An ultra-fast gas delivery system for producing abrupt compositional switching in OMVPE

Abstract

We present here the design and testing of an ultra-fast gas handling/switching system for OMVPE which provides a very sharp compositional abruptness during growth. The system was made from commercially available proportioning electromagnetic valves, with modifications to provide a dead-space H 2 flush. The valves, in conjunction with flow and pressure transducers, function both as an ON/OFF as well as mass flow controller valves. The switching characteristics and stability of this system were tested with an IR diode laser spectrometer set-up tuned to the vibrational absorption frequency of the OM species flowing in the reactor or the associated methyl radical produced upon decomposition over a hot substrate. The ON/OFF switching time of this system (0.9s) is about ten times faster than the conventional vent/run linear manifold configuration used on our OMVPE reactor. For GaAs/AlGaAs growth, the 0.9s corresponds to a compositional transition of 7 Å. In addition to the fast switching, this new injection system has other attributes such as the ability to vary the OM concentration in a few hundred milliseconds and to deliver source material more efficiently.