Intrinsic, p-type and n-type samples were grown separately at low temperatures, together with a combined p-i-n structure. These were used to study the formation of As precipitates during annealing (800C). In the case of the separate structures, the fewest precipitates were found in n-type material. The highest density of precipitates appeared in the n-type region of the p-i-n structure. In addition, a clear band which was depleted of precipitates existed in the intrinsic region near to the n/i interface. A vacancy model, which included Fermi-level effects and the crystal bonding strength (thermodynamic factor), was developed in order to explain the results. Thus, in n-type material, Ga vacancies were favoured over As antisites; which gave rise to lower As precipitation in n-type low-temperature material than in p-type material. However, in the case of the p-i-n structure, AsGa diffused to a vacancy-rich region and increased the As precipitate concentration. In heterostructures, more As precipitates formed in regions which had lower melting points (bond energies) because of the higher vacancy concentration; which encouraged the influx of AsGa.

M.N.Chang, J.W.Pan, J.I.Chyi, K.C.Hsieh, T.E.Nee: Applied Physics Letters, 1998, 72[5], 587-9