Vacancy generation during Cu diffusion in GaAs

Abstract

Positron lifetime and Doppler broadening spectroscopy were applied for a study of defect properties of semi-insulating GaAs after diffusion of copper. A 30 nm layer of Cu was deposited by evaporation to the undoped GaAs samples. The diffusion of Cu was performed during an annealing step at 1100 °C at different arsenic vapor pressures. The samples were quenched into room temperature water. The initial semi-insulating (SI) undoped GaAs sample shows no positron traps. After annealing, a vacancy-type complex and a shallow positron trap were observed to be efficient positron traps. Due to the Cu contamination during the annealing process, the shallow trap is believed to be the CuGa double acceptor. The nature of the vacancy-type defects could not be determined unambiguously. The concentration of these vacancies shows inverse relationship to the As vapor pressure that refers to the arsenic vacancy as a part of this complex. Moreover, Doppler-coincidence spectroscopy shows clearly that Cu atoms are not bound in the direct vicinity to the observed vacancies.

Defect Study in CoCrFeMnNi High Entropy Alloy by Positron Annihilation Lifetime Spectroscopy

“…The average lifetime decreases with decreasing measurement temperature. An average lifetime of 129 ps is This behavior of the temperature-dependent average positron lifetime is well known in semiconductors and ascribed to detection of shallow positron traps, [13][14][15][16][17][18] where negative ions act as non-open volume shallow positron traps. Interstitial clusters of alloying elements and dislocation lines act as shallow positron traps in alloys, as mentioned above.…”

Identification of defect properties by positron annihilation in Te-doped GaAs after Cu in-diffusion

“…Finally, their concentration drops below the sensitivity range of the positrons. 32,46 The vacancy clusters may also be dissolved, which would lead to a disappearance of the vacancy signal, too. These two possibilities cannot be discriminated by the obtained data alone.…”

“…In the samples under investigation, after Cu diffusion, Cu double acceptors act as shallow trap centers. 32 It was suggested that residual impurities (e.g. C − As ) and native defects, such as gallium antisite, Ga − As , are responsible for the formation of negative centers acting as shallow traps for positrons in undoped GaAs.…”

“…It was found that Cu atoms form double acceptors Cu 2− Ga which act as a positron shallow trap. 32 The coincident detection of both 511-keV gamma quanta from one annihilation event reduces the disturbing background and hence permits the observation of the high-momentum annihilation distribution. [19][20][21] Ga vacancies in Si-doped GaAs were observed using coincidence Doppler-broadening spectroscopy (CDBS).…”

“…Coincidence Doppler-broadening spectroscopy showed that Cu is not bound to the observed vacancy complex. 32 Cu in-diffusion in the investigated samples was performed upon annealing the samples at 1100 • C under different As pressure, where the samples were covered with a thin layer of Cu. These Cu pre-introduced samples were subjected to isochronal annealing at ambient conditions, containing no further Cu source, which leads to Cu out-diffusion.…”