Materials Science and Engineering B82 (2001) 253 – 255 Improvement of diodes performance with a multiple-pair buffer layer by MOCVD Chien-Cheng Yang a,b, *, Meng-Chyi Wu b , Gou-Chung Chi c , Chang-Cheng Chuo d , Jen-Inn Chyi d a Microsystems Laboratory, Industrial Technology Research Institute, Hsinchu 310, Taiwan b Department of Electrical Engineering, National Tsing Hua Uniersity, Hsinchu 300, Taiwan c Optical Science Center, National Central Uniersity, Chung -Li 320, Taiwan d Department of Electrical Engineering, National Central Uniersity, Chung -Li 32054, Taiwan Abstract The GaN homo-junction light-emitting diodes (LEDs) with a multiple-pair buffer layer (MBL) were grown by metalorganic vapor phase epitaxy on sapphire substrates. Each pair of the buffer layer consists of a 300 A  thick GaN nucleation layer grown at a low temperature of 525°C and a 4 m thick GaN epitaxial layer grown at a high temperature of 1025°C. It is found that the GaN LEDs with a three-pair buffer layer will exhibit a low turn-on voltage, stronger electroluminescence intensity and higher light-output power as compared to the conventional growth without a buffer layer. This is attributed to the effective reduction in the propagation of defects and dislocations near the p – n junction for the LEDs with MBL. © 2001 Elsevier Science B.V. All rights reserved. Keywords: GaN; LED; MBL; multiple buffer layer www.elsevier.com/locate/mseb 1. Introduction The GaN-based alloys are clearly emerging as the most important materials, while the commercial super- brightness blue light-emitting diodes (LEDs) and room- temperature blue laser diodes (LDs) have been demonstrated as commercial products from Nichia Chemical Industries. In order to improve the device performance and reliability further, the way in which to reduce the dislocation density remaining in the GaN films has become the most critical issue at this time. Many attempts have been made to reduce the disloca- tion density and etch-pit density (EPD) in the GaN epitaxial layers, such as using the GaN bulk substrates [1], a second nucleation layer [2] and epitaxial laterally overgrowth (ELOG) [3]. Our previous work reported that the quality of the GaN epitaxial layer can be improved by growing the multiple-pair buffer layer (MBL) at low and high temperatures (550 and 1025°C) [4]. However, there still lacks the effect of the GaN device performance on the multiple-pair buffer layer. In this letter, we investigate the improvement of current – voltage (I – V ) and light-output characteristics on the homo-structure GaN LEDs with the different pair numbers in the MBL. 2. Experimental The p – n homo-junction GaN LEDs with the two or three pairs of buffer layer were grown on (0001) sap- phire by metalorganic chemical vapor deposition (MOCVD). Here, each pair of the buffer layer consists of a 300 A  thick GaN nucleation layer grown at a low temperature of 525°C and a 4 m thick GaN epitaxial layer grown at a high temperature of 1025°C. The growth procedure of MBL structure was given else- where [4]. The LED structure grown on the MBL consists of a 1.5 m Si-doped GaN (n =3–5 ×10 18 cm -3 ), a 0.3 m Si-doped GaN (n = 7 ×10 17 cm -3 ), and a 0.6 m Mg-doped GaN. The epitaxial wafer was then thermally annealed for 20 min at 750°C in N 2 * Corresponding author. Tel.: +886-3-5790177; fax: +886-3- 5790289. E-mail address: jcyang@oic.com.tw (C.-C. Yang). 0921-5107/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0921-5107(00)00693-0