AVS 57th International Symposium & Exhibition
    Energy Frontiers Topical Conference Tuesday Sessions
       Session EN+TF-TuA

Paper EN+TF-TuA8
Growing Low-Dislocation-Density Ge on Si through Nanometer Sized Voids in Chemical Oxide and Subsequent Integration of III-V Films for Multijunction Solar Cells

Tuesday, October 19, 2010, 4:20 pm, Room Pecos

Session: Thin Films for Photovoltaics
Presenter: D. Leonhardt, University of New Mexico
Authors: D. Leonhardt, University of New Mexico
J.J. Sheng, University of New Mexico
J.G. Cederberg, Sandia National Laboratories
M.S. Carroll, Sandia National Laboratories
M.J. Romero, National Renewable Energy Laboratory
S.M. Han, University of New Mexico
Correspondent: Click to Email
In an effort to reduce the manufacturing cost of multijunction solar cells, which currently utilize Ge substrates, we have scaled up a process to produce low-defect-density Ge films on 2-inch-diameter Si substrates. This process begins with the nucleation of over 1x1011/cm2 Ge islands on Si through 3-to-7 nanometer diameter voids in chemical SiO2. It is shown that upon Ge island coalescence, the Ge film primarily contains stacking faults as opposed to threading dislocations. We have found that annealing the Ge islands at an early stage of island growth removes the stacking faults, but results in the formation of 5x107/cm2 threading dislocations upon further growth. Herein, we report on a detailed investigation using transmission electron microscopy (TEM) to clarify the mechanism of the stacking fault formation in the Ge. We will also discuss the effect of annealing both on the Ge island morphology and in eliminating the stacking faults. Additionally, the origin of the threading dislocations obtained after annealing is revealed through the TEM study. Lastly, we report characterization results of GaAs-based double heterostructures integrated on the annealed Ge films, whose photoluminescence intensity over the entire 2-inch wafer is comparable to the same structures grown on commercially available GaAs and Ge substrates.