Abstract
Optical rectennas are expected to be applied as power sources for energy harvesting because they can convert a wide range of electromagnetic waves, from visible light to infrared. The critical element in these systems is a diode, which can respond to the changes in electrical polarity in the optical frequency. By considering trade-off relationship between current density and asymmetry of IV characteristic, we reveal the efficiency limitations of MIM diodes for the optical rectenna and suggest a novel tunnel diode using a double insulator with an oxygen-non-stoichiometry controlled homointerface structure (MOx/MOx−y). A double-insulator diode composed of Pt/TiO2/TiO1.4/Ti, in which a natural oxide layer of TiO1.4 is formed by annealing under atmosphere. The diode has as high-current-density of 4.6 × 106 A/m2, which is 400 times higher than the theoretical one obtained using Pt/TiO2/Ti MIM diodes. In addition, a high-asymmetry of 7.3 is realized simultaneously. These are expected to increase the optical rectenna efficiency by more than 1,000 times, compared to the state-of-the art system. Further, by optimizing the thickness of the double insulator layer, it is demonstrated that this diode can attain a current density of 108 A/m2 and asymmetry of 9.0, which are expected to increase the optical rectenna efficiency by 10,000.
Highlights
Optical rectennas are expected to be applied as power sources for energy harvesting because they can convert a wide range of electromagnetic waves, from visible light to infrared
The diode performances for the optical rectenna system can be clearly understood from Fig. 2, which displays the current density at an operating voltage of 1 V on the x-axis and the maximum asymmetry of the diode on the y-axis
We analytically show that it is difficult to realize a good diode for optical rectenna device only by optimizing the material in a general MIM tunnel diode because they have trade-off relationship between current density and asymmetry of IV characteristic
Summary
Optical rectennas are expected to be applied as power sources for energy harvesting because they can convert a wide range of electromagnetic waves, from visible light to infrared. A high-asymmetry of 7.3 is realized simultaneously These are expected to increase the optical rectenna efficiency by more than 1,000 times, compared to the state-of-the art system. By optimizing the thickness of the double insulator layer, it is demonstrated that this diode can attain a current density of 108 A/m2 and asymmetry of 9.0, which are expected to increase the optical rectenna efficiency by 10,000. The performance of the diode affects the photoelectric conversion efficiency, considerably. Conventional diodes, such as p-n diodes and Schottky barrier diodes, cannot respond to the ultrafast pole changes with the optical frequency. The high-frequency-response efficiency of tunnel diodes is equivalent to the impedance matching efficiency, ηc, between the diode and antenna. The efficiency, ηβ, that depicts the rectification performance of the diode is a crucial parameter. ηβ is expressed as the product of the operating voltage, VD, and quantum efficiency, βisc, as in Eq (2)[13]
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