New contact resistivity characterization method for non-uniform ohmic contacts on GaN

Uniform and non-uniform ohmic contacts on GaN were investigated by using a newly developed transfer length method (narrow TLM). The contact resistivity and the series resistance of laser diode (LD) were calculated from a conventional and a newly developed narrow TLM and a laser diode structure. The contact resistivity of uniform Pd contacts did not change with varying the width of the contacts, while that of non-uniform Ni/Au contacts showed an increase with narrower contacts. These results were attributed to a decrease of ohmic contact area in the Ni/Au sample as a result of non-uniform ohmic contact formation. Investigation of Pd (uniform) and Ni/Au (non-uniform) ohmic contacts with the newly developed narrow TLM indicated that the contact resistivity of a p-contact metal on a ridge waveguide laser diode should be considered using narrow TLM, particularly for non-uniform ohmic contacts, to enhance the performance of laser diodes.