Study of GaN thin films grown on intermediate-temperature buffer layers bymolecular beam epitaxy

A detailed characterisation study of GaN thin films grown by rf-plasma mole cular beam epitaxy on intermediate-temperature buffer layers (ITBL) was car ried out with Hall, photoluminescence (PL) and deep-level transient Fourier spectroscopy (DLTFS) techniques. The unique feature of our GaN thin films is that the GaN epitaxial layers are grown on top of a double layer that co nsists of an ITBL, which is grown at 690 degreesC, and a conventional low-t emperature buffer layer deposited at 500 degreesC. It is observed that 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 d emonstrated systematic improvements with the thickness of the ITBL. The DLT FS results suggest a three-order-of-magnitude reduction in the deep level a t E-c-0.40 eV in the device fabricated with the GaN films grown on an ITBL thickness of 1.25 mum in comparison with the control device without an ITBL . Our analyses indicate that the utilization of an ITBL in addition to the conventional low-temperature buffer layer leads to the relaxation of residu al strain within the material, resulting in an improvement in the optoelect ronic properties of the films. (C) 2002 Elsevier Science BN. All rights res erved.