Short-period superlattices: is thinner better?

For type-II superlattices with spatially indirect optical transitions across the band gap, short-period superlattices are often employed. The oscillator strength of intraband transitions, from holes states confined in one layer to electron states confined in a neighboring layer, are enhanced by increasing the wave function overlap of these states through reduced superlattice period. However, there are limits to accurately controlling an epitaxially grown semiconductor superlattice structure as the number of monolayers in each layer is decreased. For InAs/GaSb type superlattices, periods of 40Å or less are relevant to mid-infrared detection. Characterization and modeling results for a series of InAs/GaSb superlattices with periods ranging 50Å to 20Å will be presented. These results explore the break point between when thinner is better and when reducing the period no longer optimizes the superlattice optical performance.