Electrically tunable infrared metamaterial devices
A wavelength-tunable, depletion-type infrared metamaterial optical device is provided. The device includes a thin, highly doped epilayer whose electrical permittivity can become negative at some infrared wavelengths. This highly-doped buried layer optically couples with a metamaterial layer. Changes in the transmission spectrum of the device can be induced via the electrical control of this optical coupling. An embodiment includes a contact layer of semiconductor material that is sufficiently doped for operation as a contact layer and that is effectively transparent to an operating range of infrared wavelengths, a thin, highly doped buried layer of epitaxially grown semiconductor material that overlies the contact layer, and a metallized layer overlying the buried layer and patterned as a resonant metamaterial.
1. An optical device having tunable wavelength selectivity, comprising:
a layer of semiconductor material that is sufficiently doped for operation as a contact layer and that is effectively transparent to an operating range of infrared wavelengths (the “contact layer”);
a layer of epitaxially grown semiconductor material (the “buried layer”) that overlies the contact layer, is of a thickness not more than 0.025 times a vacuum wavelength in the operating range, and that is doped with the same polarity as the contact layer but at 5 times or more the dopant concentration of the contact layer; and
a metallized layer overlying the buried layer and patterned as a resonant metamaterial having at least one absorptive infrared resonance at a wavelength relative to which the buried layer exhibits metallic-dielectric transition behavior.
2. The device of claim 1 , further comprising a barrier layer between the buried layer and the metamaterial, wherein the barrier layer has a higher band gap than the buried layer.
3. The device of claim 2 wherein the barrier layer is of a thickness that is no more than twice the thickness of the buried layer.
4. The device of claim 1 , further comprising an arrangement for applying a voltage bias between the metamaterial and the contact layer at least of a polarity that tends to deplete the buried layer of majority carriers.
5. The device of claim 1 , wherein the buried layer is in sufficient proximity to the metallized layer for electromagnetic coupling to take place, in the infrared operating range of wavelengths, between plasmonic excitations of the metallized layer and plasmonic excitations of the buried layer.
6. The device of claim 5 , wherein the buried layer has a doping level selected such that for some range of gate bias voltages applied to the device, wherein the metallized layer functions as the gate electrode, there is sufficient carrier depletion in the buried layer to extinguish the electromagnetic coupling between plasmonic excitations of the metallized layer and plasmonic excitations of the buried layer.
7. The device of claim 1 , wherein the buried layer is n+ doped.