Excimer laser annealing: An alternative route and its optimisation to effectively activate Si dopants in AlN films grown by plasma assisted molecular beam epitaxy

• Published in: Materials research bulletin 2018-01, Vol.97, p.300-305
• Main Authors: Ghosh, Kankat, Busi, Pratik, Das, Sudipta, Rathore, Jaswant Singh, Laha, Apurba
• Format: Article
• Language: English
• Subjects: Hall measurement; Laser annealing; MBE; Nitrides; Raman spectroscopy; X-ray diffraction
• ISSN: 0025-5408; 1873-4227
• DOI: 10.1016/j.materresbull.2017.09.016

In this paper we investigate the possibility of employing laser annealing as a potential method to activate Si dopants in AlN films. Nitrogen plasma assisted molecular beam epitaxy (MBE) system was used to grow Si doped AlN films on GaN/Sapphire substrate followed by an excimer laser annealing in a pulsed laser deposition (PLD) chamber. Under a set of specified conditions (mentioned in the manuscript) different pieces of the MBE grown sample were annealed with varying number of laser pulses. We found that the available electron concentration and mobility in the film increases with increasing laser shots and reaches a maximum. Thus we propose laser annealing as a suitable method to activate deep donors in AlN films which is required for optoelectronic devices. [Display omitted] •Si doped AlN films are grown by PAMBE.•Si doped films are annealed by excimer laser.•∼5×1018cm−3 n-type carrier concentration was achieved by annealing the AlN films under optimized condition.•Sub nm (0.76nm) roughness and minimum residual biaxial stress were achieved under the optimized annealing condition. Si doped AlN films were grown on GaN/Sapphire templates by plasma assisted molecular beam epitaxy (PAMBE) technique. We show that employing an excimer laser annealing with optimized power and frequency rather than the conventional thermal annealing could be a potential alternative route towards improving the structural and electrical properties of AlN layers. Upon optimized laser annealing of the Si-doped AlN layer, the electron concentration was achieved to be as high as ∼4.9×1018cm−3 which was measured by Raman spectroscopy measurement and was further cross checked by standard Hall measurement which estimated the same as ∼7.4×1018cm−3 with a mobility of 109cm2/V-sec. The improvement of free carrier concentration was leveraged by improvement of structural properties. The r.m.s surface roughness of the Si-doped AlN layers measured by atomic force microscopy was reduced to 0.76nm and corresponding residual stress estimated by high resolution XRD and Raman measurement was found to be less than half compared to the in-situ Si-doped sample. Thus laser annealing is proposed to be a suitable method to achieve high electron concentration in Si doped AlN films without compromising the structural quality.