IMPROVEMENT OF GAS-SWITCHING ABRUPTNESS FOR ATMOSPHERIC-PRESSURE ORGANOMETALLIC VAPOR-PHASE EPITAXY

A simple gas dilution technique was implemented to minimize the limitations of the organometallic gas delivery manifold with a vent/run configuration in an organometallic vapor phase epitaxy (OMVPE) system. The dead space created in a switching valve upon closing can serve as a memory cell for the reactants. The importance of the problem depends on the volume and shape of the cavity. This paper reports on the effects of diluting the organometallic-saturated H-2 carrier gases before the switching valves. Significant improvement in intra-layer composition uniformity and interface abruptness of AlxGa1-xAs/GaAs quantum wells (QWs) was observed. Without the dilution flow, residual trimethylaluminum in the dead space of the switching valve resulted in a slow transition at the barrier and well interface, leading to graded heterojunctions and possibly aluminum incorporation in the well. Diluting the reactants with 50 SCCM of H-2 provided more abrupt interfaces and resulted in excellent agreement between the well width obtained by the scaled bulk growth rate and that calculated with photoluminescence data and a square well model.