| AVS 59th Annual International Symposium and Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF+NS+EM-ThM |
| Session: | Thin Films: Growth and Characterization-II |
| Presenter: | N. Nepal, U.S. Naval Research Laboratory |
| Authors: | N. Nepal, U.S. Naval Research Laboratory J.K. Hite, U.S. Naval Research Laboratory N. Mahadik, U.S. Naval Research Laboratory M.A. Mastro, U.S. Naval Research Laboratory C.R. Eddy, Jr., U.S. Naval Research Laboratory |
| Correspondent: | Click to Email |
AlN and its alloys with GaN and InN are of great interest for number of applications. In a device structure that employes an ultrathin layer of these materials, thickness control at the atomic scale is essential. Atomic layer epitaxy (ALE) is one of the most promising growth methods for control of epilayer thickness at the atomic scale. There are reports on atomic layer deposition of AlN on GaN and Si substrates [1]. In those reports, the AlN layers were either amorphous or composed of nm-sized crystallites. Since ALE is a low temperature growth process, there is significantly reduced thermal energy for adatoms to bond at preferred lattice sites and promote growth of crystalline material, therefore, surface preparation plays a very important role to ensure a crystalline layer.
In this work, we present recent efforts to improve the crystalline quality of ALE AlN layers on MOCVD grown GaN/sapphire templates, including the influence of ex situ and in situ surface pretreatments to promote uniform two-dimensional (2D) nucleation of AlN layers and ALE growth of crystalline AlN films thereupon. AlN layers were grown at 500°C by ALE simultaneously on Si(111) and GaN/sapphire templates and characterized using spectroscopic ellipsometery (SE), x-ray diffraction (XRD), and atomic force microscopy measurements. The SE measurements indicate that the AlN growth on Si(111) is self-limited for trimethyaluminum (TMA) pulse of length 0.04 to 0.06 sec. However, the AlN nucleation has a bimodal island size distribution for TMA pulses < 0.06 sec. The AlN nucleation becomes uniform and 2D for a pulse length of 0.06 sec, therefore, this pulse length was used to study the GaN surface pretreatment on the nucleation of AlN layer. GaN surfaces were pre-treated ex situ with HF and HCl wet chemical etches. Alternating pulses of trimethylgallium and hydrogen plasma followed by an hour of annealing at 500°C (emulating a Ga-flash-off process) were employed in situ before growing an AlN layer. For 3 cycles of Ga-flash-off the AlN nucleation is uniform and replicates the GaN surface morphology on both HF and HCl pretreated GaN. XRD measurements on 36 nm thick AlN films reveal that the ALE AlN on GaN/sapphire is crystalline with only a wurtize structure and a (0002) peak rocking curve FWHM of 630 arc-sec, which is close to the typical value for AlN grown by MBE and MOCVD [2,3]. Electrical characterization of 2D electron gas at the AlN/GaN interface will also be presented.
References:
1. M. Alevli et al., Phys. Status SolidiA 209, 266 (2012), and references therein.
2. T. Koyama et al., Phys. Stat. Sol. (a) 203, 1603 (2006).
3. K. Balakrishnan et al., Phys. Stat. Sol. (c) 3, 1392 (2006).