Microwave sensing of nanostructured semiconductor surfaces

In this paper, we present a method for the characterization of the lifetime of photoinduced carriers in semiconductor nanostructures based on the interaction of the photocarriers with the evanescent electric field of a microwave, propagating in a coplanar waveguide. The limited spatial extension of the evanescent field ensures that only a defined portion of material is analyzed. The nanostructures are illuminated by pulses of ultraviolet light which ensures that absorption and photogeneration occur mainly within the semiconductor nanostructure. Absorption due to photogenerated carriers produces weak variations of the power of microwaves travelling along the coplanar structure. Time variations of transmitted power through the waveguide thus follow the time variations of photogenerated charges. The technique is completely contactless, and ensures fast and non-destructive test capability. The measurement was applied for monitoring of lifetime of photogenerated carriers in macroporous silicon, proving to be strongly effective.