Dopant and Alloying Effects in Gamma Irradiated GaAs Light Emitters

Techniques for producing radiation hardening in GaAs light emitters by use of donor dopants and isovalent anion substitutional alloying are reported. Six different donor dopants, within the concentration range from 1 to 20 x 1017 cm-3, were added to GaAs substrates. P-N light emitters were then fabricated and exposed to gamma irradiation from a 60Co source in steps to a total absorbed dose of 108 rads(Si). Results of the study are reported in terms of the damage parameter K¿ ¿¿ where K¿ is the damage coefficient and ¿¿ is the preirradiated minority carrier lifetime. Selenium (Se) was the most effective dopant for hardening GaAs light emitters followed in order of decreasing effectiveness by Sn, Si (donor), Te, Ge (amphoteric), and Si (amphoteric). Two additional observations in this portion of the investigation also seemed to favor the use of Se for hardening: (1) The recovery of the emitters following isochronal annealing occurs in the sequence Se, Sn, Si, Te, and Ge, with the Se-doped samples showing the greatest annealing (to 60% of original quantum efficiency). (2) The shift of the peak emitting wavelength with irradiation (always toward shorter wavelengths) is found to be least for the Se-doped samples. The second technique for hardening involved substituting the isovalent anion phosphorus (P) into the GaAs lattice in place of As. This action resulted in a lowering of the damage coefficient, K¿ , by several orders of magnitude as the P content increased to about 50%.