Graded band-gap ohmic contacts to n- and p-type InP

Abstract

W-Sb and W-In-Sb thin films were deposited by co-sputtering independent targets on n- and p-type InP wafers. The composition of the films was ascertained by monitoring the sputtering rate of each target. Au was sputtered on the back side and the sandwiched wafers were annealed in a quartz furnace to up to 400 °C. The conduction and diffusion characteristics of the films were studied as a function of the annealing temperatures. The Auger depth profile shows an outdiffusion of In to the surface of the WInSb film. P from the substrate out-diffuses into the W matrix while Sb forms an interfacial In-Sb phase. The x ray diffractogram of samples annealed to 400 °C shows the transition of as-deposited amorphous W into the crystalline state and formation of In-Sb related interfacial phase. The electrical characteristics are ohmic for as-deposited films on n-type material, whereas it becomes ohmic below 400 °C for p-type substrate. The 1000-Å-thick WInSb film when annealed to 400 °C showed a sheet resistance of ∼12 ohm/⧠ and a contact resistance in the 10−6 Ω cm2 range.