Incorporation of nitrogen in nitride-arsenides: Origin of improved luminescence efficiency after anneal

A key to the utilization of nitride-arsenides for long wavelength optoelect ronic devices is obtaining low defect materials with long nonradiative life times. Currently, these materials must be annealed to obtain device quality material. The likely defect responsible for the low luminescence efficienc y is associated with excess nitrogen. Photoluminescence and capacitance-vol tage measurements indicate the presence of a trap associated with excess ni trogen which decreases in concentration upon anneal. Our films are grown by elemental source molecular beam epitaxy and the background impurity concen tration is low, thus we have investigated the role of crystalline defects. High resolution x-ray diffraction showed improved crystal quality after ann eal. We observed that the lattice parameter does not decrease linearly with nitrogen concentration for levels of nitrogen above 2.9 mol % GaN. The fac t that Vegard's law is not observed, despite theoretical calculations that it should, indicates that nitrogen incorporates in locations other than the group V lattice sites. X-ray photoelectron spectroscopy revealed that nitr ogen exists in two bonding configurations in not-annealed material: a Ga-N bond and another nitrogen complex in which N is less strongly bonded to gal lium atoms. Annealing removes this second nitrogen complex. A combined nucl ear reaction analysis and channeling technique showed that not annealed GaN As contains a significant concentration of interstitial nitrogen that disap pears upon anneal. We believe that this interstitial nitrogen is responsibl e for the deviation from Vegard's law and the low luminescence efficiency o f not annealed GaNAs and GaInNAs quantum wells. (C) 2001 American Institute of Physics.