Authors: Gustavo E Fernandes DoJoong Lee Jin Ho Kim KiBum Kim Jimmy Xu
Publish Date: 2012/12/04
Volume: 48, Issue: 6, Pages: 2536-2542
Abstract
The system of atomiclayer Aldoped ZnO AZO superlattice is rather interesting in that it exhibits a “bipolar transparency” as it is transparent in the visible and opaque in the infrared to microwave Here we report on our measurements of the infrared and microwave shielding properties of thin films ~150 nm of an Aldoped ZnO superlattice grown via atomic layer deposition ALD These optically transparent conductive oxide thin films have large DC electrical conductivity 50000 S/m which increases with Al doping Their infrared optical properties are well described by a freeelectron Drude model which results from the very large carrier concentrations 3 × 1020 cm−3 resulting from AlO x heterolayerdoping It is found that increasing Al concentrations lead to an increase in the relaxation energy which however is not strong enough to cause the plasma frequency to redshift Microwave shielding properties were investigated in the frequency range from 1 to 30 GHz and shielding efficiencies as high as ~22 dB were observed confirming that the freeelectron picture extends into the microwave regime The dynamic conductivity in the microwave range was found to correspond well to the measured DC values Due to their high electrical conductivity and high microwave shielding efficiency in thin film format these materials may be desirable for applications in transparent electronics optically transparent EMI shielding coatings and heat/microwave reflecting coatings for windows
Keywords: