An STM and LEED study of MOCVD-prepared P/Ge (1 0 0) to (1 1 1) surfaces

Certain device applications such as high-efficiency multijunction III–V solar cells require high-quality GaAs deposition on Ge substrates. Commercially, this is done using metal-organic chemical vapor deposition (MOCVD). If the GaAs is grown directly on Ge, pre-deposition etching of the Ge substrate by arsine can roughen the surface, producing poor GaAs/Ge epitaxy. If instead a GaAs/GaInP2/Ge growth sequence is used, the template for growth is a phosphine-exposed P/Ge surface. Indeed, high-quality GaInP2 and GaAs films are routinely grown using this method, yet little is known about the initial P/Ge surface. For this reason, we have conducted a survey of MOCVD-prepared P/Ge(mnn) surfaces, over the 54.75° range of surfaces between (1 1 1) and (1 0 0). Low-energy electron diffraction (LEED) and atomic-resolution scanning tunneling microscopy (STM) images reveal interesting new reconstructions on very flat surfaces. Almost all of the surfaces support ordered defect arrays, presumably to relieve P-induced surface stress.