Effects of surface treatments and metal work functions on electrical properties at p-GaN/metal interfaces

Abstract

In order to examine the possibility of preparing a nonreacted (nonalloyed) Ohmic contact to p-GaN, the effects of GaN surface treatments and work functions of the contact metals on the electrical properties between the metal contacts and p-GaN were investigated. A contamination layer consisting of GaOx and adsorbed carbons was found on the GaN substrate grown by metalorganic chemical vapor deposition. The contamination layer was not completely removed by sputtering the GaN surface with Ar and N ions where the ion densities were ∼10−2 μA/cm2. Although the contamination layer was partially removed by immersing in a buffered HF solution, little improvement of the electrical properties of the GaN/metal interfaces was obtained. Most of the contamination layer was removed by annealing the Ni and Ta contacts at temperatures close to 500 °C. These annealed contacts exhibited slightly enhanced current injection from the contact metal to the GaN. The present surface treatment study indicated that removal of the contamination layer did not significantly reduce the contact resistance. On the other hand, the resistance decreased exponentially with increasing the metal work functions, where Pt, Ni, Pd, Au, Cu, Ti, Al, Ta, and Ni/Au were deposited on the GaN. This result suggests that the Schottky barrier height at the p-GaN/metal interface might not be pinned at the GaN surface. The present study concluded that a contact metal with a large work function is desirable for nonreacted Ohmic contacts to p-GaN. However, these contacts did not provide the low contact resistance required for blue laser diodes.

Structural and Electrical Characterization of GaN Thin Films on Si(100)

“…Figure 7(c) shows Ga 3d spectra for the films. No bond formation between Ga and O was observed since the Ga 3d spectrum did not show any peak corresponding to Ga 2 O 3 as reported by Ishikaua et al [24]. The above results confirm the formation of pure GaN without the presence of elemental gallium and Ga 2 O 3 in this film.…”

Etch Processing of III-V Nitrides

“…Despite this importance there have been far fewer reports on electronic damage [24][25][26][27][28][29]. The general conclusions from these efforts are that high density plasma etching renders the n-type GaN surface less conductive (due primarily to mobility reduction) and semi-insulating GaN surfaces n-type conducting and that the degree of conduction enhancement or degradation is a strong function of incident ion energy and mass.…”

Thermal reaction of Pt film with 〈110〉 GaN epilayer

“…On the other hand, the choice of a metal as contact for n-type as well as for p-type GaN is facilitated because indications exist that the barrier height depends on the metal work function. [3][4][5][6][7][8][9][10] The lack of Fermi level pinning at the metal/semiconductor interface is predicted by the ionic nature of GaN. 11 However, the dependence of the barrier height on the metal work function does not follow a linear relation of unity slope as predicted by the Schottky model, 12 and interfacial reactions between the metal and the GaN substrate further affect this relationship.…”

“…15,21 A GaN metal-semiconductor field effect transistor ͑MESFET͒ with Au/Pt as Schottky gate is reported to withstand heating in nitrogen at 400°C for 1000 h. 22 Other authors, though, report the degradation of Pt diodes after annealing at 400°C for 1 h. 19 Low-resistance, ohmic contacts to p-type GaN are achieved by using metals with a high work function, 8 and indeed, Pt or Pd yield a lower value of the total resistance compared to other metals. [7][8][9][10] Platinum is not stable with GaN. 23 The reaction at the interface between a Pt film and a GaN substrate is poorly investigated.…”