We have studied the effects of 16‐MeV proton irradiation on the performance of a variety of light emitting diodes (LED’s) emitting between 820 and 1300 nm. Total light output and current were measured at room temperature as a function of forward bias prior to and following a sequence of room temperature 16‐MeV proton irradiations. Our results indicate that the relative amount of proton‐induced degradation from one LED type to another is similar to that observed for neutron and gamma irradiations. More specifically, the most sensitive device is the amphoterically Si‐doped GaAs LED which is characterized by a long preirradiation minority carrier lifetime. The most resistant LEDs are the high radiance GaAlAs (820 nm) and InGaAsP (1300 nm) LEDs. As in the case of Si devices, the degradation rate per irradiating particle fluence is significantly greater for proton irradiation of these LEDs than it is for neutron exposure. Neutron damage data presented herein indicate that the ratio of proton‐to‐neutron degradation rates can be as high as 100. Lifetime‐damage constant products for constant current operation are calculated for each LED type and vary from 1.5×10−13 cm2/p for the InGaAsP LED to 1.1×10−10 cm2/p for the amphoterically Si‐doped GaAs LED.

Proton damage effects on light emitting diodes

This paper discusses radiation effects in light-emitting diodes (LEDs) and laser diodes in the visible and near infrared region. Although initial evaluations of radiation damage in these types of optical emitters were done more than 30 years ago, modern LEDs and laser diodes respond somewhat differently to radiation because of the many advances in fabrication and materials technology that have occurred during the last 30 years. Results from newer technologies are discussed, along with revised interpretations of older results in the literature. The dependence of damage on particle type and energy, which has been revised by more recent experimental work, is also discussed in the paper.

Radiation effects in light-emitting and laser diodes

The need to characterize the radiation hardness of certain classes of devices in terms of atomic displacement damage rather than total absorbed dose is addressed. Resistive-network displacement damage monitors irradiated with 1.0-MeV protons and 7.3-MeV electrons indicate that these radiations are both about twenty times as damaging as /sup 60/Co gamma radiation for the same total absorbed dose. Preliminary results are presented on an alternative monitor consisting of a GaAs LED (light-emitting diode) that offers a two-order-of-magnitude increase in sensitivity over the resistive network monitors. Other characteristics of the two monitors, such as range, linearity, annealing and reuse, and neutron sensitivity, are compared. >

Response of GaAs displacement damage monitors to protons, electrons, and gamma radiation

The effect of gamma irradiation on the electrical and optical properties of amphoterically Si-doped GaAs LEDs has been investigated. The lifetime-damage constant product, tau/sub 0/K/sub ..gamma../, for degradation of the light output at constant low voltage was found to be 7.5 x 10/sup -7/ Rads/sup -1/. However, because of the presence of space charge limited current (SCLC) flow at higher currents, which conform to the practical operating range of 10 to 50 mA, the light output degraded more rapidly than at lower voltages. It is shown that the same value of tau/sub 0/K/sub ..gamma../ can be used to predict the degradation at practical operating currents when the SCLC is taken into account. Consequently, the practical implications of the results are that care must be taken in predicting degradation with a low voltage tau/sub 0/K/sub ..gamma../, and that the doping conditions leading to the presence of the SCLC should be avoided for LEDs that must operate in a radiation environment.

Application of Damage Constants in Gamma Irradiated Anphoterically Si Doped GaAs LEDs

Although amphoterically Si doped GaAs LEDs are commercially popular because of their high light output, they are extremely sensitive to irradiation. Therefore, it would be desirable to have a viable alternative available for radiation environment applications. In this work it is shown that by increasing the hole concentration in the active region of nonamphoterically doped GaAs LEDs, one can simultaneously achieve high light output and law radiation sensitivity. Experimental results indicate that the minority carrier lifetime is smaller in more heavily doped devices so that the lifetime-damage constant, ?oK, is also smaller. Hence, the heavily doped devices should have greater radiation hardness. Neutron-induced light output degradation data as a function of hole concentration confirm this conclusion. The results also show that the pre-irradiation light output is greatest in the heavily doped LEDs. The accompanying decrease of ?O in the heavily doped devices indicates that the total minority carrier lifetime is at least partially controlled by tne radiative lifetime; a requirement for simultaneously achieving radiation hardness and high initial light output. Finally, an experimental comparison with amphoterically Si doped LEDs shows that the heavily doped devices are superior for neutron fluences greater than 2 × 1012 n/cm2

Development of Efficient, Radiation-Insensitive Gaas: Zn LEDs

An optimum technique has been devised for measuring radiation damage constants of LED's, which avoids "injection annealing" of the damage that can occur during post-irradiation evaluation. It is shown that the low current densities necessary to avoid this annealing may require that measurements be made at constant junction voltage, and may preclude the use of the reverse-charge-recovery technique for direct measurement of carrier lifetime. The correction necessary for the varying voltage drop across the diode series resistance is facilitated by the low measuring currents, and by a novel technique for the accurate measurement of diode series resistance at low currents. Precise measurement techniques permit damage constants to be evaluated by application of only a small radiation dose. Using this method, proton, neutron, and gamma damage constants have been evaluated for commercial (Texas Instruments TIXL-13) GaAs LED's. Agreement between the damage constant describing degradation at these low current densities and the higher levels used in practical applications has been verified.

R. H. Hum

Papers

Radiation Damage Constants of Light-Emitting Diodes by a Low-Current Evaluation Method