  Inserting molecular monolayers within metal / semiconductor interfaces
provides one of the most powerful expressions of how minute chemical
modifications can affect electronic devices. This topic also has direct
importance for technology as it can help improve the efficiency of a variety of
electronic devices such as solar cells, LEDs, sensors and possible future
bioelectronic devices, which are based mostly on non-classical semiconducting
materials (section 1). The review covers the main aspects of using chemistry to
- control alignment of energy levels at interfaces (section 2): - passivate
interface states (section 3), - insert molecular dipoles at interfaces (section
4), - induce charge rearrangement at and around interfaces (section 5). After
setting the stage, we consider the unique current-voltage characteristics that
result from transport across metal / molecular monolayer / semiconductor
interfaces. Here we focus on the interplay between the monolayer as tunneling
barrier on the one hand, and the electrostatic barrier within the
semiconductor, due to its space-charge region (section 6), on the other hand,
as well as how different monolayer chemistries control each of the these
barriers. Section 7 provides practical tools to experimentally identify these
two barriers, and distinguish between them, after which section 8 concludes the
story with a summary and a view to the future. While this review is concerned
with hybrid semiconductor / molecular effects (see Refs. 1,2 for earlier
reviews on this topic), issues related to formation of monolayers and contacts,
as well as charge transport that is solely dominated by molecules, have been
reviewed elsewhere[3-6], including by us recently[7].
