Effect of As flux on InAs submonolayer quantum dot formation for infrared photodetectors

The performance of infrared photodetectors based on submonolayer quantum dots was investigated as a function of the arsenic flux. All the devices showed similar figures of merit and a very high specific detectivity above 1 × 1011 cm Hz1/2/W at 12 K, despite the fact that cross-sectional scanning tunneling microscopy images pointed out a strong reduction in the density of such nanostructures with decreasing arsenic flux. This contrast is a consequence of the small size and low In content of the submonolayer quantum dots that lead to a strong delocalization of the electrons wave function and, therefore, reduce the advantage of samples having a very high density of quantum dots. A simple strain model showed that the properties of these nanostructures are limited by the lack of vertical alignment of the small two-dimensional InAs islands resulting from the strong segregation of In atoms. We have proposed some ways to improve the growth of submonolayer quantum dots and believe that, after further optimization, such nanostructures might provide devices with superior performance.