The use of laser doped Li contacts on semiconductor nuclear radiation detectors

Abstract

Ultra-thin (<0.1 μm), highly doped Li contacts have been fabricated on n- and p-type Ge and Si nuclear radiation detectors by the Q-switched ruby laser melting technique. Fwhm resolutions for 5.48 MeV α-particles of 17.4 keV on 2 kΩ · cm p-type Si, 21.7 keV on 300 Ω · cm p-type Si and 15.3 keV on p-type Ge ( N A - N D = 1.7 × 10 10 cm −3) were obtained. Best resolutions for 662 keV 137Cs γ-rays were 2.3 keV for n-type Ge ( N D - N A = 1 × 10 10 cm ⇔3) and 4.6 keV (pulser resolution 3.4 keV) for p-type Ge ( N A - N D = 6 × 10 10 cm −3). Used as an ohmic contact on a 90 kΩ · cm, n-type Si X-ray detector at 80 K the contact allows operation at 1300 V (depletion at 235 V). Crystal heating data and deep level transient spectroscopy results show significant laser damage in the contacts fabricated on Ge but far less damage on Si. Owing to the narrow fluence range, careful control of the homogenized laser output energy is necessary for good fabrication yields.