Effect of magnetic field on GaAs photo-conductive detectors

A photo-conductive detector (PCD) with active medium such as GaAs can be a useful plasma diagnostic, particularly in the EUV-to-soft X-ray regime. However, for laser-plasma or other high-bandpass applications, an important limitation can be a relatively long output decay time. A major (sometimes dominant) contributor to this tail is the electron-hole recombination time. This can be shortened with dopants or crystal damage (e.g., from neutron irradiation), but such lattice disruptions also decrease detector responsivity and are, of course, permanent. The authors present an alternative scheme that decreases recombination time without affecting the material. This is done by using the Hall effect to concentrate the charge carriers, thereby increasing the probability of recombination per unit time. This mechanism, as manifested by detector decay times, was tested with GaAs PCDs of various geometries. As decay times were on the order of 1 ns, a 24 ps light pulse (Nd:YAG) was used as a stimulus to give an (effectively) delta-function input. Experimental observations of the effect of the magnetic field on decay times are presented