J. M. DeLucca

Analysis of a thin AlN interfacial layer in Ti/Al and Pd/Al ohmic contacts to n-type GaN

Using high resolution transmission electron microscopy, a thin pseudomorphic AlN layer (2–3 nm) has been observed at the metal/GaN interfaces of Ti/Al (35/115 nm) and Pd/Al (25/125 nm) ohmic contacts to n-type GaN annealed in Ar at 600 °C for 15 and 30 s, respectively. The interfacial layer has a c-plane (002) lattice spacing of 2.48±.03 A and an a-plane (100) spacing matching that of GaN (2.76 A), and the identification of this layer as AlN is consistent with chemical analysis by energy dispersive x-ray spectroscopy. The formation of this interfacial AlN layer coincides with the onset of ohmic behavior in Ti/Al and Pd/Al contacts annealed at 600 °C and may be the cause.

An investigation into the early stages of oxide growth on gallium nitride

Abstract The early stages of thermal oxidation of gallium nitride epilayers in dry O 2 have been studied using surface sensitive analytical techniques and transmission electron microscopy. Deconvolution of the Ga 3d core level spectra from X-ray photoelectron spectroscopy revealed peak positions representing gallium nitride, gallium oxide, and an intermediate phase. Transmission electron microscopy revealed an overlayer approximately 1.5–3.0 nm thick with registry to the (0001) GaN after dry oxidation at 800°C for 1 h. Based on the data from X-ray photoelectron spectroscopy, this layer is believed to be a Ga ( x +2) N 3 x O (3−3 x ) compound. Atomic force microscopy and transmission electron microscopy revealed the formation of discrete oxide crystallites on top of the oxynitride layer. The crystallites become more numerous and grow with continued oxidation.

Phase Formation and Morphology in Nickel and Nickel/Gold Contacts to Gallium Nitride

Metallurgical reactions between Ni and GaN have been explored at temperatures between 400 and 900 °C in N 2 , Ar, and forming gas. A trend of increasing Ga content in the reacted films was observed with increasing temperature. The reactions are consistent with the thermodynamics of the Ni-Ga-N system. Changes in the film morphology on annealing were also examined. Metal island formation and a corresponding deep, non-uniform metal penetration into GaN were observed at high temperatures. The relevance of the observed nature of phase formation and morphology in these thin films to electrical properties of Ni/GaN and Au/Ni/GaN contacts is also considered.

Pt Schottky contacts to n-GaN formed by electrodeposition and physical vapor deposition

Electrodeposited, dc magnetron sputtered, and electron beam evaporated Pt contacts to n-GaN (n=1.5×1017 cm−3) are reported. All contacts were rectifying in the as-deposited condition, and values of the barrier height were determined by current–voltage (I–V) and capacitance–voltage (C–V) measurements. The influence of deposition conditions on the electrical characteristics of the sputtered and electrodeposited Pt contacts was further studied. Additionally, a dependence of the barrier height with time following deposition is shown. Taking into consideration all parameters of this study, the barrier height could differ by as much as 0.65 eV by I–V measurements and 0.64 eV by C–V measurements, with I–V and C–V barriers as high as 1.43 and 1.57 eV, respectively. Reverse current densities are reported for a −5 V bias with the highest and lowest median values differing by a factor of 104 as a result of the different deposition conditions. The electrical properties are believed to be strongly influenced by the presence of electrically active defects introduced during metal deposition. Deep level transient spectroscopy data support this hypothesis.Electrodeposited, dc magnetron sputtered, and electron beam evaporated Pt contacts to n-GaN (n=1.5×1017 cm−3) are reported. All contacts were rectifying in the as-deposited condition, and values of the barrier height were determined by current–voltage (I–V) and capacitance–voltage (C–V) measurements. The influence of deposition conditions on the electrical characteristics of the sputtered and electrodeposited Pt contacts was further studied. Additionally, a dependence of the barrier height with time following deposition is shown. Taking into consideration all parameters of this study, the barrier height could differ by as much as 0.65 eV by I–V measurements and 0.64 eV by C–V measurements, with I–V and C–V barriers as high as 1.43 and 1.57 eV, respectively. Reverse current densities are reported for a −5 V bias with the highest and lowest median values differing by a factor of 104 as a result of the different deposition conditions. The electrical properties are believed to be strongly influenced by the pr...

Morphology of nickel and nickel/gold contacts to gallium nitride

Changes in film morphology upon annealing Ni and Ni/Au contacts to GaN were examined using scanning electron microscopy and atomic force microscopy. Atomic force microscopy was performed on the GaN surface that was exposed by etching away the metal film. This technique was demonstrated to be a convenient and effective way to evaluate the morphology of the contact/semiconductor interface, rapidly providing spatial information in three dimensions. Metal island formation and a corresponding deep, nonuniform metal penetration into GaN were observed after annealing Ni/GaN and Au/Ni/GaN contacts above 800 and 700 °C, respectively.

Ohmic contacts formed by electrodeposition and physical vapor deposition on p-GaN

Electrodeposited Pt and sputtered Ni/Pt contacts to p-GaN (p=4.6×1017 cm−3) are reported and compared to sputtered Ni, Pt, and Ni/Au contacts and electron beam and thermally evaporated Ni contacts. Sequential rapid thermal annealing was employed with samples receiving an initial five minute heat treatment of 400 °C followed by 1 min anneals at 500, 600, and 700 °C, all under flowing N2. Plots of current versus voltage for all contacts showed nonlinearity through the origin as deposited and for all annealing conditions. Extracted values of specific contact resistance are thus determined using the measured resistance for a given value of applied current. The lowest contact resistivity was reproducibly provided by the electrodeposited Pt contacts. After a 1 min anneal at 600 °C, a contact resistivity of 1.50×10−2 Ω cm 2 was obtained using the circular transmission line method at a measurement current of 10 mA. Sputtered Ni/Pt contacts provided a contact resistivity of 1.81×10−2 Ω cm2 at 10 mA after a 1 min a...

Approaches to designing thermally stable Schottky contacts to n-GaN

The barrier heights of PdIn, Ni/Ga/Ni and Re Schottky contacts to n-GaN were investigated by current-voltage and capacitance-voltage measurements. Elemental Pd and Ni contacts were also investigated for comparison. In each case, the barrier heights were determined as a function of annealing temperature. It was shown that stoichiometric PdIn contacts were more stable than Pd-only contacts. Similarly, Ni/Ga/Ni diodes were found to be more stable than Ni diodes. Both the Ni/Ga/Ni contact and the elemental Re contact were stable on short-term annealing up to 700 ?C.

Erratum: “Ohmic contacts formed by electrodeposition and physical vapor deposition on p-GaN” [Appl. Phys. Lett. 73, 3402 (1998)]

~Received 9 February 1999; accepted for publication 11 February 1999!@S0003-6951~99!02714-X#In Fig. 1 of p. 3403, the label for the Ni/Au contact should indicate an annealing time of 5 min rather than 1 min,consistent with the 5 min annealing time stated in the text. In addition, in the caption of Table I on p. 3403, the symbol ‘‘N