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Effects of undoped photo-absorption layers in modified uni-traveling carrier photodiode structures on quantum efficiency and bandwidth are reported. Modified uni-traveling carrier photodiode structures having different undoped photo-absorption layer thicknesses were fabricated and characterized. Efficiency and bandwidth of photodiodes having an optimized undoped photo-absorption layer were larger than those of photodiodes without such a layer, which agrees well with the theoretical analysis of the dynamic behavior of the photodiodes using drift-diffusion model. The results indicate that both the quantum efficiency and bandwidth of the uni-traveling carrier photodiode structures can be extended by incorporating an optimized thickness of undoped photo-absorption layer.

We demonstrated the efficiency improvement of GaAs single-junction (SJ) solar cells with the single-material zinc sulfide (ZnS) bi-layer based on the porous/dense film structure, which was fabricated by the glancing angle deposition (GLAD) method, as an antireflection (AR) coating layer. The porous ZnS film with a low refractive index was formed at a high incident vapor flux angle of 80° in the GLAD. Each optimum thickness of ZnS bi-layer was determined by achieving the lowest solar weighted reflectance (SWR) using a rigorous coupled-wave analysis method in the wavelength region of 350-900 nm, extracting the thicknesses of 20 and 50 nm for dense and porous films, respectively. The ZnS bi-layer with a low SWR of ~5.8% considerably increased the short circuit current density (J(sc)) of the GaAs SJ solar cell to 25.57 mA/cm(2), which leads to a larger conversion efficiency (η) of 20.61% compared to the conventional one without AR layer (i.e., SWR~31%, J(sc) = 18.81 mA/cm(2), and η = 14.82%). Furthermore, after the encapsulation, its J(sc) and η values were slightly increased to 25.67 mA/cm(2) and 20.71%, respectively. For the fabricated solar cells, angle-dependent reflectance properties and external quantum efficiency were also studied.

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In this letter, we investigate the electrical behavior of vacancy V Ge defects in Ge at various thermal annealing conditions through electrochemical capacitance-voltage analysis. Then, the effects of the annealing process on Ge n + /p junction diodes were also studied with J −V , transmission electron microscopy, and secondary ion mass spectroscopy measurements in the aspects of point-defect healing and dopant diffusion/loss phenomena. The V Ge defects tend to heal by recombining with Ge interstitial atoms as the annealing process temperature increases. However, the diffusion/loss problems of P atoms in Ge become severe at above 500 • C. Therefore, an optimal postfabrication annealing process at 600 • C is proposed in terms of point-defect healing and dopant diffusion/loss reduction.