Low-resistance Ohmic contact for GaN-based laser diodes

Low-resistance Ohmic contact is critical for the high efficiency GaN-based laser diodes. This study investigates the introduction of the In0.15Ga0.85N contact layer on the specific contact resistance. Experimental results reveal that adopting the In0.15Ga0.85N contact layer yields a minimized specific contact resistance of 2.57 x 10-5 Omega<middle dot>cm2 which is two orders of magnitude lower than the GaN contact layer (7.61 x 10-3 Omega<middle dot>cm2). A decrease in the specific contact resistance arises from the reduction of the barrier between the metal and p-type In0.15Ga0.85N. To develop an optimal metal electrode combination on the In0.15Ga0.85N contact layer, the Pd/Au and Ni/Au electrode stacks which are most commonly used in the formation of Ohmic contact with p-GaN are investigated. Metal stack of 10/30 nm Pd/Au is demonstrated effective in reducing the specific contact resistance to 10-5 Omega<middle dot>cm2 level. The mechanism of the variation of the specific contact resistance under different annealing atmospheres is explained by auger electron spectroscopy.