Epitaxial Growth of GaN Thin Films Using a Hybrid Pulsed Laser Deposition System
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*INRS-tnergie et Mat6riaux, 1650 boul. Lionel Boulet, Varennes, Qu6bec, Canada J3X IS2. [email protected] "**Departmentof Physics, American University of Beirut, P.O. Box: 11-0236, Bliss Street, Beirut, Lebanon. ABSTRACT A hybrid Pulsed Laser Deposition system was developed to perform epitaxial growth of GaN on sapphire(0001). This system combines the laser ablation of a cooled Ga target with a well-characterized atomic nitrogen source. Taking advantage of the flexibility of this unique deposition system, high quality GaN thin films were deposited by optimizing both the laser intensity and the nitrogen flux. To date, our best GaN films show a FWHM of the GaN(0002) rocking curve peak equal to 480 arcsec. This result has been obtained at a laser intensity of I = 7x10 7 W/cm 2 , a substrate temperature of 800'C and under Ga-rich growth conditions. INTRODUCTION Gallium nitride (GaN) and similar materials (AIN, InN) are the subject of intensive research because of their numerous applications in the fields of UV-visible light emitting/detecting devices and high power electronics [I]. The growth of GaN layers with a low density of defects has proved to be a challenge due to the lack of a high quality lattice matched substrate. Many conventional deposition techniques, like MOCVD [2] and MBE [3], have been used to grow these layers with a reasonable amount of success when combined with specific substrate preparation like the ELOG (Epitaxial Lateral Over Growth) process [4]. In this relatively new field, it is essential to search for alternative deposition techniques which could produce high quality thin films while offering a relatively simple process. Also, the comparison of the layers obtained using different growth methods can help to understand better the fundamental aspects of GaN heteroepitaxy. One of the interesting features of Pulsed Laser Deposition (PLD) is that the ablated species (ions and neutrals) are available at high kinetic energy (10-100 eV) in the ablation plume [5]. Other advantages include its simplicity and its versatility. Also, PLD can be used with a reactive background gas leading to the growth of new compounds. This work presents preliminary results on the epitaxial growth of GaN thin films using a hybrid Pulsed Laser Deposition (PLD) system combining the laser ablation of a cooled Ga target with an atomic nitrogen source developed at INRS-Energie et Mat6riaux [6]. EXPERIMENT The deposition system is presented in Fig. 1. The atomic nitrogen source is provided by a high-frequency (HF) plasma generated by an electromagnetic surface wave excited by a Ro-box [7] (applied field frequency f= 13.56 or 40.68 MHz) or a Surfatron [8] (f= 440 or 2450 MHz) wave launcher. The total HF absorbed power, PA, is varied from 10 watts to 200 watts. The discharge is generated in a 4.5 mm inner diameter fused silica tube, 25 cm long, through which 401 Mat. Res. Soc. Symp. Proc. Vol. 572 © 1999 Materials Research Society
pure N2 flows. gas flow, Q, and the pressure inbytheflow source, Ps, and are ina Baratron
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