Abstract
We report an investigation of the effects of different metal systems and surface treatment on the contact performance of GaN lasers. We found that multi-element metal alloy and surface chemical treatment are the keys to achieve good ohmic behavior contacts on GaN laser diodes. Pd/Ni/Au contact demonstrates excellent thermal stability and lowest specific contact resistivity in these metal systems. Properly adjusting the thickness of the Pd and Ni layer and pretreating with the KOH solution can further improve the ohmic contact performance. The improved ohmic behavior of the KOH solution pretreated Pd/Ni/Au contact is attributed to removing surface oxides and the reduction of the schottky barrier heights due to the metal Pd has a high work function and the interfacial reactions occurring between the Pd, Ni, Au, and GaN extends into the GaN film. As a result, a low contact resistivity of 1.66 × 10−5 Ω·cm2 can be achieved from Pd(10 nm)/Ni(10 nm)/Au(30 nm) contacts with KOH solution pretreated on top of the laser diode structure. The power of the GaN based laser diode with the Pd/Ni/Au metallization ohmic contact can be enhanced by 1.95 times and the threshold current decreased by 37% compared to that of the conventional ohmic contact Ni/Au.
Highlights
Gallium nitride (GaN) based opto-electronic devices such as laser diodes [1,2,3], light emitting diodes [4,5,6,7], power devices [8,9], and violet photodetectors [10,11,12], among others, have received considerable attention in the last decade
We have systematically investigated the influence of different metal systems on the ohmic contact of the GaN laser by a series of four ohmic contact metal experiments
Pd/Ni/Au metallization ohmic contact with a suitable electrode thickness has the lowest specific contact resistance of 7.5 × 10−5 Ω·cm2, which is due to the reduction of schottky barrier heights by larger work function of metal Pd, and the
Summary
Gallium nitride (GaN) based opto-electronic devices such as laser diodes [1,2,3], light emitting diodes [4,5,6,7], power devices [8,9], and violet photodetectors [10,11,12], among others, have received considerable attention in the last decade. There are many factors that could affect the performances of the laser devices such as material quality, ohmic contact, cleavage, facet coating, etc. Among these factors, ohmic contact is arguably the most important one. Since the laser diode usually operates at a large current density, p-type ohmic contact is critical for reducing the operating voltage. The device would heat up severely under high current injection, which is detrimental to the device lifetime and reliability, and it Coatings 2019, 9, 291; doi:10.3390/coatings9050291 www.mdpi.com/journal/coatings
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
