Double carrier pulse DLTS

DC-DLTS is used in asymmetric n+-p or p+-n junctions (Khan et al., 2005). It aims to check whether a trap is a recombination center or not. As shown in Fig. 1, two pulsed biases are applied to the sample, in turn, to inject majority and minority carriers to an electron trap. At the initial state, the junction is under reverse bias, and the energy level ET of the trap is higher than the Fermi level (EFn).When the first pulse voltage is applied to the sample, EFn is higher than ET, which allows the trap to capture electrons. During the second reverse biased pulse, with a duration tip, holes are injected to the SCR from the p-side of the junction. After the junction pulse is turned off, electrons and holes are thermally emitted. The amount of trapped carriers can be observed as a change in the DLTS peak height of the trap. If the trap captures both electrons and holes, the DLTS maximum of the corresponding level decreases compared with that in conventional DLTS. Such a decrease is explained by the electron-hole (e-h) recombination process, which indicates that the level is a recombination center. 1

To formulate the recombination process, we consider the same notation in § 2.1.2, with assuming that n & ND. The relationship between the total density of recombination centers and that only occupied by electrons in the n-side of the junction can be expressed by

where <p) is the average of injected holes. As a solution of Eq. (10), we have

<dn – _ nT (t, P) = птИ + [nT (0)-nT (®)]exp(-—) (11)

dt t

where nT(<») = (<p)cp+ en)/(T"1NT), г*1 = <p)cp+ NDcn + en + ep), and tip is the width of the injected pulse. Considering the IDLTS and IDC-DLTS the peak heights of the recombination center in conventional and DC-DLTS, respectively. Equation (11) can be rewritten properly as

nT (tip ) _ ( IDLTS 1DCDLTS )

NT

Similarly for hole trap in the p-side of a n+-p junction, which acts as recombination center, we obtain

where <n) is the average of injected electrons.