Fabrication And Characterization Of Al/Znse Thin Film Schottky Diode

ABSTRACT

The desire for smaller, more efficient and faster semiconductor devices has made the design of the Schottky devices, material preparation and characterization very vital. There is little research if any on the effect of Schottky contact geometry on I-V characteristics. In this study various circular and rectangular thin filmed Al/ZnSe Schottky diodes were designed by varying; the shape, area of the Schottky contact, the inter electrode distance and thickness of the thin film ZnSe. Fabrication was done by thermal vacuum evaporation technique of zinc (99.99%) and selenium (99.99%) alloy powder onto masked glass slides using an Edward Auto 306 RF/DC magnetron evaporation chamber. Transmittance and reflectance data in the range of 300 nm to 3000 nm were obtained using a UV-VIS NIR spectrophotometer solid state 3700 DUV. Transmittance values of 77.71%, 75.81 % and 67.42% of annealed samples of thickness 233 nm, 237 nm and 289 nm respectively, were obtained for photons of wavelength 1000nm.The experimental data was exported to and simulated using Scout 98 software to extract optical constants and optical band gap of the thin films. Band gap values of 3.20eV, 3.15eV and 2.95eV were obtained for annealed ZnSe thin films of thickness 233nm, 237nm and 289nm respectively. The surface sheet resistivities at a room temperature of 300K were found to vary for the as-deposited and annealed thin films of ZnSe of different thickness. Sheet resistivity decreased on annealing and ranged between to Ω.cm. Silver paste was used as the ohmic contacts due to its high work function of 4.75eV. I-V characteristics of were obtained using the Keithley 2400 source meter and data analyzed using Origin Software. From the J-V characteristic curves, the dark diode ideality factor was found to range between 6.0 and 7.3 and was lower for circular Schottky devices than for rectangular ones. Circular geometry had a uniform electric field unlike rectangular which had enhanced electric field at the corners that caused an avalanche of charge carriers. Diode with circular Schottky contact area of 2.0423×10-4m2; a smaller inter-electrode spacing of 4mm and a ZnSe semiconductor thin film of 289 nm had the lowest diode ideality factor of 6.361 and thus superior diode properties; therefore size and geometry of Schottky contact affects I-V properties of the diode and should be considered when designing thin film devices.