Transcript Slide 1
Defect-related Recombination And Free-Carrier Diffusion Near An Isolated Defect In GaAs Mark Crowley Tim Gfroerer Davidson College, Davidson, NC Mark Wanlass National Renewable Energy Lab, Golden, CO Funded by The American Chemical Society - Petroleum Research Fund Side View of a Solar Cell Photons Absorption Layer ~ 2 µm Mechanisms for Recombination Isolated Dislocations in a high quality GaAs sample Zoomed View of a Single Isolated Dislocation with Changing Laser Excitation Diffusion Dislocation Side View of Isolated Dislocation Defects in a Solar Cell under High Illumination Photons Dislocations ~ 2 nm Absorption Layer ~ 2 µm Side View of Isolated Dislocation Defects in a Solar Cell under Low Illumination Absorption Layer ~ 2 µm DislocationDead Volume Modeling the Dislocation Experimental Images Computational Model Total 2 recom binat ion An Bn rate Defect-Related Recombination Radiative Recombination Better fits with a more Complex Model Experimental Images 1W 1.0 .1W .75 .5 .9 1W .6 .66 .01W Computational Model .001W .3 .2 1.0 .1W .66 .01W .75 .9 .6 .001W .5 Total recom bination A (dP * dDN dN * dDP) B * dP * dN rate .3 .2 Conclusions • Defects produce “dead spots” where defect-related recombination is high. • These defects act as sinks, drawing in nearby charge carriers by diffusion. • When modeling these defects, if we use a recombination model that does not account for the occupation of defect and band states separately, we are unable to reproduce the experimental images. • Simulating this behavior accurately requires that state occupations are computed and vary independently with a more flexible computational model.