Correlation Between the AlN Buffer Layer Thickness and the GaN Polarity in GaN/AlN/Si(111) Grown by MBE
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Correlation Between the AlN Buffer Layer Thickness and the GaN Polarity in GaN/AlN/Si(111) Grown by MBE A.M. Sanchezb1, P. Ruterana1, P. Vennegues2, F. Semond2, F.J. Pacheco3, S.I. Molina3, R. Garcia3, M.A. Sanchez-Garcia4 and E. Calleja4 1
ESCTM-CRISMAT, UMR6508-CNRS, ISMRA. 6, Boulevard Maréchal Juin, 14050 Caen Cedex, France
2
CRHEA-CNRS, B. Grégory, 06560 Valbonne, France
3
Departamento de Ciencia de los Materiales e I. M. y Q. I., Universidad de Cadiz. Apdo. 40 E11510 Puerto Real (Cadiz), Spain
4
Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica, Apdo. 28040 Madrid, Spain
ABSTRACT In this work it is shown that thin AlN buffer layers cause N-polarity GaN epilayers, with a high inversion domains density. When the AlN thickness increases, the polarity of the epilayer changes to Ga. The use of a low temperature AlN nucleation layer leads to a flat AlN/Si(111) interface. This contributes to decrease the inversion domains density in the overgrown GaN epilayer with a Ga polarity. INTRODUCTION The III-N semiconductor compounds are of great interest for the fabrication of optoelectronic devices, particularly with short wavelength. Moreover, III-nitrides have excellent electronic properties in comparison with materials frequently used for electronic devices. Moreover, they can be used for high temperature and high power applications. GaN has been epitaxially grown on a large variety of substrates (6H-SiC, ZnO, GaAs, Si, different mixed oxides, etc) due to the lack of III-N semiconductors wafers. The growth of GaN over Si(111) substrates is an interesting challenge. The realization of GaN-based devices on this substrate would help to combine the optoelectronic and electronic properties of these materials to the well-known silicon technology. Although, the knowledge of heterostructures based on GaN grown over sapphire has considerably advanced, the GaN heteroepitaxy growth on Si(111) has received less attention. The direct growth of GaN on Si(111) is not possible due to the large lattice mismatch, difference of thermal coefficients as well as the surface chemistry. A thin amorphous layer is generated between both materials because of the reaction of the Si (111) surface with the reactive nitrogen species1,2. Due to the poor GaN nucleation on Si(111) it is necessary to introduce a buffer layer in order to obtain an improved GaN epitaxy. An AlN thin layer was found to be an effective buffer for the growth of GaN films over Si(111)3 and, up to now, it has been the most used buffer layer in this kind of growth4,5. In GaN/AlN/Sapphire heterostructures, the control of b
Corresponding author, Tel. +33 2 31 45 26 53, Fax. +33 2 31 45 26 60, e-mail: [email protected]
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the AlN buffer layer thickness is not as critical as in GaN/GaN/Sapphire, and good results have been obtained in a large range of thickness (30-100 nm)6. The anions in GaN wurtzite form a hcp structure in which the cations occupy half of the tetrahedral sites. There are two different kind of tetrahedr
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