Self-assembled monolayers of Lewis bases: effects on surface and interfacial electronic properties in III-V optical semiconductors

The nature and disposition of surface states can have a dramatic effect on the near-surface electronic properties in semiconductor heterostructures. In particular the lack of a well-defined surface oxide in III-V materials means that surface band bending can cause surface recombination velocities to be up to 10³ larger than in Si-based materials. Raman scattering by coupled longitudinal optic phonons and 2D electron gas electrons in In _0.52Al_0.48AsIn_0.53Ga_0.47As δ-doped heterostructures is used to demonstrate the extreme sensitivity to surface states. The two highest frequency modes, of the three coupled electron-phonon modes expected in this system, were observed, with the L₊ mode being identified for the first time in InGaAs-based systems. The large dispersion of this mode makes it a particularly sensitive probe for changes in such properties as carrier concentration and subband energy. For structures with higher carrier concentrations coupling of the longitudinal optic phonon to multiple electron intersubband transitions is resolved. In order to passivate native surface states organic thiols are being investigated. Measurements on bulk GaAs indicate a change in the surface depletion region thickness, within the abrupt junction model, of up to 50 angstrom (ca. 30%). Changes in carrier scattering times up to 50% have also been observed.