Reactive ion beam etching and characterization of high-Tc superconductor Bi2212

Abstract

The lack of coherent, continuous and tunable compact solid-state sources of electromagnetic radiations at terahertz (THz) frequency range (0.3-30 THz) can be solved by high temperature superconductors (HTS) which are better candidates for generation of THz radiation. THz sources have potential application areas in materials characterization, biology, communication, medicine and security. The HTSs have large energy gap intervals which are available for radiations at THz frequency range, so recently, they were used as better converters from DC-voltage to high frequency radiation in junction technologies. Bi2Sr2CaCu2O8+. (Bi2212) HTS single crystals include natural superconductor-insulator-superconductor multi-junctions called intrinsic Josephson junctions. For generation of coherent continuous and powerful THz radiations, we have fabricated large and tall mesas on Ca rich Bi2212, although mesas with small planar and lateral dimensions were preferred in recent studies because of the heating effect. We have used underdoped Bi2212 to control the heating problem. By using the vacuum thermal evaporation, optical photolithography, magnetron sputtering and reactive ion beam etching techniques, the mesas with size of 40-100x300 um2 have been fabricated by using single layer mask (PR) and two different multilayer masks, which are Ta/PR and PR./Ta/PR. Their heights and lateral dimensions were analyzed by Atomic Force Microscopy, profilometer and SEM. We have investigated temperature dependence of c-axis resistivity and current-voltage (I-V) tunneling characteristics of under-doped Bi2212 which exhibit exponentially increases in resistivity from 300 K to Tc. The influences of heating effect were analyzed at temperature evolution of I-V measurements. Finally, bolometric detections of emission from long edges of mesas were done.