Ni/Si-Based Contacts to GaN: Thermally Activated Structural Transformations Leading to Ohmic Behavior
- PDF / 2,427,241 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 10 Downloads / 308 Views
b)Institute
Cite this article as: MRS Internet J. Nitride Semicond. Res. 4S1, G9.9 (1999) ABSTRACT Structural transformations in Ni/Si-based contacts to GaN occurring under heat treatment have been studied using transmission electron microscopy and secondary ion mass spectrometry. Transition from non-ohmic to ohmic behavior correlates with reaction between Ni and Si, and decomposition of the initially formed interfacial Ni:Ga:N layer. Transport of dopant atoms from metallization into GaN testifies in favour of the SPR process of ohmic contact formation INTRODUCTION One of the key problems in GaN-based devices is a poor quality of ohmic contacts to pGaN. The commonly adopted procedure for making ohmic contacts involves the use of highwork-function metallization schemes. These contacts convert from Schottky to ohmic-like after annealing, yielding resistivities of about 10-2Qcm 2 [I j.
In order to reduce the contact resistivity, procedures enhancing the concentration of the active dopant in the semiconductor superficial region should be considered. To achieve that, we have adopted the idea of Sands et al. [2] of the incorporation of a dopant into the subeontact region by solid-state dissolution and subsequent regrowth (SPR). We have used Ni/Si metallization, with Mg as a dopant to produce contacts to p-GaN. For n-GaN, Si was the intended donor dopant. It has been shown that these contacts became ohmic after annealing at 2 temperatures ranging from 400 to 600 0C, with resistivity of - 1*10-3 •Qcm on p-type GaN with hole concentration 3* 101' cm-3 [3]. In order to further elucidate structural changes that take place during the formation of ohmic contacts, a study of the microstructure of Ni/Si-based contacts has been performed. We have used transmission electron microscopy (TEM) methods and SIMS. The high spatial resolution of TEM provides details about the morphology of metal/semiconductor interfaces, phase compositions and crystallographic relationships in the contact region. SIMS was applied to probe the elemental depth profiles. The question of dissimilarities in the behavior of p-type and ntype metallizations during the formation of ohmic contacts has been of special concern. EXPERIMENTAL PROCEDURE Contacts under investigation have been made to (0001) oriented GaN epilayers, 1-2 ýtm thick, grown via organometallic vapour phase epitaxy on AIN buffer layers predeposited on 6HG 9.9 Mat. Res. Soc. Symp. Proc. Vol. 537 © 1999 Materials Research Society
SiC substrates [4]. Prior to metal deposition, the samples were etched in buffered HF and in NH 4 OH:H 20 (1:10). The cleaning was finished in the deposition chamber by heat treatment at 4000 C for 10 min., under UHV conditions, for thermal desorption of hydrocarbon contaminants. The metallization in the form of sandwich structures Ni/Mg/Ni/Si and Ni/Si/Ni/Si for p- and ntype GaN, respectively, was deposited by e-beam evaporation. The thickness of consecutive metallization films was 25 nm/8 nm/25 nm/240 nm. In view of a high thermal stability of GaN, contacts were fabri
Data Loading...
