High-quantum-efficiency II-VI photodiode beats silicon in the blue
The silicon (Si) PIN photodiode, widely used for the detection of low-power radiation in the 300?500-nm range, now has competition. Researchers at the Physikalishes Institut der Universit?t W?rzburg (W?rzburg, Germany) have fabricated PIN photodiodes of zinc magnesium sulfur selenide (ZnMgSSe), a II-VI semiconductor material that previously was used primarily in the construction of some blue-emitting diode lasers. The ZnMgSSe photodiodes have an external quantum efficiency of 58% at 430 nm and a peak internal quantum efficiency of 80%.
Using molecular-beam epitaxy, the researchers grow the diodes on gallium arsenide substrates. The lattice mismatch between the diode and the substrate is 0.03%. Both x-ray diffraction and low-temperature photoluminescence data show that the photodiodes have low defect densities. The researchers have made diodes with light-sensitive areas of 1, 1.44, 4, 9, and
16 sq mm. The devices all exhibit a sharp cutoff in spectral response, with their quantum efficiency dropping to less than 10?4 for wavelengths longer than 500 nm?an advantage in some applications that require stray-light rejection. The researchers estimate that their photodiodes have a noise-equivalent power below 10?15 W(Hz)1/2/mm2, a figure surpassing ultraviolet-
optimized silicon-based detectors. Contact Markus Ehinger at [email protected].