The effect of (NH4)2Sx passivation on the (311)A GaAs surface and its use in AlGaAs/GaAs heterostructure devices

We have studied the efficacy of (NH4)(2)S-x surface passivation on the (311) A GaAs surface. We report XPS studies of simultaneously-grown (311) A and (100) heterostructures showing that the (NH4)(2)S-x solution removes surface oxide and sulfidizes both surfaces. Passivation is often characterized using photoluminescence measurements; we show that while (NH4)(2)S-x treatment gives a 40-60x increase in photoluminescence intensity for the (100) surface, an increase of only 2-3x is obtained for the (311) A surface. A corresponding lack of reproducible improvement in the gate hysteresis of (311) A heterostructure transistor devices made with the passivation treatment performed immediately prior to gate deposition is also found. We discuss possible reasons why sulfur passivation is ineffective for (311) A GaAs, and propose alternative strategies for passivation of this surface.