P-cracker cell temperature effects on the optical properties of AlGaInP:Be layers grown by SSMBE

The optical properties of Be-doped Al0.2Ga0.3In0.5P layers grown on GaAs by solid source molecular beam epitaxy have been studied. In particular, we investigated a set of heavy doped samples grown at different phosphorous cracking temperatures (PCT). The analysis of the 15 K-PL spectra showed three strong transitions below the AlGaInP band edge associated to Be acceptor levels (A0, X), shallow impurities (A, X) and a broad signal related with oxygen deep levels (O, DL). The Photoluminescence (PL) spectra from samples dramatically change as the PCT is increased, in such a way that in the spectrum from the sample grown at the highest P-cracking zone temperature, the (O, DL) intensity is visibly dominant. Besides, we found that despite that the Be cell temperature being maintained at 1015 °C for all the samples, the Be-doping concentration is reduced as the PCT is increased. Therefore, as PCT increases, the active Be-concentration decreases as a consequence of Be-compensation with O. This phenomena is reflected in the PL properties of the samples as a reduction of the (A0, X) intensity. The rocking curves of the (0 0 4) planes obtained by high resolution X-ray diffraction (HRXRD) justify the inclusion of impurities and the reduction of the crystal quality of the sample grown at the highest PCT. This work shows that the incorporation of defects during the growth of the AlGaInP:Be films due to O contamination can be reduced using low PCT.