Silicon effect on GaN surface morphology Z. Benzarti a , I. Halidou a , O. Tottereau b , T. Boufaden a , B. El Jani a, * a Laboratoire de Ge ´nie Me ´canique, Equipe de Physique des Mate ´riaux, Faculte ´ des Sciences, 5000 Monastir, Tunisie b Centre de Recherche sur l’He ´te ´roEpitaxie et ses Applications (CRHEA-CNRS), Sophia Antipolis, F-06560 Valbonne, France Received 12 March 2002; revised 17 May 2002; accepted 27 May 2002 Abstract Si-doped GaN epitaxial layers have been grown at 1050 8C on optimized-AlN buffered (0001) sapphire substrates by atmospheric pressure metalorganic vapor phase epitaxy. In order to investigate the Si effect on the surface morphology of GaN epilayers, several samples were grown by varying the silane partial pressure. When the silane partial pressure increases above 1.7 £ 10 28 atm, the surface quality becomes rough. This shows the Si surfactant effect. A correlation between an in situ laser reflectometry and ex situ optical and atomic force microscopy characterizations on the one hand and between electrical properties and surface quality on the other hand were made. As the electron concentration increases, the surface becomes more and more rough and the mobility drops dramatically. q 2002 Published by Elsevier Science Ltd. Keywords: Metalorganic vapor phase epitaxy; Si-doped GaN; Reflectometry; Morphology 1. Introduction The III – V nitrides have great potential for electronic and optoelectronic applications in short-wavelength regions from blue to ultraviolet (UV) due to its wide band-gap range (1.9 – 6.2 eV) and stability at high temperature [1]. The current progress in growth technology has permitted the commercialization of light emitting diodes (LEDs) and lasers based on these materials. However, further under- standing of n and p type doping are still needed to improve the performance of the devices. The doping of GaN has been extensively studied. In general, the n used dopants are silicon (Si), germanium (Ge) or selenium (Se) [1,2]. Si is the most efficient n-type dopant. It gives an electron concentration (n) as high as 10 20 cm 23 with a dramatical decrease of the mobility (m ). Many compensation mechanisms were reported to explain such decrease [3]. In our previous study [4] of GaN doping with Si by the decomposition of silane (SiH 4 ), we have proposed the amphoteric behavior of Si to be main scattering mechanism. But, we cannot rule out the surface scattering effect for higher SiH 4 pressure since this precursor is known to affect the surface morphology. However, the transport and optical properties depend on crystal surface quality. The dependence of electrical properties on surface morphology is not well understood. Therefore, the study of the relation between electrical properties and crystal surface quality is of great interest. In this paper, we investigate the Si-doping effect on GaN surface morphology with the aim to correlate the electrical properties and crystal quality. The introduction of SiH 4 in the growth chamber shows high effect on the sample surface. We discuss the relation between electron concen- tration and mobility and surface roughness due to SiH 4 effect. 2. Experiment Si-doped GaN epilayers (GaN/Si) were deposited on the (0001) sapphire (Al 2 O 3 ) substrates covered with AlN buffer layer in an horizontal atmospheric pressure metalorganic vapor phase epitaxy (AP-MOVPE) reactor. Trimethyl- gallium (TMG), trimethylaluminum (TMA), ammonia (NH 3 ) and SiH 4 diluted in 500 ppm of H 2 were used as Ga, Al, N and Si precursors, respectively. H 2 was the carrier gas. The growth procedure can be found in Ref. [4]. After a nitridation step followed by a deposition of a thin AlN buffer layer, the doping began by the simultaneous introduction of TMG and SiH 4 in the reactor. This avoids carrier concentration gradient in the layer. The 0026-2692/02/$ - see front matter q 2002 Published by Elsevier Science Ltd. PII: S0026-2692(02)00066-6 Microelectronics Journal 33 (2002) 995–998 www.elsevier.com/locate/mejo * Corresponding author. Tel.: þ 216-73-500-274; fax: þ216-73-500-278. E-mail address: belgacem.eljani@fsm.rnu.tn (B. El Jani).