James J. Wiczer

Permanent Damage Effects in Si and AlGaAs/GaAs Photodiodes

We report here on a study of permanent damage effects in photodiodes due to total dose exposures of 108 rad (Si) ionizing-radiation from a Co60 source. Specifically, we compare the degradation of optical quantum efficiency and increases in photodiode leakage current in Si PIN structures with specially designed and fabricated, double heterostructure AlGaAs/GaAs photodiodes. Results indicate some degradation in quantum efficiency (20-30%) for both types of devices. Leakage currents were found to increase signficantly after 108 rad in the Si PIN structures but only increase slightly in the AlGaAs/GaAs structures.

Transient Effects of Ionizing Radiation in Photodiodes

We report here on photodiode structures designed and fabricated to reduce the amplitude of unwanted, noise current induced during exposure to ionizing-radiation environments, without significantly reducing the desired photodiode signal current. For the optical wavelength range from .7 ¿m to 1.4 ¿m, we have studied three types of photodiode structures fabricated from AlGaAs, AlGaSb, and InGaAsP compound semiconductor materials. We also have tested and compared these specially fabricated, radiation insensitive photodiodes with commercially available photodiodes in an ionizing-radiation environment.

Invited Paper Radiation-Hardened Optoelectronic Components: Detectors

In this talk, we will survey recent research in the area of radiation hardened optical detectors. We have studied conventional silicon photodiode structures, special radiation hardened silicon photodiodes, and special double heterojunction AlGaAs/GaAs photodiodes in neutron, gamma, pulsed x-ray and charged particle environments. We will present results of our work and summarize other research in this area. Our studies have shown at detectors can be made to function acceptably after exposures to neutron fluences of 1015 n/cm2, total dose gamma exposures of 108 rad (Si), and flash x-ray environments of 108 rad/sec (Si). We will describe detector structures that can operate through these conditions, pre-rad and post-rad operational characteristics, and experimental conditions that produced these results.

Computer Modeling and Radiation Testing of AlGaAs Photodiode Structures

A detailed one-dimensional computer model has been used to identify the device characteristics which determine the undesirable current induced in various AlGaAs photodiode structures by ionizing radiation. The calculations were performed to aid in the design of AlGaAs photodiode structures operating at ¿=.82¿m with optimized radiation insensitivities. Various AlGaAs photodiode structures have been grown and experimentally characterized to test the model. Good agreement between calculated and measured characteristics have been obtained, indicating that the model provides a good description of the factors affecting the radiation sensitivity and the optical response of AlGaAs photodiodes.

Optoelectronic Data Link Designed for Applications in a Radiation Environment

We report here on component studies on a 10 m long, optoelectronic data transmission link designed for operation in a radiation environment. Our results show good immunity to neutron fluence levels of approximately 2 × 1014 n/cm2 and gamma radiation levels of 107 rad (Si). These results suggest that radiation hardened optoelectronic data links can be designed to operate in severe environments by carefully selecting components from the existing optoelectronics technology base.

Direct Bandgap, Ionizing-Radiation Insensitive, Photodiode Structures

This paper reports on photodiode structures designed and fabricated to reduce unwanted ionizing-radiation induced noise currents without significantly reducing the optical sig-nal currents. For the optical wavelength range from 0.7 µm to 1.4 μm, we have studied three types of photodiode structures fabricated from GaAlAs/GaAs, GaAlSb, and InGaAsP compound semiconductor materials. In addition, we compare the results of testing these specially designed direct bandgap photodiodes with commercially available direct and indirect hand qap photodiodes in an ionizing-radiation environment.

A1Gaas/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.

Neutron Damage Effects in AlGaAs/GaAs Solar Cells

Certain anticipated space radiation environments in which electronic devices must operate include significant neutron fluences. We have measured the effects of neutron irradiation on the performance of AlGaAs/GaAs solar cells. At wavelengths greater than 700 nm, there is an initial, rapid decrease in quantum efficiency with neutron fluence followed by a much more gradual decline. While the degradation at shorter wavelengths is more uniform, it can be significant, especially in 20% Al containing active region cells. In general, the results demonstrate important differences and similarities between proton and neutron irradiation effects.