CBE Regrown InGaAs/InP p-i-n Photodiodes for OEIC´s

A two-step growth approach was used to monolithically integrate p-i-n InGaAs photodiodes with a InAlAs/InGaAs lattice matched on InP HEMT circuit. The HEMT structure is first grown by MBE and exhibits a Hall mobility in excess of 11000 cm²/Vs with a ns of 2.6.10¹² cm^¿2 at room temperature. After the patterning of these epilayers, the p-i-n diode structure is selectively regrown by CBE using SiO2 as a mask layer. The use of a dielectric mask layer was found to diminish dramatically the transport properties of the underlaying HEMT layers. The same integration scheme was also applied without using a SiO2 mask layer. In that case the selective regrowth was replaced by the selective wet etching of the p-i-n material regrown on the top of the HEMT structure. With this way of integration, the HEMT transport properties after the regrowth was measured to be 10000 cm²/Vs and 2.1.10¹² cm^¿2 for the mobility and ns respectively. The characteristics of the regrown p-i-n photodiodes were very close to the diodes grown on epi-ready InP substates and exhibited an ultra-low dark current of 500 pA for 25 ¿m diameter photodiodes after polyimide passivation.