Intrinsic and thermal stress in gallium nitride epitaxial films
- Lawrence Berkeley National Lab., CA (United States). Materials Sciences Div.
- Polish Academy of Sciences, Warsaw (Poland)
- North Carolina State Univ., Raleigh, NC (United States)
- Hewlett Packard, San Jose, CA (United States). Optoelectronics Div.
Strain in GaN epitaxial layers at room temperature is measured with three complementary methods: Raman spectroscopy (via shifts of phonon frequencies), low temperature photoluminescence (via shifts of band-edge luminescence), and X-ray diffraction (via shifts in lattice spacings). GaN films grown on the c-plane of sapphire tend to be in compression. Increasing the Si-dopant concentration (up to 10{sup 19} cm{sup {minus}3}) is observed to add compressive strain to the layer. Axially resolved measurements obtained by micro-Raman in 4 {micro}m thick Si-doped films reveal strain relaxation toward the sample surface at Si concentrations above 10{sup 18} cm{sup {minus}3}. Mg- and Si-doped GaN films on SiC substrates are found to be in tension. An experimental methodology is presented that separates two contributions to the room temperature residual stress in GaN epilayers: (1) the thermal stress due to differences in the thermal expansion coefficients of the epilayer and substrate and (2) the intrinsic stress, which is influenced by the growth conditions. The authors measure stress as a function of temperature up to 325 C, about one-third of the growth temperature, by monitoring the frequency of the E{sub 2} phonon mode by Raman spectroscopy. A high-quality bulk single crystal of GaN is used as a strain-free standard. Over this temperature range, most layers behave elastically; the observed stress trends are well-fit by a thermal expansion model using previous reported values of the thermal expansion coefficients of GaN and the substrates. The intrinsic stress states at the growth temperature for films grown on sapphire and SiC are predicted to be tensile and compressive, respectively, in agreement with the a-plane lattice coefficient mismatch.
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 585817
- Report Number(s):
- CONF-961202-; ISBN 1-55899-353-3; TRN: IM9810%%47
- Resource Relation:
- Conference: 1996 Fall meeting of the Materials Research Society (MRS), Boston, MA (United States), 2-6 Dec 1996; Other Information: PBD: 1997; Related Information: Is Part Of III-V nitrides; Ponce, F.A. [ed.] [Xerox Palo Alto Research Center, CA (United States)]; Moustakas, T.D. [ed.] [Boston Univ., MA (United States)]; Akasaki, I. [ed.] [Meijo Univ., Nagoya (Japan)]; Monemar, B.A. [ed.] [Linkoeping Univ. (Sweden)]; PB: 1278 p.; Materials Research Society symposium proceedings, Volume 449
- Country of Publication:
- United States
- Language:
- English
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