Variable-energy positron beam spectroscopy and X-ray photo-electron spectroscopy were used to study excess As and related defects in samples which had been grown by means of molecular beam epitaxy at low temperatures. The use of X-ray photo-electron spectroscopy revealed the presence of about 1.3% of excess As in as-grown low-temperature material, and a non-uniform depth profile of the As concentration in annealed low-temperature material. On the basis of S-parameter data, a non-uniform depth profile was deduced for defects in annealed low-temperature material. From a similarity between the depth profiles of the S-parameter and the As concentration, it was concluded that the positrons were trapped in vacancy complexes that were associated with As clusters in annealed low-temperature material.

N.Hozhabri, A.R.Koymen, S.C.Sharma, K.Alavi: Applied Surface Science, 1995, 85, 311-4