Substrate Defects Filtration During Epitaxial Lateral Overgrowth of GaAs

Abstract

Results on the growth of GaAs on (001) GaAs substrates by the epitaxial lateral overgrowth technique are reported. We show that the ratio of normal to lateral growth rates in the epitaxial lateral overgrowth process can be controlled by the crystallographic orlentation of the seeds and by Si adding to the melt. Experimental data showing that the dislocations threading from the substrate are efficiently filtered and cannot propagate to the epitaxial lateral overgrowth layers are presented. These findings prove that the epitaxial 1ateral overgrowth process is the powerful method to grow epilayers with low dislocation density on high dislocation density substrates. PACS numbers: 68.55.Ln There is a continuous effort to reduce the defect denSity in heteroepitaxial structures grown on lattice mismatched substrates. Very sophisticated techniques of buffer layers and of defects filtration by superlattices have been elaborated to improve the quality of epitaxial layers thicker than the critical thickness. Unfor- tunately, very often the number of defects is still unacceptably high. Therefore, the growth of dislocation free epitaxial layers remains one of the most important goals in heteroepitaxy. The very promising way to reduce the dislocation den- sity in heteroepitaxy is the epitaxial lateral overgrowth (ELO) technique when combined with liquid phase epitaxy (LPE) growth method. However, controversy exists about the growth mechanism and the defect structure in layers grown by ELO. In this work we report the results on the growth of GaAs epilayers on (001) GaAs substrates using the ELO method. The growth mechanism and the effect of substrate defects filtration during the ELO procedure are discussed. The principle of the epitaxial lateral overgrowth technique is shown schemat- ically in Fig. 1. The substrate was covered by a 0.1 μm thick SiO2 film and pat- terned by a conventional photolithography to form on its whole area a grating of 10 μm wide oxide-free seeding windows. Then, an epitaxial layer was deposited on such substrate by the LPE technique. In our experiments the growth was initiated by covering the substrate with the saturated Ga-As solution at the temperature of 7500C while cooling the system. GaAs nucleated on the line seeds and the growth proceeded in the direction normal to the substrate. Then, the growth in lateral