Light-Absorbing Devices

Semiconductors are well suited to absorb light in the near-IR to UV region of the spectrum and convert the photon flux into an electron current. This opens up many possibilities to detect or harvest light emitted by natural or technical sources. Based on our so far discussed knowledge of semiconductor properties like, e.g., band structure, band-to-band transitions and carrier dynamics we elaborate how semiconductors can be used for the named applications. We illustrate how the device performance can be optimized by tuning properties of the materials and multi-layer structures thereof. First some general material properties like the spectral absorption are reviewed. Then the focus is on two selected important applications. The first example is the solar cell. We start with a general concept of the working principle based on selective charge extraction. We then shortly discuss the electrical performance of solar cells as well as their conversion efficiency and its limitations. Some typical realizations like high-efficiency Si cells, thin-film and tandem cells are given. The second example is the photodiode whose principle operation and responsivity is treated.