Optimization of growth and device performance for InAs quantum dot solar cells

Substrate misorientation was investigated as a mechanism to control InAs quantum dot density and size. Results have shown that both 2° and 6° substrate misorientation toward the <;110>; direction can lead to high InAs QD density (4.8×10¹⁰ cm-2) as well as suppress QD ripening. In the 6° misoriented samples the critical thickness for QD formation was higher than in the 2° misoriented samples (1.9 ML versus 1.7-1.8ML, respectively). Substrate misorientation also shows that smaller QDs can be grown by increasing misorientation. GaAs solar cells with a 10 layer QD superlattice were also investigated as a function of misorientation angle and InAs coverage. On the 2° substrate, short circuit current (23.3 mA/cm2) was improved over 2° baseline samples. The EQE versus InAs coverage shows that quantum confined absorption and collection is complex, with coupling between wetting layer and excited state levels in the QD. QD contributed short circuit current density for the 2° misorientation substrates was calculated form EQE as 0.027 mA/cm² per QD layer while the 6° misorientation substrates gave 0.019 mA/cm² per QD layer.