DONOR PASSIVATION IN N-ALINAS LAYERS BY FLUORINE

The mechanism of thermal degradation of both the carrier concentration and mobility in AlInAs layers due to thermally diffused fluorine is d iscussed. The thermal degradation occurs only in n-type AlInAs layers at temperatures as low as 350 degrees C. In contrast, a similar therma l degradation was never observed for AlInAs containing only acceptor i mpurities. This phenomenon is explained by the reaction of fluorine at oms with exclusive donor impurities, which forms an ionized fluorine ( anion: F-) and results in a reduction in carrier concentration. The cr eated F- ions form a scattering center which leads to a reduction in c arrier mobility. Experimental data support that fluorine atoms are of environmental origin and not incorporated during the growth of layers. From further comprehensive annealing studies for several kinds of (Al GaIn)As material systems, it is found that this donor passivation beha vior is peculiar to those compounds which contain both AlAs and InAs.