As covered in the chapters on jets a new simplified jet is being suggested which should be much easier to characterize, and this is probably the only way to go to perform experiments in a controlled fashion. The goal is to compare the jet versus a leak valve using NH_3 in terms of growth rate and crystal quality, and how jet parameters effect the growth, especially as a function nozzle temperature. The possibility of using a RF plasma heated N_2 jet will also be explored.
The growth rate model developed so far has to be verified experimentally and modified if necessary. It is planned to map out in detail the growth rate as a function of Ga flux, NH_3 flux, and substrate temperature, as well as in relation to the `balance line'. The substrate temperature calibration technique has also to be verified by using for example eutectics. Auger spectroscopy will be used to study GaN surfaces to obtain more information about surface condition, especially in conjunction with the hysteresis of `dips' observed. Experiments are also planned on determining the decomposition rate of GaN with and without fluxes so they can be included in the growth rate model. Currently the RHEED gun is being modified to permit rastering to explore the effects of an e-beam on the sample. The search for RHEED oscillations will continue in conjunction with the quest of determining growth conditions to obtain the best possible surfaces. More emphasis will be placed on sample preparation and growth initiation to achieve this goal.
Post growth characterization will continue to be performed with a variety of techniques. RBS and X-Ray will be explored in more detail to obtain data on crystal quality as a function of growth conditions. Auger depth profiling and RBS will be employed to obtain complimentary sets of data concerning growth rates. It is also planned to use TEM to study the substrate - initiation layer interface to optimize the growth initiation procedure.
Recently a Si and Mg source have been prepared to permit controlled doping of our films, hopefully leading to the fabrication of devices. A current issue is still the question of why our samples are insulating, due to good crystal quality or unintentional doping. Major efforts will be undertaken to determine the cause.
Future projects, still in the planning stages, will be the use of a surface electron microscope to study the growth kinetics of III-Nitride films, as well as the use of in situ surface mass spectroscopy.
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