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Probing the formation of two-dimensional electron gas in AlInGaN/ GaN heterostructures by photoluminescence spectroscopy

Published online by Cambridge University Press:  01 February 2011

C. B. Soh ,
W. Liu ,
S. J. Chua ,
S. Tripathy  and
D. Z. Chi
C. B. Soh
Affiliation:
Centre of Optoelectronics, Department of Electrical and Computer Engineering, National University of Singapore, 2 Engineering Drive 3, Singapore 117576 Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602
W. Liu
Affiliation:
Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602
S. J. Chua
Affiliation:
Centre of Optoelectronics, Department of Electrical and Computer Engineering, National University of Singapore, 2 Engineering Drive 3, Singapore 117576 Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602
S. Tripathy
Affiliation:
Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602
D. Z. Chi
Affiliation:
Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602
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Abstract

Using temperature-dependent photoluminescence (PL), we report a detailed study on the optical transitions in AlyInxGa1−x−yN (0.01≤ × ≤ 0.023, 0.07 ≤ y ≤ 0.14) of variable thickness (20 – 100 nm) grown on GaN by metalorganic chemical vapor deposition (MOCVD). At 100 K, highest electron mobility has been obtained for samples with 40 nm thick AlInGaN epilayer and this is due to the contribution from the two-dimensional electron gas (2DEG) in the confined two dimensional potential well. In literature, such 2DEG phenomenon is not discussed for AlInGaN quaternary alloys. In our samples, we have clearly observed such effects from low-temperature PL spectroscopy for AlInGaN epilayer of thickness ≥ 40 nm. The PL peaks observed due to the interband transitions from 2DEG sub-bands to the valence band are in the range 3.55 – 3.68 eV for the sample with an epilayer thickness of 100 nm. Due to the composition pulling effect in this alloy, there is a higher incorporation of Al towards the surface for thicker AlInGaN epilayer, which generates a stronger piezoelectric field and a deeper triangular potential for electron confinement. This is evident from the observation of higher intensity ratio for 2DEG transition compared to band-edge transitions, I2DEG/IBE in sample with thicker AlInGaN epilayer at higher temperature. The intensity ratio, I2DEG/IBE however decreases subsequently for all the samples with further increase in temperature due to thermal excitation.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 831: Symposium E – GaN, AlN, InN, and Their Alloys , 2004 , E3.43
Copyright
Copyright © Materials Research Society 2005

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References

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