Abstract
The effects of chemisorbed molecules on the electronic transport through an ungated high electron mobility transistor and through an ungated field effect transistor are examined, Current versus voltage measurements in the dark reveal that the adsorbed molecules and their chemical nature have a pronounced effect on the structures' performance, as they reduce the current by up to one order of magnitude. The molecular specificity of the devices is expressed in the wavelength dependence of photo current decay. The decay time, which increases by several orders of magnitude upon adsorption of the molecules, changes drastically when the excitation wavelength matches the absorption of the adsorbed molecules. Effect of Cu ions caught by adsorbed organic molecules on the photo current decay is clearly demonstrated. The observations open new possibilities in constructing semiconductor based light and chemical sensors.