STUDIES OF SI SEGREGATION IN GAAS USING CURRENT-VOLTAGE CHARACTERISTICS OF QUANTUM-WELL INFRARED PHOTODETECTORS

Segregation of Si in molecular beam epitaxy grown GaAs quantum wells i s investigated using current-voltage characteristics (I-V) of quantum well infrared photodetectors. Theoretical modeling is used to derive t he extent of segregation from the measured ratio of dark currents thro ugh the device in forward and reverse directions. The segregation leng th, expressed in angstrom per decade of concentration decay, increases from 12 to 52 angstrom on increasing the growth temperature from 550 to 605-degrees-C. Tle character of this increase indicates that Si seg regation is kinetically limited in this temperature range, but approac hes thermal equilibrium above 600-degrees-C. The effect of arsenic ove rpressure on the segregation length at a growth temperature of 595-deg rees-C is also studied. An increased overpressure of arsenic suppresse s Si segregation for both dimeric and tetrameric forms of As. The effe ct of As2 is Very small, with the segregation length decreasing from 5 2 to 48 angstrom on increasing the arsenic flux by a factor of eight f rom its nominal value. The same increase in flux gives a much stronger suppression of Si segregation if AS4 is used: the segregation length decreases from 51 to 40 angstrom.