Impurity diffusion and layer interdiffusion in Al_xGa _1-xAs-GaAs heterostructures

Data are presented and a model describing the diffusion of the donor Si in GaAs from grown-in dopant sources. In addition, the effects of background impurities on Si diffusion and layer interdiffusion in Al_xGa _1-xAs-GaAs superlattices are described. These results are obtained on epitaxial GaAs samples with alternating doped and undoped layers and on Al _xGa_1-xAs-GaAs superlattices with doped (Si or Mg) layers. The layer-doped GaAs and the Al_xGa_1-xAs-GaAs superlattices have been grown using metalorganic chemical vapor deposition and are characterized using secondary ion mass spectroscopy and transmission electron microscopy. Different annealing conditions are used to study the interaction between the grown-in impurities and the native defects of the crystal controlling the diffusion processes. The model describing the impurity diffusion and layer (Al-Ga) interdiffusion is based on the behavior of column III vacancies, V_III, and column III interstitials, I_III, and the control of their concentration by the position of the crystal Fermi level and the crystal stoichiometry. Experimental data show that n-type Al _xGa_1-xAs-GaAs superlattices undergo enhanced layer interdiffusion because of increased solubility of the V_III defect, while enhanced layer interdiffusion in p-type superlattices is caused by an enhanced solubility of I_III. The model employed is consistent with the experimental data and with the data of previous work.