COVALENT CHARGE TRANSFER IN 3-V COMPOUNDS

Covalent charge transfer in GaAs, InAs and GaSb has been determined from electron density synthesis of x-ray diffraction data for powder samples. The distribution of valence electrons was determined by means of an extended difference synthesis. The experimental results indicate that there is a transfer of electronic charge from the V atom to the III atom giving es * = -0·52±0·05 e for GaAs, -0·46±0·05 e for InAs and -0·50±0·05 e for GaSb. This configuration suggests that the bonding is intermediate between covalent and neutral bonding types. Polar mobilities were recalculated for these compounds. The charge transfer was compared with the results of optical measurements. The optical values are consistent with the x-ray values if the effects of the difference in polarizability of the atoms is taken into account. From an empirical relation, the covalent charge transfer was deduced to be -0·52 e for InP and -0·53 e for GaP. The significance of suitable atomic scattering factors in the determination of valence structure is discussed. Interpretation of piezoelectric measurements yields e s* = -0·46 e for AlSb.