Investigation on the Effect of Annealing Temperature on the Side Ohmic Contact Characteristics for Double Channel GaN/AlGaN Epitaxial Layer

Abstract

A side ohmic contact mode for the double channel GaN/AlGaN epitaxial layer is proposed in this paper. Rectangle transmission line model (TLM) electrodes are prepared, and the specific contact resistance is tested at the annealing temperatures from 700 °C to 850 °C. The results show that the minimum specific contact resistance is 2.58 × 10−7 Ω·cm2 at the annealing temperature of 750 °C, which is three to four times lower than the surface contact mode. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and atomic force microscope (AFM) were carried out for the analysis of the morphology, element composition, and the height fluctuation at the contact edge. With the increase in the annealing temperature, the specific contact resistance decreases due to the alloying of electrodes and the raised number of N vacancies. However, when the annealing temperature exceeds 800 °C, the state of the stress in the electrode films transforms from compressive stress to tensile stress. Besides, the volume expansion of metal electrode film and the increase in the roughness at the contact edge leads to the degradation of the side ohmic contact characteristics.

Solid-mechanics analysis and modeling of the alloyed ohmic contact proximity in GaN HEMTs using µRaman spectroscopy

“…More recently, the stress induced by the alloyed ohmic contacts has also been recognized as a major source of mechanical stress by two independent studies [37,38]. Hightemperature processing required for alloying was deemed the culprit behind the stress generation by these two references.…”

“…Hightemperature processing required for alloying was deemed the culprit behind the stress generation by these two references. First, Meng et al investigated ohmic contacts to double channel AlGaN/GaN HEMTs and discovered that high temperature annealing leads to a considerable volume expansion, thereby increasing the tensile stress in the film [37]. Similarly, Whiting et al studied alloyed ohmic contacts on single channel HEMTs and proposed that due to (1) material mixings such as nitrogen out-diffusion into the metal stack, (2) gold migration from the metal surface to the deeper layers, and (3) aluminium reactions with titanium and gold, large strain fields may form [38].…”

Editorial for the Special Issue on Advanced Manufacturing Technology and Systems

“…They proved that the width of a single grating line in the standard could be regulated with great uniformity by precisely utilizing ALD. Meng et al [ 12 ] proposed a side ohmic contact mode for the double-channel GaN/AlGaN epitaxial layer. Rectangle transmission line model (TLM) electrodes are prepared, and the specific contact resistance is tested at annealing temperatures ranging from 700 °C to 850 °C.…”