Size Distribution Effects on Mobility and Intraband Gap of HgSe Quantum Dots

In this work, we investigate the effect of size distribution on the mobility, the conductivity gap, and the intraband photoconduction of HgSe colloidal quantum dots (CQDs). Using electrochemistry, we measure the mobility for a series of ethandithiol cross-linked n-doped HgSe quantum dot films with different size distribution but a similar average size. The results show that mobility is exponentially dependent on size dispersion. This is interpreted as the size dispersion causing an increase in the average activation energy for hopping transport and the effect is reproduced by a model and a simulation. Comparing with the interband HgTe where the optical gap is between the valence and the conduction band, the conductivity gap in n-doped HgSe between the 1Se and 1Pe states is more strongly softened by the size distribution. This harms the intraband photoconductive properties and it implies that improved size distribution will be needed when using intraband photodetectors.