Cr/Al and Cr/Al/Ni/Au ohmic contacts to n-type GaN

Abstract

Disorder induced semiconductor to metal transition and modifications of grain boundaries in nanocrystalline zinc oxide thin film J. Appl. Phys. 112, 073101 (2012) Control of normal and abnormal bipolar resistive switching by interface junction on In/Nb:SrTiO3 interface Appl. Phys. Lett. 101, 133506 (2012) Cross-plane electronic and thermal transport properties of p-type La0.67Sr0.33MnO3/LaMnO3 perovskite oxide metal/semiconductor superlattices J. Appl. Phys. 112, 063714 (2012) Polarization Coulomb field scattering in In0.18Al0.82N/AlN/GaN heterostructure field-effect transistorsIn this work we investigate the performance of Cr/Al and Cr/Al/Ni/Au ohmic contacts on n-type GaN. Annealing of the contacts was achieved by using a low temperature conventional quartz tube furnace in an Ar ambient and a new vacuum annealing technique using a tungsten strip heater. Low specific contact resistivity ( c ) metallizations were achieved with furnace annealing at considerably lower temperatures ͑550-600°C͒ than those typically required for GaN contacts by halogen lamp rapid thermal annealing ͑ϳ900°C͒. Vacuum annealing was found to require temperatures similar to those used in halogen lamp rapid thermal annealing for forming ohmic contacts on n-type GaN, but with minimal oxidation of the Al surface. For the Cr/Al bilayer on GaN with n doping of 10 18 cm Ϫ3 , minimum specific contact resistivities of 1.6ϫ10 Ϫ4 ⍀ cm 2 and 2.3ϫ10 Ϫ5 ⍀cm 2 were achieved for furnace annealing and vacuum annealing, respectively. Our experiments showed that, when Cr was used as a contact material, the simultaneous presence of Cr and Al was necessary in order to obtain the best possible ohmic properties. Furthermore, the Cr/Al contacts maintained good stability at elevated temperatures. The Cr/Al/Ni/Au system offers lower c values and even greater temperature stability than the Cr/Al system when annealed in the 800-1200°C temperature range. Atomic force microscopy investigations indicated that the introduction of the Ni/Au overlayer had the effect of increasing the surface roughness after annealing.

Two-step surface treatment technique: Realization of nonalloyed low-resistance Ti/Al/Ti/Au ohmic contact to n-GaN

“…1 Both laser diodes and optical detectors have been demonstrated. [3][4][5][6][7][8][9] While the energy band gap for InN is 0.78 eV, that for GaN is 3.39 eV, and for AlN is 6.28 eV. 2 Furthermore, diodes emitting in other regimes of the visible and ultraviolet spectra, can, in theory, be built as GaN alloyed with AlN and/or InN compounds can be created.…”

Effects of surface treatment using aqua regia solution on the change of surface band bending of p-type GaN

“…[4][5][6] However, such low contact resistivities to p-type GaN have been difficult to routinely achieve because of the low hole concentrations in ptype GaN and high Schottky barrier height (SBH) at metal/p-type GaN interfaces. For ntype GaN, low resistance ohmic contacts (<10 -5 Ωcm 2 ) have been obtained using Ti/Al, Ti/Au and Ti/Al/Ti/Au metal schemes.…”

Investigation of Cr- and Al-based metals for the reflector and Ohmic contact on n-GaN in GaN flip-chip light-emitting diodes

“…6 The outer Au prevents the oxidization of Al. Cr replaces Ti to form the type-II composite metal herein because it has greater thermal stability at high temperatures 7,8 and similar Ohmic contact characteristics to those of Ti on n-GaN. 9 Additionally, a composite metal without Al, type-III of Cr/ Ti/ Au, was examined.…”

“…The improved c values of Ti/ Al/ Ti/ Au and Cr/ Al/ Cr/ Au follow similar trends and have similar values as reported elsewhere. 7,8 The drop in the specific contact resistances as the stress increases is caused by the formation of a binary phase of Cr-N ͑in the form of CrN͒ in the GaN / Cr system. 7,10 Notably, the specific contact resistances of n-GaN Ohmic contacts are not state of the art because of the nonalloyed process.…”

“…7,8 The drop in the specific contact resistances as the stress increases is caused by the formation of a binary phase of Cr-N ͑in the form of CrN͒ in the GaN / Cr system. 7,10 Notably, the specific contact resistances of n-GaN Ohmic contacts are not state of the art because of the nonalloyed process. Works have shown that Cr-based 8 and Al-based 11-13 metals have achieved the specific contact resistances of 10 −5 -10 −7 ⍀ cm 2 after annealing.…”