Electrically adjustable intersubband absorption of a GaN∕AlN superlattice grown on a transistorlike structure

The authors report on electromodulated intersubband (ISB) absorption experiments on AlN∕GaN superlattices (SLs) grown on a transistorlike structure. A sample containing five SL periods shows two distinct absorption peaks related to ISB transitions in the SL and in the two dimensional electron gas located at the interface of the lowest SL barrier and the underlying GaN buffer. The ratio of those two absorption peaks can be adjusted by applying an external field, which influences the overall band structure and, more specifically, the free carrier density in the SL. This is a proof of concept of an on-off electro-optical modulator at 1.5μm.