Appl. Phys. Lett. 105, 202603 (2014)

Research into generating terahertz (THz) radiation from the superconductor Bi2Sr2CaCu2O8+δ (Bi2212) has received attention recently, with the aim of creating a new compact THz light source. However, strong Joule heating associated with the large current flowing through the devices has hampered efforts. Now, T. Kitamura and co-workers from Japan and the USA have developed a stand-alone mesa fabrication procedure that greatly improves the thermal contact of the Bi2212 mesa with a surrounding thermal bath and thus allows the emission of high-power, continuous, broadly tunable THz radiation from 0.29 to 1.06 THz. The Bi2212 rectangular mesa with a 74 μm top width, 84 μm bottom width, 290 μm length and 2 μm thickness was fabricated using standard metal masks and Ar ion milling. The top and bottom surfaces were coated with Ti/Ag/Au metal layers and fixed to a sapphire substrate. As the temperature of the device increased from 10 K, the power of the output THz radiation gradually increased and then suddenly jumped up at a temperature of 54 K, peaked at 56 K and then decreased sharply above 70 K. The maximum power of the device was estimated to be about 20 μW. A radiation frequency of 1.06 THz was observed around 10 K, whereas a frequency of 0.29 THz was observed around 70 K.