Application of Ge quantum wells fabricated by laser annealing as energy selective contacts for hot-carrier solar cells

In this study, a lower-cost and highly compatible laser scanning method was implemented as an alternative annealing process to fabricate quantum well (QW) structures. Ge QW films were fabricated by continuous-wave laser annealing and their potential for energy selective contact (ESC) applications was assessed by structural, optical and electrical characterization. The structural properties were observed by transmission electron microscopy (TEM), Raman spectroscopy and x-ray diffraction (XRD) techniques. Cross-sectional TEM images showed the dimension of the QWs to be larger along the direction of laser scanning. Uni-axial tensile strained film properties were found in XRD investigations which showed crystal growth favored in a series of orthogonal direction <110> along the laser scan direction due to the laser dragging the liquid phase Ge. Rapid quenching from liquefied Ge introduced stress in the film as shown by peak shifts in XRD and in Raman spectra. Despite that strong optical absorption by amorphous features in the film possibly hinder the quantum confinement presentation as shown in the absorption curves, Preliminary data, presenting tentative current fluctuations in the room temperature I-V measurement, suggest that a double barrier resonant tunneling structure is possible, showing its potential application for ESCs.