Effects of growth interruption upon silicon delta layers in gallium arsenide

We describe a study of samples grown by molecular-beam epitaxy, designed to examine the limitations to silicon (Si) δ-doping of gallium arsenide (GaAs) at elevated growth temperatures. Samples (Si δ-doped to 1 × 1013cm−2) were grown at 630°C, during which the growth was paused (for times between 0 and 18 min) after depositing the Si. Total electron sheet densities were measured (using Hall and Shubnikov-de Haas (SdH) effect measurements) to determine the electrically active Si concentration. The free electron concentration showed a reduction from about 8 × 1012cm−2 for zero pause time, to 5 × 1012cm−2 for 18 min pause time. These results can be explained convincingly using simple models of impurity background in the MBE chamber or surface aggregation. Further experiments to distinguish these mechanisms are discussed.