Growth of high quality GaN thin films by MBE on intermediate-temperature buffer layers

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-tempera ture buffer layer (ITBL), which is grown at 690 degreesC and a conventional low-temperature buffer layer deposited at 500 degreesC. It is observed tha t the electron mobility increases steadily with the thickness of the ITBL, which peaks at 377 cm(2)V(-1)s(-1) for an ITBL thickness of 800 nm. The PL also demonstrated systematic improvements with the thickness of the ITBL. O ur analyses of the mobility and the photoluminescence characteristics demon strate 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 t he films. A maximum electron mobility of 430 cm(2)V(-1)s(-1) can be obtaine d using this technique and further optimizing the growth conditions for the low-temperature buffer layer.