Series in Quantum Electronics
edited by
Henry Baltes, Peter Günter, Ursula Keller,
Fritz K. Kneubühl †, Walter Lukosz,
Hans Melchior, Markus W. Sigrist
Vol. 43
Valeria Liverini
From Passive to Active Devices:
GaInNAs as Absorber and Emitter for
1.3 μm Lasers
1st edition 2007.
XXII, 128 pages; € 64,00. ISBN 3-86628-159-5
This thesis deals with the development of GaInNAs as
the absorber for semiconductor saturable absorber mirrors (SESAMs) and as the
gain medium for vertical external-cavity surface-emitting lasers (VECSELs). The
use of this quaternary alloy allows the development of such devices in the interesting
near-infrared wavelength region of 1.3 μm, where cost-effective pulsed laser sources are
needed for telecommunication applications, optical clocking of future
generation processors and other applications such as laser displays and laser
sources for biomedical use. The growth of GaInNAs was carried out by molecular
beam epitaxy. The material worked very well as-grown and with mild post-growth
annealing as a saturable absorber in SESAMs. Using these SESAMs, we achieved
modelocking in the megahertz repetition rate region of Nd:YLF and Nd:YVO4
lasers, while the repetition rate was pushed up to 10 GHz with close to
transform-limited pulses for the Nd:YVO4 laser. Careful optimizations of both
the growth and post-growth annealing conditions were necessary to improve the
GaInNAs PL efficiency to obtain material quality adequate for lasing. By
studying the GaInNAs annealing-induced blueshift of the bandgap energy and its
PL efficiency improvement, we could correlate these effects with nitrogen
concentration and with the annealing parameters of time and temperature. We
discovered that the nitrogen content in GaInNAs influences the total amount of
blueshift but does not affect the improvement of the PL efficiency. GaInNAs
quantum wells optimized for the gain region of the VECSELs were grown at a lower
temperature than the ones used for the SESAMs and annealed in-situ at high
temperature for a short time and at lower temperatures for a longer time. Finally,
we developed GaInNAs VECSELs to obtain 1.3 μm lasers with sizes even more compact than the
solid-state lasers presented above. We demonstrated optically pumped continuous
wave (cw) VECSELs with output powers as high as 607 mW and an
optical-to-optical efficiency of 10%, results comparable to the
state-of-the-art. By using a GaInNAs SESAM in the external cavity of these
VECSELs, we obtained for the first time self-starting cw modelocking of a 1.3 μm VECSEL. The average output power of the modelocked VECSEL
was 57 mW in 18.7 ps pulses at a repetition rate of 6.1 GHz. Both the cw and
modelocked lasers had close to diffraction-limited beam qualities
Valeria Liverini received her Bachelor of Science in Physics at the
University of Texas, Austin in 1999 and her Master of Science in Electrical
Engineering – Photonics at the University of California, San Diego in 2002. She
joined the Institute of Quantum Electronics at the Swiss Federal Institute of
Technology in Zurich (ETHZ) in 2003. Her research focused on the development by
molecular beam epitaxy of GaInNAs semiconductor saturable absorber mirrors and vertical
external-cavity surface-emitting lasers. Her work also included material and
optical characterization of these devices and their design and testing.
Keywords: GaInNAs, dilute
nitrides, molecular beam epitaxy (MBE), vertical external-cavity
surface-emitting lasers (VECSELs), semiconductor saturable absorber mirrors
(SESAMs), modelocking
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