Crack-free and c-axis in-plane aligned superconducting Y0.7Ca0.3Ba2Cu3O7-delta films for terahertz radiating Josephson plasma devices

External excitation of the Josephson plasma in YBa(2)Cu(3)o(7-delta) by inj ecting current is expected to result in the emission of light in the terahe rtz (THz) region. In order to fabricate such THz light emitting devices, on e has to grow underdoped (T-c = 60 K), c-axis in-plane aligned YBa2Cu3O7-de lta films free from cracks. However, the large thermal expansion coefficien t of this compound along the e-axis due to the oxygen incorporation makes i t difficult to avoid cracking. Here we report that substitution of Y by Ca made it possible to obtain crack-free, 60 K phase Y0.7Ca0.3Ba2Cu3O7-delta f ilms with a larger oxygen deficiency (delta) than YBa2Cu3O7-delta. This exp eriment is designed so as to compensate the reduction of hole concentration due to the large oxygen deficiency with the hole doping by Ca substitution .