Metamorphic InGaAs p-i-n Photodetectors with 1.75 mu m Cut-Off Wavelength Grown on GaAs

Top-illuminated metamorphic InGaAs p-i-n photodetectors (PDs) with 50% cut-off wavelength of 1.75 mu m at room temperature are fabricated on GaAs substrates. The PDs are grown by a solid-source molecular beam epitaxy system. The large lattice mismatch strain is accommodated by growth of a linearly graded buffer layer to create a high quality virtual InP substrate indium content in the metamorphic buffer layer linearly changes from 2% to 60%. The dark current densities are typically 5 x 10(-6) A/cm(2) at 0 V bias and 2.24 x 10(-4) A/cm(2) at a reverse bias of 5 V. At a wavelength of 1.55 mu m, the PDs have an optical responsivity of 0.48 A/W, a linear photoresponse up to 5 mW optical power at -4 V bias. The measured -3 dB bandwidth of a 32 mu m diameter device is 7 GHz. This work proves that InGaAs buffer layers grown by solid source MBE are promising candidates for GaAs-based long wavelength devices