Photoinduced current transient spectroscopy of deep defects in n-type ultrapure germanium

Photoinduced current transient spectroscopy (PICTS) is used to study deep minority carrier traps in n-type ultrapure germanium (shallow concentration of the order 109 cm−3). In this technique, which is a variant of deep level transient spectroscopy (DLTS), a neutral structure with two ohmic contacts applied on two opposite faces of the sample is illuminated through one of the contacts with intrinsic, strongly absorbed light. The current transients which follow after interrupting the photoexcitation are analyzed using classical double lock-in DLTS resulting in the detection of centers in the minority half of the band gap (provided the back ohmic contact is negative). After correcting the PICTS spectra for the temperature dependence of the mobility, six peaks superimposed on a broad background are clearly resolved. The peaks are the same as the ones found earlier in high-purity n-type germanium (shallow concentration of the order 1010 cm−3) using optical DLTS. These peaks are mainly Cu related. A formula to...