PT/TI OHMIC CONTACT TO P++-INGAASP (1.3 MU-M) FORMED BY RAPID THERMAL-PROCESSING

Nonalloyed Ohmic contacts of evaporated Pt/Ti to p-InGaAsP (λg=1.3 μm) with different Zn doping levels ranging 5×1018-2×1019 cm -3 have been fabricated by rapid thermal processing. These contacts showed Ohmic behavior prior to any heat treatment with a specific contact resistance of 4×10-3 Ω cm2 for the lowest doping level and 1×10-4 Ω cm2 for the highest level. A decrease in the specific resistance was achieved by supplying rapid thermal processing to the contacts, while the lowest values were observed on all the contacts as a result of heating at 450 °C for 30 sec. The lowest resistance of 1×10-6 Ω cm2 was achieved at the contact that was formed on the 2×1019 cm-3 Zn-doped InGaAsP layer. Measurements of the conduction activation energy yields a good linear dependence of the specific resistance on temperature in all the contacts as deposited and after the different heat treatments. The higher the doping level and the rapid thermal processing temperature up to 450 °C, the lower the activation energy, which may suggest an increase in the tunneling carrier transport mechanism contribution at the expense of the thermionic-emission one. The morphology and microstructure of these contacts were not influenced by the variations in the Zn doping concentration.