InAs and InP Quantum Dot Molecules and their Potentials for Photovoltaic Applications

摘要

Self-assembled InAs and InP quantum dot molecules (QDMs) are grown on GaAs substrates using different molecular beam epitaxial (MBE) growth techniques. The structural and optical properties of the two types of QDMs are then compared and reported. Multi-stack high-density (10{sup}12cm{sup}(-2)) InAs QDMs are grown and when inserted into GaAlAs/GaAs heterostructure results in high-efficiency solar cells. As an alternative to InAs, InP QDMs are grown by droplet epitaxy of In and annealing under P{sub}2 pressure. While the number of quantum dots per QDM in the case of InP is in the range of 10 to 12 dots, those in the case of InAs can be smaller or much larger depending on exact growth parameters prior to QD growth. Photoluminescence (PL) measurements show that while InAs QDMs provide room-temperature optical output that peaks at 1.1eV, InP QDMs have no PL output, possibly due to crystal defects created by low-temperature processing associated with droplet epitaxy. Discussion on the practicality of our QDMs as material for intermediate band solar cells is also provided.