Browsing by Author "Tekcan, B."

Now showing 1 - 10 of 10

Open Access
Atomic layer deposited HfO2 based metal insulator semiconductor GaN ultraviolet photodetectors
(Elsevier BV, 2014) Kumar, M.; Tekcan, B.; Okyay, Ali Kemal
A report on GaN based metal insulator semiconductor (MIS) ultraviolet (UV) photodetectors (PDs) with atomic layer deposited (ALD) 5-nm-thick HfO2 insulating layer is presented. Very low dark current of 2.24 × 10-11 A and increased photo to dark current contrast ratio was achieved at 10 V. It was found that the dark current was drastically reduced by seven orders of magnitude at 10 V compared to samples without HfO2 insulating layer. The observed decrease in dark current is attributed to the large barrier height which is due to introduction of HfO2 insulating layer and the calculated barrier height was obtained as 0.95 eV. The peak responsivity of HfO2 inserted device was 0.44 mA/W at bias voltage of 15 V.
Open Access
Electronic and optical device applications of hollow cathode plasma assisted atomic layer deposition based GaN thin films
(A I P Publishing LLC, 2015) Bolat, S.; Tekcan, B.; Ozgit Akgun, C.; Bıyıklı, Necmi; Okyay, Ali Kemal
Electronic and optoelectronic devices, namely, thin film transistors (TFTs) and metal-semiconductor-metal (MSM) photodetectors, based on GaN films grown by hollow cathode plasma-assisted atomic layer deposition (PA-ALD) are demonstrated. Resistivity of GaN thin films and metal-GaN contact resistance are investigated as a function of annealing temperature. Effect of the plasma gas and postmetallization annealing on the performances of the TFTs as well as the effect of the annealing on the performance of MSM photodetectors are studied. Dark current to voltage and responsivity behavior of MSM devices are investigated as well. TFTs with the N2/H2 PA-ALD based GaN channels are observed to have improved stability and transfer characteristics with respect to NH3 PA-ALD based transistors. Dark current of the MSM photodetectors is suppressed strongly after high-temperature annealing in N2:H2 ambient. © 2014 American Vacuum Society.
Open Access
Low temperature thin films transistors with hollow cathode plasma-assisted atomic layer deposition based GaN channels
(AIP Publishing LLC, 2014) Bolat, S.; Ozgit Akgun, C.; Tekcan, B.; Bıyıklı, Necmi; Okyay, Ali Kemal
We report GaN thin film transistors (TFT) with a thermal budget below 250 °C. GaN thin films are grown at 200 °C by hollow cathode plasma-assisted atomic layer deposition (HCPA-ALD). HCPA-ALD-based GaN thin films are found to have a polycrystalline wurtzite structure with an average crystallite size of 9.3 nm. TFTs with bottom gate configuration are fabricated with HCPA-ALD grown GaN channel layers. Fabricated TFTs exhibit n-type field effect characteristics. N-channel GaN TFTs demonstrated on-to-off ratios (ION/I OFF) of 103 and sub-threshold swing of 3.3 V/decade. The entire TFT device fabrication process temperature is below 250 °C, which is the lowest process temperature reported for GaN based transistors, so far. © 2014 AIP Publishing LLC.
Open Access
Low-temperature hollow cathode plasma-assisted atomic layer deposition of crystalline III-nitride thin films and nanostructures
(Wiley - V C H Verlag GmbH & Co. KGaA, 2015) Ozgit Akgun, C.; Goldenberg, E.; Bolat, S.; Tekcan, B.; Kayaci, F.; Uyar, Tamer; Okyay, Ali Kemal; Bıyıklı, Necmi
Hollow cathode plasma-assisted atomic layer deposition (HCPA-ALD) is a promising technique for obtaining III-nitride thin films with low impurity concentrations at low temperatures. Here we report our previous and current efforts on the development of HCPA-ALD processes for III-nitrides together with the properties of resulting thin films and nanostructures. The content further includes nylon 6,6-GaN core-shell nanofibers, proof-of-concept thin film transistors and UV photodetectors fabricated using HCPA-ALD-grown GaN layers, as well as InN thin films deposited by HCPA-ALD using cyclopentadienyl indium and trimethylindium precursors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Memory effect by charging of ultra‐small 2‐nm laser‐synthesized solution processable Si‐nanoparticles embedded in Si–Al2O3–SiO2 structure
(Wiley-VCH Verlag, 2015) El-Atab, N.; Rizk, A.; Tekcan, B.; Alkis, S.; Okyay, Ali Kemal; Nayfeh, A.
A memory structure containing ultra-small 2-nm laser-synthesized silicon nanoparticles is demonstrated. The Si-nanoparticles are embedded between an atomic layer deposited high-κ dielectric Al2O3 layer and a sputtered SiO2 layer. A memory effect due to charging of the Si nanoparticles is observed using high frequency C-V measurements. The shift of the threshold voltage obtained from the hysteresis measurements is around 3.3V at 10/-10V gate voltage sweeping. The analysis of the energy band diagram of the memory structure and the negative shift of the programmed C-V curve indicate that holes are tunneling from p-type Si via Fowler-Nordheim tunneling and are being trapped in the Si nanoparticles. In addition, the structures show good endurance characteristic (>105program/erase cycles) and long retention time (>10 years), which make them promising for applications in non-volatile memory devices. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Metal-semiconductor-metal ultraviolet photodetectors based on gallium nitride grown by atomic layer deposition at low temperatures
(SPIE, 2014) Tekcan, B.; Ozgit Akgun, C.; Bolat, S.; Bıyıklı, Necmi; Okyay, Ali Kemal
Proof-of-concept, first metal-semiconductor-metal ultraviolet photodetectors based on nanocrystalline gallium nitride (GaN) layers grown by low-temperature hollow-cathode plasma-assisted atomic layer deposition are demonstrated. Electrical and optical characteristics of the fabricated devices are investigated. Dark current values as low as 14 pA at a 30 V reverse bias are obtained. Fabricated devices exhibit a 15× UV/VIS rejection ratio based on photoresponsivity values at 200 nm (UV) and 390 nm (VIS) wavelengths. These devices can offer a promising alternative for flexible optoelectronics and the complementary metal oxide semiconductor integration of such devices. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE).
Open Access
A near-infrared range photodetector based on indium nitride nanocrystals obtained through laser ablation
(IEEE, 2014) Tekcan, B.; Alkis, S.; Alevli, M.; Dietz, N.; Ortac, B.; Bıyıklı, Necmi; Okyay, Ali Kemal
We present a proof-of-concept photodetector that is sensitive in the near-infrared (NIR) range based on InN nanocrystals. Indium nitride nanocrystals (InN-NCs) are obtained through laser ablation of a high pressure chemical vapor deposition grown indium nitride thin film and are used as optically active absorption region. InN-NCs are sandwiched between thin insulating films to reduce the electrical leakage current. Under-1 V applied bias, the recorded photoresponsivity values within 600-1100-nm wavelength range are as high as (3.05 × 10-2) mA/W. An ultrathin layer of nanocrystalline InN thin film is, therefore, a promising candidate for NIR detection in large area schemes. © 2014 IEEE.
Open Access
Performance enhancement of GaN metal-semiconductor-metal ultraviolet photodetectors by insertion of ultrathin interfacial HfO2 layer
(AVS Science and Technology Society, 2015) Kumar, M.; Tekcan, B.; Okyay, Ali Kemal
The authors demonstrate improved device performance of GaN metal-semiconductor-metal ultraviolet (UV) photodetectors (PDs) by ultrathin HfO2 (UT-HfO2) layer on GaN. The UT-HfO2 interfacial layer is grown by atomic layer deposition. The dark current of the PDs with UT-HfO2 is significantly reduced by more than two orders of magnitude compared to those without HfO2 insertion. The photoresponsivity at 360 nm is as high as 1.42 A/W biased at 5 V. An excellent improvement in the performance of the devices is ascribed to allowed electron injection through UT-HfO2 on GaN interface under UV illumination, resulting in the photocurrent gain with fast response time. © 2015 American Vacuum Society.
Open Access
Using nanogap in label-free impedance based electrical biosensors to overcome electrical double layer effect
(Springer Verlag, 2017) Okyay, Ali Kemal; Hanoglu, O.; Yuksel, M.; Acar, H.; Sülek, S.; Tekcan, B.; Agan, S.; Bıyıklı, Necmi; Güler, Mustafa O.
Point-of-care biosensor applications require low-cost and low-power solutions. They offer being easily accessible at home site. They are usable without any complex sample handling or any kind of special expertise. Impedance spectroscopy has been utilized for point-of-care biosensor applications; however, electrical double layer formed due to ions in the solution of interest has been a challenge, due to shielding of the electric field used for sensing the target molecules. Here in this study, we demonstrate a nanogap based biosensor structure with a relatively low frequency (1–100 kHz) measurement technique, which not only eliminates the undesired shielding effect of electrical double layer but also helps in minimizing the measurement volume and enabling low concentration (µ molar level) detection of target molecules (streptavidin). Repeatability and sensitivity tests proved stable and reliable operation of the sensors. These biosensors might offer attributes such as low-cost label-free detection, fast measurement and monolithic chip integrability.
Open Access
UV/vis range photodetectors based on thin film ALD grown ZnO/Si heterojunction diodes
(IOP Publishing, 2013) Alkis, S.; Tekcan, B.; Nayfeh, A.; Okyay, Ali Kemal
We present ultraviolet-visible (UV/vis) range photodetectors (PDs) based on thin film ZnO (n)/Si (p) heterojunction diodes. ZnO films are grown by the atomic layer deposition (ALD) technique at growth temperatures of 80, 150, 200 and 250 ° C. The fabricated ZnO (n)/Si (p) photodetectors (ZnO-Si-PDs) show good electrical rectification characteristics with ON/OFF ratios reaching up to 103. Under UV (350 nm wavelength) and visible (475 nm wavelength) light illumination, the ZnO-Si-PDs give photoresponsivity values of 30-37 mA W-1 and 74-80 mA W-1 at 0.5 V reverse bias, respectively. Photoluminescence (PL) spectra of ALD grown ZnO thin films are used to support the results.