Table of Contents Author Guidelines Submit a Manuscript
Advances in OptoElectronics
Volume 2018, Article ID 8908354, 7 pages
https://doi.org/10.1155/2018/8908354
Research Article

1 ML Wetting Layer upon Ga(As)Sb Quantum Dot (QD) Formation on GaAs Substrate Monitored with Reflectance Anisotropy Spectroscopy (RAS)

1Integrated Optoelectronics and Microoptics (IOE) Research Group, Physics Department, Technische Universität Kaiserslautern (TUK), P.O. Box 3049, D-67653 Kaiserslautern, Germany
2Nano Structuring Center (NSC), Physics Department, Technische Universität Kaiserslautern (TUK), P.O. Box 3049, D-67653 Kaiserslautern, Germany

Correspondence should be addressed to Henning Fouckhardt; ed.lk-inu.kisyhp@rahkcuof

Received 12 September 2018; Accepted 1 November 2018; Published 14 November 2018

Academic Editor: Vasily Spirin

Copyright © 2018 Henning Fouckhardt et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

III/V semiconductor quantum dots (QD) are in the focus of optoelectronics research for about 25 years now. Most of the work has been done on InAs QD on GaAs substrate. But, e.g., Ga(As)Sb (antimonide) QD on GaAs substrate/buffer have also gained attention for the last 12 years. There is a scientific dispute on whether there is a wetting layer before antimonide QD formation, as commonly expected for Stransky-Krastanov growth, or not. Usually ex situ photoluminescence (PL) and atomic force microscope (AFM) measurements are performed to resolve similar issues. In this contribution, we show that reflectance anisotropy/difference spectroscopy (RAS/RDS) can be used for the same purpose as an in situ, real-time monitoring technique. It can be employed not only to identify QD growth via a distinct RAS spectrum, but also to get information on the existence of a wetting layer and its thickness. The data suggest that for antimonide QD growth the wetting layer has a thickness of 1 ML (one monolayer) only.

1. Introduction

III/V semiconductor quantum dots (QD) are investigated for about 25 years now, mostly since they can be considered “artificial or designer atoms” [1, 2], or since they can be used to make semiconductor lasers more efficient [3], at least in principle, or since they might be employable as fundamental digital data storage units (see, e.g., [4]).

Usually QD are grown in a specific epitaxial mode, which is called Stransky-Krastanov (SK) growth [5]. This mode is based on QD self-organization during growth on a substrate/buffer with equal lattice structure (in the case of cubic III/V semiconductors blende (sphalerite)), but with a native layer lattice constant larger by a few percent than the lattice constant of the substrate/buffer material.

After (at most) a few monolayers of grown material serving as a wetting layer, the mechanical stress forces the deposited material into three-dimensional (3D) growth, i.e., growth into the third dimension. Nano-islands typically with flat, pyramidal shape form statistically at the growth front [1, 2]. If the material supply is cut off soon enough (after a few seconds), the islands will stay so small, that they can be considered 3D quantum wells, i.e., QD, presupposed that the surrounding materials have larger band gaps, acting as potential barriers for carriers.

SK growth had been shown for InAs QD on GaAs substrate and innumerable contributions have been made by other authors in this context (see, e.g., again [1, 2]).

There is less experience in the community with Ga(As)Sb (so-called antimonide) QD on GaAs substrate, but even in this regard quite a number of papers have been published (e.g., [4, 620]). Very interesting results have been achieved by the Huffaker group [1215], which brought the aerial density of antimonide QD to 290 m−2. The authors of the current contribution have been successful in increasing the aerial QD density even further, i.e., to values of about 1000 m−2, which lets the QD nearly abut in the growth plane [1620]. E.g., dense lying QD are important to improve semiconductor laser efficiency.

There is a disagreement in the community on the existence of a wetting layer and its thickness for antimonide QD growth. Sometimes photoluminescence (PL) peaks (measured ex situ after the epitaxial process) are attributed to wetting layers, although the spectral peak positions (after all a thin wetting layer before QD growth should optoelectronically have the properties of a very thin quantum well) and peak heights (thin wetting layers should have very small to vanishing PL peaks due to their vanishing luminescent mass) do not fully support the assumption of a thin wetting layer. This contribution wants to help to settle the case.

First we show results of ex situ PL measurements as well as atomic force microscopy (AFM). Then we verify that reflectance anisotropy/difference spectroscopy (RAS/RDS) is also capable of identifying the formation of a wetting layer as well as of the antimonide QD themselves—in situ and real-time.

Indeed other groups and these authors have already shown that RAS can be used to monitor SK growth of InAs QD on GaAs [2124] and of antimonide QD on GaAs [20, 2530], since the QD RAS spectra considerably differ from those of layers of similar composition. Here—for antimonide QD growth—we report on further details of the signal peaks in RAS spectra: they suggest a wetting layer of just one monolayer (1 ML) (for cubic III/V semiconductors, a monolayer constitutes a double atomic layer, one atomic layer made of atoms from the group III element the other made from atoms of the group V element; sometimes 1 ML is also taken as a unit for thicknesses; in that case 1 ML equals half a lattice constant and double the thickness of an atomic layer).

2. Some Growth Details

Ga(As)Sb QD formation on GaAs substrate/buffer is initiated by supply of Ga and Sb atoms only. Due to As and Sb diffusion and intermixing [31] and without further action the resulting QD are not made of pure GaSb, but rather of with a relatively high As content of up to = 72% in our case. In order to avoid a high As content in the QD, they are stabilized in an Sb atmosphere (background pressure) for 10 s, before we grow a 50 nm thick GaAs cap.

Photoluminescence (PL) measurements were performed and atomic force microscope (AFM) images were taken as well—for six samples with different nominal coverage of 1-6 ML. Since the QD would immediately oxidize/degrade upon the air-break during the transport of the samples from the MBE machine to the AFM, a special sample design had to be used, which is given in the top of Figure 1. Actually two identical QD “films” were grown with a 50 nm thick GaAs layer in-between, which has been called “cap” above (this layer is thick enough to compensate for the stress of the QD; a smooth, nonstrained surface can be assumed after growth of the “cap”). The bottom QD layer was taken for retrieval of the PL spectrum (and before of the RAS spectrum), and the top QD layer was used for the AFM measurements.

Figure 1: Sketch of layer sequence and atomic force microscope (AFM) images of GaAs surfaces after GaSb growth with nominal coverages of 1-6 ML. The lateral scaling is equal in all cases, and the vertical/gray scaling is not. For a coverage of 1 ML no QD can be observed. For a nominal coverage of 6 ML the QD are too close to each other to be reckoned as completely separated. E.g., for the pyramidal QD and 3 ML nominal coverage the side length is 27 nm and the height amounts to 4 nm.

3. Experimental PL and AFM Results

The AFM micrographs in Figure 1 reveal that no QD have been grown for the case of 1 ML nominal coverage, but for all other used coverages (2-6 ML). This finding supports the conclusion that a 1 ML thick wetting layer exists.

In Figure 2, the corresponding PL spectra are given. In case of no growth or growth with a coverage of 1 ML only (black curve in the main graph and identically in the inset) there is no peak to be attributed to quantum dots (QD).

Figure 2: Photoluminescence (PL) spectra for the cases of GaSb growth with nominal coverages of 1-6 ML. The (single) peaks can be attributed to the occurrence of Ga(As)Sb QD, the always occurring double peak to excitonic levels of the pure GaAs buffer [32]. For 1 ML no QD peak is observed. The black curve in the inset is identical to the black curve in the main graph.

The (always) observable double peak is related to the GaAs substrate/buffer. The double peak is caused by excitonic levels and appears, whenever the GaAs buffer is extremely pure [32].

For coverages of 2-6 ML, there is one additional peak each. It is attributed to the occurrence of Ga(As)Sb QD. The peak for 6 ML nominal coverage is small and broad, but noticeable.

Since only the double peak of the buffer can be observed for 1 ML coverage, again it can be concluded that no QD arose in this case and that indeed a wetting layer exists upon Ga(As)Sb QD growth, but that it has a maximum thickness of 1 ML.

4. RAS Principle and Signal Representations

RAS/RDS had indeed been developed for in situ epitaxial growth control by Aspnes, Harbison et al. [3346] and has mostly been employed for MOCVD (metal-organic chemical vapor deposition), but also for MBE (molecular beam epitaxy), as in our case. RAS signal peaks in the spectra are often, but not always related to orderly oriented electronic surface states (electric dipoles at the crystalline surface) [4753].

In Figure 3, a typical RAS beam path is sketched. A broad-band light source, typically a Xe lamp (with photon energies between 1.5 and 4.5 eV), is used. The emitted originally nonpolarized light wave is linearly polarized with the help of a polarizer. Then the wave enters the epitaxy vacuum chamber via a viewport and impinges (nearly) perpendicularly onto the growth front on the sample surface.

Figure 3: Perspective sketch of a RAS beam path. On the contrary to the drawing, the real angle of light incidence onto the wafer surface is ≈0.

The light wave can be considered as composed of two wave parts with orthogonal linear polarization. Whenever the plane of polarization of one wave part incorporates a main crystal axis, in case of cubic crystals the plane of polarization of the other wave part will include another main crystal axis.

For the hypothetical case of a perfectly flat and homogeneous surface normal incidence should not give any differences in reflectance for the two wave parts (not even a plane of incidence can be defined in the case of normal light incidence). But surface anisotropies like, e.g., the above-mentioned orderly arranged electric dipoles (especially prevalent for crystalline III/V semiconductors due to their ionic bond portion) break the symmetry and a reflectance difference will occur for the two wave parts. The genuine RAS signal iswith the symbol for reflectivities/reflectances and taking the main crystal axes and exemplarily here. is the mean reflectivity, averaged over the two wave parts. Typical signal levels are around 10−3, but the technique is sensitive down to around 10−5.

In general, due to the reflectance difference the state of polarization of the overall wave should change from linear to slightly elliptical upon reflection at the growth front (see Figure 3). In order to detect the ellipticity of the wave’s state of polarization, the reflected light wave is monitored with the help of a photoelastic modulator (PEM) (with 50 kHz modulation frequency), used as a switchable /2 wave-plate, a second polarizer (analyzer), and finally a monochromator with a detector. The PEM in connection with the analyzer allows for periodical detection of both linearly, orthogonally polarized wave parts. (During epitaxy the wafer is usually rotated with 1/s, so that there are only certain angular windows of the sample orientation (occurring periodically and twice per cycle), when/where the reflectances can be measured. The software of the RAS system manufacturer is tuned such that only absolute values of the RAS signal acc. to (1) are extracted.)

Due to the normal light incidence typical ellipsometric information is deliberately suppressed. The retrieved information is rather directly related to the ordered and oriented anisotropies at the surface (and possibly to optical Fabry-Perot resonances from the currently grown layer with increasing thickness).

Figure 4 contains a photograph of our R450 MBE system (by DCA Oy, Turku, Finland) with the EpiRAS apparatus (by Laytec, Berlin, Germany) in front of the central flange which is oriented normal to the wafer/sample surface.

Figure 4: Photograph of the R450 MBE machine by DCA Oy, Turku, Finland, with the RAS system EpiRAS by Laytec, Berlin, Germany in front.

There are different ways to represent the RAS signal data. For a RAS color plot the signal level is color-coded and given simultaneously in dependence on photon energy and on elapsed epitaxy time (a colored two-dimensional plot). For a RAS transient the signal height at a specific photon energy is plotted over elapsed time. A RAS spectrum contains the RAS signal for a fixed point in time in dependence on photon energy.

5. Experimental RAS Results

Figure 5 contains RAS spectra (for 11 photon energies with 0.3 eV separation between adjacent spectral sampling points) for different objects [54, 55], i.e.:(1)a fresh GaAs surface during epitaxial growth on a GaAs substrate/buffer without As stabilization (solid red line),(2)a fresh GaSb surface during epitaxial growth on a GaSb substrate/buffer without Sb stabilization (solid green line),(3)surfaces with definite Ga(As)Sb QD on GaAs substrate/buffer—the solid black line has been retrieved as an average over more than ten quantum dot growths and RAS measurements accompanied by the verification of QD existence with PL and AFM,(4)after nominal coverage of the substrate/buffer (the nominal coverage is the amount of material, which is supplied for QD growth; it is measured in monolayers (ML), although QD instead of just monolayers are grown) with 1 ML, 2 ML, or 3 ML of GaSb (broken dark-blue, broken purple, broken light-blue line, respectively).

Figure 5: RAS spectra for relevant epitaxial objects, defined in the text. The lines between measured data points are only guides to the eye. The ±1 error bar, which is valid for all data points, is shown in the legend; the standard deviation amounts to 0.034.

The RAS spectra in Figure 5 exhibit clear distinctions for the cases GaAs layer, GaSb layer, and definite Ga(As)Sb QD (solid lines). This is an important result and it will be a necessary condition, if Ga(As)Sb QD growth is intended to be identified with RAS. E.g., there is a distinct minimum at ≈2.4 eV photon energy and a maximum at around 1.8 eV for the definite QD, while it is the other way around for the GaSb layer (on GaSb substrate/buffer). The double standard deviation 2 = 2·0.034 (i.e., the error bar) of the signal data points is smaller than the height of the characteristic spectral RAS peaks; thus the peaks are considered significant.

Moreover, for the growth of just 1 ML, the RAS spectrum is completely different to the spectra of the GaSb layer and for higher nominal coverages, whereas the cases with 2 ML or 3 ML show similar spectra to the case with definite QD formation. This result alone already indicates that a wetting layer exists and that it has a maximum thickness of 1 ML.

That means that the occurrence of the wetting layer and/or of QD can already be identified undoubtedly in situ and real-time upon SK antimonide QD growth, if RAS is employed. Any tedious ex situ verification is not necessary.

6. Conclusions

Reflectance anisotropy/difference spectroscopy (RAS/RDS) has been used to get in situ and real-time evidence of the existence of a wetting layer in Ga(As)Sb (antimonide) quantum dot (QD) formation on GaAs substrate in the Stransky-Krastanov (SK) growth mode and of its thickness.

The solid-state physics result is that Ga(As)Sb QD formation on GaAs substrate/buffer incorporates the initial formation of a wetting layer with a thickness of just one monolayer (1 ML).

The technological result is that the RAS spectra for epitaxial growth with different nominal coverages of a couple of monolayers yield the same results in situ, as photoluminescence (PL) spectra and as atomic force microscope (AFM) images deliver ex situ. This finding includes the opportunity to make QD growth processes easier to be controlled.

A corresponding conclusion should very likely be drawable for QD growth of any suitable III/V semiconductor combination due to the ionic bond share and related surface states of III/V semiconductors.

Data Availability

The data used to support the findings of this study are included within the article.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.

Acknowledgments

This research has partially been funded by the (German) State of Rhineland-Palatinate under contract INST 248/61-1 FUGG for large research instrumentation and in the framework of the VIP Project HOFUS of the German Federal Ministry of Education and Research (BMBF). The authors are grateful to Laytec GmbH, Berlin, Germany, for assistance with the RAS technique and to the Nano Structuring Center (NSC) at the Technische Universiät Kaiserslautern (TUK) for technological help. We also like to thank Johannes Richter for his earlier work on this subject.

References

  1. D. Bimberg, M. Grundmann, and N. N. Ledentsov, Quantum Dot Heterostructures, Wiley, 1999.
  2. M. Grundmann, “The physics of semiconductors: An introduction including devices and nanophysics,” The Physics of Semiconductors: An Introduction Including Devices and Nanophysics, pp. 1–689, 2006. View at Google Scholar · View at Scopus
  3. L. A. Coldren and S. W. Corzine, Diode Lasers and Photonic Integrated Circuits, John Wiley & Sons, Inc., Hoboken, NJ, USA, 2012. View at Publisher · View at Google Scholar
  4. J. Richter, J. Strassner, T. H. Loeber et al., “GaSb quantum dots on GaAs with high localization energy of 710 meV and an emission wavelength of 1.3 μm,” Journal of Crystal Growth, vol. 404, pp. 48–53, 2014. View at Publisher · View at Google Scholar · View at Scopus
  5. K.-N. Tu, J. W. Mayer, and L. C. Feldman, “Electronic Thin Film Science for Electrical Engineers and Material Scientists,” Macmillan, 1992. View at Google Scholar
  6. V. Tasco, N. Deguffroy, A. N. Baranov et al., “High-density, uniform InSb/GaSb quantum dots emitting in the midinfrared region,” Applied Physics Letters, vol. 89, no. 26, 2006. View at Google Scholar · View at Scopus
  7. F. Hatami, N. N. Ledentsov, M. Grundmann et al., “Radiative recombination in type-II GaSb/GaAs quantum dots,” Applied Physics Letters, vol. 67, p. 656, 1995. View at Publisher · View at Google Scholar · View at Scopus
  8. F. Hatami, M. Grundmann, N. N. Ledentsov et al., “Carrier dynamics in type-II GaSb/GaAs quantum dots,” Physical Review B: Condensed Matter and Materials Physics, vol. 57, no. 8, pp. 4635–4641, 1998. View at Publisher · View at Google Scholar
  9. T. Wang and A. Forchel, “Growth of self-organized GaSb islands on a GaAs surface by molecular beam epitaxy,” Journal of Applied Physics, vol. 85, no. 5, pp. 2591–2594, 1999. View at Publisher · View at Google Scholar · View at Scopus
  10. T. Wang and A. Forchel, “Experimental and theoretical study of strain-induced AIGaAs/GaAs quantum dots using a self-organized GaSb island as a stressor,” Journal of Applied Physics, vol. 86, no. 4, pp. 2001–2007, 1999. View at Google Scholar · View at Scopus
  11. M. Geller, C. Kapteyn, L. Müller-Kirsch, R. Heitz, and D. Bimberg, “450 meV hole localization in GaSb/GaAs quantum dots,” Applied Physics Letters, vol. 82, no. 16, pp. 2706–2708, 2003. View at Publisher · View at Google Scholar · View at Scopus
  12. G. Balakrishnan, J. Tatebayashi, A. Khoshakhlagh et al., “III/V ratio based selectivity between strained Stranski-Krastanov and strain-free GaSb quantum dots on GaAs,” Applied Physics Letters, vol. 89, no. 16, 2006. View at Google Scholar · View at Scopus
  13. J. Tatebayashi, A. Khoshakhlagh, S. H. Huang, L. R. Dawson, G. Balakrishnan, and D. L. Huffaker, “Formation and optical characteristics of strain-relieved and densely stacked GaSbGaAs quantum dots,” Applied Physics Letters, vol. 89, no. 20, 2006. View at Google Scholar · View at Scopus
  14. S. H. Huang, G. Balakrishnan, M. Mehta et al., “Epitaxial growth and formation of interfacial misfit array for tensile GaAs on GaSb,” Applied Physics Letters, vol. 90, no. 16, 2007. View at Google Scholar · View at Scopus
  15. J. Tatebayashi, A. Khoshakhlagh, S. H. Huang et al., “Lasing characteristics of GaSbGaAs self-assembled quantum dots embedded in an InGaAs quantum well,” Applied Physics Letters, vol. 90, no. 26, 2007. View at Google Scholar · View at Scopus
  16. T. H. Loeber, D. Hoffmann, and H. Fouckhardt, “Dense lying self-organized gaassb quantum dots on GaAs for efficient lasers,” Beilstein Journal of Nanotechnology, vol. 2, no. 1, pp. 333–338, 2011. View at Publisher · View at Google Scholar · View at Scopus
  17. T. H. Loeber, D. Hoffmann, and H. Fouckhardt, “Dense lying GaSb quantum dots on GaAs by Stranski-Krastanov growth,” in Proceedings of the Quantum Dots and Nanostructures: Synthesis, Characterization, and Modeling VIII, USA, January 2011. View at Scopus
  18. T. H. Loeber, J. Richter, J. Strassner, C. Heisel, C. Kimmle, and H. Fouckhardt, “Efficient Ga(As)Sb quantum dot emission in AlGaAs by GaAs intermediate layer,” in Proceedings of the Quantum Dots and Nanostructures: Synthesis, Characterization, and Modeling X, USA, February 2013. View at Scopus
  19. T. H. Loeber, E. A. Hein, D. Hoffmann, C. Heisel, and H. Fouckhardt, “Generation of dense lying Ga(As)Sb quantum dots for efficient quantum dot lasers,” Advanced Materials Research, vol. 684, pp. 285–289, 2013. View at Publisher · View at Google Scholar · View at Scopus
  20. J. Strassner, J. Richter, Th. H. Loeber, and H. Fouckhardt, “Growth control of Ga(As)Sb quantum dots (QD) on GaAs with reflectance anisotropy spectroscopy (RAS),” in Proceedings SPIE 9288, 92880F-1 – 92880F-8.
  21. E. Steimetz, J.-T. Zettler, F. Schienle et al., “In situ monitoring of InAs-on-GaAs quantum dot formation in MOVPE by reflectance-anisotropy-spectroscopy and ellipsometry,” Applied Surface Science, vol. 107, pp. 203–211, 1996. View at Publisher · View at Google Scholar · View at Scopus
  22. E. Steimetz, F. Schienle, J.-T. Zettler, and W. Richter, “Stranski-Krastanov formation of InAs quantum dots monitored during growth by reflectance anisotropy spectroscopy and spectroscopic ellipsometry,” Journal of Crystal Growth, vol. 170, no. 1-4, pp. 208–214, 1997. View at Publisher · View at Google Scholar · View at Scopus
  23. U. W. Pohl, K. Pötschke, I. Kaiander, J.-T. Zettler, and D. Bimberg, “Real-time control of quantum dot laser growth using reflectance anisotropy spectroscopy,” Journal of Crystal Growth, vol. 272, no. 1-4, pp. 143–147, 2004. View at Publisher · View at Google Scholar · View at Scopus
  24. A. Hospodková, J. Vyskočil, J. Pangrác, J. Oswald, E. Hulicius, and K. Kuldová, “Surface processes during growth of InAs/GaAs quantum dot structures monitored by reflectance anisotropy spectroscopy,” Surface Science, vol. 604, no. 3-4, pp. 318–321, 2010. View at Publisher · View at Google Scholar · View at Scopus
  25. K. Möller, Z. Kollonitsch, C. Giesen, M. Heuken, F. Willig, and T. Hannappel, “Optical in situ monitoring of MOVPE GaSb(1 0 0) film growth,” Journal of Crystal Growth, vol. 248, pp. 244–248, 2003. View at Publisher · View at Google Scholar · View at Scopus
  26. O. J. Pitts, S. P. Watkins, and C. X. Wang, “RDS characterization of GaAsSb and GaSb grown by MOVPE,” Journal of Crystal Growth, vol. 248, pp. 249–253, 2003. View at Publisher · View at Google Scholar · View at Scopus
  27. L. Müller-Kirsch, R. Heitz, U. W. Pohl et al., “Temporal evolution of GaSb/GaAs quantum dot formation,” Applied Physics Letters, vol. 79, no. 7, pp. 1027–1029, 2001. View at Publisher · View at Google Scholar · View at Scopus
  28. C.-K. Sun, G. Wang, J. E. Bowers et al., “Optical investigations of the dynamic behavior of GaSb/GaAs quantum dots,” Applied Physics Letters, vol. 68, no. 11, pp. 1543–1545, 1996. View at Publisher · View at Google Scholar · View at Scopus
  29. E. R. Glaser, B. R. Bennett, B. V. Shanabrook, and R. Magno, “Photoluminescence studies of self-assembled InSb, GaSb, and AlSb quantum dot heterostructures,” Applied Physics Letters, vol. 68, no. 25, pp. 3614–3616, 1996. View at Publisher · View at Google Scholar · View at Scopus
  30. R. A. Hogg, K. Suzuki, K. Tachibana, L. Finger, K. Hirakawa, and Y. Arakawa, “Optical spectroscopy of self-assembled type II GaSb/GaAs quantum dot structures grown by molecular beam epitaxy,” Applied Physics Letters, vol. 72, no. 22, pp. 2856–2858, 1998. View at Publisher · View at Google Scholar · View at Scopus
  31. R. Timm, H. Eisele, A. Lenz et al., “Structure and intermixing of GaSb/GaAs quantum dots,” Applied Physics Letters, vol. 85, no. 24, pp. 5890–5892, 2004. View at Publisher · View at Google Scholar · View at Scopus
  32. K. Kudo, Y. Makita, I. Takayasu et al., “Photoluminescence spectra of undoped GaAs grown by molecular-beam epitaxy at very high and low substrate temperatures,” Journal of Applied Physics, vol. 59, no. 3, pp. 888–891, 1986. View at Publisher · View at Google Scholar · View at Scopus
  33. D. E. Aspnes, “Above-bandgap optical anisotropies in cubic semiconductors: A visible–near ultraviolet probe of surfaces,” Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, vol. 3, no. 5, p. 1498. View at Publisher · View at Google Scholar
  34. D. E. Aspnes, J. P. Harbison, A. A. Studna, and L. T. Florez, “Optical reflectance and electron diffraction studies of molecular-beam-epitaxy growth transients on GaAs(001),” Physical Review Letters, vol. 59, no. 15, pp. 1687–1690, 1987. View at Publisher · View at Google Scholar · View at Scopus
  35. D. E. Aspnes, J. P. Harbison, A. A. Studna, and L. T. Florez, “Application of reflectance difference spectroscopy to molecular-beam epitaxy growth of GaAs and AlAs,” Journal of Vacuum Science & Technology A, vol. 6, no. 3, pp. 1327–1332, 1988. View at Publisher · View at Google Scholar · View at Scopus
  36. J. P. Harbison, D. E. Aspnes, A. A. Studna, and L. T. Florez, “Optical reflectance measurements of transients during molecular-beam epitaxial growth on (001) GaAs,” Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, vol. 6, no. 2, pp. 740–742, 1988. View at Publisher · View at Google Scholar
  37. J. P. Harbison, D. E. Aspnes, A. A. Studna, L. T. Florez, and M. K. Kelly, “Oscillations in the optical response of (001)GaAs and AlGaAs surfaces during crystal growth by molecular beam epitaxy,” Applied Physics Letters, vol. 52, no. 24, pp. 2046–2048, 1988. View at Publisher · View at Google Scholar · View at Scopus
  38. D. E. Aspnes, E. Colas, A. A. Studna, R. Bhat, M. A. Koza, and V. G. Keramidas, “Kinetic limits of monolayer growth on (001) gaas by organometallic chemical-vapor deposition,” Physical Review Letters, vol. 61, no. 24, pp. 2782–2785, 1988. View at Publisher · View at Google Scholar · View at Scopus
  39. S. M. Koch, O. Acher, F. Omnes, M. Defour, M. Razeghi, and B. Drévillon, “In situ investigation of InAs metalorganic chemical vapor deposition growth using reflectance anisotropy,” Journal of Applied Physics, vol. 68, no. 7, pp. 3364–3369, 1990. View at Publisher · View at Google Scholar · View at Scopus
  40. R. W. Collins, “Automatic rotating element ellipsometers: Calibration, operation, and real-time applications,” Review of Scientific Instruments, vol. 61, no. 8, pp. 2029–2062, 1990. View at Publisher · View at Google Scholar · View at Scopus
  41. D. E. Aspnes, R. Bhat, C. Caneau et al., “Optically monitoring and controlling epitaxial growth,” Journal of Crystal Growth, vol. 120, no. 1-4, pp. 71–77, 1992. View at Publisher · View at Google Scholar · View at Scopus
  42. D. E. Aspnes, “Real-time optical diagnostics for epitaxial growth,” Surface Science, vol. 307-309, pp. 1017–1027, 1994. View at Publisher · View at Google Scholar · View at Scopus
  43. D. E. Aspnes, “Real-time optical analysis and control of semiconductor epitaxy: Progress and opportunity,” Solid State Communications, vol. 101, no. 2, pp. 85–92, 1997. View at Publisher · View at Google Scholar · View at Scopus
  44. D. E. Aspnes and N. Dietz, “Optical approaches for controlling epitaxial growth,” Applied Surface Science, vol. 130-132, pp. 367–376, 1998. View at Publisher · View at Google Scholar · View at Scopus
  45. J.-T. Zettler, K. Haberland, M. Zorn et al., “Real-time monitoring of MOVPE device growth by reflectance anisotropy spectroscopy and related optical techniques,” Journal of Crystal Growth, vol. 195, no. 1-4, pp. 151–162, 1998. View at Publisher · View at Google Scholar · View at Scopus
  46. K. Haberland, O. Hunderi, M. Pristovsek, J.-T. Zettler, and W. Richter, “Ellipsometric and reflectance-anisotropy measurements on rotating samples,” Thin Solid Films, vol. 313-314, pp. 620–624, 1998. View at Publisher · View at Google Scholar · View at Scopus
  47. S. R. Armstrong, M. E. Pemble, A. G. Taylor et al., “Laser-surface diagnostics of GaAs growth processes II. Reflectance anisotropy studies of GaAs growth by MBE,” Applied Surface Science, vol. 54, no. C, pp. 493–496, 1992. View at Publisher · View at Google Scholar · View at Scopus
  48. N. Esser, M. Köpp, P. Haier, and W. Richter, “Optical characterization of surface electronic and vibrational properties of epitaxial antimony monolayers on III–V (110) surfaces,” Physica Status Solidi (a) – Applications and Materials Science, vol. 152, no. 1, pp. 191–200, 1995. View at Publisher · View at Google Scholar
  49. M. Wassermeier, J. Behrend, J.-T. Zettler, K. Stahrenberg, and K. H. Ploog, “In-situ spectroscopic ellipsometry and reflectance difference spectroscopy of GaAs(001) surface reconstructions,” Applied Surface Science, vol. 107, pp. 48–52, 1996. View at Publisher · View at Google Scholar · View at Scopus
  50. Z. Sobiesierski, D. I. Westwood, and C. C. Matthai, “Aspects of reflectance anisotropy spectroscopy from semiconductor surfaces,” Journal of Physics: Condensed Matter, vol. 10, no. 1, pp. 1–43, 1998. View at Publisher · View at Google Scholar · View at Scopus
  51. A. I. Shkrebtii, N. Esser, W. Richter et al., “Reflectance anisotropy of GaAs(100): Theory and experiment,” Physical Review Letters, vol. 81, no. 3, pp. 721–724, 1998. View at Publisher · View at Google Scholar · View at Scopus
  52. D. I. Westwood, Z. Sobiesierski, E. Steimetz, T. Zettler, and W. Richter, “On the development of InAs on GaAs(001) as measured by reflectance anisotropy spectroscopy: Continuous and islanded films,” Applied Surface Science, vol. 123-124, pp. 347–351, 1998. View at Publisher · View at Google Scholar · View at Scopus
  53. C. I. Medel-Ruiz, A. Lastras-Martínez, R. E. Balderas-Navarro et al., “In situ monitoring of the 2D-3D growth-mode transition in In 0.3Ga0.7As/GaAs (0 0 1) by reflectance-difference spectroscopy,” Applied Surface Science, vol. 221, no. 1-4, pp. 48–52, 2004. View at Publisher · View at Google Scholar · View at Scopus
  54. J. H. Strassner, Epitaktisches Wachstum und optoelektronische Eigenschaften von Ga(As)Sb-Quantenpunkten auf (Al)GaAs bei Variation der Barrieren [Ph.D. thesis], Physics Department Technische Universität Kaiserslautern (TUK) (2016) and Verlag Dr. Hut, 2016.
  55. J. Richter, Optimierte Überwachung des Wachstums von Antimonid-Quantenpunkten und Quantenpunktumgebungen mit Hilfe von Reflektivitätsanisotropie-Spektroskopie [Ph.D. thesis], Physics Department Technische Universität Kaiserslautern (TUK) (2014) and Verlag Dr. Hut, 2015.