Abdulkerim Karabulut

Capacitance–conductance characteristics of Au/Ti/Al2O3/n-GaAs structures with very thin Al2O3 interfacial layer

High-k Al2O3 with metallic oxide thickness of about 3 nm on n-type GaAs substrate has been deposited by the atomic layer deposition (ALD) technique. Thus, it has been formed the Au-Ti/Al2O3/n-GaAs MIS structures. It has been seen that the MIS structure exhibits excellent capacitance-voltage (C–V) and current-voltage (I–V) properties at 300 K. The saturation current of the forward bias and reverse bias I–V characteristics was the same value. An ideality factor value of 1.10 has been obtained from the forward bias I–V characteristics. The C–V characteristics of the structure have shown almost no hysteresis from +3 V to −10 V with frequency as a parameter. The reverse bias C–V curves have exhibited a behavior without frequency dispersion and almost hysteresis at each frequency from 10 kHz to 1000 kHz.

Production and Neutron Irradiation Tests on a New Epoxy/Molybdenum Composite

Molybdenum powder was added in an epoxy matrix to increase the neutron-shielding capacity of pure epoxy. FLUKA and GEANT4 Monte Carlo programs were used to design new neutron-shielding material. After finding the epoxy/Mo ratio for the best shielding capacity, neutron equivalent dose rate measurements were performed. Results were compared to commonly used neutron-shielding materials such as paraffin, steel, concrete, and B4C. The produced new sample has a high neutron shielding capacity and it can be used for neutron protection purposes.

Electrical characteristics of Au/Ti/n-GaAs contacts over a wide measurement temperature range

We have fabricated Au/Ti/n-GaAs/In Schottky barrier diodes using the magnetron dc sputter technique. The capacitance–temperature (C–T) measurements with bias voltage as a parameter and the current–voltage (I–V) and capacitance–voltage (C–V) measurements have been made in the temperature range of 60–300 K. The temperature-dependent capacitance measurements have been made at 1.0 MHz. The capacitance versus temperature curve at each bias voltage has four regions with slopes different from each other. The capacitance decreases with a decrease in temperature at each bias voltage. Such a temperature-dependent behavior could be attributed to modulation of the space charge region caused by the emission of deep-level impurities or interface states. The carrier concentration calculated in the �1.0 to �2.0 V range of C �2 –V plots was close to the value of 7.43×10 15 cm �3 given by the manufacturer around room temperature. The ideality factor value from the I–V characteristics has remained almost unchanged between 1.07 and 1.10 in the temperature range of 150–300 K, indicating that the current across the device obeys the thermionic emission current model quite well over the whole bias range at temperatures above 150 K. Therefore, the conventional Richardson plot in this temperature range has given a Richardson constant of 8.21 A (cm K) �2 , within experimental error, which is in very close agreement with the theoretical value of 8.16 A (cm K) �2 for n-type GaAs. Again, it has been seen that the ideality factor with the values of 1.10 at 150 K and 1.22 at 60 K does not show a considerable decrease. The experimental parameters show that the Au(90 nm)/Ti(10 nm)/nGaAs contact is a good candidate for electronic device applications.

The Characteristic Parameters of Ni/n-6H-SiC Devices Over a Wide Measurement Temperature Range

Ni/n-type 6H-SiC/Ni Schottky barrier diodes (SBDs) have been prepared by the DC magnetron sputtering deposition technique. Their current-voltage characteristics (I-V) have been measured in the measurement temperature range of 40-400 K with steps of 20 K under dark conditions. The barrier height (BH) values from the temperature-dependent forward and reverse bias I-V characteristics by different methods coincide with each other which indicates the elimination of the polarity between the Si and C ions. The ideality factor value remains almost unchanged in the 160-400 K range, and below 160 K, it has the values of 1.57 at 140 K, and 3.82 at 60 K. The BH has the values of 0.79 eV at 400 K, and 0.71 eV at 300 K. The decrease in the BH is due to the fact that the current will preferentially flow through the lowest BH with decreasing temperature due to barrier inhomogeneity. The value of 0.71 eV at 300 K is in close agreement with the values of 0.65 and 0.83 eV reported from the forward bias I-V characteristics for the Ni /n-type 6H-SiC in the literature. Thus, it has been concluded that the reduced barrier devices are promising for applications in devices operating at cryogenic temperatures as infrared detectors, sensors in thermal imaging and small signal zero-bias rectifiers and microwave mixers.

Influence of Al2O3 barrier on the interfacial electronic structure of Au/Ti/n-GaAs structures

The Au/Ti/n-GaAs structures with and without Al 2 O 3 interfacial layer have been fabricated.The Al 2 O 3 interfacial layer has been formed on the GaAs substrate by atomic layer deposition.The effects of the interfacial layer on the current-voltage ( I - V ) and capacitance-voltage ( C - V ) characteristics of the devices have been investigated in the temperature range of 60-300 K.It has been seen that the carrier concentration from C - V characteristics for the MIS (metal/insulating layer/semiconductor) diode with Al 2 O 3 interfacial layer has a higher value than that for the reference diode without the Al 2 O 3 interfacial layer (MS).Such a difference in the doping concentration has been attributed not to doping variation in the semiconductor bulk but to the presence of the Al 2 O 3 interfacial layer because both diodes have been made on the pieces cut from the same n-type GaAs wafer.The temperaturedependent I - V characteristics of the MIS diode do not obey the thermionic emission current theory because of the presence of the Al 2 O 3 layer.An electron tunneling factor, aδ ( χ ) 1/2 , value of 20.64 has been found from the I - V - T data of the MIS diode.An average value of 0.627 eV for the mean tunneling barrier height, χ , presented by the Al 2 O 3 layer has been obtained.

Cadmium Oxide:Titanium Dioxide Composite Based Photosensitive Diode

Cadmium oxide:titanium dioxide (CdO:TiO2) composite thin films with various ratios of CdO contents were prepared on p-type silicon semiconductor substrates by the sol–gel spin coating method. Al/CdO:TiO2/p-Si/Al heterojunction devices exhibited optoelectronic device behavior due to their photocurrent under solar light illuminations. The photoresponse behavior of the diodes is controlled by changing the molar ratio of CdO to TiO2. The fabricated CdO:TiO2 (2:1) based device exhibited the highest photoresponse of about 7.5 × 103. The interface properties of the devices are changed with the molar ratio of CdO:TiO2. The obtained results suggest that CdO:TiO2 composite film/p-type Si structure can be used in optoelectronic applications.