The Effect of Nitrogen Ion Damage on the Optical and Electrical Properties of MBE GaN Grown on MOCVD GaN/Sapphire Templa
- PDF / 83,577 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 91 Downloads / 162 Views
Alexander P. Young and Leonard J. Brillson Department of Electrical Engineering, The Ohio-State University, 2015 Neil Avenue, Columbus, OH 43210-1272, U.S.A. Yoshiki Naoi and Charles W. Tu Department of Electrical Engineering, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0407, U.S.A.
ABSTRACT We have established a correlation between localized states responsible for mid-gap optical emission and film mobility of GaN grown under different nitrogen conditions. By imposing a deflector voltage at the tip of the plasma source, we varied the ion/neutral flux ratio to determine how N ions affect mid-gap luminescence and electrical mobility. Low energy electron-excited nanometer scale luminescence (LEEN) spectroscopy in ultrahigh vacuum (UHV) showed mid-gap emission intensities in the bulk that decreased in the ratio, 50 : 1.3 : 1 with increasing deflector voltage. Hall measurements indicated over a factor of two increase in mobility, and a factor of 8 decrease in residual charge density with increasing deflector voltage. The correlation of optical and electrical properties with a reduction in N ion flux suggests the primary role of native defects, such as N or Ga vacancies, in the mid-gap emissions.
INTRODUCTION Advanced heterostructures based on GaN are increasingly viewed as the materials system of choice for implementing light emitting diodes, solar blind photo detectors, solid state lasers, and high power microwave devices. The performance of these devices is critically dependent upon control of point defects and dislocations in order to make full use of these new materials. While impressive achievements have already been made, the electrical and optical properties of the nitrides remain relatively poorly controlled. A deeper understanding of fundamental growth parameters is still necessary to realize the continued improvement of these devices based on the nitrides. The nitrogen source of choice for the production of state-of-the-art GaN by molecular beam epitaxy MBE is the RF plasma source [1,2]. While GaN films made using this source are superior to others, the material quality is dependent on many variables including: RF power, RF frequency, nitrogen flow rate, and the ratio of group III to group V fluxes. Because of the many parameters involved when using a plasma source to grow GaN, it’s difficult to isolate any one parameter as being of fundamental importance to the production of defect free, single crystal layers. Of particular concern in this article is the sensitivity of the growth to the ratio of N ions to neutral atomic species in the N flux. Different plasma sources are known to have a complex mixture of N components with widely varying amounts of ions, atomic N, and meta stable molecular N species[3,4] By placing a perpendicular electrostatic potential at the tip of the plasma gun source, ions are deflected away from the growth path. In this way, we can directly
F99W11.56
observed the effect of the N ion/neutral ratio on material quality. In this work, we directly measured
Data Loading...
