Ätzuntersuchungen an natürlichen Spaltflächen von (Ga,Al) As/GaAs-Heterostrukturen

This communication reports on etching of {110} cleaved faces of (Ga,Al)As/GaAs heterostructures with and without an additional pn-junction. The etching agents are dilute HNO₃ and mixtures of NH₃ and H₂O₂. The lines appearing in the etch patterns are attributed to the related steep changes in the physicochemical features of the crystals. The etch patterns can be correlated with the aluminum concentration profiles throughout the epitaxial layers as obtained by electron microprobe analysis. The optimum temperatures, times and compositions of the etch solutions are given. Preferential etching of GaAs by NH₃/H₂O₂ mixtures is discussed.     

Untersuchung epitaktischer Molybdänkarbidschichten an Molybdän-(110)-Oberflächen

The initial phases of high temperature (1700 K) carburization of (110) molybdenum surfaces by C₆H₆ at low pressure are examined with low energy electron diffraction (LEED) and emission electron microscopy. After an exposition of about 8 · 10⁻⁵ Torr · sec a (4 × 4) superstructure was observed by means of LEED, interpreted as coincidence lattices with the Mo₂C (10.0) plane parallel to the Mo (110) surface. Heating a sample without further exposition resulted in the appearance of a complex and of a (2 × 2) superstructures. After an exposition of about 2 … 9 · 10⁻³ Torr · sec needle shaped molybdenum carbide crystallites grew on the surface into the [111] and [111] directions. The orientation Mo₂C (10.1) parallel to Mo (110) was concluded from the LEED patterns.