Electrical Characteristics and Reliability of Ohmic Contacts for InGaAs/InGaAlAs/InP Lasers

Ohmic contacts to p-type In1-x GaxAs/InP with an intermediate superlattice region have been examined for use in InGaAs/InGaAlAs/InP lasers. Four metallizations (Pd/Zn/Pd/Au, Pd/Mn/Sb/Pd/Au, Ni/Zn/Ni/Au and Au/Zn/Au) were evaluated in these contacts for the first time. All of the metallizations exhibited a low resistivity, a smooth surface morphology and thermal stability. However, the Pd/Zn/Pd/Au contacts produced the lowest value of specific contact resistance, pc, of 7.5 ×10^¿6 ¿ cm² after annealing at 500°C for 60 s. The Pd/Zn/Pd/Au contacts also maintained the lowest pc of the contact schemes during ageing at 400°C and for periods of ¿ 5 hrs at 500°C.