ISSN 10637397, Russian Microelectronics, 2013, Vol. 42, No. 8, pp. 529–531. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © S.V. Tikhov, D.A. Pavlov, N.O. Krivulin, published in Izvestiya Vysshikh Uchebnykh Zavedenii. Materialy Elektronnoi Tekhniki, 2011, No. 4, pp. 29–31.
Silicononsapphire (SOS) layers can be used for
manufacturing complementary fieldeffect transistors
and phototransistors, which are resistant to radiation
. However, the possibility of creating these units is
very largely determined by the properties of the sili
con–sapphire boundary, which are complicated to
control and difficult to measure. This boundary is usu
ally monitored by measuring the quasiequilibrium
strongsignal effect of the field , when a sapphire
substrate is used as an insulator of the field electrode.
However, this method requires applications of high
control voltages for obtaining a minimum point of the
surface conduction (up to 10 kV and higher; only in
this case, can the type of conduction and other char
acteristics of the sapphireadjacent silicon surface be
determined) or thinning the sapphire substrate . It
is quite difficult to implement both events. A simple
combined method for diagnosing the conduction type
of the sapphireadjacent silicon surface is proposed
below. It is based on the joint measurements of volt–
ampere characteristics (VAChs) and strongsignal
photoemf in SOSbased Au/Si diode structures.
These procedures do not require applications of high
voltages and thinning the sapphire substrate.
Autodoped SOS layers with thickness
were obtained by the lowtemperature molecular
beam epitaxy of silicon from an evaporation source
(KEF0.005) on the Rcut (1 02) of the sapphire sub
strate at a temperature of 700
C. Si layers were of
type conduction and they were perfect single crys
tals (Kikuchi lines were observed in the reflection elec
tron diffraction patterns) with a mirrorsmooth sur
face. In the visible region of an atomicforce micro
scope, the average surface roughness of the SOS layer
= 0.7–1.8 nm. The equilibrium electron con
in the layers was
Based on SOS layers with the abovestated charac
teristics, diode structures (DSs) with Au Shottky elec
trodes were obtained. Auelectrodes that are virtually
transparent to the light (the transmission factor is
70%) were obtained by the vacuum deposition
method. These DSs had two planar electrodes to the
silicon layer: the first is made of Au and the second
(ohmic) is made of Sn + Sb . The area of the Au
. Samples with two pla
nar ohmic contacts were used to measure the field
effect. The control voltage was applied to these contacts
through a sapphire substrate. The control electrode was
produced by Au thermal sputtering in vacuum. The top
view of the sample is schematically shown in Fig. 1.
The stationary strongsignal photoemf
highpower single nonfocused light pulses from a
FIL107 photoflash lamp was measured at the DS .
The maximum radiation of this lamp corresponded to
the sunlight (0.5
m). The light intensity was regulated
by nonselective grid filters in the range of 4
s). The signal of the photoemf was
recorded by a GDS71022 digital storage oscilloscope.
The VACh and external photoelectric effect from the
Auelectrode in Si in the DSs were measured .
In the SOS samples with two ohmic contacts, the
dynamic field effect (DFE) was measured from the
conduction  at frequency
= 60 Hz in nearsurface
silicon layer, adjacent to the sapphire, at low control
voltages at the field electrode (~100 V).
RESULTS AND THEIR DISCUSSION
It was established that the studied Au/
contact always formed the Schottky barrier type con
The barrier height
at the Au/
Si contact was
determined by two methods: (i) extrapolation of the
exponential part of the straight VACh branch up to the
intersection with the axis of currents
= 0 (
in accordance with expression :
A Method for Determining the State of the Silicon–Sapphire
Boundary in Thin SilicononSapphire Layers
S. V. Tikhov, D. A. Pavlov, and N. O. Krivulin
Lobachevskii Nizhegorodskii State University, Nizhni Novgorod, Russia
—A simple method for determining the state of the silicon–sapphire boundary in thin siliconon
sapphire layers, which is based on measuring a saturation photoemf and volt–ampere characteristics in
Au/Si diode structures is proposed. It is shown that in silicononsapphire layers that are obtained by the low
temperature molecular beam epitaxy a
type conduction layer is formed at the silicon–sapphire boundary.