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

TL;DR

This study evaluates (NH4)2Sx passivation on (311)A GaAs surfaces, revealing limited photoluminescence improvement and gate hysteresis reduction, and discusses reasons and alternatives for its ineffectiveness.

Contribution

It provides a detailed analysis of (NH4)2Sx passivation effects on (311)A GaAs, highlighting its limitations and proposing alternative surface passivation strategies.

Findings

Significant PL increase on (100) surfaces with passivation

Minimal PL improvement on (311)A surfaces

No consistent reduction in gate hysteresis for (311)A devices

Abstract

We have studied the efficacy of (NH4)2Sx surface passivation on the (311)A GaAs surface. We report XPS studies of simultaneously-grown (311)A and (100) heterostructures showing that the (NH4)2Sx solution removes surface oxide and sulfidizes both surfaces. Passivation is often characterized using photoluminescence measurements, we show that while (NH4)2Sx treatment gives a 40 - 60 x increase in photoluminescence intensity for the (100) surface, an increase of only 2 - 3 x 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.