2D and 3D growth mode of nitride layers

Krzysztof Pakuła Jacek Baranowski 1

1. Warsaw University, Institute of Experimental Physics (IEP UW), Hoża 69, Warszawa 00-681, Poland

Abstract

Heteroepitaxial three dimensional (3D) and two dimensional (2D) growth mode of nitride layers on sapphire substrates are discussed. It is shown that the 3D or 2D growth mode of AlGaN layers depends predominantly on the growth conditions of the underneath grown low temperature (LT) nucleation layer.

Commonly described in literature 3D growth mode is obtained on LT GaN or AlN nucleation layer grown relatively fast. Successive growth of secondary layer at high temperature begins from separated sites, where individual 3D crystallites are formed. Threading dislocations present in crystallites are bending on their facets, which reduces the quantity of dislocations. However, from the other hand, slight crystallographic misorientations between crystallites leads to creation of new dislocations which are generated during coalescence of the crystallites. As result edge and mix dislocations appearing are at similar density of about 109 cm-2.

Modification of growth conditions of LT AlN nucleation layer, especially reduction of their growth rate leads to drastic changes in properties of the layer. Successive growth of secondary AlGaN layer at high temperature starts evenly on whole surface retaining atomic flatness. Thus, the growth at high temperature occurs only at 2D mode. Therefore, it is possible to grow a very thin AlGaN layers directly on top of LT AlN nucleation layer. Such layers contain large number (1010 cm-2) of edge dislocations, and relatively small number (less then 108 cm-2) of mix dislocations.

It is also shown, that decisive factors which determine the growth mode of AlN nucleation layer is a growth of the first few atomic layers on substrate surface. The slow growth of this few first atomic layers decide about the 2D growth mode, and the fast one about the 3D one.

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Presentation: Invited oral at Joint Fith International Conference on Solid State Crystals & Eighth Polish Conference on Crystal Growth, by Krzysztof Pakuła
See On-line Journal of Joint Fith International Conference on Solid State Crystals & Eighth Polish Conference on Crystal Growth

Submitted: 2007-02-19 15:22
Revised:   2009-06-07 00:44
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