Effects of continuously or step-continuously graded buffer on the performance of wavelength extended InGaAs photodetectors

High In content In0.83Ga0.17As photodetector structures with a new kind of buffer scheme have been grown on InP substrate by gas source molecular beam epitaxy. The effects of buffer scheme on material properties and device performances have been investigated both experimentally and theoretically. The structures with the combination of step and continuously graded buffers show reduced surface roughness, improved photoluminescence intensity and lower device dark current than those with simplex continuously graded buffer at the same buffer thickness. The mechanisms have been discussed from X-ray diffraction, photoluminescence, dark current measurements and model analysis.