZ growth are tested. They are different in crystal orientations lang100rang and lang111rang with different wafer resistivities. The sensors were irradiated with 70-MeV protons and characterized in views of the leakage current increase, noise figures, electrical strip isolation, full depletion voltage evolution, and charge collection efficiency.

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Development of Radiation Hard ${\rm N}^{+}$ -on-P Silicon Microstrip Sensors for Super LHC

Pulsed irradiaion of optimized, MBE grown, AlGaAs/GaAs radiation hardened photodiodes

We report here new results including the effects of neutron irradiation of AlGaAs/GaAs double hetero-junction photodiodes and special, small active volume, PIN silicon photodiodes. Results from high energy electron irradiations are also presented. Finally we report on improvements in processing and growth of these radiation hardened, AlGaAs/GaAs, double heterojunction, photodiodes. Neutron irradiation studies have shown that the double heterojunction, AlGaAs/GaAs photodiodes degrade only slightly after exposure to 3.6 × 1015 n/cm2. The special "rad-hard" silicon PIN photodiodes showed considerably greater degradation in both optical responsivity and leakage current characteristics after exposure to neutron fluences of 1.0 × 1015 n/cm2. Measurements of ionizing-radiation induced photocurrent during exposures to pulsed electron beams and pulsed x-rays show that the AlGaAs/GaAs structures generate only a fraction (0.03 to 0.1) of the current generated by the small active volume, radhard, silicon photodiodes. Optimization of the device growth and fabrication processes have resulted in significantly better electrical characteristics while maintaining good optical properties. The irradiation test results reported here expand our knowledge of the radiation hardness of these devices to include other types of irradiation threats beyond previously published work.

Pulsed Irradiation of Optimized, MBE Grown, AlGaAs/GaAs Radiation Hardened Photodiodes

We report on AlGaAs/GaAs double heterojunction photodiodes designed and fabricated to be resistant to the effects of ionizing-radiation. The work described here includes new results comparing optimized, AlGaAs/GaAs photodiodes grown with two different growth processes: liquid phase epitaxy and molecular beam epitaxy. These devices were processed with similar photo-lithographic masks and exposed to high energy neutrons, electrons, and photons. Electrical and optical characterizations were completed before and after each irradiation; degradation trends are reported.

A1Gaas/Gaas Radiation Hardened Photodiodes

An AlGaAs/GaAs double heterojunction, mesa isolated, photodiode grown by molecular beam epitaxy was irradiated with 18 MeV electrons, 1 to 10 MeV x-rays, and neutrons from a pulsed reactor. Test results indicate that the AlGaAs/GaAs photodiodes generate approximately 10 to 20 times less photocurrent during exposure to a pulse of ionizing-radiation than radiation hardened silicon PIN photodiodes. Studies of neutron induced permanent damage in the AlGaAs/GaAs photodiode show only small changes in optical responsivity and a factor of 8 increase in leakage currents after exposure to 3.6 x 10/sup 15/ neutrons/cm/sup 2/ and 900 krad gamma. The silicon PIN photodiode was exposed to only 28% of the fluence used on the AlGaAs photodiodes and we observed a 40% decrease in optical responsivity and a factor of 7000 increase in leakage current.

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T. A. Fischer

Papers

Pulsed irradiaion of optimized, MBE grown, AlGaAs/GaAs radiation hardened photodiodes

Pulsed Irradiation of Optimized, MBE Grown, AlGaAs/GaAs Radiation Hardened Photodiodes

A1Gaas/Gaas Radiation Hardened Photodiodes

Pulsed irradiation of optimized, MBE grown, AlGaAs/GaAs radiation hardened photodiodes. Rev