Study of ultrafast polarization and carrier dynamics in semiconductor nanostructures [Elektronische Ressource] : a THz spectroscopy approach / vorgelegt von Dmitry Turchinovich

Sujets

• Physik

Informations

• Publié par: albert-ludwigs-universitat_freiburg
• Publié le: 01 janvier 2004
• Nombre de lectures: 10
• Langue: English
• Poids de l'ouvrage: 4 Mo

Extrait

Study of Ultrafast Polarization
and Carrier Dynamics in
Semiconductor Nanostructures:
a THz Spectroscopy Approach
Inaugural-Dissertation
zur
Erlangung des Doktorgrades
der Fakult¨ at fur¨ Mathematik und Physik
der Albert-Ludwigs-Universit¨at
Freiburg im Breisgau
vorgelegt von
Dmitry Turchinovich
aus St.Petersburg
im Mai 2004Dekan: Prof. Dr. Rolf Schneider
Leiter der Arbeit: HD Dr. Peter Uhd Jepsen
Referent: HD Dr. Peter Uhd Jepsen
Korreferent: Prof. Dr. Hellmut Haberland
Tag der Verkundig¨ ung
des Prufung¨ sergebnisses: 01.07.2004
2Publications in Refereed Journals
Part of the work presented in this thesis is based on the following pub-
lications in refereed journals:
• D.Turchinovich, A.Kammoun, P.Knobloch, T.Dobbertin, and M.Koch
”Flexible all-plastic mirrors for the THz range”
Appl. Phys. A 74, 291 (2002)
• D.Turchinovich, K.Pierz, and P.Uhd Jepsen
”InAs/GaAs quantum dots as efficient free carrier deep traps”
phys. stat. sol. (c) 0, 1556 (2003)
• D.Turchinovich, P.Uhd Jepsen, B.S.Monozon, M.Koch, S.Lahmann, U.Rossow,
and A.Hangleiter
”Ultrafast polarization dynamics in biased quantum wells under strong fem-
tosecond optical excitation”
Phys. Rev. B 68, 241307(R) (2003)
• D.Turchinovich, B.S.Monozon, M.Koch, S.Lahmann, A.Hangleiter, and P.Uhd
Jepsen
”Ultrafast polarization dynamics in optically excited biased quantum wells”
Proceedings of SPIE 5354, 151 (2004)
• D.Turchinovich, P.Uhd Jepsen, and B.S.Monozon
”Biased semiconductor quantum wells under ultrafast optical excitation:
theoretical model of dynamical screening”
submitted to Phys. Rev. B (2004)
Publications not included in this thesis:
• D.Turchinovich, P.Knobloch, G.Luessem, and M.Koch
”THz time-domain spectroscopy on 4-(trans-4-pentylcyclohexyl)-benzonitril”
Proceedings of SPIE 4463, 65 (2001)
Patents:
• T.Dobbertin, P.Knobloch, D.Turchinovich, and M.Koch
Patent DE 100 33 259 A1 Optisches Bauelement (Plastic dielectric mirrors
for THz frequency range) (2002)
34Preface
Most of the results presented in this Thesis were obtained at the Department
of Molecular and Optical Physics, University of Freiburg, in the group of
HD Dr. Peter Uhd Jepsen.
The results presented in the Section 2.4 of the Chapter 2 of this Thesis were
obtained during the author’s stay at the Institut fur¨ Hochfrequenztechnik,
Technical University of Braunschweig, in the group of Prof. Dr. Martin
Koch.
5Preface
6Contents
Introduction 9
1 Principles of generation and detection of electromagnetic tran-
sients in nonlinear crystals. 15
1.1 Maxwell’s equations. Wave equation and its solution in the far field. 16
1.2 Linear and nonlinear contributions to polarization. . . . . . . . . . 18
1.3 Optical rectification and second harmonic generation. . . . . . . . . 20
1.4 Linear electrooptic effect and phase retardation. . . . . . . . . . . . 21
1.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2 Terahertz time-domain spectroscopy.
Design and characterization of the experimental setup. 27
2.1 Experimental THz-TDS setup driven by a femtosecond amplifier. . 28
2.1.1 Femtosecond Ti:Sapphire amplifier system. . . . . . . . . . . 28
2.1.2 THz spectrometer based on ZnTe generation and detection
crystals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.2 Propagation of an electromagnetic wave packet through the medium.
THz spectral analysis. . . . . . . . . . . . . . . . . . . . . . . . . . 40
2.3 Simulation of the experimental THz pulses. Phase matching and
absorption considerations. . . . . . . . . . . . . . . . . . . . . . . . 46
2.4 Plastic dielectric mirrors designed for the THz range. . . . . . . . . 51
2.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3 Ultrafast polarization dynamics in the biased semiconductor quan-
tum wells under ultrafast optical excitation.
Dynamical screening effect. 61
3.1 Optical transitions in a biased quantum well. Quantum-confined
Stark effect. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.2 Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.3 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.3.1 THz emission spectroscopy. . . . . . . . . . . . . . . . . . . 68
3.3.2 Time-integrated photoluminescence spectroscopy. . . . . . . 72
3.4 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
7Contents
3.4.1 Model of dynamical screening . . . . . . . . . . . . . . . . . 74
3.4.2 Theoretical results and discussion . . . . . . . . . . . . . . . 76
3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
4 Trapping of the free carriers in InAs/GaAs quantum dot struc-
tures. 91
4.1 Contribution of the free carriers into the dielectric function. Drude
conductivity model. . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.2 Samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.3 Experiment and discussion. . . . . . . . . . . . . . . . . . . . . . . 99
4.4 Extraction of the spectral information. . . . . . . . . . . . . . . . . 108
4.5 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Bibliography 113
Acknowledgements 119
8Introduction
Ultrafast carrier and polarization dynamics in semiconductors is one of the most
exciting areas in modern physics.
Contemporary electronics and optoelectronics is nearly entirely based on the ad-
vanced semiconductor technology. Since in our information-oriented society there
is an ever-growing demand for the higher bandwidth in the telecom systems and
for the higher clock rate in the computers, the ultrafast phenomena in semiconduc-
tors start to play a crucial role in the development of new devices. In the modern
telecommunications systems the information is already transferred through the op-
tical fibers at the terabit/s rate (although not yet using a single laser source), and
the computers are operating at the several gigahertz clock rate.
From the point of view of the fundamental physics, experimental and theoret-
ical investigations of the processes occurring on the femtosecond and picosecond
timescale are also of a great interest, since it allows us to understand the mech-
anisms of such extremely important processes as the transport in strong fields,
relaxation, recombination and trapping of the charge carriers, formation of the
excitons, modification of the semiconductor band structure due to the optical ex-
citation and many others.
The ultrafast phenomena in semiconductors is a booming research area for
already two decades, since the femtosecond lasers came into the market. The
experimental techniques such as degenerate and non-degenerate pump-probe ex-
periments, four-wave mixing, time-resolved photoluminescence and many others
are widely used by the semiconductor research community.
In the recent decade the terahertz (THz) spectroscopy began to play an ever-
increasing role in the experiments. The frequency of 1 THz corresponds to one
oscillation per picosecond. In the equivalent units 1 THz is:
−1 −11 THz≡ 1 ps ≡ 4.1 meV≡ 0.3 mm≡ 33 cm ≡ 47.6 K
The THz range is thus bridging the gap between the microwave and the infrared
ranges, and is sometimes referred to as far-infrared. One should notice here that the
low THz range lies below the room-temperature background of 26 meV = 6.3 THz.
The lack of efficient emitters and detectors in the THz frequency range was the
main problem for the experimentalists in the past. The main workhorses in the
9Introduction
millimeter and submillimeter wave spectroscopy were the continuous-wave sources
such as backward-wave oscillators (BWO) [1] or sum-frequency mixed Schottky
and Gunn diodes (see e.g. [2] and [3]) used as the emitters, and helium-cooled
bolometers used as the detectors. In this case the useful spectroscopy bandwidth
typically covered the range between 0.01 and 1.5 THz, and no time-resolved ex-
periments were possible.
Another approach to generate THz radiation is a quantum-cascade laser (QCL),
first proposed by R.F.Kazarinov and R.A.Suris back in 1971 [4]. For the THz
generation the QCL employs the intraband transitions in a biased doped semicon-
ductor heterostructure. The first operating device was demonstrated however only
in 1994 by J.Faist and coworkers [5], and despite the impressive progress in the
QCL development achieved ever since, these devices are not yet able to operate at
a room temperature.
Also in 1971 a completely new approach to generate the ultrashort electromag-
netic transients was proposed by the group of Y.R.Shen: optical rectification of
strong picosecond laser pulses in the nonlinear crystals [36]. They demonstrated
the THz emission in the range 0.05− 0.5 THz. This approach is based on the
fundamental nonlinear optical effect and it does not require cooling of the THz
generation crystal, although in this first demonstration the helium-cooled bolome-
ter was again used as a detector. The optical rectification effect will be discussed
in detail in this Thesis and will be widely employed in the experiments presented
here.
In the 1980s the group of D.H.Auston at Bell Laboratories pioneered yet an-
other approach to ge