Sodium overlayers on n-type and p-type InP(110) surfaces

The formation of Schottky barriers at the interface between sodium and the clean cleaved InP(110) surface has been studied both during the initial stages of metal deposition and for thick metal contacts. Measurements of the current-voltage characteristics for the metal-n-InP contact indicate clear rectification with a calculated barrier height, Φ_BN=0.52-0.55 V. For diodes prepared in the same way on clean cleaved p-type InP(110) surfaces a barrier height, Φ_BP=0.82-0.87 V is obtained. The microscopic interactions occuring at the Na-n-InP interface for low metal coverages were investigated by soft X-ray photoelectron spectroscopy (SXPS). This data indicates that the interface is chemically reactive with evidence of rigid shifts in peak position associated with the movement of the surface Fermi level. The measured value of the barrier height for this low work function metal-III-V semiconductor interface cannot be accounted for by simple theory and so the results are discussed in terms of more recently proposed models of Schottky barrier formation.