|M.Sc Student||Tessler Renana|
|Subject||Investigation of InSb (001) Native Oxide Desorption and|
Surface Smoothing Induced by Hydrogen and Thermal
Annealing for Molecular Beam Epitaxial
|Department||Department of Physics||Supervisors||Dr. Cecile Saguy|
|Professor Alon Hoffman|
|Full Thesis text|
Indium Antimonide (InSb) is a narrow-gap (0.17 eV) III-V semiconductor which makes it suitable material for device applications. Producing high quality devices requires high quality layer growth. Molecular Beam Epitaxy (MBE) is a common technique used to grow InSb films on InSb substrates. This technique requires a smooth, oxide free, stoichiometric, and atomically clean surface. The removal of the native oxide layer on InSb proved to be difficult compared to other III-V materials.
In this research we report on the development of a new process used to desorb the native oxides from InSb(100). We examined several processes to desorb the oxides: thermal oxide desorption (TOD), atomic hydrogen cleaning (AHC) and molecular hydrogen cleaning (MHC). We investigated for each method the chemical composition, surface stoichiometry and morphological structure of the surfaces.
TOD was performed at 400 °C under ultrahigh vacuum conditions. It was found that TOD does not result in complete oxide removal from the surface. In addition, small droplets associated with In are produced at this annealing temperature. Surface stoichiometry shows In enrichment after TOD in vacuum above 360 °C.
AHC was utilized by exposure to atomic hydrogen produced by thermal cracker heated at 2000°C. The pressure in the vacuum chamber was kept at 5X10-7 Torr and the substrates were not heated intentionally during the exposure. It was found that AHC is able to desorb InSb native oxides. However, the desorption efficiency depends on the distance between the substrate and the cracker. The closer the cracker is to the substrate, the oxide desorption is faster. In all case, AHC results in oxide free and smooth surfaces with-out In droplets. AHC has several disadvantages: the hot tungsten filament should be heated at 2000°C inside the vacuum chamber with cracking efficiency of 5% at this temperature.
MHC was investigated for the first time in this study. This process involved the use of molecular hydrogen at relatively low substrate temperatures and without any Sb4 flux. MHC at substrate temperature of 250 °C and at hydrogen pressure of 5X10−6 Torr resulted in complete desorption of the native oxide layer. Following this process, the surface morphology of the samples was found to be very smooth with no droplet structure. In:Sb ratio was nearly stoichiometric with extra Sb concentration and was kept almost constant during the MHC process. Furthermore, annealing the sample at 400 °C in vacuum after MHC process maintains the surface smoothness and stoichiometry.