DOI: 10.1007/s00339-007-4077-7 Appl. Phys. A 89, 177–181 (2007) Materials Science & Processing Applied Physics A j. sun 1, ✉ j. chen 1 x. wang 1 j. wang 2 w. liu 2 j. zhu 2 h. yang 2 Stress evolution influenced by oxide charges on GaN metal–organic chemical vapor deposition on silicon-on-insulator substrate 1 The State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, P.R. China 2 State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, P.R. China Received: 27 November 2006/Accepted: 14 April 2007 Published online: 28 June 2007 • © Springer-Verlag 2007 ABSTRACT GaN epilayers have been deposited on silicon-on- insulator (SOI) and bulk silicon substrates. The stress transition thickness and the initial compressive stress of a GaN epilayer on the SOI substrate are larger than those on the bulk silicon substrate, as shown in in situ stress measurement results. It is mainly due to the difference of the three-dimensional island density and the threading dislocation density in the GaN layer. It can increase the compressive stress in the initial stage of growth of the GaN layer, and helps to offset the tensile stress generated by the lattice mismatch. PACS 81.15.Gh 1 Introduction GaN and related nitrides are promising materials for their applications in UV/blue/green/white light emitter diodes (LEDs) [1] and high-power, high-temperature elec- tronic devices [2]. GaN on silicon has attracted much interest for its use as a light emitter in optoelectronic integrated cir- cuits [3]. Due to the large lattice mismatch (∼ 17%) and the coefficient of thermal expansion (CTE) mismatch (∼ 60%), the GaN layer deposition on silicon always exhibits crack lines which would be detrimental to GaN-based devices. An AlGaN or AlN buffer layer is commonly used to avoid the generation of cracks and the diffusion of silicon atoms. From in situ stress measurement results, the GaN top layer is found to be initially under compressive strain due to the lattice mis- match between the AlGaN or AlN layer and the top layer, which has been described in our previous work [4]. Use of a silicon-on-insulator (SOI) substrate is one of the effective methods to reduce the mismatch stress and improve the quality of the GaN layer. Cao et al. reported GaN deposited on a (001) SOI substrate and found that the compliant top sili- con layer can improve the quality of the GaN epilayer [5, 6]. Recently, (111) SOI and (111) Si/CoSi 2 /Si substrates were used for the GaN deposition [7], and the strong and weak bonded SOI substrates were used for the InGaN/GaN multi- quantum wells [8], exploiting the advantages of this com- pliant substrate. A SOI substrate has been an important ma- terial for the GaN metal–organic chemical vapor deposition ✉ Fax: +86-21-62513510, E-mail: jiayinsun@mail.sim.ac.cn (MOCVD). Therefore, the further research of the stress evolu- tion in the GaN epilayer is very useful for the GaN deposition on a SOI substrate. In this paper, we deposit the GaN epilayer on SOI and bulk silicon substrates, and then investigate the initial stage of the MOCVD process. The initial three-dimensional (3D) island density and the stress transition in deposition related to the oxide charges in a buried oxide (BOX) layer are reported in this paper. 2 Experiment The SOI substrate, with 230-nm top silicon layer and 390-nm BOX layer, was fabricated with separation by im- planted oxygen (SIMOX). The SOI and bulk silicon substrates used for deposition were 2 × 2 cm 2 , 500-μ m-thick squares. The GaN films were deposited by MOCVD. The GaN films with ∼ 40 nm high-temperature AlN (HT-AlN) buffer layers were deposited on bulk silicon and SOI substrates, respec- tively. The source materials for Ga, Al, and N were trimethyl- gallium (TMGa), trimethylaluminum (TMAl) and NH 3 , and H 2 was used as the carrier gas. The AlN buffers were deposited at 1180 ◦ C with a V/III ratio of 1028, and GaN layers were de- posited at 1070 ◦ C with a V/III ratio of 560. The whole struc- tures of the samples are shown in Fig. 1. A multiple beam opti- cal stress sensor (MOSS) was used to monitor the surface mor- phological evolution and Stoney’s equation was used to calcu- late the stress in the deposited GaN layers [4, 9, 10]. The meas- urement of X-ray diffraction (XRD) was performed for the estimate of the GaN crystal quality. The measurement of oxide charge density was performed using a pseudo-MOS transistor with a two-probe system connected to a HP-4155 Semicon- ductor Parameter Analyzer, as shown in Fig. 2. Atomic force microscope (AFM) measurement was performed to demon- strate the roughness of the surface after MOCVD. 3 Results and discussion The typical in situ stress × thickness vs. thickness curves measured by the MOSS system are shown in Fig. 3. We can see that the GaN layers were under the compressive stress in the initial stage of deposition, and then transferred to the tensile stress. Such a transition was attributed to the decrease in dislocation density with thickness [11]. Comparing the two curves in Fig. 3, we can see that the transition thickness of the GaN epilayer on the SOI substrate is much larger than that