THE LATTICE LOCATIONS OF SILICON ATOMS IN DELTA-DOPED LAYERS IN GAAS

We have used secondary ion mass spectrometry, local vibrational mode infrared absorption, and electrical characterization to study the incorporation of Si delta-doped planes in GaAs grown by molecular beam epitaxy at 400-degrees-C, in the concentration range 0.01-0.5 monolayers. A correspondence is observed between the density of Si(Ga) donors, the free electron concentration and the total Si coverage, up to a coverage of approximately 10(13) cm-2; however, above this value, the electron density falls, while [Si(Ga)] remains constant up to a coverage of approximately 10(14) cm-1, and then falls below the detection limit at 0.5 monolayer coverage. These effects have been interpreted in terms of a model which takes account of Si migration and aggregation on the delta-doped plane during deposition.