Formation of ohmic contacts to p-ZnTe

Formation and temperature stability of sputter deposited gold ohmic contacts to molecular beam epitaxially grown p-type ZnTe (doped with nitrogen to a free hole concentration of approximate to 3 x 10(18) cm(3)) have been studied using current-voltage (I-V), Auger electron spectroscopy, secondary ion mass spectrometry, and optical and scanning electron microscopy. The I-V characteristics of approximate to 1500 Angstrom Au/p-ZnTe contacts were measured as-deposited and after heat treatments at 150, 200, 250, and 350 degrees C for 15 min intervals up to 90 min. As deposited, the contacts were poor Schottky contacts, but became ohmic after 15 min at all temperatures. There was an increased resistance at t>15 min for T less than or equal to 250 degrees C, and a very large resistance increase upon heat treatment for all times at 350 degrees C. The interface between the metallization and ZnTe was initially very planar, and remained planar upon formation of the ohmic contact. Upon heating at T greater than or equal to 250 degrees C, Au diffused into ZnTe. The ohmic behavior of the Au/p-ZnTe contacts is attributed to this diffusion which created a highly doped near-surface region in the ZnTe. Microscopy showed that Au also migrated across the ZnTe surface forming an extended reaction zone (approximate to 100 mu m) around the dot contact at T greater than or equal to 250 degrees C.