Luminescence Properties of Si-Doped GaN and Evidence of Compensating Defects As the Origin of the Yellow Luminescence

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PROPERTIES OF Si-DOPED GaN AND EVIDENCE OF THE YELLOW DEFECTS AS THE ORIGIN OF

I.D. Goepfert*, E.F. Schubert*, J.M. Redwing**

*Center for Photonics Research and Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215; **ATMI, Danbury, Connecticut 06810 ABSTRACT We investigate the optical properties of n-type Gallium Nitride (GaN) with concentrations ranging from 5x1016 to 7x101 cm"3. The near-band edge ultraviolet (UV) transition increases monotonically with the doping concentration. The photoluminescence linewidth of the near-bandgap optical transition increases from 47 to 78 meV as the doping concentration is increased. The broadening is modeled by taking into account potential fluctuations caused by the random distribution of donor impurities. Excellent agreement is found between experimental and theoretical results. We also investigate the origin of the yellow luminescence in GaN. At low excitation densities the experimental ratio of the UV-to-yellow photoluminescence does not change significantly as the doping concentration is increased by two orders of magnitude. Analysis of the luminescence in terms of a theoretical model indicates that the yellow luminescence is due to compensating impurities or defects. INTRODUCTION The optical properties of n-type GaN are investigated for Si doping concentrations ranging from 5x 1016 to 7x10" cm"3. The peak intensities of the near bandedge UV transition increases mcG.Atonically with a corresponding increase in doping concentration. The photolumine'.ence linewidth of the near-bandgap optical transition increases from 47 to 78 meV as the doping concentration is increased. The broadening is modeled by taking into account potential fluctuations caused by the random distribution of donor impurities. Excellent agreement is found between experimental and theoretical results'. At low excitation intensities, the experimental ratio of the bandedge-to-yellow photoluminescence does not change significantly as the doping concentration is increased by two orders of magnitude. A theoretical model based on rate equations is developed for the bandedge-to-yellow intensity ratio. Analysis of the experimental data in terms of our model reveals that the concentration of the defect causing the yellow photoluminescence increases linearly with doping concentration. A linear dependence, such as we observed, indicates that the yellow luminescence is due to a compensating defect 2. EXPERIMENT Four Si-doped GaN samples were grown by metal-organic chemical vapor deposition (MOCVD) on the c-plane of sapphire substrates. The samples were grown at 1100 *Cwith a growth rate of 2 aim/h. A dilute silane (Sil- 4) precursor was systematically varied to incorporated doping concentrations ranging between 5x1016 to 7x10" cm 3. Room temperature photoluminescence measurements were performed using a HeCd laser, emitting at 325 nm, with an excitation density of 3 W/cm 2. The luminescence is dispersed in a 0.75 m spectrometer, 679 Mat. Res. Soc. Symp. Proc. Vol. 482 ©1998

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