Omer Salihoglu

Plasmon-polaritons on graphene-metal surface and their use in biosensors

We studied excitation of surface plasmon-polaritons on graphene-metal surface. The metal surface is functionalized by transfer printing of graphene grown by chemical vapor deposition on copper foils. Surface plasmon resonance characteristics of monolayer and multilayer graphene on the metal surface are presented. We were able to obtain the dispersion relation of graphene-metal surface which reveals the essential feature of the plasmon-polaritons. As an application, we fabricated a surface plasmon resonance sensor integrated with a microfluidic device to study nonspecific physical interaction between graphene layer and proteins.

Synthesis of graphene on gold

Here we report chemical vapor deposition of graphene on gold surface at ambient pressure. We studied effects of the growth temperature, pressure, and cooling process on the growngraphene layers. The Raman spectroscopy of the samples reveals the essential properties of the graphenegrown on gold surface. In order to characterize the electrical properties of the growngraphene layers, we have transferred them on insulating substrates and fabricated field effect transistors. Owing to distinctive properties of gold, the ability to growgraphene layers on gold surface could open new applications of graphene in electrochemistry and spectroscopy.

“N” structure for type-II superlattice photodetectors

In the quest to raise the operating temperature and improve the detectivity of type II superlattice (T2SL) photodetectors, we introduce a design approach that we call the “N structure.” N structure aims to improve absorption by manipulating electron and hole wavefunctions that are spatially separated in T2SLs, increasing the absorption while decreasing the dark current. In order to engineer the wavefunctions, we introduce a thin AlSb layer between InAs and GaSb layers in the growth direction which also acts as a unipolar electron barrier. Unlike the symmetrical insertion of AlSb into GaSb layers, N design aims to exploit the shifting of the electron and hole wavefunctions under reverse bias. With cutoff wavelength of 4.3 μm at 77 K, temperature dependent dark current and detectivity measurements show that the dark current density is 3.6 × 10−9 A/cm2, under zero bias. Photodetector reaches background limited infrared photodetection (BLIP) condition at 125 K with the BLIP detectivity (D*BLIP) of 2.6 × 1010 ...

Atomic layer deposited Al2O3 passivation of type II InAs/GaSb superlattice photodetectors

Taking advantage of the favorable Gibbs free energies, atomic layer deposited (ALD) aluminum oxide (Al2O3) was used as a novel approach for passivation of type II InAs/GaSb superlattice (SL) midwave infrared (MWIR) single pixel photodetectors in a self cleaning process (λcut-off ∼ 5.1 μm). Al2O3 passivated and unpassivated diodes were compared for their electrical and optical performances. For passivated diodes, the dark current density was improved by an order of magnitude at 77 K. The zero bias responsivity and detectivity was 1.33 A/W and 1.9 × 1013 Jones, respectively at 4 μm and 77 K. Quantum efficiency (QE) was determined as %41 for these detectors. This conformal passivation technique is promising for focal plane array (FPA) applications.

Effect of the Passivation Layer on the Noise Characteristics of Mid-Wave-Infrared InAs/GaSb Superlattice Photodiodes

The authors describe the noise characterization of a mid-wavelength-infrared (MWIR) photodiode based on indium arsenide and gallium antimonide (InAs/GaSb) superlattice (SL), addressing the influence of different passivation layers applied to the surface of the device. The MWIR InAs/GaSb SL design structure is based on p-i-n configuration grown by the molecular beam epitaxy on a (001) n-GaSb substrate. The SiO2-passivated SL photodiodes demonstrated a Schottky-limited noise up to a bias voltage of -0.1 V where the measured peak responsivity is 1.37 AAV with a cut-off wavelength of 4.9 μm and the specific detectivity as high as 1.23 × 1012 cm. Hz1/2 /W, demonstrating the high quality of the fabricated MWIR SL photodiodes. The noise measurements exhibited a frequency-dependent plateau (i.e., 1/f noise) for unpassivated and Si3N4-passivated samples, whereas 1/f-type noise suppression (i.e., frequency-independent plateau) with a noise current reduction at about 30 Hz of more than one order of magnitude was observed for the SiO2-passivated ones.

Skin-like self-assembled monolayers on InAs/GaSb superlattice photodetectors

We report on the effects of monolayer (ML) thick skin-like octadecanethiol (ODT, CH3[CH2]17SH) on type-II InAs/GaSb MWIR photodetectors. Circumventing the ageing effects of conventional sulfur compounds, we use ODT, a self-assembling, long molecular chain headed with a sulfur atom. Photodiodes coated with and without the self-assembled monolayer (SAM) ODT were compared for their electrical and optical performances. For ODT-coated diodes, the dark current density was improved by two orders of magnitude at 77 K under −100 mV bias. The zero bias responsivity and detectivity were 1.04 A W −1 and 2.15 × 10 13 Jones, respectively, at 4 µm and 77 K. The quantum efficiency was determined to be 37% for a cutoff wavelength of 5.1 µm. (Some figures may appear in colour only in the online journal)

A Comparative Passivation Study for InAs/GaSb Pin Superlattice Photodetectors

In the quest to find ever better passivation techniques for infrared photodetectors, we explore several passivation layers using atomic layer deposition (ALD). We compare the impact of these layers on detectors fabricated under same conditions. We use ALD deposited Al₂O₃, HfO₂, TiO₂, ZnO, plasma enhanced chemical vapor deposition deposited SiO₂, Si₃N₄, and sulfur containing octadecanethiol self assembled monolayer passivation layers on InAs/GaSb p-i-n superlattice diodes with an average cutoff wavelength of 5.1 μm. Passivated and unpassivated photodetectors compared for their electrical performances.

Femtosecond laser crystallization of amorphous Ge

Ultrafast crystallization of amorphous germanium (a-Ge) in ambient has been studied. Plasma enhanced chemical vapor deposition grown a-Ge was irradiated with single femtosecond laser pulses of various durations with a range of fluences from below melting to above ablation threshold. Extensive use of Raman scattering has been employed to determine post solidification features aided by scanning electron microscopy and atomic force microscopy measurements. Linewidth of the Ge optic phonon at 300 cm−1 as a function of laser fluence provides a signature for the crystallization of a-Ge. Various crystallization regimes including nanostructures in the form of nanospheres have been identified.

Atomic layer deposited passivation layers for superlattice photodetectors

The authors report on the effects of atomic layer deposited Al2O3, TiO2, HfO2, and ZnO layers as a passivation material for type-II InAs/GaSb superlattice midwave infrared photodetectors. Low temperature and plasma free operation with defect free and conformal coating of the atomic layer deposition technique creates an efficient passivation layer. In this study, photodiodes coated with and without passivation layer were compared for their dark current and surface resistivity performances. For Al2O3 coated diodes, the dark current density was improved by more than two orders of magnitude at 77 K under −50 mV bias. As a result, HfO2 and TiO2 passivated diodes are better than reference diodes, but they are not as good as Al2O3 passivated diodes. Low Gibbs free energy of the aluminum oxides helps eliminating conductive native surface oxides in a self cleaning process.

Passivation of type II InAs/GaSb superlattice photodetectors with atomic layer deposited Al 2 O 3

We have achieved significant improvement in the electrical performance of the InAs/GaSb midwave infrared photodetector (MWIR) by using atomic layer deposited (ALD) aluminium oxide (Al2O3) as a passivation layer. Plasma free and low operation temperature with uniform coating of ALD technique leads to a conformal and defect free coverage on the side walls. This conformal coverage of rough surfaces also satisfies dangling bonds more efficiently while eliminating metal oxides in a self cleaning process of the Al2O3 layer. Al2O3 passivated and unpassivated diodes were compared for their electrical and optical performances. For passivated diodes the dark current density was improved by an order of magnitude at 77 K. The zero bias responsivity and detectivity was 1.33 A/W and 1.9 x 1013 Jones, respectively at 4 μm and 77 K. Quantum efficiency (QE) was determined as %41 for these detectors.