Fabrication and characterisation of transparent-gate field effect transistors using indium tin oxide

Ion-implanted GaAs MESFETs with transparent indium tin oxide (ITO) gate electrodes have been fabricated using both sputtered and evaporated ITO gates. High-quality ITO films with transparency greater than 90% and low sheet resistance of 8 Ω/□ have been used in the fabrication of RF sputtered transparent gates. Transparent-gate FETs have also been fabricated using thermally evaporated ITO which have shown excellent electrical device performance comparable to the conventional GaAs MESFET. The optical responsivity of these devices is about 4.5 A/W for a radiation wavelength of 6328 Å. Fabrication details are also discussed for optoelectronic devices with transparent electrodes where the fine-structure processing are not compatible with standard lithography techniques