Effect of in situ annealing on highly-mismatched In0.75Ga0.25As on InP grown using molecular beam epitaxy

We demonstrate that the electrical quality of junctions fabricated in latti ce-mismatched In0.75Ga0.25As on InP grown by molecular beam epitaxy can be improved with the addition of in situ anneals in the buffer layer that sepa rates the substrate from the In0.75Ga0.25As device layers. Near infrared ph otodetectors fabricated using this material had dark current densities of a pproximately 2.5 mA/cm(2) at a reverse bias of 1 V, which is more than one order of magnitude smaller than commercially available photodetectors grown using vapor phase epitaxy. Transmission electron microscopy revealed that dislocations due to the lattice mismatch between the substrate and the epit axial layer are confined primarily to the buffer layer for all samples stud ied. No significant differences in x-ray diffraction spectra or dislocation distribution were observed on samples with and without in situ annealing. Atomic force microscopy indicated that all samples had a crosshatch pattern , and that the average surface roughness of the sample that contained in, s itu anneals is a factor of three greater than the sample without in situ an neals.