Characteristics of BeTe films grown by molecular beam epitaxy

Systematic investigations are performed on the surface morphology, structural properties, and p-type dopability of BeTe epilayers grown on GaAs (001) by molecular beam epitaxy under various growth temperatures and p(Te)/p(Be) flux ratios. A phase diagram for surface reconstruction is obtained with regard to the BEP (beam equilibrium pressure) ratio of p(Te)/p(Be) and growth temperature. Irrespective of growth temperature (300-500 degrees C), a surface phase transition from weak (4 x 1) to (2 x 1) reconstruction occurs near p(Te)/p(Be)similar to 10 as the p(Te)/p(Be) value increases. Epilayers grown at a low Te pressure of p(Te)/p(Be)less than or equal to 10 show Be droplets on the surface as observed by atomic force microscopy, which eventually leads to degraded crystallinity. It is noted that such growth features are different from conventional II-VI compounds. The differences in growth features are discussed in terms of the relationships between the equilibrium vapor pressures of the compound and constituent elements. By optimizing growth conditions, i.e., flux ratio of 15 <p(Te)/p(Be)<20, epilayers with high structural quality and smooth surface are obtained. Good correlation between the surface morphology and crystallinity is found. p-type BeTe layers doped with N are grown using a radio-frequency nitrogen plasma source. The net acceptor concentration increases as the p(Te)/p(Be) flux ratio is decreased. It is shown that p-BeTe with high hole concentrations above 6x10(18) cm(-3) can be readily grown. (C) 2000 American Vacuum Society. [S0734-2101(00)00502-9].