Browsing by Author "Tansel, T."

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Open Access
Atomic layer deposited Al 2O 3 passivation of type II InAs/GaSb superlattice photodetectors
(AIP, 2012) Salihoğlu, Ömer; Muti, Abdullah; Kutluer, Kutlu; Tansel, T.; Turan, R.; Kocabaş, Coşkun; Aydınlı, Atilla
Taking advantage of the favorable Gibbs free energies, atomic layer deposited (ALD) aluminum oxide (Al 2O 3) 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 (λ cut-off ∼ 5.1 m). Al 2O 3 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 × 10 13 Jones, respectively at 4μm 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. © 2012 American Institute of Physics.
Open Access
Effect of the passivation layer on the noise characteristics of mid-wave-infrared InAs / GaSb superlattice photodiodes
(IEEE, 2012) Tansel, T.; Kutluer, K.; Salihoglu, Ö.; Aydınlı, Atilla; Aslan, B.; Arikan, B.; Kilinc, M. C.; Ergun, Y.; Serincan, U.; Turan, R.
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 SiO 2-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 A/W with a cut-off wavelength of 4.9 μm and the specific detectivity as high as 1.23 × 10 12 cm. Hz 1/2 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 Si 3N 4-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 SiO 2-passivated ones.
Open Access
Electrical performance of InAs/AlSb/GaSb superlattice photodetectors
(Academic Press, 2016) Tansel, T.; Hostut M.; Elagoz, S.; Kilic A.; Ergun, Y.; Aydınlı, Atilla
Temperature dependence of dark current measurements is an efficient way to verify the quality of an infrared detector. Low dark current density values are needed for high performance detector applications. Identification of dominant current mechanisms in each operating temperature can be used to extract minority carrier lifetimes which are highly important for understanding carrier transport and improving the detector performance. InAs/AlSb/GaSb based T2SL N-structures with AlSb unipolar barriers are designed for low dark current with high resistance and detectivity. Here we present electrical and optical performance of such N-structure photodetectors.
Open Access
Electronic and optical properties of 4.2 lm‘‘N’’ structured superlattice MWIR photodetectors
(Elsevier B.V., 2013-01-05) Salihoglu, O.; Hostut M.; Tansel, T.; Kutluer, K.; Kilic A.; Alyoruk, M.; Sevik, C.; Turan, R.; Ergun, Y.; Aydınlı, Atilla
We report on the development of a new structure for type II superlattice photodiodes that we call the ‘‘N’’ design. In this new design, we insert an electron barrier between InAs and GaSb in the growth direction. The barrier pushes the electron and hole wavefunctions towards the layer edges and under bias, increases the overlap integral by about 25% leading to higher detectivity. InAs/AlSb/GaSb superlattices were studied with density functional theory. Both AlAs and InSb interfaces were taken into account by calculating the heavy hole–light hole (HH–LH) splittings. Experiments were carried out on single pixel photodiodes by measuring electrical and optical performance. With cut-off wavelength of 4.2 lm at 120 K, temperature dependent dark current and detectivity measurements show that the dark current is 2.5 10 9 A under zero bias with corresponding R0A resistance of 1.5 104 X cm2 for the 500 500 lm2 single pixel square photodetectors. Photodetector reaches BLIP condition at 125 K with the BLIP detectivity (D BLIP) of 2.6 1010 Jones under 300 K background and 0.3 V bias voltage.
Open Access
Electronic and optical properties of 4.2 μm"N" structured superlattice MWIR photodetectors
(Elsevier, 2013) Salihoglu, O.; Hostut M.; Tansel, T.; Kutluer, K.; Kilic A.; Alyoruk, M.; Sevik, C.; Turan, R.; Ergun, Y.; Aydınlı, Atilla
We report on the development of a new structure for type II superlattice photodiodes that we call the "N" design. In this new design, we insert an electron barrier between InAs and GaSb in the growth direction. The barrier pushes the electron and hole wavefunctions towards the layer edges and under bias, increases the overlap integral by about 25% leading to higher detectivity. InAs/AlSb/GaSb superlattices were studied with density functional theory. Both AlAs and InSb interfaces were taken into account by calculating the heavy hole-light hole (HH-LH) splittings. Experiments were carried out on single pixel photodiodes by measuring electrical and optical performance. With cut-off wavelength of 4.2 μm at 120 K, temperature dependent dark current and detectivity measurements show that the dark current is 2.5 × 10 -9 A under zero bias with corresponding R0A resistance of 1.5 × 104 Ω cm2 for the 500 × 500 μm2 single pixel square photodetectors. Photodetector reaches BLIP condition at 125 K with the BLIP detectivity (DBLIP) of 2.6 × 10 10 Jones under 300 K background and -0.3 V bias voltage. © 2012 Elsevier B.V. All rights reserved.
Open Access
Gibbs free energy assisted passivation layers
(SPIE, 2016) Salihoğlu, Ömer; Tansel, T.; Hoştut, M.; Ergun, Y.; Aydınlı, Atilla
Reduction of surface leakage is a major challenge in most photodetectors that requires the elimination of surface oxides on etched mesas during passivation. Engineering the passivation requires close attention to chemical reactions that take place at the interface during the process. In particular, removal of surface oxides may be controlled via Gibbs reactivity. We have compared electrical performance of type-II superlattice photodetectors, designed for MWIR operation, passivated by different passivation techniques. We have used ALD deposited Al2O3, HfO2, TiO2, ZnO, PECVD deposited SiO2, Si3N4 and sulphur containing octadecanethiol (ODT) selfassembled monolayers (SAM) passivation layers on InAs/GaSb p-i-n superlattice photodetectors with cutoff wavelength at 5.1 μm. In this work, we have compared the result of different passivation techniques which are done under same conditions, same epitaxial structure and same fabrication processes. We have found that ALD deposited passivation is directly related to the Gibbs free energy of the passivation material. Gibbs free energies of the passivation layer can directly be compared with native surface oxides to check the effectiveness of the passivation layer before the experimental study.
Open Access
High quantum efficiency Type-II superlattice N-structure photodetectors with thin intrinsic layers
(SPIE, 2013) Ergun, Y.; Hostut, M.; Tansel, T.; Muti, bdullah; Kilic, A.; Turan, R.; Aydınlı, Atilla
We report on the development of InAs/AlSb/GaSb based N-structure superlattice pin photodiode. In this new design, AlSb layer in between InAs and GaSb layers acts as an electron barrier that pushes electron and hole wave functions towards the GaSb/InAs interface to perform strong overlap under reverse bias. Experimental results show that, with only 20 periods of intrinsic layers, dark current density and dynamic resistance at -50 mV bias are measured as 6×10-3 A/cm2 and 148 ωcm2 at 77K, respectively. Under zero bias, high spectral response of 1.2A/W is obtained at 5 μm with 50% cut-off wavelengths (λc) of 6 μm. With this new design, devices with only 146 nm thick i-regions exhibit a quantum efficiency of 42% at 3 μm with front-side illimunation and no anti-reflection coatings. © 2013 SPIE.
Open Access
Low-frequency noise behavior at reverse bias region in InAs/GaSb superlattice photodiodes on mid-wave infrared
(SPIE, 2013) Tansel, T.; Kutluer, K.; Muti, Abdullah; Salihoğlu, Ömer; Aydınlı, Atilla; Turan, R.
We describe a relationship between the noise characterization and activation energy of InAs/GaSb superlattice Mid- Wavelength-Infrared photodiodes for different passivation materials applied to the device. The noise measurements exhibited a frequency dependent plateau (i.e. 1/f-noise characteristic) for unpassivated as well as Si3N4 passivated samples whereas 1/f-type low noise suppression (i.e. frequency independent plateau) with a noise current reduction of more than one order of magnitude was observed for SiO2 passivation. For reverse bias values below -0.15V, the classical Schottky-noise calculation alone did not appear to describe the noise mechanism in a SL noise behavior, which shows a divergence between theoretically and experimentally determined noise values. We identify that, the additional noise appears, with and without passivation, at the surface activation energy of < 60 meV and is inversely proportional to the reverse bias. This is believed to be caused by the surface dangling-bonds (as well as surface states) whose response is controlled by the applied reverse bias. The calculated noise characteristics showed a good agreement with the experimental data. © 2013 SPIE.
Open Access
N structure for type-II superlattice photodetectors
(American Institute of Physics, 2012-08-14) Salihoglu, O.; Muti, A.; Kutluer, K.; Tansel, T.; Turan, R.; Ergun, Y.; Aydınlı, Atilla
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 mu m at 77 K, temperature dependent dark current and detectivity measurements show that the dark current density is 3.6 x 10(-9) A/cm(2), under zero bias. Photodetector reaches background limited infrared photodetection (BLIP) condition at 125 K with the BLIP detectivity (D-BLIP*) of 2.6 x 10(10) Jones under 300 K background and -0.3 V bias voltage.
Open Access
N-structure based on InAs/AlSb/GaSb superlattice photodetectors
(Academic Press, 2015) Hostut, M.; Alyoruk, M.; Tansel, T.; Kilic, A.; Turan, R.; Aydınlı, Atilla; Ergun, Y.
We have studied the theoretical and experimental properties of InAs/AlSb/GaSb based type-II superlattice (T2SL) pin photodetector called N-structure. Electronic properties of the superlattice such as HH-LH splitting energies was investigated using first principles calculations taking into account InSb and AlAs as possible interface transition alloys between AlSb/InAs layers and individual layer thicknesses of GaSb and InAs. T2SL N-structure was optimized to operate as a MWIR detector based on these theoretical approaches tailoring the band gap and HH-LH splitting energies with InSb transition layers between InAs/AlSb interfaces. Experimental results show that AlSb layers in the structure act as carrier blocking barriers reducing the dark current. Dark current density and R0A product at 125 K were obtained as 1.8 × 10-6 A cm-2 and 800ωcm2 at zero bias, respectively. The specific detectivity was measured as 3 × 1012 Jones with cut-off wavelengths of 4.3 μm at 79 K reaching to 2 × 109 Jones and 4.5 μm at 255 K. ©2014 Elsevier Ltd. All rights reserved.
Open Access
Passivation of type II InAs / GaSb superlattice photodetectors with atomic layer deposited Al2O3
(SPIE, 2012) Salihoğlu, Ömer; Muti, Abdullah; Kutluer, K.; Tansel, T.; Turan, R.; Kocabaş, Coşkun; Aydınlı, Atilla
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.
Open Access
Skin-like self-assembled monolayers on InAs / GaSb superlattice photodetectors
(IOP Institute of Physics Publishing, 2012) Salihoglu, O.; Muti, A.; Kutluer, K.; Tansel, T.; Turan, R.; Aydınlı, Atilla
We report on the effects of monolayer (ML) thick skin-like octadecanethiol (ODT, CH 3[CH 2] 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 77K under 100mV bias. The zero bias responsivity and detectivity were 1.04AW 1 and 2.15 × 10 13 Jones, respectively, at 4μm and 77K. The quantum efficiency was determined to be 37% for a cutoff wavelength of 5.1μm.
Open Access
Surface recombination noise in InAs / GaSb superlattice photodiodes
(IOP Institute of Physics Publishing, 2013) Tansel, T.; Kutluer, K.; Muti, A.; Salihoglu, Ö.; Aydınlı, Atilla; Turan, R.
The standard Schottky noise approach alone is not sufficient to describe the noise mechanism in an InAs/GaSb superlattice photodetector at reverse negative bias. The additional noise identified appears at surface activation energies below 60meV and is inversely proportional to the reverse bias. In order to satisfactorily explain the experimental data, we hereby propose the existence of a surface recombination noise that is a function of both the frequency and bias. The calculated noise characteristics indeed show good agreement with the experimental data.