Structure of AIN on Si (111) Deposited with Metal Organic Vapor Phase Epitaxy
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Cite this article as: MRS Internet J. Nitride Semicond. Res. 4S1, G3.56 (1999) Revised Jan. 18. 1999
ABSTRACT The surface morphology and structure of AIN deposited by metal organic vapor phase epitaxy (MOVPE) on Si (111) at growth temperatures ranging from 825 to 1175 'C was investigated. Transmission electron microscopy (TEM), reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS) techniques were used to study the resulting film structure. Growth at high temperatures but less than -1100 'C, resulted in a wire texture with some degree of in-plane alignment with ( 0 0 0 1)AIN //(1l1 l)s, AIN//s,, and A. /H< 10>s. Deposition at temperatures greater than I 100°C results in single crystal films consisting of domains 60 nm across with an aspect ratio near unity. Growth below I 100°C leads to degraded crystal quality with the grains developing random rotational misalignments around the AIN [0001] axis. Growth at lower temperatures produces islands elongated along the [1120] direction. At the growth temperature of 825°C, the aspect ratio of the islands increased to 3 and a width of 25 nm. Cross -sectional TEM reveals that these islands are faceted due to slow growth on the (I101} planes.
INTRODUCTION Nitride-based II1-V materials have been receiving attention due to their ability to lase in the green and blue spectral regions. However, these materials are difficult to fabricate. The strong bonding of N 2 and low nitrogen solubility in molten Ga results in very high nitrogen overpressures during crystallization of a nitride crystal from the melt. These difficulties have prevented the production of useful GaN bulk crystals. Lack of a single-crystal nitride substrate requires devices to be made through heteroepitaxial growth. GaN and AIN also have a coefficient of thermal expansion, lattice constant and crystal structure different from other III-V semiconductors. Nitrides therefore need to be grown on a substrate different from those normally used for compound semiconductor growth, such as GaAs or InP. The highest quality materials have used either silicon carbide or sapphire substrates [1,2]. These materials can be expensive and limited in size. Additionally, the lattice mismatch to these substrates is quite large and even the highest quality materials contain a high concentration of lattice mismatch related structural defects. Silicon substrates have been successfully used for nitride growth. A Si (111) substrate will have the required hexagonal surface symmetry. The low cost and availability of this substrate makes it an attractive alternative to silicon carbide and sapphire substrates. Previous work using Si substrates centered upon growth of AIN and GaN. Much of this work was done in ultra-high vacuum (UHV) using molecular beam epitaxy (MBE) or sputtering to produce the layers [3,4]. Single crystal films could be grown under optimized conditions. As with most nitride heteropitaxial growth, the films contained a dense network of structural defects. D
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