Germanium clean surfaces

Schlier, R. E. and Farnsworth, H. E. Structure and adsorption characteristics of clean surfaces of germanium and silicon. Journal of Chemical Physics 30, 917 (1959). 

Hovis, J. S., Hamers, R. J. and Greenlief, . M. Preparation of clean and atomically flat germanium(OOl) surfaces. Surface Science 440, L815-19 (1999). 

METHODS OF OBTAINING atomically-clean surfaces of solids are listed with comments on their advantages and limitations. The method of argon-ion bombardment is reviewed with a discussion of the operating conditions and precautions necessary for successful results. The low-energy electron-diffraction method is used to determine the condition of the surface. Experimental results indicate that the relative positions of the atoms in the clean (100) surface planes of germanium and silicon are not the same as those of similar planes in the bulk crystals. 

Knowledge of the adsorption of hydrogen on silicon and germanium surfaces is important in order to obtain information on interfacial phenomenon of semiconductors. The adsorption of hydrogen on Si (111) surfaces is one of the best understood systems, although the exact nature of the clean surfaces is not well understood. 

This is a specialised technique which has been applied in field emission and field ion microscopy (see Section 2.1.5c). It is achieved by giving the tip a positive potential. Tungsten can then be removed at liquid helium temperatures with an applied field of 5.7 x 10 V.cm Perfectly regular surface structures are exposed containing many different lattice planes. Clean surfaces have been produced on tungsten, nickel, iron, platinum, copper, silicon and germanium. It is potentially applicable to a wide range of materials, but the area of clean surface exposed is only about 10 ° cm . 

The atomic relaxations visualized here are small repositionings of surface atoms. This is shown by the ease with which such relaxation transformations can take place. For example, Palmberg 346) has made the observation that the Ge(lll)-(2 x 8) and Ge(lll)-(1 x 2) clean surface structures relax to (1 X 1) when sodium is deposited with the germanium crystal held at the very low temperature of — 195°C. 

Results for the clean (100), (111), and (110) germanium faces and the (100) silicon face indicate that the atomic positions in the surface planes are not the same as the corresponding positions in the bulk structure. .. It is to be noted that half-integral-order beams are present in the (Oil) azimuth... The presence of half-integral-order beams. .. requires a double spacing in (110) azimuth but a single spacing in the (100) azimuth. .. The observed structures are not due to surface contamination but are characteristic of atomically clean surfaces [15]. 

Kim, J., Saraswat, K. and Nishi, Y. Study of germanium surface in wet chemical solutions for surface cleaning applications, ECS Transactions 1, 214—219 (2005). 

A BRIEF REVIEW of the research in semiconductor surface physics is presented. Emphasis is placed on die limits of present theory and the importance of knowing the composition and structure of the surface of interest. The feasibility of new experimental approaches to the study of surfaces such as nuclear magnetic resonance and quadrupole res -onance is discussed. A review of recent developments in an understanding of the energy level diagram of the cleaned germanium surface is reviewed. 

Recently Koutecky (23) has shown that localized subsurface states may also occur if the perturbing potential due to the existence of the surface is large enough. These states would have wave functions localized about subsurface atoms and their energy in the forbidden zone would be between the surface states and the band out of which the states had been perturbed. These treatments have all assumed that the potential depends only on the direction into the crystal a one-dimensional potential. The discussion above of the cleaned germanium surface has shown that a three-dimensional potential may be necessary. A second failing of these treatments is their lack of consistency the effect on the potential of the filling of the surface states with... 

We have not yet studied the Influence of inhibitors on germanium electrodes. The problem is that germanium dissolves in parallel with most redox reactions at germanium electrodes. The dissolution causes a steady cleaning of the surface which should hinder the effect of contamination. The situation is very complicated in the case of cathodic polarization where the surface is covered with hydrogen atoms which act in some respects as inhibitors for others like catalysts. 

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