Transformation of Gold in N-Type Silicon from a New Deep Level to the Gold Acceptor Level

Abstract

ABSTRACTUsing deep level transient spectroscopy (DLTS) on gold-doped n-type Czochralski (CZ) and float zone (FZ) silicon we observe a new gold-related acceptor level (G) with an activation energy σn= 0.19 eV and an electron capture cross section On = 1–10-17 cm2. The center anneals out at a temperature of 250°C, simultaneously as the gold acceptor concentration increases. Annealing at temperatures below 250°C does not reverse this process. However, etching a few microns off the sample surface using HF:HNO3 based etch reforms the G center and the gold acceptor concentration decreases accordingly. From DLTS depth-profiling we determine that the new center is only found at depths less than 5 μm, and in the same region we observe neutralization of phosphorus dopants and a reduction in the gold acceptor concentration.We propose that in-diffusion of hydrogen during the etching process is responsible for the three observed transitions, i.e. neutralization of both phosphorus donors and gold acceptors and formation of the G center. We suggest that there are (at least) two possible Au-H complex centers, one which is electrically inactive and another which gives rise to an acceptor level (ΔE = 0.19 eV) in the bandgap of n-type silicon. The electrically active center anneals out at 250°C while the electrically inactive one is more stable and has been observed earlier in remote plasma hydrogenation experiments performed at 150–350°C.