Aqueous synthesis of III–V semiconductor GaP and InP exhibiting
pronounced quantum confinement†
Shanmin Gao, Jun Lu, Nan Chen, Yan Zhao and Yi Xie*
Structure Research Laboratory and Department of Chemistry, University of Science and Technology of
China, Hefei, Anhui 230026, P. R.. China. E-mail: yxielab@ustc.edu.cn
Received (in Cambridge, UK) 16th October 2002, Accepted 4th November 2002
First published as an Advance Article on the web 20th November 2002
A mild aqueous synthesis route was successfully established
to synthesize well crystallized and monodisperse GaP and
InP nanocrystals, which were proved to exhibit pronounced
quantum confinement by room-temperature UV/Vis adsorp-
tion and photoluminescence (PL) spectra.
Group III–V nanocrystalline semiconductors have received
much attention due to their usefulness in high-speed digital
circuits, microwave devices, and optoelectronics. Compared to
I–VII and II–VI semiconductors, III–V materials have a greater
degree of covalent bonding, a less ionic lattice, and larger
exciton diameters. For this reason, quantum size effects on the
Scheme 1 Schematic growth path of nanocrystalline GaP; (II)–(VI)
represent the corresponding reactions in the text.
optical spectra have been predicted to be more pronounced in
the III–V class of materials than in II–VI materials.1
Several routes to III–V compound semiconductors have
about 12%. In order to improve the yield of GaP, we added
iodine to induce the dismutation of white phosphorus, based on
reaction (IV).
2
emerged in the last decade, including dehalosilylation and
related reactions,3 a metathesis reaction, pyrolysis of single-
,4
5,6
source precursors that incorporate the elements of a compound
7
8,9
P + 2I + 4OH
2
+ 4H O ?2PH + 2H PO + 4I
2
(IV)
in a single molecule, and chemical vapor deposition. These
4
2
2
3
3
4
methods are very mild in comparison with conventional solid-
The addition of iodine, on one hand, accelerated the rate of
white phosphorus dismutation, and on the other, induced
state reaction (usually above 1000 °C),1
0,11
but they still require
a relatively high processing temperature or post-treatment
temperature (200–500 °C) to obtain well-crystallized products.
Recently, there have been considerable efforts to explore new
solution routes to III–V semiconductors, with the goals of
searching for mild preparation conditions,12 for instance,
decreasing processing temperature, avoiding complex reactions
and toxic precursors. However, up to now, it has been very
challenging to prepare III–V semiconductors in aqueous
another circular reaction between H
known that H PO can be immediately reduced to H
white phosphorus based on reaction (V), while H
unstable and decomposes to PH and H PO
regenerated H PO reacting with white phosphorus again, so
that reactions (V) and (VI) occur in a cycle:
3 4 3 3
PO and H PO . It is well
3
4
3
PO
PO
3
by
is
3
3
3
3
4
, with the
3
4
P
4
+ 6H PO + 6H O ? 10H
PO ? PH + 3H PO
Thus, the amount of PH
III) progresses continually until one of the raw materials runs
3
4
2
3
PO
3
(V)
solutions, mainly due to the strong hydrolysis of GaX
3
, InX
3
(X
(VI)
4
H
3
3
3
3
4
=
Cl, Br, I) and their corresponding organometallic com-
3
is significantly improved. Reaction
pounds. More important, from the green chemistry point of
view, water is the ideal media for the solution route to III–V
semiconductors, which has been driving us to explore the
possibility of preparing III–V semiconductors in aqueous
solution under mild conditions.
Herein, we present the first aqueous preparation of high-
yield, relatively monodisperse, well crystallized GaP and InP
nanocrystallites, exhibiting pronounced quantum confinement.
The reaction is carried out in an aqueous solution at 120–160 °C
(
out. As a result, the yield of GaP reached above 90% after the
addition of iodine to the system. For circulation to be most
efficient white phosphorus should be present in excess in the
experiment.
XRD patterns as shown in Fig. 1 can be indexed to the zinc
blende structure of GaP (Fig. 1A) with a = 5.48 Å and InP (Fig.
1
B) with a = 5.89 Å. Average crystallite sizes estimated by the
Scherrer equation are about 5 nm for GaP and 8 nm for InP.
and involves the transportation of phosphorus by I
2
and a
13
3 4 3 3
circulation between H PO and H PO .
The whole process
can be formulated as Scheme 1, taking GaP as the example.
Initially, our research revealed that in fact little GaP and InP
could be obtained in an alkali solution, taking advantage of the
2
reaction of Ga(OH)
4
3
with PH which was produced from
white phosphorus dismutation in alkali solutions.
+ 3OH2 + 3H
Ga
+ 2OH2 + 3H
Ga(OH)
2
2 2
PO
(I)
(II)
P
4
2
O ? PH
3
+ 3H
2
2
O
3
2
O ? 2Ga(OH)
4
2
O + OH2
? GaP + 3H
2
(III)
4
+ PH
3
However, the rate of white phosphorus dismutation in alkali
solutions is very slow, and thus, the amount of PH is too small.
Our experiment shows the yield of GaP in alkali solution is only
3
†
Electronic supplementary information (ESI) available: experimental
Fig. 1 The X-ray powder diffraction (XRD) patterns of the as-prepared
details. See http://www.rsc.org/suppdata/cc/b2/b210164e/
products, (A) for GaP nanocrystals and (B) for InP nanocrystals.
3
064
CHEM. COMMUN., 2002, 3064–3065
This journal is © The Royal Society of Chemistry 2002
Gao, Shanmin
