The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Growth and In Situ Characterisation of Dilute Nitride Quantum Well Structures

Outi Reentilä

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Large Seminar Hall of Micronova at Helsinki University of Technology (Espoo, Finland) on the 13th of April, 2007, at 12 noon.

Overview in PDF format (ISBN 978-951-22-8731-4)   [2923 KB]
Dissertation is also available in print (ISBN 978-951-22-8730-7)

Abstract

In this work epitaxial growth and in situ characterisation of dilute nitride quantum well (QW) structures are studied. Dilute nitrides are III-V compound semiconductors with low (typically < 5%) composition of nitrogen in the lattice. Metal organic vapor phase epitaxial (MOVPE) system was used to grow the structures and in situ reflectance monitoring in normal incidence at a wavelength of 635 nm was utilised to study the growth process of the structures. Ex situ characterisation was performed by x-ray diffractometry and photoluminescence measurements.

The nitrogen content of (In)GaAsN was found to depend on many MOVPE growth parameters. Increased nitrogen content was obtained with decreasing growth temperature, increasing DMHy/V and TBAs/III ratios and when nitrogen (N2) was used as a carrier gas instead of hydrogen (H2).

In situ reflectance data was measured during growth of GaAsN/GaAs, InGaAs/GaAs and InGaAsN/GaAs multi quantum well (MQW) structures. The reflectance curve was observed to be different when MQW structures with different compositions were grown. The reflectance data was analysed by an experimental method utilising the dependence of the reflectance change observed during growth of the QW on the QW composition. Additionally, reflectance curves for multi layer stacks were calculated and the measured curves were compared to the calculated ones. With both methods the sample composition can be determined in situ if the growth rates of the layers are known.

In the process of comparing calculated and measured reflectance curves, the high temperature complex refractive indices of the various QW materials were obtained. The imaginary part of the complex refractive index of (In)GaAsN was found to be linearly dependent on the nitrogen content, as well as both real and imaginary parts of the complex refractive index of InGaAs depended linearly on the indium content. However, changing the nitrogen content did not change the real part of the complex refractive index of (In)GaAsN.

The in situ analysis methods of MQW structures developed in this work can be used to obtain information about the growth process as well as about the materials themselves.

This thesis consists of an overview and of the following 6 publications:

  1. O. Reentilä, M. Mattila, M. Sopanen, and H. Lipsanen, Nitrogen content of GaAsN quantum wells by in situ monitoring during MOVPE growth, Journal of Crystal Growth 290 345-349 (2006). © 2006 Elsevier Science. By permission.
  2. O. Reentilä, M. Mattila, L. Knuuttila, T. Hakkarainen, M. Sopanen, and H. Lipsanen, In situ determination of nitrogen content in InGaAsN quantum wells, Journal of Applied Physics 100 013509 (2006). © 2006 American Institute of Physics. By permission.
  3. O. Reentilä, M. Mattila, L. Knuuttila, T. Hakkarainen, M. Sopanen, and H. Lipsanen, Comparison of H2 and N2 as carrier gas in MOVPE growth of InGaAsN quantum wells, Journal of Crystal Growth 298 536-539 (2007). © 2007 Elsevier Science. By permission.
  4. O. Reentilä, M. Mattila, M. Sopanen, and H. Lipsanen, In situ determination of InGaAs and GaAsN composition in multiquantum-well structures, Journal of Applied Physics 101 033533 (2007). © 2007 American Institute of Physics. By permission.
  5. O. Reentilä, M. Mattila, M. Sopanen, and H. Lipsanen, Simultaneous determination of indium and nitrogen contents of InGaAsN quantum wells by optical in situ monitoring, Applied Physics Letters 89 231919 (2006). © 2006 American Institute of Physics. By permission.
  6. L. Knuuttila, O. Reentilä, M. Mattila, and H. Lipsanen, Comparison of Ge and GaAs substrates for metalorganic vapor phase epitaxy of GaIn(N)As quantum wells, Japanese Journal of Applied Physics 44 L1475-L1477 (2005).

Keywords: MOVPE, epitaxy, quantum wells, in situ monitoring, dilute nitrides

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© 2007 Helsinki University of Technology

Last update 2011-05-26