Interfacial Reactions Between Metal Thin Films and p-GaN

Abstract

The reactions between Au, Au/Ni and Au/C/Ni thin films on p-GaN have been studied using current-voltage (I-V) measurements, Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS). The metallization schemes consisted of ≈2000Ǻ sputtered Au, 1000Ǻ Au/500Ǻ Ni, and 1000Ǻ Au/100Ǻ C/500Ǻ Ni electron beam evaporated. The Au/Ni metallization scheme is of particular interest since it is the basis for the most commonly used ohmic p-type contacts for blue GaN LED’s. Au does not decompose the GaN matrix, while Ni has been shown to react with GaN above a temperature of 400° C for times longer than 5 minutes. Upon decomposition of the GaN by Ni, incorporation of C at the metal/GaN interface occurred. It is believed that a regrowth of GaN occurred, with the surface region being doped with C. Attempts at increasing this doping concentration by introducing an interfacial C layer were not successful.

A study of the electrical characteristics of various metals on p-type GaN for ohmic contacts

“…Previous studies of Ni/Au p-type GaN contacts show that I/V characteristics also become more linear with annealing. 23,24 The improvement in conductivity of the contacts have been attributed to the reduction of the Schottky barrier height from the formation of GaNi and Ga-Au compounds found present from x-ray diffraction analysis. 23 In addition, it is suggested that the out diffusion of Ga may leave Ga vacancies that can behave as p-type dopants.…”

“…23 In addition, it is suggested that the out diffusion of Ga may leave Ga vacancies that can behave as p-type dopants. 24 Still earlier studies of other semiconductors suggest that alloying can form highly disordered or amorphous material between the metal and the semiconductor of a contact having states in the bandgap (see Sebestyen 25 for a review). This layer allows for phonon-assisted and field-assisted hopping between localized states in the bandgap of the material with normal drift and diffusion in the states in the valance band.…”

Metal contacts on ZnSe and GaN

“…Figure 2.12a shows an XRD spectrum fiom their paper of the NiGaN system after annealing at 400°C. Trexler et al (Trexler et al, 1995) observed the behavior of Au and Au/Ni contacts after annealing up to 600°C. They found no apparent decomposition of GaN for either system.…”

W and WSix Ohmic contacts on p- and n-type GaN

“…In the search for improved contact characteristics, a wide variety of metallizations have been investigated on p-GaN besides the standard N~/Au,(*-~) including Ni, (4,581 (ii) (4,779910) Pd (4) pd/Au,(' 1,'2) Pt/Au (6) Au/Mg/Au,(9.l3) Au/C/Ni (14) Nj/cr/A~('~,'~) and Au,…”