Low-temperature MOVPE using TEGa for suppressed layer undulation in InxGa1−xAs/GaAs1−yPy superlattice on vicinal substrates

Abstract

InxGa1−xAs/GaAs1−yPy strain-balanced superlattice (SL) is a promising narrow-gap material that can be lattice-matched to Ge or GaAs. When growing uniform SLs on vicinal substrates for Ge-based application, formation of step-bunching and the resultant layer undulation is a critical problem. The present paper reports low-temperature metal–organic vapor phase epitaxy (MOVPE) with triethylgallium (TEGa) to improve the stability and the uniformity of SL growth. Using trimetylgallium (TMGa), steps were severely bunched especially during InGaAs growth at high temperature, and the average reflectance of SLs significantly decreased due to lattice relaxation above 580°C. Lowering the growth temperature to 550–530°C was effective in order to grow 100-period SLs with a mirror-like surface, but an apparent lateral layer undulation was still confirmed by ex-situ X-ray-diffraction and STEM observation. Growth of SLs below 530°C with TMGa was found to result in serious crystal degradation due to unstable growth in the kinetically-limited temperature range. In contrast, use of TEGa enabled 100-period SLs to be successfully grown even at lower temperature owing to its efficient pyrolysis process. Highly uniform SLs with negligible layer undulation were grown at 510°C with TEGa, showing a photoluminescence spectrum which was as sharp as the one for SLs grown on an exact-oriented substrate. The absorption spectra for the SLs grown with TEGa showed similarly sharp edge with a strong exciton peak.