Gain in three-dimensional metamaterials utilizing semiconductor quantum structures

Abstract

We demonstrate gain in a three-dimensional metal/semiconductor metamaterial by the integration of optically active semiconductor quantum structures. The rolling-up of a metallic structure on top of strained semiconductor layers containing a quantum well allows us to achieve a three-dimensional superlattice consisting of alternating layers of lossy metallic and amplifying gain material. We show that the transmission through the superlattice can be enhanced by exciting the quantum well optically under both pulsed or continuous wave excitation. This points out that our structures can be used as a starting point for arbitrary three-dimensional metamaterials including gain.Metamaterials are composite materials made of artificial building blocks whose size and lattice constant is small compared to the wavelength of the transmitted light. An advantage of metamaterials compared to conventional natural materials is that their properties can be tailored by varying the size and shape of the artificial building blocks. In particular using metallic structures, negative index of refraction in the near-infrared and visible regime had been realized using metallic split ring resonators [1] or fishnet structures [2][3][4]. To prove bulk properties and use metamaterials for devices one has to achieve a three-dimensional structure which is usually planar lithographically defined and fabricated sequentially until the desired thickness is reached [5][6][7]. All these metamaterials are hampered by absorption which is caused by ohmic losses in the metallic compound or, in other words, by the finite imaginary part of the dielectric function of the metal. A proposal to compensate these losses is to integrate a gain medium into the metamaterial which amplifies the transmitted light [8] like, e.g. dye [9] or semiconductor quantum structures [10,11]. Recently it has been shown that a dye surrounding the metallic structures can compensate the losses in a metamaterial [12]. In contrast to dyes, semiconductor quantum structures exhibit no photo bleaching, a higher damage threshold and the possibility of electrical pumping. Investigations on two-dimensional planar systems show that metallic structures can be coupled to a quantum structure and partially compensate the ohmic losses [13][14][15].In this letter, we present three-dimensional radial metamaterials consisting of alternating layers of metal structures and amplifying semiconductor quantum structures. For the fabrication we utilize the concept of selfrolling strained layers [16-18] which we recently extended to strained metal/semiconductor metamaterials with a possible application as a hyperlens [19,20]. Here we investigate a novel structure with active quantum wells integrated into the semiconductor layer. As a result we ob- tain a truly three-dimensional metamaterial containing optical amplifiers which enhance the light transmission by stimulated emission. We present transmission measurements which show a transmission enhancement of about 5 % under optical continuous wave (cw) excitatio...

Electronically reconfigurable metal-on-silicon metamaterial

“…Given the potential for active metamaterial-semiconductor devices, [54][55][56] the combined modeling of semiconductor physics and electromagnetic scattering becomes attractive. The results found here demonstrate that quantitative predictions of a complete, dynamically controlled metamaterial device can be achieved.…”

“…In particular, single-pixel imaging devices that rely on the modulation of the transmission or reflection of a collection of elements could be readily formed using a voltage-controlled metamaterial such as that shown here. 53 Given the potential for active metamaterial-semiconductor devices, [54][55][56] the combined modeling of semiconductor physics and electromagnetic scattering becomes attractive. The results found here demonstrate that quantitative predictions of a complete, dynamically controlled metamaterial device can be achieved.…”

Rolled-up nanotechnology for the fabrication of three-dimensional fishnet-type GaAs-metal metamaterials with negative refractive index at near-infrared frequencies

“…In contrast to dielectrics like MgF 2 and HSQ, GaAs allows the incorporation of optically active quantum wells which could compensate for the ohmic losses in the metallic compound. [15][16][17] We show by means of finite-integration technique simulations that, despite the relatively high refractive index of GaAs, the fabricated structure exhibits a negative refractive index at 1000 nm and 1400 nm wavelength with a very high figure of merit (FOM) of 0.8. We show that the intervals where the refractive index is negative can be shifted to arbitrary frequencies between 195 THz and 320 THz (938 nm < k < 1538 nm) by changing the Ag and (In)GaAs layer thicknesses.…”

Enhanced transmission in rolled-up hyperlenses utilizing Fabry-Pérot resonances

“…We utilize FabryPérot resonances related to the total thickness of the metamaterial to obtain increased transmission in a desired frequency regime. We illustrate this concept for the example of a RHL [15][16][17][18] consisting of alternating layers of Ag and semiconductor as sketched in Fig. 1(a).…”

“…The heterostructure consists of a GaAs buffer layer (500 nm), an AlAs sacrificial layer (40 nm) followed by a strained Al 20 In 13 Ga 67 As layer (23 nm), a strained In 16 Ga 84 As layer (7 nm), and an unstrained Al 23 Ga 77 As layer (21 nm). On top of these semiconductors an Ag layer is deposited by thermal evaporation.…”