Effects of deep n-implants on the electrons' transport in silicon drift detectors

A silicon drift detector has been designed to experimentally verify the effects of deep n-implants on the electrons' transport. Regions of deep n-implants have been introduced underneath the p(+) field strips in close proximity to one detector surface. The presence of deep n-implants reduces the amplitude of the potential perturbation that propagates into the semiconductor volume caused by the segmentation of the p(+) strips. As a consequence higher carrier velocities and more insensitivity to surface properties can be obtained with respect to the conventional design (without deep n-implants). This effect is of particular interest when carrier transport must take place at few micrometers from the surface and when position sensing requires the measurement of the drift time. The experimental characterization of the electron velocity as a function of the drift field and the interpretation of the results are reported. At 11 mum from the surface and with a drift field as low as 25 V/cm in presence of deep n-implants we measured an electron velocity of 0.027 cm/mus.