Investigation of cadmium-donor pairs in silicon

Abstract

The formation of indium-donor pairs (donors: P, As, Sb) in silicon is identified by perturbed angular correlation spectroscopy. After the electron capture decay of the 111 In probe atoms to 111 Cd, the electric field gradient (EFG) is measured at the corresponding cadmium-donor pairs. For all three complexes a similar temperature dependence of the EFG is observed which can be explained quantitatively by a model based on the charge state of the cadmium-donor acceptors. The corresponding energy levels are given.

Exploring solid state physics properties with radioactive isotopes

“…The implantation dose for 111m Cd was of the order of 5 × 10 12 to 5 × 10 13 cm −2 , resulting in a maximum peak concentration for Cd of 10 18 -10 19 cm −3 . The values measured at low temperatures are identical within the experimental accuracy (∼ 1 MHz) [154,157,158].…”

“…With increasing temperature the Fermi level shifts to the centre of the energy gap and the probability to find the Cd-D acceptor in its neutral state Cd-D 0 increases. The temperature dependence of the EFG is determined by the Fermi statistics and figure 28 shows the results of a fit of this theory to the data [157,158].…”

“…In silicon, however, at least the Cd-donor pair reveals a strong temperature dependence, which can be explained by assuming a deep level for this configuration. In the case of a deep level the strong localization of the charge carriers results in a drastic temperature dependence of the corresponding EFGs [154,158,160]. Therefore one has to assume that no charge fluctuations at the Cd-donor complexes in Ge are observable due to one of the following reasons: • the corresponding Cd-donor complex is electrically inactive • it is a shallow level and the valence electron wavefunction is delocalized • it is a deep level but the position of the Fermi level allows either no ionization (→ static EFG) or only full ionization (→ motional narrowing).…”

The Potential of the Perturbed Angular Correlation Technique in Characterizing Semiconductors

“…In the past, PAC spectroscopy has been utilized to observe the dopant-defect/dopant interaction in various semiconductors, e.g., using 111 In/Cd probe atoms, In-defect/dopant pairs have been observed in Ge 11,12 and Si. [8][9][10][17][18][19]44 Recently, we have observed such pairs with 100 Pd/Rh probe atoms in highly doped Si, i.e., Pd-vacancy defect pair in highly doped n-Si 41 and Pd-B defect pair in highly doped p-Si. 42 The corresponding PAC spectra are shown in Fig.…”

“…2b, 1 where the sample containing the radioactive probe atoms is placed at the center of the detector assembly. 37 Recently, PAC measurements using LaBr 3 (Ce) scintillator detectors have been performed with 44 Ti probe atoms, where the c-c cascade of 68 keV to 78 keV could easily be resolved. 38 The times of the start and stop signals are determined by constant fraction discriminators (CFD) before being fed to a time-to-amplitude (TAC) counter.…”