HOLE MOBILITY IN GE-GA FAR-INFRARED PHOTOCONDUCTIVE SEMICONDUCTORS ATLOW-TEMPERATURES

We have examined drift mobility of holes in Ge:Ga semiconductor crysta ls with low compensation at low temperature (2-4 K) through the measur ement of magnetoresistance. The hole mobility of Ge:Ga with Ga concent ration of 2 x 10(14) cm(-3) is 5.1-6.6 x 10(5) cm(2) V-1 s(-1) at bias field of 1.2 V/cm at 2-4.2 K and that with Ga concentration of 1 x 10 (14) cm(-3) is larger by a factor of 1.5. The dependence of the hole m obility on temperature is small. These experimental results clearly sh ow that the mobility of holes is mainly determined by neutral-impurity scattering. The dependence of the hole mobility on bias electric fiel d is also small. Ge:Ga crystal uniaxially stressed at about 6 x 10(3) kg/cm(2) shows larger hole mobility by a factor of 1.5 than the unstre ssed Ge:Ga when they are compared at nearly zero bias field at 2 K, bu t they have almost the same value when compared at the bias field of a half of each breakdown field. The hole lifetime of the stressed Ge:Ga , which is derived from the photoconductive gain using the measured ho le mobility, is 60 times longer than that of the unstressed Ge:Ga.