Commercially available diodes were irradiated at a flash X-ray source, a /sup 60/Co gamma ray source, and a 14-MeV neutron generator. During irradiation at the /sup 60/Co source, the light output of the LEDs and LDs was measured continuously. From time to time their emission spectrum was also observed. With the PDs the authors measured the preamplifier output during /sup 60/Co irradiation as well as dark current noise before and after irradiation. Determination of the sensitivity against neutrons was made offline. After pulsed irradiation of PDs the authors measured how long a certain type of preamplifier was overdriven by the induced photocurrent. LEDs and LDs showed a maximum decrease of output power of only 0.5 dB up to a total gamma dose of 10/sup 6/ Gy or neutron fluences of 4*10/sup 13/ cm/sup -2/ (1 MeV), respectively. Irradiations of PDs with /sup 60/Co gammas up to a total dose of 10/sup 6/ Gy as well as irradiations with neutrons up to fluences of >

Radiation sensitivity of light emitting diodes (LED), laser diodes (LD) and photodiodes (PD)

A variety of commercially available LEDs, LDs, PDs, and optocouplers from two German manufacturers were irradiated at a flash X-ray source, a /sup 60/Co gamma ray source, and a 14 MeV neutron generator Light output and emission spectrum of the LEDs and LDs were measured before and after irradiation at the /sup 60/Co source With the PDs we measured the dark current and the photo current before and after /sup 60/Co irradiation Determination of the sensitivity against neutrons was made off-line With PDs we measured the photo current induced by pulsed X-rays The GaAs LED showed a maximum decrease of output power of 28 dB after a total gamma dose of 10/sup 6/ Gy and LDs a threshold current shift of 80% after neutron fluences of 4/spl middot/10/sup 14/ cm/sup -2/ (1 MeV) Irradiations of PDs and APDs with /sup 60/Co gammas up to a total dose of 10/sup 6/ Gy as well as irradiations with neutrons up to fluences of /spl lsim/4/spl middot/10/sup 14/ cm/sup -2/ (1 MeV) led to significant changes of the device parameters The main effect was a strong increase of the dark current The consequence was a reduction of the minimum detectable light power Optocouplers are very sensitive to ionizing radiation Gammas as well as neutrons led to a decrease of the CTR and a change of the bandwidth up to a complete failure (after neutron irradiation) >

Radiation effects in light emitting diodes, laser diodes, photodiodes, and optocouplers

Neutron radiation testing was performed on a total of 125 silicon photodiodes to investigate the changes in the device parameters after neutron exposure. A californium-252 source was used to irradiate the photodiodes with 1-MeV equivalent neutrons having fluences in the range of 5*10/sup 11/ to 10/sup 14/ n/cm/sup 2/. The photodiode forward voltage drop, ideality factor, and series resistance increased after neutron exposure. The increased series resistance caused a degradation in diode photocurrent linearity. An empirical expression for post-neutron-irradiation changes in photodiode linearity is presented. Neutron-induced changes in the photodiode shunt resistance and dark current were modeled using simple expressions that allow device designers to estimate changes in photocurrent linearity, shunt resistance, and dark current after neutron exposure. No postirradiation change in the ultraviolet quantum efficiency of diodes without recombination in the front region was observed. This suggests that neutron irradiation does not affect the Si-SiO/sub 2/ interface recombination velocity of p-n junction diodes. >

The effect of neutron irradiation on silicon photodiodes

A historical review of radiation effects on III-V semiconductor devices is presented. The discussion ranges from examining early material and device studies to present-day understanding of III-V radiation effects. The purpose of this paper is to provide present researchers with a summary of discoveries and lessons learned from previous failures and successes.

Historical perspective on radiation effects in III-V devices

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

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.

Permanent Damage Effects in Si and AlGaAs/GaAs 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.

Transient Effects of Ionizing Radiation in Photodiodes

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.

Computer Modeling and Radiation Testing of AlGaAs Photodiode Structures

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.

L. R. Dawson

Papers

Permanent Damage Effects in Si and AlGaAs/GaAs Photodiodes

Transient Effects of Ionizing Radiation in Photodiodes

Computer Modeling and Radiation Testing of AlGaAs Photodiode Structures

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