INTEGRATED INFRARED CIRCULAR POLARIZATION DETECTOR WITH HIGH EXTINCTION RATIO AND DESIGN METHOD THEREOF

Abstract

The present disclosure provides an integrated infrared circular polarization detector with a high extinction ratio and a design method thereof. The detector structurally includes a metal reflective layer, a bottom electrode layer, a quantum well layer, a top electrode layer, and a two-dimensional chiral metamaterial layer. Under circularly polarized light with the selected handedness, surface plasmon polariton waves are generated at the interface between the two-dimensional chiral metamaterial layer and the semiconductor, and has a main electric field component aligned with the absorption direction of the quantum wells, thereby enhancing the absorption of the quantum wells. Under circularly polarized light with the opposite handedness, since most of the optical power is reflected, surface plasmon polariton waves cannot be effectively excited, and the absorption of the quantum wells is extremely low, thus realizing the capability of infrared circular polarization detection with a high extinction ratio.

Claims

1. An integrated infrared circular polarization detector with a high extinction ratio, wherein the detector structurally comprises a bottom metal reflective surface (1), a bottom electrode layer (2), a quantum well layer (3), a top electrode layer (4) and a two-dimensional chiral metamaterial layer (5) in sequence from bottom to top, with the two-dimensional chiral metamaterial layer (5) being of a Z-shaped periodic antenna structure; the bottom metal reflective plane (1) is a metal reflective layer with a thickness of h.sub.1 which is not less than twice the skin depth of an electromagnetic wave in the metal reflective layer; and the metal reflective plane (1) is made of a highly conductive metal; the bottom electrode layer (2) and the top electrode layer (4) are GaAs heavily doped with silicon; and the quantum well layer (3) is made of a single-stack or multi-stack semiconductor quantum well composed of GaAs/Al.sub.xGa.sub.1-xAs or InGaAs/GaAs.

2. The integrated infrared circular polarization detector with a high extinction ratio according to claim 1, wherein the two-dimensional chiral metamaterial layer (5) is designed as follows: fabricating the two-dimensional chiral metamaterial layer (5) with a highly conductive metal, wherein the two-dimensional chiral metamaterial layer (5) has a thickness not less than twice the skin depth of an electromagnetic wave in the metal, is periodic in the x- and the y-direction; the period in the x-direction (P.sub.x) and that in the y-direction (P.sub.y) are a quarter wavelength to a half of wavelength of light, and has a width of W.sub.1 at a middle thereof in the y-direction, a width of W.sub.2 at both ends thereof, and a length of L at an outer side in a protruding position in the x-direction, with W.sub.1>W.sub.2, W.sub.1 being a quarter to a half of P.sub.y, and L>P.sub.x/2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a diagram of an integrated circular polarization quantum well infrared detector.

[0020] FIG. 2 shows the Z-component of a relative permittivity of a quantum well.

[0021] FIG. 3 shows the absorption spectra of the quantum wells in the chiral metamaterial integrated quantum well infrared detector under LCP light (full line) and RCP light (dotted line) illumination.

[0022] FIG. 4 shows a circular polarization extinction ratio of the light absorption in the quantum wells.

[0023] FIG. 5 is a diagram of the enantiomer of the Z-shaped antenna for LCP light absorption.

[0024] FIG. 6 shows the absorption spectra of the quantum wells in the composite structure in FIG. 5 under LCP light (full line) and RCP light illumination.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The design and fabrication method of a circular polarization quantum-well infrared detector provided in the present disclosure are completely compatible with a focal plane array. For ease of description, a specific embodiment of the present disclosure will be described in detail by taking a GaAs/Al.sub.xGa.sub.1-xAs quantum-well circular polarization detector operating at the wavelength of 12 μm for example.

[0026] 1. First, a bottom electrode layer (GaAs heavily doped with silicon at a doping concentration of 2×10.sup.17 cm.sup.−3), a multi-stack GaAs/Al.sub.xGa.sub.1-xAs quantum well layer, and a top electrode layer (GaAs heavily doped with silicon at a doping concentration of 2×10.sup.17 cm.sup.−3) are grown on a GaAs substrate by molecular beam epitaxy.

[0027] 2. A mesa of a quantum well infrared detection device is defined by lithography. The developed area of a photoresist will be etched, while the undeveloped area of the photoresist will be protected.

[0028] 3. The quantum well sample is etched to the bottom electrode to form the mesas and the common electrodes by chemical etching or inductively coupled plasma (ICP).

[0029] 4. A pattern is defined by lithography, and with a photoresist as a mask, electron beam evaporation is performed to deposit AuGe/Ni/Au. A lift-off process is then conducted to obtain metal contacts for the top electrode and the bottom electrode. The Schottky barrier between the AuGe/Ni/Au and the semiconductor material is eliminated by a rapid annealing process to form an ohmic contact.

[0030] 5. Electron beam evaporation is performed to deposit a Ti (50 nm)/Au (150 nm) metal layer as a bottom metal reflective layer.

[0031] 6. Plasma enhanced vapor deposition (PECVD) is adopted to grow a 300 nm SiN.sub.x film on the surface of the chip as a passivation layer, which plays a main role in isolating air and water vapor and shielding surface electric leakage to protect the chip.

[0032] 7. Open windows in the SiN.sub.x film are defined by lithography, and formed by reactive ion etching (RIE), allowing for indium bump joining between the chip and the read out integrated circuit.

[0033] 8. Indium bumps with a height about 7 μm are prepared at the windows in the SiN.sub.x film by lithography, thermal evaporation, and lift-off process.

[0034] 9. The device is interconnected with a read out circuit on the sapphire wafer by flip-chip bonding.

[0035] 10. An appropriate amount of epoxy glue is injected into a gap between the chip and the sapphire wafer by a glue dispenser. After being cured, the epoxy glue can protect the internal structure of the device and cushion the effect of the thermal expansion coefficient mismatch within the device.

[0036] 11. The GaAs substrate is removed by mechanical polishing and selective etching.

[0037] 12. A two-dimensional chiral metamaterial structure is prepared by electron beam lithography.

EXAMPLE

[0038] The quantum-well circular polarization detector of this example is designed for the detection wavelength of 12 μm, and the metal is gold. The chiral metamaterial is a Z-shaped metal grating. After electromagnetic simulation and optimization, the structure size of the periodic unit is obtained as follows: P.sub.x=3.85 μm, P.sub.y=3 μm, W.sub.1=0.6 μm, W.sub.2=1 μm, L=2.5 μm, and h.sub.1=50 nm.

[0039] The quantum well layer includes 9 stacks of GaAs/Al.sub.0.55Ga.sub.0.45As materials. Each stack has a thickness of 66.5 nm, including a 60 nm Al.sub.0.55Ga.sub.0.45As barrier layer and a 6.5 nm GaAs potential well layer. The top electrode layer and the bottom electrode layer are GaAs and each has a thickness of 200 nm. The metal reflective layer is a gold film with a thickness of 100-200 nm.

[0040] FIG. 2 shows a dielectric function of the quantum well in the Z-direction. The absorption and circular polarization extinction ratios of the quantum wells in the chiral metamaterial integrated QWIP with optimized structural parameters are shown in FIGS. 3 and 4, and the circular polarization extinction ratio reaches 14.