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We report the growth of high quality GaN epitaxial layers by rf-plasma MBE. The unique feature of our growth process is that the GaN epitaxial layers are grown on top of a double layer that consists of an intermediate-temperature buffer layer (ITBL), which is grown at 690°C and a conventional low-temperature buffer layer deposited at 500°C. It is observed that the electron mobility increases steadily with the thickness of the ITBL, which peaks at 377 cm2V−1s−1 for an ITBL thickness of 800 nm. The PL also demonstrated systematic improvements with the thickness of the ITBL. Our analyses of the mobility and the photoluminescence characteristics demonstrate that the utilization of an ITBL in addition to the conventional low-temperature buffer layer leads to the relaxation of residual strain within the material resulting in improvement in the optoelectronic properties of the films. A maximum electron mobility of 430 cm2V−1s−1 can be obtained using this technique and further optimizing the growth conditions for the low-temperature buffer layer.

Deep level transient spectroscopy in plasma-assisted molecular beam epitaxy grown Al 0.2 Ga 0.8 N / GaN interface and the rapid thermal annealing effectWe report detailed investigations of low-frequency excess noise in GaN thin-film cross-bridge structures deposited by rf-plasma assisted molecular-beam epitaxy on top of an intermediate-temperature buffer layer ͑ITBL͒ grown at 690°C. The experimental data indicates strong dependence of the voltage noise power spectra on the thickness of the ITBL with an optimal thickness of 800 nm. A model has been presented to account for the observed noise, which stipulates that the phenomenon arises from the thermally activated trapping and detrapping of carriers. The process results in the correlated fluctuations in both the carrier number and the Coulombic scattering rate. Detailed computation shows that number fluctuation dominates in our samples. Our numerical evaluation indicates a reduction in the trap density by over an order of magnitude with the use of an ITBL in the growth of GaN thin films.

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