Gettered GaP Substrates for Improved Multi-junction Solar Cell Devices
Jerry M. Woodall, Charles R. Allen, Kyle H. Montgomery, Jong-Hyeok Jeon, Isaac H. Wildeson, Anant K. Ramdas
52nd Electronic Materials Conference, South Bend, IN, 2010.
Extended Abstract (pdf)
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It is known that during LPE fabrication of GaAs minority carrier devices, the Ga component can getter carrier lifetime reducing traps from bulk GaAs wafers. Using this knowledge we performed gettering experiments on a commercial p-type GaP substrate normally used for the MBE fabricated cells. For this study, gettering was accomplished by immersing the GaP substrate into the phosphorus saturated Ga melt with 0.381 wt.% Al at 975°C for 1 hour. The gettering results were then determined by low temperature PL using a 325 nm HeCd laser. Any melt left on the substrate or AlGaP growth that occurred during soaking was removed by an HCl etch prior to the PL measurements. The as-received substrate showed 4 K PL peaks at 2.2, 1.83 and 1.35 eV. These peaks have been identified in the literature as donor-acceptor recombination, nearest neighbor Zn-O recombination and widely separated O-Zn recombination, respectively. Compared with the substrate PL, the gettered sample showed the 2.2 eV peak at the same intensity, a vastly decreased 1.83 eV peak, and minimal 1.35 eV emission. These results strongly suggest that using gettered GaP substrates for subsequent cell fabrication will greatly enhance the collection efficiency of minority carriers generated in the p material of the cell. We will report the results of getter depth profiling and spectral response of Schottky cells made on the gettered substrates at the conference.
gettering, liquid phase epitaxy, GaP, minority carrier lifetime
J. M. Woodall, C. R. Allen, K. H. Montgomery, J-H. Jeon, I. Wildeson, and A. K. Ramdas, “Gettered GaP Substrates for Improved Multi-junction Solar Cell Devices,” presented at the 52nd Electronic Materials Conference, South Bend, IN, 2010.