Fundamental optical transitions in GaN - Semantic Scholar
Fundamental optical transitions in GaN G. D. Chen, M. Smith, J. Y. Lin, H. X. Jiang, SuHuai Wei, M. Asif Khan, and C. J. Sun Citation: Applied Physics Letters 68, 2784 (1996); doi: 10.1063/1.116606 View online: http://dx.doi.org/10.1063/1.116606 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/68/20?ver=pdfcov Published by the AIP Publishing
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 129.118.248.40 On: Mon, 03 Mar 2014 05:54:55
Fundamental optical transitions in GaN G. D. Chen,a) M. Smith, J. Y. Lin, and H. X. Jiang Department of Physics, Kansas State University, Manhattan, Kansas 66506-2601
Su-Huai Wei National Renewable Energy Laboratory, Golden, Colorado 80401-3393
M. Asif Khan and C. J. Sun APA Optics, Inc., 2950 N.E. 84th Lane, Blaine, Minnesota 55449
~Received 2 January 1996; accepted for publication 8 March 1996! A coherent picture for the band structure near the G point and the associated fundamental optical transitions in wurtzite ~WZ! GaN, including the electron and hole effective masses and the binding energies of the free excitons associated with different valence bands, has been derived from time-resolved photoluminescence measurements and a theoretical calculation based on the local density approximation. We also determine the radiative recombination lifetimes of the free excitons and neutral impurity ~donor and acceptor! bound excitons in WZ GaN and compare ratios of the radiative lifetimes with calculated values of the ratios obtained with existing theories of free and bound excitons. © 1996 American Institute of Physics. @S0003-6951~96!02220-6#
GaN has been recognized as one of the most important wide-band-gap semiconductors recently due to its potential applications for optical devices such as blue-UV lasers and for high-temperature electronic devices.1,2 In spite of the recognition of the importance of GaN, many of its fundamental physical properties are not yet well known. For example, key parameters which describe the band structure near the G point, including the values of the valence band splitting and the hole effective masses, are not well established. In this letter, we present a coherent picture for the fundamental optical transitions and the detailed band structures near the G point in GaN, derived from time-resolved photoluminescence measurements and a first-principles band structure calculation based on the local density approximation ~LDA!. Three GaN samples grown by metalorganic chemical vapor deposition ~MOCVD! were used in this study: Sample A is a 3.8 mm n-type ~ n5531016 cm23! epitaxial layer; sample B is a 2.8 mm n-type ~n52.431017 cm23! epitaxial layer; and sample C is a 0.2 mm p-type ~Mg-doped! epitaxial layer. All layers were grown on sapphire substrates with AlN buffer layers.3,4 The picosecond laser spectroscopy system used for time-resolved photoluminescence measurements has been described previously.3 Figure 1 shows three low-temperature photoluminescence emission spectra obtained for samples A, B, and C. The spectral peak positions shift with temperature following the temperature variation of the band gap. Two emission peaks located at about 3.485 and 3.491 eV observed in sample A are identified as due to the recombination of the ground state of free excitons ~FX! associated with the top two valence bands, or A and B excitons @A(n51) and B(n 51!#. These assignments have been further confirmed by the following three observations: ~a! the emission intensities of the observed transition lines decrease with temperature with activation energies correspond to FX binding energies; ~b! a!
Permanent address: Department of Applied Physics, Xi’an Jiaotong University, People’s Republic of China.
the emission intensities depend strongly on the excitation light polarization direction, as expected for FX in WZ crystals; and ~3! the emission intensities increase superlinearly with excitation intensity, as expected for FX. Our results show that the energy separation between the A- and B-exciton transition lines is about 6 meV; the binding energy of the A exciton is about 19 meV if we use the accepted value of the low-temperature band gap of 3.504 eV.5–7 We show the 40 K emission spectrum for sample A because the B-exciton line is more pronounced at T
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 129.118.248.40 On: Mon, 03 Mar 2014 05:54:55
Fundamental optical transitions in GaN G. D. Chen,a) M. Smith, J. Y. Lin, and H. X. Jiang Department of Physics, Kansas State University, Manhattan, Kansas 66506-2601
Su-Huai Wei National Renewable Energy Laboratory, Golden, Colorado 80401-3393
M. Asif Khan and C. J. Sun APA Optics, Inc., 2950 N.E. 84th Lane, Blaine, Minnesota 55449
~Received 2 January 1996; accepted for publication 8 March 1996! A coherent picture for the band structure near the G point and the associated fundamental optical transitions in wurtzite ~WZ! GaN, including the electron and hole effective masses and the binding energies of the free excitons associated with different valence bands, has been derived from time-resolved photoluminescence measurements and a theoretical calculation based on the local density approximation. We also determine the radiative recombination lifetimes of the free excitons and neutral impurity ~donor and acceptor! bound excitons in WZ GaN and compare ratios of the radiative lifetimes with calculated values of the ratios obtained with existing theories of free and bound excitons. © 1996 American Institute of Physics. @S0003-6951~96!02220-6#
GaN has been recognized as one of the most important wide-band-gap semiconductors recently due to its potential applications for optical devices such as blue-UV lasers and for high-temperature electronic devices.1,2 In spite of the recognition of the importance of GaN, many of its fundamental physical properties are not yet well known. For example, key parameters which describe the band structure near the G point, including the values of the valence band splitting and the hole effective masses, are not well established. In this letter, we present a coherent picture for the fundamental optical transitions and the detailed band structures near the G point in GaN, derived from time-resolved photoluminescence measurements and a first-principles band structure calculation based on the local density approximation ~LDA!. Three GaN samples grown by metalorganic chemical vapor deposition ~MOCVD! were used in this study: Sample A is a 3.8 mm n-type ~ n5531016 cm23! epitaxial layer; sample B is a 2.8 mm n-type ~n52.431017 cm23! epitaxial layer; and sample C is a 0.2 mm p-type ~Mg-doped! epitaxial layer. All layers were grown on sapphire substrates with AlN buffer layers.3,4 The picosecond laser spectroscopy system used for time-resolved photoluminescence measurements has been described previously.3 Figure 1 shows three low-temperature photoluminescence emission spectra obtained for samples A, B, and C. The spectral peak positions shift with temperature following the temperature variation of the band gap. Two emission peaks located at about 3.485 and 3.491 eV observed in sample A are identified as due to the recombination of the ground state of free excitons ~FX! associated with the top two valence bands, or A and B excitons @A(n51) and B(n 51!#. These assignments have been further confirmed by the following three observations: ~a! the emission intensities of the observed transition lines decrease with temperature with activation energies correspond to FX binding energies; ~b! a!
Permanent address: Department of Applied Physics, Xi’an Jiaotong University, People’s Republic of China.
the emission intensities depend strongly on the excitation light polarization direction, as expected for FX in WZ crystals; and ~3! the emission intensities increase superlinearly with excitation intensity, as expected for FX. Our results show that the energy separation between the A- and B-exciton transition lines is about 6 meV; the binding energy of the A exciton is about 19 meV if we use the accepted value of the low-temperature band gap of 3.504 eV.5–7 We show the 40 K emission spectrum for sample A because the B-exciton line is more pronounced at T
