GE-GA FAR-INFRARED PHOTOCONDUCTOR WITH A LOW GA CONCENTRATION OF 1X10(14)CM(-3)

Germanium doped with gallium (Ge:Ga) far-infrared photoconductors with a Ga concentration of 1 x 10(14) cm(-3) are fabricated or use in sens ors for detecting extremely weak radiation, such as for astronomical o bservations by a space-borne cooled telescope, The performance of the photoconductor at low temperatures and under low background photon inf luxes to simulate operation in a space environment was evaluated, The responsivity of the new Ge:Ga photoconductor is approximately double t hat of the previous Ge:Ga photoconductors with a Ga concentration of 2 x 10(14) cm(-3) which was developed for astronomical observations usi ng the Infrared Telescope in Space (IRTS) satellite. This increase in responsivity: which is proportional to the product of hole mobility, h ole lifetime, and quantum efficiency, is interpreted as being due to t he enlargement of both hole mobility and hole lifetime and also becaus e or almost equal quantum efficiency due to the utilization of a metal cavity in which the photoconductor is mounted, The new photoconductor has a slow transient response to a step change in photon influx simil ar to that in the previous photoconductors, but its magnitude is large r than that: of the previous ones. We found good agreement between the time constants estimated from curve-fitting lu the response to a step change in photon influx and the transient time constants derived by a nalytical considerations based on the two-region, model of the Ge:Ga p hotoconductor with ion-implanted ohmic contacts.