Simulation of Hydrogenated Amorphous Silicon Germanium Alloys for Bandgap Grading

Computer simulations are reported of hydrogenated amorphous silicon germanium (a-SiGe:H) layers that make up the graded part of the intrinsic layer near the interfaces of a-SiGe:H solar cells. Therefore the graded part is approached with a ‘staircase’ bandgap profile, consisting of three layers within which the material properties are constant. Calibrated model parameters are obtained by matching simulation results of material properties of intrinsic a-SiGe:H single layers to measurements. Using the obtained model parameter sets subsequent simulations of p-i-n devices with intrinsic material similar to the single layers are matched to measured current-voltage characteristics. The changes in parameter values are evaluated as a function of optical gap.