COMPENSATION PHENOMENA IN GAAS IMPLANTED WITH 1 MEV SILICON IONS

We have investigated the nature of the compensation phenomena that limit carrier activation in GaAs implanted with 1 MeV Si ions to a dose of 3 x 10(15) ions/cm2, and subsequently annealed at 900-degrees-C for 10 s. The depth profiles of the Si implants and the net carrier concentration, measured using secondary ion mass spectrometry and electrochemical capacitance-voltage profiling, respectively, reveal a large disparity in the region around the maximum of the Si distribution. Structural characterization, using ion channeling and transmission electron microscopy, reveals the formation of a buried band of interstitial dislocation loops in approximately the same region where the carrier concentration is highly compensated. However, previous works have shown that the remnant loops are not directly responsible for the deactivation of Si. The apparent paradox is resolved with the help of photoluminescence measurements as a function of depth performed on samples bevel-etched into a wedgelike shape. The photoluminescence experiments show that Si atoms sitting on As sites are mainly responsible for the compensation of the Si donors. Indeed self-compensation is to be expected due to the amphoteric nature of Si in GaAs. In addition, emissions corresponding to gallium-vacancy complexes, arsenic-vacancy complexes, as well as other implantation induced residual defects are observed. It is argued that a fraction of the vacancies and interstitials generated during the implantation collapse separately upon annealing giving rise to either vacancy-type defects or interstitial-type defects, respectively. The effect of these defects on the carrier concentration is discussed.