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P.Chen', B.Shen, R.Zhang, M.Wang, Y.G.Zhou, Z.Z.Chen, L.Zhang, and Y.D.Zheng Departmentof Physics and Solid MicrostructuresLab, Nanjing University, Nanjing 210093, P.R.China

ABSTRACT Nanometer-scale GaN dots were successfully fabricated on sapphire using metalorganic chemical vapor deposition(MOCVD) by two-step method, including depositing around 500 IC and annealing at 1050 °C. The density of GaN dots is from 5xl0 8cm 2 to 6x10 9 cm-2 , and the size is around 40nm in diameter. The density and size of GaN dots are determined by an atomic force microscope(AFM), and they are controllable by changing temperature and duration of the growing. GaN dots only formed after annealing at high temperature, which is explained that the initial layer deposited around 500 'C is a high energy intermediate phase in which the large strain energy can not be relaxed because of the low temperature growing.

I. INTRODUCTION Recently, the quantum dots or nanostructures of GaN have been reported by several research groups[1,2], which shows a raising interesting in this topic. Low dimension structures of quantum wire or dot bring lots of new physical phenomena and new technology on application of devices. Now, the wide gape III-V nitrides have been successfully used in light emitting and laser diodes(LED/LDs) [3,4]. Similar to the devices fabrication with Si and other Ill-V semiconductors, reducing the dimension of the active layer may greatly improve the quality and extend the application of the GaN-based devices. According to the Stranski-Krastanow(S-K) growth model[5], if the lattice mismatch exists between the epilayer and the substrate, initial growth of the epilayer is layer by layer, then the island growth will occurs due to the releasing of the large strain in the thicker epilayer. Actually, the fabrication of III-V compounds[6-8] and Ge/Si[9,10] quantum dots using CVD or MBE techniques is based on the S-K growth model. Usually, in the growth of III-V compound quantum dots, an initial cladding layer is grown on the substrate, then quantum dots are grown on the layer surface during a very short time, typically 3 to 10 seconds. Obviously, the short time growth brings some difficulties in controlling size and density of dots. The idea of a system progressing through a succession of phases to reach the final equilibrium phase is well known[1 1]. If the direct formation of the equilibrium phase has a large kinetic barrier, a system may find it easier to reach this state through intermediate phases, each of which has a lower barrier for formation. In this work, we fabricated GaN quantum dots by two-step method, including depositing at low temperature, and then

Email address: ydzheng(a•iju.edu.cn

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Mat. Res. Soc. Symp. Proc. Vol. 512 ©1998 Materials Research Society

annealing over 1000 V, using the layer deposited at low temperature as an intermediate phase of the system. The experimental results are determined by an atomic force microscope(AFM).

II. Experimental The GaN quantum dots were grown on a-A120 3(0001) substrates in a hor