Chemistry Reference
In-Depth Information
CHAPTER
27
Gallium and Semiconductor Compounds
BRUCE A. FOWLER AND MARY J. SEXTON
ABSTRACT
2 METHODS AND PROBLEMS
OF ANALYSIS
Gallium is a member of Group III of the Periodic
Table of Elements, and new uses have been found for
different chemical forms of this metal over the past
two decades in the fi elds of semiconductor materials,
lasers, cancer and malaria chemotherapy, and dental
materials. The production of gallium for these uses
has increased greatly during this period. Analytical
methods for gallium include atomic absorption/emis-
sion spectrometry, X-ray fl uorescence, and, more
recently, inductively coupled plasma spectrometry. The
main health concerns for gallium have been centered
on workers in the semiconductor industry engaged in
production of gallium arsenide-based devices. Gallium
is transported in the circulation bound to transferrin,
and competition with iron for transferrin binding seems
to be one mechanism by which it may act as an anticancer
agent. Toxicity studies in experimental animal systems
have shown gallium nitrate and gallium arsenide to
produce toxicity to the lungs, immune system, kidneys,
and hematopoietic systems. The International Agency for
Research on Cancer (IARC) has classifi ed gallium arsenide
as a human carcinogen. Studies of semiconductor workers
are limited, but clinical trials in humans treated with gal-
lium nitrate for various cancers have demonstrated renal
toxicity as the primary side effect.
Atomic emission spectroscopy, X-ray fl uorescence,
ICP (inductively coupled plasma) with an LOD (limit of
detection) of .03
g/mL electrothermal atomic absorp-
tion spectrometry has been reported to provide a
detection limit of 0.08
µ
g/cm
3
after preconcentration
by precipitation with synthetic zeolites (Minamisawa
et al
., 2004). Cathodic adsorptive voltammetry with
a gallium-alizarin red S complex has been reported
to provide a detection limit of 0.01
µ
g/L (Li
et al
.,
2004). Spectrophotometric determination of gallium
as thiocarbohydrazone derivatives has been reported
(Lucena
et al
., 1994) to provide limits of detection in the
5-8 ng/mL range.
µ
3 PRODUCTION AND USES
World production of gallium has risen steadily in the
past two decades to reach a peak in 1998 of 93.3 metric
tons with a recent decline to 61 metric tons in 2002
(USGS, 2004). The recent decline may be a refl ection of
the increasing use of indium compounds in the III-V
semiconductor industry (see Figure 1).
3.1 Uses
Gallium has a number of uses, most notably in the
semiconductor industry as a dopant material for silicon
computer chips and in the formation of III-V semi-
conductors such as gallium arsenide (GaAs) (Fowler
and Sexton, 2002; Jenkins
et al
., 1994; Pan
et al
., 2003).
1 PHYSICAL AND CHEMICAL PROPERTIES
Gallium (Ga), atomic number, 31; atomic weight,
69.735; valence states, +2, +3; melting point, 29.78°C;
specifi c gravity, 5.904 at 29.6°C.
