Structural and Electrical Properties of Thermally Annealed InN Thin Films on Native and Ain-Nucleated (00.1) Sapphire
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T. J. KISTENMACHER,* S. A.ECELBERGER,* W. A. BRYDEN,* and M. E. HAWLEY" *Milton S. Eisenhower Research Center, Applied Physics Laboratory The Johns Hopkins University, Laurel, Maryland 20723 Los Alamos National Laboratory, Los Alamos, New Mexico 87545 ABSTRACT
The effects of thermal annealing at 4000C in 5 mTorr of N2 on the structural and electrical properties of thin films of InN grown at 1000C on native and AIN-nucleated (00.1) sapphire by reactive magnetron sputtering have been studied. The variations in the properties of the two sets of films have qualitatively similar, yet quantitatively different dependencies on anneal time. In each case, surface decomposition to give (101) textured rods of elemental indium is seen at short anneal times, and markedly so in the more highly strained films on the AIN-nucleated substrates. The electrical properties in both cases improve with annealing time, yielding a Hall mobility that is enhanced 2-3 times relative to as-deposited films and similar to that for films grown at a substrate temperature of 4000C. The evolution of the electrical properties appears to be relatively insensitive to the surface decomposition and to largely reflect the nature of the bulk InN matrix. INTRODUCTION
Indium nitride (InN) is one of a family of direct bandgap semiconductors actively under investigation for utilization inthin film form in a host of electronic and optoelectronic technologies. [1] One of the particular concerns with thin films of InN is their thermal stability under normal semiconducting processing conditions, owing to its low heat of formation (21n + N2 -• 21nN, &Hf = -4.6 kcal/mole). [2] Given this, it is surprising how little data is available on the stability of polycrystalline [2] or post-deposition annealed InN films. [3] To this end, we have initiated a wide-ranging study of the thermal stability and temporal degradation of InN thin films, with particular emphasis attached to the effects of native and AIN-nucleated substrates. Herein, our studies are reported on the evolution of the structural and electrical properties of thermally annealed InN films grown by reactive magnetron sputtering on native and AIN-nucleated (00.1) sapphire, a substrate of considerable technological utility for the III-V nitride semiconductors. [1] EXPERIMENTAL
The reactive magnetron sputtering system employed here has been described previously. [4] Briefly, the system employs a pair of planar magnetron sputtering sources mounted on a baseplate in the sputter-up configuration. Above the sputtering sources are shutters and a heater/substrate assembly, the latter of which is rotatable and can place the substrate over either sputtering source for the sequential deposition required of nucleated films. The targets are water-cooled Al or In disks with purity in excess of 99.99%. Reactive growth is carried out in 99.999% pure N2 gas at a pressure of 5 mTorr. To reduce oxygen contamination in the films and to improve the background pressure (ultimately near 5 x 10-8 Torr), the active sputtering area is s
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