Epitaxy Single Crystal GaN on AlN Prepared by Plasma-enhanced Atomic Layer Deposition

doi:10.15541/jim20230490

Abstract

Abstract:

As the third generation semiconductor material, gallium nitride (GaN) is widely used in electronic devices and optoelectronic devices due to its excellent characteristics such as wide band gap, high breakdown field strength, high electron mobility, outstanding thermal conductivity, and direct band gap. However, it is difficult to obtain high quality single crystal GaN thin films due to the mismatch between GaN material and substrate in early phase of preparation. Until the two-step growth method is proposed, in which the nucleation layer of aluminum nitride (AlN) is firstly grown on the substrate at low temperature, and then GaN is grown at high temperature, the quality of GaN is greatly improved. Nowadays, AlN nucleation layers are fabricated via magnetron sputtering and molecular beam epitaxy, etc. To further improve the quality of GaN crystals, this study used plasma-enhanced atomic layer deposition (PEALD) method to prepare AlN nucleation layers for the epitaxial growth of GaN on a two-inch c-plane sapphire substrate. Compared with the magnetron sputtering method and molecular beam epitaxy method, the crystal quality of AlN prepared by PEALD method displays advantages of simple process, low cost and high yield. Measurements on deposited AlN films show that the deposition rate is 0.1 nm/cycle and the films have island-like structures varying with its thickness. Epitaxial GaN measurements show that GaN epitaxial layer can obtain the smoothest surface with a root mean square roughness of 0.272 nm, the best optical properties, and the lowest dislocation density when AlN is deposited with a thickness of 20.8 nm. In conclusion, a new method of epitaxial single crystal GaN on AlN prepared by PEALD has been built with optimal deposition at 20.8 nm of AlN to obtain high quality GaN thin films, it can be used to prepare high electron mobility transistors and light-emitting diodes.

Key words: GaN, AlN, plasma-enhanced atomic layer deposition, nucleation layer, epitaxy

CLC Number:

TM23

LU Hao, XU Shengrui, HUANG Yong, CHEN Xing, XU Shuang, LIU Xu, WANG Xinhao, GAO Yuan, ZHANG Yachao, DUAN Xiaoling, ZHANG Jincheng, HAO Yue. Epitaxy Single Crystal GaN on AlN Prepared by Plasma-enhanced Atomic Layer Deposition[J]. Journal of Inorganic Materials, 2024, 39(5): 547-553.

Figures/Tables 10

Fig. 1 Schematic diagram of plasma-enhanced atomic layer deposition (PEALD) process of AlN

Fig. 2 Cross-sectional TEM image of sample 4

Fig. 3 Surface topographies of AlN AFM 3D images of (a) sample 1, (b) sample 2 and (c) sample 3

Fig. 4 XRD patterns of AlN films

Fig. 5 SEM images of GaN (a) Sample a; (b) Sample b; (c) Sample c

Fig. 6 AFM image of sample b

Fig. 7 Raman spectra of epitaxial GaN on AlN nucleation layers with different thicknesses

Fig. 8 PL spectra of GaN with different thicknesses of AlN nucleation layers

Fig. 9 Rocking curves of sample b on different crystal planes (a) (002); (b) (102)

Fig. 10 Rocking curves of (002) crystal plane for sample a (a) and sample c (b)

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