Study of deleterious aging effects in GaN/AlGaN heterostructures

A study of aging effects on the electron transport properties of AlGaN/GaN heterostructures grown on sapphire and silicon carbide substrates using temperature dependent Hall effect measurements is presented with the focus on the variations in the mobility, carrier concentration, and resistivity of these structures over time. The transport parameters for several of these structures were measured at various times after the initial measurement, including times exceeding one year. These studies show that these parameters are not stable in most of the samples. The most common effects are an increase in carrier concentration and a decrease in mobility. Changes on the order of several tens of percent were common. Since surface oxidation and other variations in surface states were suspected as possible sources of the observed changes, one sample was treated with HCl and KOH and measured again after each treatment. However, we were unable to recover the initial results although further changes in the electrical properties were observed. The study suggests that surface effects can have profound effects on the properties of the two-dimensional electron gas in these heterostructures. (C) 2003 American Institute of Physics.