skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Role of atomic nitrogen during GaN growth by plasma-assisted molecular beam epitaxy revealed by appearance mass spectrometry

Abstract

To identify the species which contribute to GaN growth, the authors investigated the discharge parameter (0.3-4.8 SCCM (SCCM denotes cubic centimeter per minute at STP), 150-400 W) dependences of the atomic N flux by appearance mass spectrometry and of the incorporated nitrogen atoms into GaN layers grown by plasma-assisted molecular beam epitaxy (PAMBE) using the rf-plasma source. Ion fluxes were also evaluated by ion current measurements. A good correlation between the supplied atomic N flux and the incorporated nitrogen flux was obtained under a wide range of plasma conditions. It was clarified that the atomic N plays a dominant role in the growth of GaN by PAMBE.

Authors:
; ; ; ; ;  [1];  [2];  [2]
  1. Department of Electrical Engineering and Computer Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan)
  2. (Japan)
Publication Date:
OSTI Identifier:
20971876
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 90; Journal Issue: 17; Other Information: DOI: 10.1063/1.2734390; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CRYSTAL GROWTH; DEPOSITION; GALLIUM NITRIDES; LAYERS; MASS SPECTRA; MASS SPECTROSCOPY; MOLECULAR BEAM EPITAXY; NITROGEN; PLASMA; SEMICONDUCTOR MATERIALS

Citation Formats

Osaka, J., Senthil Kumar, M., Toyoda, H., Ishijima, T., Sugai, H., Mizutani, T., Department of Electrical Engineering, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8603, and Department of Quantum Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan and Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603. Role of atomic nitrogen during GaN growth by plasma-assisted molecular beam epitaxy revealed by appearance mass spectrometry. United States: N. p., 2007. Web. doi:10.1063/1.2734390.
Osaka, J., Senthil Kumar, M., Toyoda, H., Ishijima, T., Sugai, H., Mizutani, T., Department of Electrical Engineering, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8603, & Department of Quantum Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan and Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603. Role of atomic nitrogen during GaN growth by plasma-assisted molecular beam epitaxy revealed by appearance mass spectrometry. United States. doi:10.1063/1.2734390.
Osaka, J., Senthil Kumar, M., Toyoda, H., Ishijima, T., Sugai, H., Mizutani, T., Department of Electrical Engineering, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8603, and Department of Quantum Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan and Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603. Mon . "Role of atomic nitrogen during GaN growth by plasma-assisted molecular beam epitaxy revealed by appearance mass spectrometry". United States. doi:10.1063/1.2734390.
@article{osti_20971876,
title = {Role of atomic nitrogen during GaN growth by plasma-assisted molecular beam epitaxy revealed by appearance mass spectrometry},
author = {Osaka, J. and Senthil Kumar, M. and Toyoda, H. and Ishijima, T. and Sugai, H. and Mizutani, T. and Department of Electrical Engineering, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8603 and Department of Quantum Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan and Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603},
abstractNote = {To identify the species which contribute to GaN growth, the authors investigated the discharge parameter (0.3-4.8 SCCM (SCCM denotes cubic centimeter per minute at STP), 150-400 W) dependences of the atomic N flux by appearance mass spectrometry and of the incorporated nitrogen atoms into GaN layers grown by plasma-assisted molecular beam epitaxy (PAMBE) using the rf-plasma source. Ion fluxes were also evaluated by ion current measurements. A good correlation between the supplied atomic N flux and the incorporated nitrogen flux was obtained under a wide range of plasma conditions. It was clarified that the atomic N plays a dominant role in the growth of GaN by PAMBE.},
doi = {10.1063/1.2734390},
journal = {Applied Physics Letters},
number = 17,
volume = 90,
place = {United States},
year = {Mon Apr 23 00:00:00 EDT 2007},
month = {Mon Apr 23 00:00:00 EDT 2007}
}
  • Utilizing a modified nitrogen plasma source, plasma assisted molecular beam epitaxy (PAMBE) has been used to achieve higher growth rates in GaN. A higher conductance aperture plate, combined with higher nitrogen flow and added pumping capacity, resulted in dramatically increased growth rates up to 8.4 μm/h using 34 sccm of N{sub 2} while still maintaining acceptably low operating pressure. It was further discovered that argon could be added to the plasma gas to enhance growth rates up to 9.8 μm/h, which was achieved using 20 sccm of N{sub 2} and 7.7 sccm Ar flows at 600 W radio frequency power, for which themore » standard deviation of thickness was just 2% over a full 2 in. diameter wafer. A remote Langmuir style probe employing the flux gauge was used to indirectly measure the relative ion content in the plasma. The use of argon dilution at low plasma pressures resulted in a dramatic reduction of the plasma ion current by more than half, while high plasma pressures suppressed ion content regardless of plasma gas chemistry. Moreover, different trends are apparent for the molecular and atomic nitrogen species generated by varying pressure and nitrogen composition in the plasma. Argon dilution resulted in nearly an order of magnitude achievable growth rate range from 1 μm/h to nearly 10 μm/h. Even for films grown at more than 6 μm/h, the surface morphology remained smooth showing clear atomic steps with root mean square roughness less than 1 nm. Due to the low vapor pressure of Si, Ge was explored as an alternative n-type dopant for high growth rate applications. Electron concentrations from 2.2 × 10{sup 16} to 3.8 × 10{sup 19} cm{sup −3} were achieved in GaN using Ge doping, and unintentionally doped GaN films exhibited low background electron concentrations of just 1–2 × 10{sup 15} cm{sup −3}. The highest growth rates resulted in macroscopic surface features due to Ga cell spitting, which is an engineering challenge still to be addressed. Nonetheless, the dramatically enhanced growth rates demonstrate great promise for the future of III-nitride devices grown by PAMBE.« less
  • In the present study, the authors report on a modified Riber radio frequency (RF) nitrogen plasma source that provides active nitrogen fluxes more than 30 times higher than those commonly used for plasma assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N{sub 2} gas flow rates between 5 and 25 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux, achieved was ∼7.6 μm/h. For optimized growth conditions,more » the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 × 3 μm) on the order of 1 nm. Secondary ion mass spectroscopy impurity analysis demonstrates oxygen and hydrogen incorporation of 1 × 10{sup 16} and ∼5 × 10{sup 17}, respectively. In addition, the authors have achieved PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ∼100 °C greater than any previously reported PAMBE growth of GaN. This growth temperature corresponds to GaN decomposition in vacuum of more than 20 nm/min; a regime previously unattainable with conventional nitrogen plasma sources. Arrhenius analysis of the decomposition rate shows that samples with a flux ratio below stoichiometry have an activation energy greater than decomposition of GaN in vacuum while samples grown at or above stoichiometry have decreased activation energy. The activation energy of decomposition for GaN in vacuum was previously determined to be ∼3.1 eV. For a Ga/N flux ratio of ∼1.5, this activation energy was found to be ∼2.8 eV, while for a Ga/N flux ratio of ∼0.5, it was found to be ∼7.9 eV.« less
  • The growth mode of N-face GaN deposited on AlN(0001) by plasma-assisted molecular beam epitaxy has been investigated. Based on reflection high-energy electron diffraction experiments, we demonstrate that for appropriate Ga fluxes and substrate temperature, a self-regulated 1-ML-thick Ga excess film can be formed on the growing surface. Depending on the presence of this Ga monolayer, the growth can proceed following either the Stranski-Krastanow or the Frank Van der Merwe growth modes, hence enabling the synthesis of either quantum dots or quantum wells.
  • Real-time analysis of the growth modes during homoepitaxial (0001) GaN growth by plasma-assisted molecular beam epitaxy was performed using reflection high energy electron diffraction. A growth mode map was established as a function of Ga/N flux ratio and growth temperature, exhibiting distinct transitions between three-dimensional (3D), layer-by-layer, and step-flow growth modes. The layer-by-layer to step-flow growth transition under Ga-rich growth was surfactant mediated and related to a Ga adlayer coverage of one monolayer. Under N-rich conditions the transition from 3D to layer-by-layer growth was predominantly thermally activated, facilitating two-dimensional growth at temperatures of thermal decomposition.