Luminescence of ZnCdSe/ZnSe ridge quantum wires
G. Prechtl, D. Stifter, H. Sitter, and G. Springholz
r Halbleiter- und Festko
t Linz, Altenbergerstraße 69,
A-4040 Linz, Austria
T. Riemann, F. Bertram, D. Rudloff, and J. Christen
r Experimentelle Physik, Universita
t Magdeburg, Universita
tsplatz 2, D-39016 Magdeburg,
G. Bley, U. Neukirch, and J. Gutowski
t Bremen, Kufsteinerstraße, D-28359 Bremen, Germany
2. Physikalisches Institut, RWTH-Aachen, Templergraben 55, D-52056 Aachen, Germany
͑Received 19 April 1999; accepted for publication 22 June 1999͒
Blue light-emitting quantum wire structures fabricated by molecular-beam epitaxial growth on
submicrometer prepatterned GaAs substrates were investigated by spatially and time resolved
luminescence experiments. The quantum wires are formed due to the different growth rates of
ZnCdSe on the ͑111͒ and ͑100͒ surfaces of the grated substrate. With decreasing wire width, the
exciton luminescence splits into two clearly distinguished lines. These lines can be assigned to the
emission of the ridge quantum wire and the emission of ZnCdSe quantum wells at the bottom of the
grooves. The two-dimensional quantum conﬁnement in the ridge wire is conﬁrmed by a maximum
of the decay time at the energy of the ridge luminescence. © 1999 American Institute of Physics.
Quantum wire structures have been investigated
due to their unique optoelectronical properties
caused by the spike-like density of states in one dimension.
Quantum wire lasers, e. g., exhibit much narrower and higher
peak gain values as compared to two-dimensional ͑2D͒
quantum well ͑QW͒ lasers.
Quantum wires are produced
mainly by lithographic techniques.
However, such nano-
structures suffer from damage at the side walls induced by
the etching processes
and their optical properties are often
dominated by strain relaxation processes.
These effects can
be overcome by growth on prepatterned substrates, which
results in the formation of V groove
or ridge quantum
This has been shown for III–V semiconductor com-
pounds emitting in the infrared.
However, recently we
demonstrated lateral conﬁnement effects in wires emitting in
These wires were fabricated by molecular beam
epitaxy ͑MBE͒ of ZnCdSe/ZnSe on prepatterned GaAs sub-
strates. In this work, we analyze these structures by spatially
and time resolved luminescence experiments in dependence
on the wire width.
As substrate a GaAs grating with a period of 800 nm
was used. This consisted of 160-nm-deep trapezoidally
shaped grooves with ͑111͒ and ͑1-1-1͒ oriented side walls,
with unetched ͑100͒ ridges in between. On the grated sub-
strate a 150 nm ZnSe buffer followed by a 5-nm-wide
Se QW and a 120-nm-thick ZnSe cap layer was
grown by MBE. The growth was controlled simultaneously
on an unpatterned reference sample.
ZnSe MBE-growth selectivity is provided by the strong
dependence of the Se sticking probability on the orientation
of the ZnSe surface. On ͑111͒ surfaces the sticking coefﬁ-
cient is 10 times smaller than on ͑100͒ surfaces.
the same orientation dependence for the growth rate on pat-
terned structures and assuming identical growth on the 2D
͑100͒ reference sample the sample cross section can be pre-
dicted. For a GaAs ridge width (W
) of 340 nm the ex-
pected cross section schematically outlined in Fig. 1͑a͒
shows ZnSe ridges with a full width at half maximum of 190
nm. This is in good agreement with the experimental value
of 170 nm derived from atomic force microscope ͑AFM͒
height proﬁles of the ZnSe surface as shown in Fig. 1͑b͒. The
growth of the ZnCdSe QWs on the prepatterned substrates is
Electronic mail: email@example.com
FIG. 1. Cross section of the sample: ͑a͒ shows an in scale sketch for
ϭ340 nm, ͑b͒ is the height proﬁle of the ZnSe surface measured with
atomic force microscopy for substrate ridges with a width of 340 ͑full line͒
and0nm͑dotted line͒, ͑c͒ shows a secondary electron micrograph for
ϭ340 nm, ͑d͒ PL spectrum at Tϭ2 K for W
varying from 0 to 340
nm and for the 2D reference sample.
APPLIED PHYSICS LETTERS VOLUME 75, NUMBER 7 16 AUGUST 1999
9740003-6951/99/75(7)/974/3/$15.00 © 1999 American Institute of Physics