Analytical determination of optimal sidewall angle for Bi2Sr2CaCu2O8+δ stacked IJJ terahertz sources
Mesa-shaped stacks of ‘intrinsic’ Josephson junctions in the high- T _c superconductor Bi _2 Sr _2 CaCu _2 O _8+ _δ are a promising source of coherent terahertz radiation. These devices consist of current-biased Josephson junctions connected in series, meaning that in order to maximize their THz pow...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | Materials Research Express |
| Subjects: | |
| Online Access: | https://doi.org/10.1088/2053-1591/addba6 |
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| Summary: | Mesa-shaped stacks of ‘intrinsic’ Josephson junctions in the high- T _c superconductor Bi _2 Sr _2 CaCu _2 O _8+ _δ are a promising source of coherent terahertz radiation. These devices consist of current-biased Josephson junctions connected in series, meaning that in order to maximize their THz power output, it is desirable to minimize the resulting spread of DC junction bias voltages, even in the presence of self-heating. In this work we analytically calculate the sidewall profile shape that results in zero junction voltage spread, by treating the heat diffusion equation as approximately linear in the limit in which self-heating of the device is small. The resulting optimal sidewall angle depends strongly upon a number of device parameters. Of these, the most important variables are the intended THz emission frequency, the doping-dependent c -axis electrical resistivity, and the vertical thickness of the stack. The optimal sidewall relative to the substrate always decreases as the intended emission frequency and/or the stack thickness is increased. For Bi _2 Sr _2 CaCu _2 O _8+ _δ doped for maximum T _c with p = 0.16 holes per Cu atom and a realistic device thickness of 1 micron, the optimal angle varies non-monotonically with cryogenic bath temperature, but always lies between 25° and 85° for realistic operating temperatures, which range from 10 K up to T _c . |
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| ISSN: | 2053-1591 |