Growth of antimony-based materials in a multiwafer planetary MOVPE-reactor
Abstract
Four-junction photovoltaic solar cells are expected to reach conversion efficiencies around 40%. Mechanical stacking of two monolithic tandem cells is suggested. As a top cell the highly developed GaInP:GaAs tandem cell is considered. Device modelling is presented for the bottom cell. An infrared monolithic tandem solar cell is proposed which is a combination of an (AlGa)(AsSb) top cell (E/sub gap/=1.03 eV) and a GaSb bottom cell based on GaSb as substrate material. The MOVPE growth of GaSb, GaAsSb and AlGaSb in a multiwafer planetary reactor that is suited to large-scale industrial production is reported. Influences of the substrate preparation, orientation of the growth surface, growth temperature and the V-III ratio on material quality are presented. Both hydrogen and nitrogen were employed as the carrier gas in different experiments. The best layers were obtained on (100) substrates oriented 2 degrees toward (111)A, using hydrogen as carrier
