Origin of a surface state above the Fermi level on Ge(001) and Si(001) studied by temperature-dependent ARPES and LEED

P. E. J. Eriksson, M. Adell, Kazuyuki Sakamoto, R. I. G. Uhrberg
2008 Physical Review B  
Origin of a surface state above the Fermi level on Ge(001) and Si(001) studied by temperature-dependent ARPES and LEED, 2008, Physical Review B. Condensed Matter and Materials Physics, (77), L8, 085406-1-085406-5. http://dx. Variable temperature photoemission studies in the literature have revealed the presence of a surface state above the Fermi level on clean Ge͑001͒. We present photoemission and low energy electron diffraction results from Ge͑001͒ obtained between 185 and 760 K. Our
more » ... 60 K. Our measurements show a peak above the Fermi level with a maximum intensity at a sample temperature of around 625 K. At higher temperatures, we observe a gradual decrease in the intensity. Angle resolved spectra show that the surface state has a k ʈ dependence and is therefore not attributed to defects. Very similar results were obtained on both an intrinsic ͑30 ⍀ cm͒ and a 10 m ⍀ cm n-type sample. The overall appearance of the spectral feature is found to be quite insensitive to sample preparation. Low energy electron diffraction investigations show how the sharp c͑4 ϫ 2͒ pattern becomes streaky and finally turns into a 2 ϫ 1 pattern. The onset of the structure above the Fermi level takes place just before all c͑4 ϫ 2͒ streaks have disappeared which corresponds to a temperature of around 470 K. On Si͑001͒, we also observe photoemission intensity above the Fermi level. It is weaker than on Ge͑001͒ and appears at higher temperature. We find that the emission above the Fermi level can be explained by thermal occupation of the * band derived from a 2 ϫ 1 ordering of asymmetric dimers on the surface.
doi:10.1103/physrevb.77.085406 fatcat:dl4txuf4rrgm5e36inmsijksmu