The growth of AlGaP was made using a Riber 32P gas-source molecular-beam epitaxy (GSMBE) system, using PH3PH3 as the phosphorus source and solid Al and Ga sources. The PH3PH3 was cracked at 850 °C by a low-pressure high-temperature cracker and its flux was controlled by a flow meter. The growth temperature was measured by a thermocouple located directly behind the GaP substrate held by its rim. Structural properties were characterized using in situ reflection high-energy MHY1485 diffraction (RHEED), x-ray diffractometer, scanning electron microscopy (SEM), and atomic force microscopic (AFM).
Samples were grown on one-side polished S-doped GaP (100) substrates with thickness of 300μm. Fig. 1 illustrates the grown structures. Each sample consists of a 0.2-μm GaP buffer, 1.0-μm Al0.85Ga0.15PAl0.85Ga0.15P, and a 80-nm GaP cap layer. The GaP layers were grown at 1.1-μm/h and the AlGaP at 1.6-μm/h. The PH3PH3 flux during the GaP growth was in every case 1.9 sccm; the PH3PH3 flux for the AlGaP growth was 2.3 or 2.7 sccm according to Table 1 A constant growth temperature was used for each sample of 480, 490, or 500 °C, again as given in Table 1. Note paleontology we grew and characterized 17 AlGaP/GaP samples. Therefore, our conclusion that the growth window is small for AlGaP layer is based on the results of RHEED, XRD, AFM, and SEM of all grown samples. We chose, however, 5 samples with the defined growth conditions in the paper as representative of our work.