Growth and annealing of GaInAsN: density-functional calculations on the reactions of surface and bulk structures

Abstract

Various experiments provide a blueshift of the band-gap during the annealing of grown GaInAsN alloys. For explanation of this effect the structure formation during the growth process at the surface as well as the changes of the as-grown bulk structure during the annealing is investigated using density-functional calculations. To find the GaInAsN bulk structures formed during the deposition at the (0 0 1) surface the reaction behaviour of dimethylhydrazine (DMH) as special precursor molecule and of nitrogen, arsenic, gallium, and indium atom pairs is investigated using cluster models for surface steps. A nitrogen deposition by DMH is only possible under high DMH exposure and balanced growth temperature. From In-substituted steps metastably bound nitrogen atom pairs are desorbed especially easy. Therefore, nitrogen atoms are preferentially deposited in the Ga 2In 2N, Ga 3In 1N, and Ga 4N units in rising order. At arsenic atoms the indium and gallium atoms should be distributed in the gas-phase relation. The annealing behaviour of bulk structures formed by deposition is investigated using energetic data calculated by the density-functional supercell method. Ga 4− m In m N centres are the most stable arrangements in the bulk. During the annealing process nitrogen atoms move from the Ga 4N centres to isolated indium atoms or pairs of indium atoms by N/As exchange. This is supported by the calculated blueshift of the band-gap during the exchange process, which agrees well with the experimental observed blueshift.