Hydrogen and thermal deoxidations of InSb and GaSb substrates for molecular beam epitaxial growth

Oxide removal processes for InSb(100) and GaSb(100) substrates utilizing exposure to molecular hydrogen at moderate temperatures were studied in an experimental UHV chamber and were compared to the common method of thermal oxide desorption (TOD). Molecular hydrogen cleaning (MHC) deoxidizes the substrate surfaces effectively at temperatures of ∼100 and ∼200 °C lower than that in TOD of GaSb and InSb, respectively. Closely related hydrogen based procedures for the cleaning of these materials before molecular beam epitaxial growth were developed. In these procedures a very low flux of atomic hydrogen was used in order to achieve short, yet mild, deoxidation of the substrates both with and without an Sb flux. These mild atomic hydrogen cleaning (MAHC) methods give smoother, cleaner, and more perfect InSb and GaSb surfaces after a shorter cleaning cycle at temperatures of 100-200 °C lower than that in TOD. An Sb flux is not necessary in MAHC, but if used it gives a smoother substrate surface, and a well ordered epilayer surface is achieved already after just a few epitaxially grown monolayers. This surface is of comparable quality to that prepared by a combination of TOD and relatively thick buffer layer growth. MHC and MAHC are more efficient for the case of InSb than for that of GaSb, since on GaSb a nonvolatile Ga2 O passivating layer is formed, whereas In2 O3 is reduced effectively to volatile species already at temperatures as low as 250 °C. For InSb the whole MAHC process can be carried out either during the heating stage of the substrate to the growth temperature or in a preparation chamber at 250 °C without an Sb flux.