On the incorporation of Mg and the role of oxygen, silicon, and hydrogen in GaN prepared by reactive molecular beam epitaxy

The temperature used for growth of GaN by molecular beam epitaxy is ultimately limited by the greatly reduced growth rate related to thermal decomposition. This limiting temperature apparently varies from group to group. Factors influencing thermal decomposition are growth species (atomic versus metastable molecular nitrogen), surface polarity (N- versus Ga-polar), the presence of atomic hydrogen, and varying Ga-overpressure. Surface polarity and growth species are the predominant influence determining the onset of thermal decomposition. There are indications that the use of a significant Ga-overpressure can suppress decomposition allowing for an increase in obtainable growth temperatures for a given polarity. Electrical properties are shown to be strongly influenced by Ga-overpressure and thermal decomposition.

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Photoconductance decay and spectral photoconductance measurements were made on a set of ten undoped layers of GaN grown by rf-plasma MBE. The layers, also characterized by Hall, photoluminescence and reflectance measurements, represented a wide variety in electrical and optical properties, and several were grown under atomic hydrogen. Spectral photoconductance indicated transitions at 1.0-1.1, 1.92, 2.15, 3.08 and 3.2-3.4 eV. All layers exhibited persistent photoconductivity to some degree. In contrast with previous reports, a clear correlation was not observed between persistent photoconductivity and yellow luminescence or, indeed, with any measurement made. Analysis of photoconductance decay indicates that more than one type of persistent photoconductivity may be present.

Growth of GaN by molecular beam epitaxy is limited by reduced growth rate related to thermal decomposition. Factors influencing thermal decomposition are growth species (atomic versus metastable molecular nitrogen), surface polarity (N-vs. Ga-polar), and varying Ga-overpressure. Surface polarity and growth species are the predominant influence determining the onset of thermal decomposition. A significant Gaoverpressure can suppress decomposition, allowing an increase in growth temperatures. Electrical properties are strongly influenced by Ga-overpressure and thermal decomposition.