Burak Tekcan

A Near-Infrared Range Photodetector Based on Indium Nitride Nanocrystals Obtained Through Laser Ablation

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.

UV/vis range photodetectors based on thin film ALD grown ZnO/Si heterojunction diodes

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 10 3 . 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

Low temperature thin film transistors with hollow cathode plasma-assisted atomic layer deposition based GaN channels

We report GaN thin film transistors (TFT) with a thermal budget below 250u2009°C. GaN thin films are grown at 200u2009°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 9.3u2009nm. 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/IOFF) of 103 and sub-threshold swing of 3.3u2009V/decade. The entire TFT device fabrication process temperature is below 250u2009°C, which is the lowest process temperature reported for GaN based transistors, so far.

Electronic and optical device applications of hollow cathode plasma assisted atomic layer deposition based GaN thin films

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.

Performance enhancement of GaN metal–semiconductor–metal ultraviolet photodetectors by insertion of ultrathin interfacial HfO2 layer

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 360u2009nm 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.

Metal-semiconductor-metal ultraviolet photodetectors based on gallium nitride grown by atomic layer deposition at low temperatures

Abstract. 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.

Low temperature ALD grown ZnO as emitter and TCO for a thin-film a-Si PIN solar cells

The use of low temperature ALD grown ZnO as emitter and TCO coating for a-Si PIN solar cells is studied. Several cells are fabricated with 30nm ALD ZnO on top. The grown ALD ZnO without any additional TCO resulted in photovoltaic behavior. This confirms that the ZnO is acting as both an n-type semiconductor and TCO layer simultaneously. The measured open circuit voltage Voc = 0.25V and short-circuit current Jsc =1.63 mA/cm2 is achieved. In addition the EQE and IQE are measured and compared.

Hollow-cathode plasma-assisted atomic layer deposition: A novel route for low-temperature synthesis of crystalline III-nitride thin films and nanostructures

Hollow cathode plasma-assisted atomic layer deposition is a promising technique for obtaining III-nitride thin films with low impurity concentrations at low temperatures. Here we report our efforts on the development of HCPA-ALD processes for III-nitrides together with the properties of resulting thin films and nanostructures. The content will further include nylon 6,6/GaN core/shell and BN/AlN bishell hollow nanofibers, proof-of-concept thin film transistors and UV photodetectors fabricated using HCPA-ALD-grown GaN layers, as well as early results for InN thin films deposited by HCPA-ALD technique.