Materials Science and Engineering, B21 (1993) 249-252 249 Metal-organic vapour-phase epitaxial growth of symmetricallystrained (Gain)As/Ga (PAs) superlattices S. Lutgen, T. Marschner, T. F. Albrecht, W. Stolz* and E. O. G6bel Materials Sciences Center and Department of Physics, Philipps-University, D-35032 Marburg (Germany) L. Tapfer CN.R.S.M., I- 72100 Brindisi (Italy) Abstract Novel symmetrically strained (Galn)As/Ga(PAs) superlattices (symm. SLS) are realized by metal-organic vapour-phase epitaxy (MOVPE). The structural and optical properties of the symm. SLS are determined by means of high-resolution X-ray diffraction (XRD) as well as by photoluminescence (PL) and excitation spectroscopy (PLE) and are compared also to one-side strained (Galn)As/GaAs as well as Ga(PAs)/GaAs SLS. The optimization of growth conditions with respect to substrate misorientation and growth temperature is presented and discussed. In order to realize high-quality symm. SLS, it is important to avoid growth surface irregularities, i.e. steps introduced by substrate misorientation, or rough surface morphologies, leading to an enhanced strain relaxation. The residual average lattice mismatch is below 5 x 10-4 for 50 period SLS layers, having lattice mismatches of up to + 2.4 x 10- 2 in the individual layers. Because of this almost perfect symmetric strain profile, the SL critical thickness becomes much larger than the typical layer thickness. Narrow XRD linewidths for the superlattice satellite peaks of 20" to 30" (FWHM) are obtained. First PL and PLE studies are briefly described and discussed with respect to the exciton binding energy in this system, providing indication of a considerably reduced in-plane hole mass in these symm. SLS. 1. Introduction Strained IIl/V-semiconductor heterostructures are becoming increasingly important, particularly for applications in optoelectronic devices [1], primarily due to the possibility of designing the valence band structure as a function of the incorporated strain. In strained layer superlattices (SLS), however, two critical layer thickness types exist with respect to strain relaxa- tion by incorporation of misfit dislocations, one being the critical thickness of the individual layers, the other the critical thickness of the total superlattice layer structure. Therefore, severe limitations exist for the strain level and/or thickness of the individual layers as well as for the number of periods in the superlattice structure. So far, most of the work has concentrated on struc- tures containing one-side strained epitaxial layers, as in the case of the (GaIn)As/GaAs material system. In order to overcome the limitations with respect to the superlattice critical thickness, the growth of symmetric- ally strained layer superlattices (symm. SLS), i.e. alter- *Author to whom correspondence should be addressed. nating layers with built-in compressive and tensile strain, by metal-organic vapour-phase epitaxy (MOVPE) has been studied for the (GaIn)As/Ga(PAs) material system on GaAs substrate. First reports on symm. SLS systems have recently been published for modulator structures in the (GaIn)As/Ga(PAs) on GaAs material system, grown by gas source molecular beam epitaxy (GSMBE) [2] as well as in the In(PAs)(GaIn)P on InP system, grown by chemical beam epitaxy (CBE) [3] and for laser applications in the (GaIn)(PAs)/(GaIn)(PAs) on InP system grown by MOVPE [4]. In the present work, the optimization of the MOVPE growth conditions of (GaIn)As/Ga(PAs) symm. SLS with respect to substrate misorientation and growth temperature, as well as the first investiga- tions of structural and optical properties, are reported and discussed. They indicate the high-crystalline quality achievable with these novel symm. SLS in com- parison to one-side strained SLS. 2. Experimental details The MOVPE growth studies have been performed using commercial equipment (Aix 200, Aixtron Corp.) at a reactor pressure of 100 mbar for growth tempera- 0921-5107/93/$6.00 © 1993 - Elsevier Sequoia. All rights reserved