ISSN 1063-7397, Russian Microelectronics, 2006, Vol. 35, No. 5, pp. 322–328. © Pleiades Publishing, Inc., 2006.
Original Russian Text © E.V. Kiseleva, S.V. Obolenskii, 2006, published in Mikroelektronika, 2006, Vol. 35, No. 5, pp. 374–381.
Point defects produced by neutron irradiation of
semiconductors are known to form clusters as a result
of the cascaded nature of atomic displacements initi-
ated by neutron impact [1, 2]. Each cluster consists of
one or more subclusters, i.e., dense aggregations of sec-
ondary displaced atoms [2–4]. In GaAs, defect clusters
generated by 1.5-MeV neutrons typically contain two
to ten stable subclusters about 10 nm in diameter, which
may overlap. Defect subclusters have individual space-
charge regions; these scatter hot electrons and combine
to impede the motion of cold electrons, with the elec-
tron energy measured relative to the thermal energy .
These phenomena may have serious implications
for microelectronics. With the current trend toward
smaller devices, some dimensions of active regions
should ultimately become comparable with intercluster
spacing and cluster size (
50 nm for GaAs).
Obolenskii  included the passage of high-energy
electrons through individual clusters in his computer
simulation of carrier transport in submicrometer
devices. However, the underlying assumption of sub-
clusters being equal in size and uniformly spatially dis-
tributed is inadequate when active regions approach
intercluster gaps and clusters themselves in size 
and/or when the neutron irradiation is of low ﬂuence.
In that situation the inﬂuence of clusters on electron
transport will be determined by the size distributions of
subclusters and intersubcluster gaps, not by the mean
It is also important to note that neutron-induced
defect clusters differ signiﬁcantly in structure depend-
ing on whether they are located near an interface or in
the bulk as a result of the difference in the properties
(atomic mass, density, and neutron interaction cross
section) of the material itself. Both stronger and weaker
radiation effects are possible in the vicinity of an inter-
face as compared with the bulk material [1, 5]. This
variation is important because it occurs on a scale com-
parable with the size of active device regions.
Thus, the structure of radiation-induced defect clus-
ters should be treated as part of the device structure
when studying neutron-irradiation effects on carrier
2. MAIN CONSIDERATIONS
This paper presents a computer simulation of elec-
tron transport to investigate the structure of neutron-
induced defect clusters in the active region of a GaAs
metal–semiconductor ﬁeld-effect transistor (MESFET).
The device structure is shown schematically in Fig. 1.
Of particular relevance to defect-cluster formation is
the gate electrode being made of a heavy metal, gold.
The simulation essentially follows a novel, inte-
grated approach that addresses the formation of radia-
tion-induced defects and their distribution over a clus-
ter in the active region.
A computer simulation of channel electron transport
as affected by radiation requires knowledge of the scat-
tering characteristics of radiation-induced entities in
the semiconductor. Scattering from radiation-induced
point defects can be included in the same manner as
that from point defects in an unirradiated material [5, 7, 8].
As already mentioned, neutron-induced defect subclus-
ters scatter hot electrons and combine to impede the
motion of cold electrons. A neutron-induced scatterer
in GaAs constitutes a potential barrier about 0.7 eV
high, and its electron scattering cross section is given
, where is the effective radius of theR
Structure of Neutron-Induced Defect
Clusters in GaAs MESFETs
E. V. Kiseleva and S. V. Obolenskii
Nizhni Novgorod State University, Nizhni Novgorod, Russia
Received July 7, 2005
—A method is proposed for the structural investigation of defect clusters produced by neutron irradi-
ation of semiconductors. It involves simulation of defect formation and analysis of the distribution of point
defects within individual clusters. The method enables one to characterize point-defect aggregations in a cluster
in terms of size, separation, and arrangement. It could be applied to advanced devices based on a nanoscale het-
PACS numbers: 85.30.Tv
ON ADVANCED GaAs DEVICES