C. E. Barnes

The Effect of Gamma Irradiation on Optical Isolators

The effects of gamma radiation on optical isolators have been investigated. This study has included the simultaneous irradiation and measurement of the individual emitters and detectors making up the isolators. In this manner, the net effect of irradiation on the isolators could be attributed to the degradation of either the emitter or detector, or both. As expected, isolators containing photodiodes are more radiation resistant than those containing phototransistors. In the photodiode isolator the LED is responsible for essentially all the gamma-induced isolator degradation. The performance of phototransistor isolators depends strongly on the phototransistor bias, VCE, and the LED input current, ILED. At high ILED and low VCE where gamma-induced surface effects in the phototransistor are minimized, the degradation of the isolator is due primarily to the LED which is more sensitive than the LED in the photodiode isolator. In contrast, at low ILED and high VCE, gamma-induced surface damage in the phototransistor is the dominant effect and the isolator is quite sensitive to irradiation.

Neutron-induced trapping levels in aluminum gallium arsenide

Deep level transient spectroscopy (DLTS) measurements have been performed on a variety of AlxGa1-xAs p-n junctions prior to and following a series of fast neutron irradiations at room temperature and subsequent isochronal anneals. In contrast with electron and proton irradiated GaAs, neutron irradiation produces a single, broad featureless DLTS band which is a majority carrier trap in both n and p type material. The characteristics of this neutron-induced trap are relatively independent of growth method, dopant type and concentration. In GaAs, the thermal emission energies of the trap are 0.58 to 0.68 eV depending on the particular junction. These energies increase with Al content to 0.94 eV at 20% Al. The trap introduction rate, which also increases with Al content, is 0.7 cm-1 in GaAs. Isochronal annealing to temperatures as high as 400‡C results in a smaller FWHM of the DLTS band, a shift in the peak to higher temperatures, and a modest decrease in magnitude. Above 400‡C the magnitude decreases rapidly, suggesting a similarity with the antisite defect, AsGa, which has been observed to anneal in this range.

Zinc-implantation-disordered (InGa)As/GaAs strained-layer superlattice diodes

We have examined the properties of (InGa)As/GaAs strained‐layer superlattices (SLSs) that have been disordered by implantation of 5×1015/cm2, 250 keV 64Zn+ followed by controlled atmosphere annealing at 680 °C for 30 min. Ion channeling techniques indicate that the Zn‐disordered regions of the SLS contain extensive crystalline damage after annealing. Simulations of the disordering process using an analytic ion range code predict that the electrical junction resulting from the implantation process is located outside the disordered region of the SLS in both the vertical and the lateral directions. Junction electroluminescence intensity for given drive current densities from the Zn‐disordered SLS devices is comparable to that from reference Be‐implantation‐doped (SLS retained) devices and greatly exceeds that from heavily dislocated grown‐junction mesa diodes in the homogeneous alloy of the average SLS composition; this result is consistent with the results of the simulations. This study demonstrates that im...

Forward bias induced annealing of the E center in silicon

It has been well established that the annealing of the E center (phosphorus vacancy) in Si is charge state dependent with the recovery proceeding more rapidly in the neutral charge state than in the negative state. Herein, we report for the first time a third annealing condition with a strongly enhanced annealing rate for the E center: forward bias induced recovery with a significantly lower activation energy of 0.48 eV.

Thermal and Injection Annealing of Neutron-Irradiated p-Type Silicon between 76°K and 300°K

Measurements of minority carrier lifetime damage constant and divacancy growth following neutron irradiation at 76°K have been used to characterize further the annealing of neutron damage in silicon below 300°K. It has been shown that electron injection into p-type silicon at 76°K causes recovery of the neutron induced defect clusters with the simultaneous appearance of divacancies. Comparison of isochronal annealing curves of damage constant taken with and without prior injection at 76°K illustrates the nature of cluster annealing below 300°K. The thermal annealing results are shown to agree with previous annealing measurements of the carrier removal rate.

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.

Radiation Effects in Electroluminescent Diodes

Following a brief discussion of the operating characteristics of light emitting diodes (LEDs), radiation effects in these devices are reviewed. Recent results on neutron damage effects in SiC LEDs are also presented. Based on this review, criteria are developed for radiation insensitivity of LEDs.

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

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.

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.

Neutron Damage in GaAs Laser Diodes: At and above Laser Threshold

The effects of fast neutron damage on GaAs laser diodes have been examined with the following results: (1) Infrared photomicrographs of laser output for diodes operating above threshold at 300 K reveal that neutron irradiation does not have a significant effect on the near-field spatial distribution. (2) Neutron irradiation of a group of laser diodes of different cavity lengths demonstrates that the damage-induced increase in threshold current at 300 K is due primarily to a decrease in gain factor. The rate of decrease of the gain factor with neutron fluence agrees with that predicted by a previously determined damage constant. (3) Preliminary measurements of total light output as a function of diode current at 300 K and 76 K show that the lasers are much less sensitive to neutron damage at currents significantly above threshold. In fact, for some diodes the light output at 76 K increases at a given current with neutron irradiation for fluences as high as 3 × 1014 n/cm2.