The electrical behaviour of GaAs MESFETs formed on high and low temperature GaAs buffer layers

Comparisons have been made between the channel currents in GaAs MESFETs prepared on GaAs buffer layers prepared at normal and low temperatures. All devices made on LT buffer layers had saturated channel currents which were about 20% of similar devices on a normal buffer. An attempt was made to remove Ga vacancies from the LT buffer by a high temperature anneal step before the epitaxial layer was prepared. This had no effect in increasing the channel current. In all cases the pinchoff voltage was unchanged indicating constancy of the channel thickness and donor concentration. It is concluded that the loss of current is due to a loss of mobile charge through trapping.