SI DELTA-DOPING IN GAAS - INVESTIGATION OF THE DEGREE OF CONFINEMENT AND THE EFFECTS OF POSTGROWTH ANNEALING

A stack of 60 delta-planes, each containing a Si areal concentration o f 3.4 x 10(14) cm-2 (approximately 0.5 monolayers, ML), grown in GaAs by molecular beam epitaxy at 400-degrees-C has been examined before an d after post-growth annealing by high-resolution x-ray diffractometry, transmission electron microscopy, secondar-ion mass spectrometry and infrared absorption localized vibrational mode (LVM) spectroscopy. The se techniques provided complementary information concerning the concen tration, spatial distribution and site occupancy of the Si atoms. It w as found for the as-grown samples that the Si was located on Ga lattic e sites (Si(Ga)) and confined to layers no more than 2 ML in thickness . Annealing at 600-degrees-C resulted in spreading of the delta-layers , with some Si remaining on the original planes, and the remainder dif fusing away, resulting in a Si concentration of 2.1 x 10(19) cm-3 betw een the delta-planes. LVM spectroscopy indicated that the diffused Si atoms were present as Si(Ga) donors, Si(As) acceptors, Si(Ga)-Si(As) p airs and Si-X complexes. After the samples were annealed at 800-degree s-C or 950-degrees-C only a uniform Si concentration of 3 x 10(19) cm- 3 was detected, although there was excess Si in the surface region whe re dislocation loops were observed. It is concluded that there is a ma ximum silicon concentration in solution that is in equilibrium with th e delta-layers at 600-degrees-C and that the Si in the delta-layers is present as dimers or larger 2D clusters.