Buffer optimization for high-quality InP-on-GaAs(001) quasi-substrates

In this work, we reported the buffers optimum of high-quality InP epilayer grown on GaAs substrate for fabrication of InP-related devices. First, LT GaAs (450 degrees C, 15nm)/LT InP((450 degrees C, 15nm) double LT buffers were deposited on the substrate as the initial layers. The effects of double LT buffers were studied compared with the results of single LT-InP buffer scheme. It was demonstrated that: (i) with a proper LT-GaAs buffer thickness, the double LT-buffer became more "compliant" for strain accommodation than single LT-InP buffer; (ii) there existed an optimal thickness of LT-GaAs buffer for a given thickness of LT InP layer at which the crystal quality reached the best, just like the conventional buffer optimum process. Second, in order to block the "escaped "dislocations from the buffer/substrate interface, InxGa1-xP/InP (x approximate to 0.2) strained superlattices (SLS) were introduced as defect filtering layers before the growth of the final InP layer. We investigated the effects of the periods and inserting position of the SLS on the stress relaxation and the crystal quality of InP top layer. It was suggested that when the total thickness of the epilayer was fixed, both the thickness and the periods and the distance from the interface should be carefully designed to reduce the stress and improve the crystal quality of the epilayer simultaneously. Finally, a 2-mu m-thick InP epilayer was grown on GaAs substrate using (450 degrees C, 15nm)/LT InP(450 degrees C, 15nm) double LT buffers combined with inserting 15-period (4nm/6nm) In(0.8)Ga(0.2)ZP/InP SLS into epilayer. Then X-ray diffraction measurements showed the best result of the full width at half maximum (FWHM) was 203 arcsec with estimated dislocation density of 2.8x10(7) cm(-2).