IR photoresponse characteristics of Mg2Ge pn-junction photodiodes fabricated by rapid thermal annealing
Abstract In this study, high purity n-type Mg 2 Ge single crystals are grown in graphite crucibles under nitrogen atmosphere using a facile growth process. X-ray diffraction proves that the grown crystal consists of only Mg 2 Ge single phase without any other additional impurity peaks. The clear symmetrical Laue diffraction pattern of the cleaved substrate demonstrates the single crystalline nature of the grown Mg 2 Ge crystal ingot. The Hall Effect measurement of the polished Mg 2 Ge wafer shows that the latter had a moderate carrier density (5.66 * 10 16  cm −3 ), mobility (253 cm 2 /V) and electrical resistivity (0.5 Ω. cm) at room temperature. Detailed analysis of the temperature dependence of the carrier density demonstrates that the shallow donor level, which gives rise to the n-type conduction of grown Mg 2 Ge crystals is due to the unintentional Al impurities from Mg source material. Mg 2 Ge pn-junction photodiodes are also manufactured for the first time by thermal diffusion of silver thin layer into n-Mg 2 Ge at 550 °C for 5 min in an argon atmosphere. The results reveal that the fabricated p-n photodiodes had a clear rectifying behavior and a remarkable spectral response in the wavelength range from 0.8 to 1.7 μm with a maximum room temperature zero-biased photoresponse of 7 mA/W at 1.2 μm. These outcomes indicate that the fabricated Mg 2 Ge photodiodes are promising to detect short-wavelength infrared (SWIR) light in the above-mentioned wavelength domain.