AVS 49th International Symposium
    Electronic Materials and Devices Monday Sessions
       Session EL+SC+MI-MoM

Paper EL+SC+MI-MoM6
Effects of LED Processing Steps on the Surface of Doped GaN Epilayers

Monday, November 4, 2002, 10:00 am, Room C-107

Session: Semiconductors
Presenter: K.H.A. Bogart, Sandia National Laboratories
Authors: K.H.A. Bogart, Sandia National Laboratories
D.D. Koleske, Sandia National Laboratories
A.A. Allerman, Sandia National Laboratories
A.J. Fischer, Sandia National Laboratories
K.W. Fullmer, Sandia National Laboratories
K.C. Cross, Sandia National Laboratories
C.C. Mitchell, Sandia National Laboratories
Correspondent: Click to Email
Gallium nitride (GaN)-based materials are critical for the creation of UV optoelectronic devices such as light-emitting diodes (LEDs). Ohmic contacts with low contact resistivities to p-type (<1x10@super-3@@OMEGA@cm@super2@) and n-type (<1x10@super-5@@OMEGA@cm@super2@) GaN are essential for improving optical device performance. Understanding the characteristics of p- and n-type GaN epitaxial layer surfaces and the interfaces formed with the contact metals is vital for optimization. Fabrication of an LED requires several processing steps including dicing, annealing, surface cleans (to remove native oxides), lithography, metal deposition, and plasma etching. The effects of processing steps on the surface morphology and electrical characteristics of the epitaxial materials and metal contacts have been investigated using scanning probe microscopies and the circular transmission line method (CTLM). One of the first LED processing steps is dicing a 50 mm wafer using photoresist for surface protection, which is later removed with solvents. For p-type GaN (5x10@super17@cm@super3@), AFM analysis showed that the surface roughness nearly doubled after photoresist exposure from an average of 0.24±0.05 nm to 0.50±0.10 nm. The source of the roughness increase was the formation of pits into the surface, ~1 nm in depth. In another LED processing step, n-type GaN is exposed by plasma etching a mesa structure into the p-type GaN overlayer. One half of a wafer with a 1.2µm n-type GaN (1.7x10@super18@cm@super3@) epitaxial film was plasma etched with chlorine-based chemistry. AFM analysis showed that the etched n-type GaN film (RMS=1.11±0.23nm) was not significantly more rough than non-etched n-type GaN film (RMS=1.70±0.59nm). However, after annealing (500°C/N@super2@), the plasma etched film had more Ohmic behavior by (CTLM) than did the non-etched film. More extensive experiments following the GaN epitaxial layers in processing will be presented and effects on contacts discussed.