Semiconductor Quantum Structures and Quantum Devices

1. 半導體量子結構與量子元件前瞻性研究(1/3) Semiconductor Quantum Structures and Quantum Devices 總計畫主持人：李建平C.P. Lee 交通大學電子工程系 • 子計劃一:半導體量子結構的成長，物理與元件應用 主持人：李建平C.P. Lee 交通大學電子工程系 • 子計劃二：量子結構之光學特性及量子點雷射之載子及增益動態研究 主持人：孫建文K.W. Sun 東華大學物理系 • 子計畫三：奈米量子元件之製作與高頻及磁傳輸特性研究 主持人：孫允武Y.W. Suen 中興大學物理系

2. Publications from this project: S.D. Lin, H.C. Lee, K.W. Sun and C.P. Lee, Investigation of electron-optical phonon interactions in moderate wide In0.15Ga0.85As/GaAs strained quantum wells, Journal of Luminescence 94-95, 761-766 (2001). B.C. Lee, S.D. Lin, C.P. Lee, H.M. Lee, J.C. Wu, and K.W. Sun, Selective growth of single quantum dots using strain engineering, Applied Physics Letters 80, 326-328 (2002). H.C. Lee, K.W. Sun and C.P. Lee, Structure effects on electron-optical phonon interaction in GaAs/AlxGa1-xAs quantum wells, Journal of Applied Physics 92, 268 (2002). K.W. Sun, J.C. Wu, B.C. Lee and C.P. Lee, Selective growth and photoluminescence studies of InAs quantum dot array on patterned GaAs (001) substrates, Nanotechnology 13, 576-580 (2002) S.D. Lin, H.C. Lee, K.W. Sun and C.P. Lee, Investigation of hot electron-neutral acceptor luminescence in moderate wide In0.15Ga0.85As/GaAs multiple quantum wells, 2001 International Conference on Dynamical Processes in Excited States of Solids, July 1-4, 2001 Lyon, France

3. H.C. Lee, K.W. Sun and C.P. Lee, Dependence of electron-optical phonon interaction on the Al composition in GaAs/AlxGa1-xAs quantum wells, Tenth International Conference on Phonon Scattering in Condensed Matter, August 12-17, 2001 Hanover, USA. H.C. Lee, C.P. Lee and K.W. Sun, Dependence of electron energy loss rate on well width and Al composition in GaAs/AlxGa1-xAs quantum well structures, Tenth International Conference on Phonon Scattering in Condensed Matter, August 12-17, 2001 Hanover, USA B.C. Lee, H.M. Lee, J.C. Wu, Y.P. Chang, K.W. Sun, and C.P. Lee, Molecular beam epitaxial growth and photoluminescence studies of InAs self-organized quantum dots grown on patterned GaAs (001) substrates, pp. 376-380, in “Physics, Chemistry and Application of Nanostructures, Reviews and Short Notes to Nanomeeting 2001”, Published by World Scientific, ISBN 981-0204618-8 S.D. Lin, C.P. Lee, W.H. Hsieh, and Y.W. Suen, Self-assembled GaAs antiwires in In0.53Ga0.47As matrix on (100) InP substrates, Applied Physics Letters 81, 3007 (2002). S.D. Lin and C.P. Lee, Hole Schottky barrier height enhancement and its application to metal-semiconductor-metal photodetector, Journal of Applied Physics 90, 5666 (2001).

4. Y. W. Suen, W. H. Hsieh, L. C. Li, T. C. Wan, C. H. Kuan, S. D. Lin, C. P. Lee, and H. H. Cheng, Using a pulsed phase lock loop to detect high-frequency magnetotransport properties of two-dimensional electron systems, Proceedings of the 15th international conference on High Magnetic Fields in Semiconductor Physics, 5 - 9 August 2002, Clarendon Laboratory, Oxford, UK H.C. Lee, K.W. Sun and C.P. Lee, Investigation of reduced dimensionality on hot carrier relaxation in highly excited GaAs, submitted to Physical Review B (November, 2002). K.W. Sun, C.L. Huang, G.B. Huang and H.C. Lee, Inter- and intra-subband relaxation of hot electrons in GaAs/AlGaAs Quantum wells, submitted to Journal of Physics: Condensed Matter (October, 2002).

5. Summary of major results : • Growth and characterization of of InAs quantum dots • Growth and characterization of quantum rings • Growth and characterization of Quantum wires • Quantum dot infrared detectors • Electron-LO phonon interactions in quantum structures • Inter- and inter-subband scattering in quantum wells • High-frequency magnetotransport properties of 2DES

6. Growth and characterization of of InAs quantum dots In this portion of the project, we have successfully grow InAs QDs inside InGaAs QWs . The luminescence from the dots are pushed toward 1.3m by changing either the In compositions or the well widths of the InGaAs QWs. We also discover that the high growth temperatures of QDs inside the wells also lead to longer emission wavelengths.

7. The emission wavelength moves toward longer wavelengths as the increasing In composition in QWs. The luminescence spectra of QDs grown inside the QWs with different well width.

8. The spectra of photoexcited QDs at room temperature with different excitation power. The photoluminescence spectra of QDs grown at different temperatures.

9. Growth and characterization of quantum rings We have demonstrated the growth of InAs quantum ring using Stranski-Krastanov growth method. A partial capping layer was first deposited on the top of the InAs QDs. After a thermal annealing process, the QDs will transform into ring structures. The AFM image of the InAs quantum rings.

10. Growth and characterization of Quantum wires Our laboratory used self-assembly methods to obtain quantum wire (QWr) and anti quantum wire structures. Moreover, we also demonstrated the correlation and anti-correlation behavior of stacking QWr and anri-QWr structures. The (110) cross-section TEM picture of stacked InAs QWrs in InAlAs matrix lattice matched to InP. The (110) cross-section TEM picture of stacked InAs QWrs in InGaAs matrix lattice matched to InP. AFM picture of GaAs anti-QWr structure on InGaAs matrix.

11. 2.00E+12 25000 // to wires 1.80E+12 1.60E+12 20000 sheet carrier density 1.40E+12 Mobility (parallel to the 1.20E+12 15000 wires) Sheet carrier density Mobility Mobility (perpendicular to 1.00E+12 the wires) 8.00E+11 10000 6.00E+11 4.00E+11 5000 to wires 2.00E+11 0.00E+00 0 10 100 1000 Temperature (K) Orientation Dependent Mobility GaAs wires InGaAs InP

12. Quantum dot infrared detectors InAs/GaAs quantum dot infrared photodetectors were fabricated. Large detection wavelength shift (5 to 15 µm) was demonstrated by changing 40 degrees of the epitaxy temperature. The smaller quantum dots grown at lower temperature generate 15 µm responses. The detectivity of the normal incident 15 µm QDIP at 77K is 3×108cmHz1/2/W. It is the best result reported so far for QDIPs in this wavelength region and comparable to the performance of QWIPs with the same cutoff wavelength. A three-color detector was also demonstrated with quantum dots grown at medium temperature. The three color detection comes from two groups of different sizes of dots within one QD layer. This new type of multicolor detector shows unique temperature tuning behavior that has never been reported before.

13. The responsivity of the QDIP measured at different temperatures and biases.

14. Electron-LO phonon interactions in quantum structures We have found theoretically that the reduced dimensionality from a bulk semiconductor to a quantum well structure has a strong effect on the hot carrier relaxation in highly excited GaAs. Comparisons of Electron energy loss rates in bulk and 2D QWs. Calculated electron energy loss rate as a function of quantum well width.

15. We have calculate the effect of phonon-plasma coupling in the electron energy loss rate in quantum well structures.

16. Inter- and inter-subband scattering in quantum wells We have studied the inter-subband and intra-subband scatterings of hot electrons in quantum wells using the hot electron-neutral acceptor luminescence technique. We have observed direct evidences of the emission of confined optical phonons by hot electrons excited slightly above the n=2 subband in GaAs/Al0.37Ga0.63As quantum wells. Scattering rates of photoexcited electrons via inter- and intra-subband LO phonon emission were calculated based on the dielectric continuum model (DCM). We found that, for wide wells with the given Al composition in our experiments, both the calculated and experimental results suggest that the scatterings of the electrons are dominated by the confined LO phonon mode.

17. Calculated electron-LO phonon scattering rates as a function of well width.

18. High-frequency magnetotransport properties of 2DES We have studied the high-frequency transport properties of a two-dimensional electron system (2DES) by using a type-II phase lock loop (PLL) for pulsed RF signals. A meandering coplanar waveguide (CPW) is patterned on the surface of a substrate, which contains a high-mobility 2DES in a modulation-doped GaAs/AlGaAs heterostructure, and is part of the traveling path for the RF signals in the PLL. The conductivities, both the real and the imaginary parts, of the 2DES will affect the propagation constant of the CPW, which can be detected by a PLL. This measurement system is extremely useful in probing quantum dot systems for which individual contact to each dot is difficult to make.

19. Schematic of a homemade PLL system for microwave signals up to 18 GHz. The most important specification of our system is that the phase resolution is about 0.001 degree even under very low average input power (~-100dBm) and the special designed homodyne amplitude detection scheme also allows us to detect very small microwave adsorption.

20. (a) (b) (a) The pattern of the meandering coplanar waveguide. The dark part is the metal. (b) The amplitude and the frequency deviation Df vs magnetic field B are shown for f0=1.39GHz at T=0.3K. Near the IQH plateau, the amplitude curve shows a relatively flat feature similar to the DC conductivity, while the phase data (Df) exhibit a very different behavior.

21. (a) (b) (a) The amplitude and (b) the frequency deviation Df (phase) vs magnetic fields for several RF frequencies. Each curve is offset for clarity. The amplitude curve shows very flat region at QH plateau region at a lower frequency but becomes curved at a higher frequency. The Df curves show a very strong dependence on the frequency. The horizontal dashed lines give a rough reference for a lossless condition given by the center of the IQH plateau.

22. Equipments and setups A. National Chiao Tung University A near field optical measurement system which is designed for the studies of micro-Ramann and photoluminescence of quantum dots and quantum structures is currently under construction. B. National Dong Hwa University We have completed the construction of a femtosecond Ti:sapphire laser based luminescence up conversion system with the proposal grant and matching funds C. National Chung Hsing University We have set up a high-sensitivity PLL detection system for pulsed signals up to 18GHz.

23. a femtosecond Ti:sapphire laser based luminescence up conversion system