T. Sass

Surface characterization of ordered (GaIn)P

Abstract The knowledge of the nature of the sample surface is important to influence and optimize growth processes and to understand growth mechanisms. Here, a study of the surface of ordered (GaIn)P grown on differently misoriented (0xa00xa01) GaAs substrates is presented using high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Whereas the surface of GaAs consists of (0xa00xa01) terraces and bunched supersteps, vicinal regions appear additionally on the (GaIn)P surface. The height of supersteps increases with increasing misorientation angle and decreasing growth temperature. The surface morphology has also been investigated as a function of the phosphorus partial pressure using three different precursors (phosphine, tertiarybutylphosphine, and ditertiarybutylphosphine) and of the zinc doping. Moreover, additional characteristic facets such as (1xa00xa0 l ), (0xa01xa0 l ), ( h xa01xa0 l ), and (1xa0 kxa0l ) were found.

Droplet Epitaxy of InAs Nanocrystals on GaN/GaAs

The growth of InAs nanocrystals fabricated on GaAs by means of droplet epitaxy in a metal-organic chemical vapour-deposition chamber was investigated. To prevent deterioration of the droplet/substrate interface a nitride passivation layer was introduced. For this purpose both, nitridation of GaAs and GaN growth at different temperatures have been applied. In all nitrided samples and when GaN was grown at Tg=450°C, deep pit-like defects have been found in the GaAs below the InAs islands, caused by In that diffused from the droplets into the substrate along the {111} planes. Only the growth of a thin cubic GaN layer at Tg=550°C effectively prevented this indiffusion of indium into the substrate. The InAs islands contained stacking faults and twins that arose from defects in the underlying GaN layer. Their sidewalls do not only consist of (001) and {111} facets, but also of the commonly not observed {110} and even {111} facets. The frequent occurrence of holes at the center base of the InAs islands is discussed within a growth model for the transformation of In droplets to InAs nanocrystals.

MOVPE Growth and Characterisation of Zn-Doped (GaIn)P Layers with Respect to Surface Structure and Ordering

(GaIn)P grown on (001)GaAs substrates by metal-organic vapour phase epitaxy (MOVPE) is highly ordered material. In this work the effect of Zn doping on the epitaxial crystal growth, the ordering behaviour and the surface morphology is investigated. Zn-doped (GaIn)P layers, grown with phosphine (PH 3 ), tertiarybutylphosphine (TBP) and ditertiarybutylphosphine (DitBuPH) as phosphorous precursors, reveal a strong drop of the binary growth rate of InP r InP with increasing Zn/III ratio, whereas r GaP remains nearly constant. The Zn doping efficiency and the ordering behaviour are observed to be dependent on the misorientation of the substrates. Finally, the surface morphology as a function of the different parameters was analysed by atomic force microscopy (AFM), and no considerable change of the growth mechanism was found for Zn-doped layers in comparison to undoped layers.