Arvind P. Ravikumar

Phased-array sources based on nonlinear metamaterial nanocavities

Coherent superposition of light from subwavelength sources is an attractive prospect for the manipulation of the direction, shape and polarization of optical beams. This phenomenon constitutes the basis of phased arrays, commonly used at microwave and radio frequencies. Here we propose a new concept for phased-array sources at infrared frequencies based on metamaterial nanocavities coupled to a highly nonlinear semiconductor heterostructure. Optical pumping of the nanocavity induces a localized, phase-locked, nonlinear resonant polarization that acts as a source feed for a higher-order resonance of the nanocavity. Varying the nanocavity design enables the production of beams with arbitrary shape and polarization. As an example, we demonstrate two second harmonic phased-array sources that perform two optical functions at the second harmonic wavelength (∼5 μm): a beam splitter and a polarizing beam splitter. Proper design of the nanocavity and nonlinear heterostructure will enable such phased arrays to span most of the infrared spectrum.

High performance, room temperature, broadband II-VI quantum cascade detector

We report on the experimental demonstration of a room temperature, II-VI, ZnCdSe/ZnCdMgSe, broadband Quantum Cascade detector. The detector consists of 30 periods of 2 interleaved active-absorption regions centered at wavelengths 4.8 μm and 5.8 μm, respectively. A broad and smooth photocurrent spectrum between 3.3 μm and 6 μm spanning a width of 1030 cm–1 measured at 10% above baseline was obtained up to 280 K, corresponding to a ΔE/E of 47%. Calibrated blackbody responsivity measurements show a measured peak responsivity of 40 mA/W at 80 K, corresponding to a detectivity of about 3.1×1010 cmHz/W. Bias dependent photocurrent measurements revealed no significant change in the spectral shape, suggesting an impedance matched structure between the different active regions.

High detectivity short-wavelength II-VI quantum cascade detector

We demonstrate the first II-VI based short-wave (λ ≤ 4 μm) Quantum Cascade Detector. Peak responsivity and background limited detectivity of 0.1 mA/W and 2.5×10¹⁰ cm√Hz/W, respectively, were measured at 80 K.

ZnCdSe/ZnCdMgSe quantum well infrared photodetector

We present the design, fabrication and characterization of a II-VI ZnCdSe/ZnCdMgSe quantum well infrared photodetector with a bound to quasi-bound transition centered at 8.7 μm. Absorption, photocurrent measurements yield results consistent with conventional III-V QWIPs.

MBE growth of ZnCdSe/ZnCdMgSe quantum-well infrared photodetectors

The authors report the growth of quantum well infrared photodetectors (QWIPs) made from wide band gap II-VI semiconductors. ZnCdSe/ZnCdMgSe QWIPs in both medium-wave infrared and long-wave infrared regions were grown by molecular beam epitaxy on InP substrates. High-resolution x-ray diffraction and photoluminescence measurements showed that the as-grown samples have high structural and optical quality. Spectral responses with peaks at 8.7 μm and 4.0 μm have been obtained.

Improved electrical properties and crystalline quality of II–VI heterostructures for quantum cascade lasers

The authors report on investigations of the doping, lattice mismatch, and interface quality for the molecular beam epitaxial growth of ZnCdSe/ZnCdMgSe/InP quantum cascade structures with improved electrical, structural, and spectral properties. An improved doping strategy, the control of the lattice mismatch to less than 0.25%, and the incorporation of growth interruptions have led to quantum cascade structures with good I–V characteristics and electroluminescence emission up to room temperature, with an emission energy of 230 meV (5.4 μm) and a full-width at half maximum of 41 meV at 80 K, the best device properties reported so far for this material system. It is expected that the addition of waveguide layers in the structure will lead to the observation of lasing.

Characterization of the three-well active region of a quantum cascade laser using contactless electroreflectance

Quantum cascade (QC) lasers with emission at wavelengths below 4 μm are difficult to achieve from conventional III-V materials systems lattice matched to GaAs and InP due to the limited conduction band offset (CBO) of those materials that results from the presence of intervalley scattering. The II-VI materials ZnCdSe/ZnCdMgSe, with a CBO as high as 1.12 eV and no intervalley scattering, are promising candidates to achieve this goal. Using molecular beam epitaxy (MBE), the authors grew a QC laser structure with a three-well active region design made of ZnCdSe and ZnCdMgSe multilayers closely lattice matched to InP. A test structure, which contains only the active region of the QC laser separated by quaternary barrier layers, was also grown. The test structure was characterized by contactless electroreflectance (CER). Photoluminescence measurements and a model based on the transfer matrix method were used to identify the CER transitions. The energy levels obtained for the test structure were then used to pr...

Two-band ZnCdSe/ZnCdMgSe quantum well infrared photodetector

An independently controllable, two-band quantum well infrared photo-detector (QWIP) based on the ZnCdSe/ZnCdMgSe material system is characterized. The two-band detector consists of two stacks of quantum wells absorbing in the mid- and long-wavelength infrared regime. Photocurrent and responsivity measurements resulted in 11 mA/W and 7 mA/W peak responsivities at 80 K with corresponding detectivities of 2 × 108 cm√Hz/W and 2 × 107 cm√Hz/W centered at 4.8 μm (258 meV) and 7.6 μm (163 meV). The two-band device can also perform as a broadband detector covering wavelengths from 4.4 μm (281 meV) to 8.2 μm (151 meV) at 80 K with a full width at half maximum of 130 meV. Two-band QWIP is tested for an absolute temperature detection application and good agreement is observed between theoretical calculation and experimental results.An independently controllable, two-band quantum well infrared photo-detector (QWIP) based on the ZnCdSe/ZnCdMgSe material system is characterized. The two-band detector consists of two stacks of quantum wells absorbing in the mid- and long-wavelength infrared regime. Photocurrent and responsivity measurements resulted in 11 mA/W and 7 mA/W peak responsivities at 80 K with corresponding detectivities of 2 × 108 cm√Hz/W and 2 × 107 cm√Hz/W centered at 4.8 μm (258 meV) and 7.6 μm (163 meV). The two-band device can also perform as a broadband detector covering wavelengths from 4.4 μm (281 meV) to 8.2 μm (151 meV) at 80 K with a full width at half maximum of 130 meV. Two-band QWIP is tested for an absolute temperature detection application and good agreement is observed between theoretical calculation and experimental results.

Long wave, room temperature II-VI-based quantum cascade emitters

We demonstrate the first long-wave, room temperature II-VI materials based Quantum Cascade emitter around 7.2 μm. At 80 K, a device differential resistance of 2.6 Ω and a narrow electroluminescent width of 16% was obtained.

Asymmetric Multi-Quantum Well Infrared Photodetector with a Bound State in the Continuum

By carefully designing a multi-quantum well infrared photodetector (QWIP) heterostructure, we present an asymmetric QWIP with a localized state in the continuum. A narrow photocurrent spectrum confirms the electron confinement above the barrier.