Quasi-persistent photoconductivity of double-heterojunction pseudomorphic high-electron-mobility transistor epitaxial wafers

Unusual electrical instability caused by light illumination in double heter ojunction pseudomorphic high-electron mobility transistor (DH-wpHEMT) epita xial wafers is reported for the first time. The principal parameters of DH- pHEMT namely, sheet carrier concentration, sheet resistance, and electron m obility, change slowly with time after illumination is shut off at 300 K. T he relaxation time of this transit is estimated to be longer than 10 min fo r some samples, grown by solid source molecular beam epitaxy. This phenomen on is called quasi-persistent photoconductivity (QPPC). The relationship be tween QPPC and interface roughness is investigated. Through atomic force mi croscopy measurements on both upper AlGaAs/InGaAs interface and lower InGaA s/AlGaAs interface of the DH-pHEMT, the lower interface of InGaAs channel i s found to be much rougher than the upper one. It is concluded that control of interface smoothness of the lower heterointerface is essential in order to obtain high-performance DH-pHEMT epitaxial wafers with high reproducibi lity. (C) 2000 Elsevier Science B.V, All rights reserved.