Quantum dot molecules for photovoltaic cell application

Abstract

We propose to significantly increase the density of self-assembled InAs quantum dots by growing quantum dot molecules using MBE growth with thin-capping-and-regrowth techniques. Anisotropic strain field of thin capped quantum dots leads to elongated nanostructures with nano-holes which become templates for the formation of quantum dot molecules during the re-growth process. Each of quantum dot molecules consists of 10-12 dots arranged in a specific pattern depending on the underlying templates. The dot density of quantum dot molecules is 3/spl times/10/sup 10/ cm/sup -2/, comparing to 10/sup 9/ cm/sup -2/ of typical quantum dot grown by slow growth rate standard MBE process which is the initial step of our proposed growth techniques. We integrate one stack of quantum dot molecules into solar cells having Schottky structure. Quantum dot molecule solar cells were tested under AM1, 100 mW/cm/sup 2/ solar simulator. We found that the short circuit current density of this quantum dot molecule solar cell is the same order of magnitude to that of multi-stacked quantum dot solar cell previously studied. Dot density over 6/spl times/10/sup 10/cm/sup -2/ is created by repeating the thin-capping-and-regrowth process for 5 cycles. High dot density covering the whole sample surface is then utilized as an active layer in quantum dot solar cell structure.