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-6
-10
ideal
x measured
nullor I
-20
Y. = s2 D
ic,
nullor I I
m-30
0=
3
a
CO
=
co
CO
-50
o
CM
f^
CO
i
1—Illr-
T
2142 A
(A
2k
V)
l
u_
Q.
CO
1
(
cb
o
X
-60
10
1427 ft
l
CO _
^ T
X
I
5-856
1861 n
U.
8-845
§•-40
10 k
50 k
100 k
frequency, Hz
500 k
1M
5M
Fig. 2 5th-order 500 kHz lowpass fJ.n.r. Chebychev filter
and d.v.c.c.s./d.v.c.v.s. applications is described. It is constructed using a standard bipolar process, is similar in complexity and chip area to the 741-type operational amplifier, and
allows RC active filters to be implemented at much higher
frequencies than has hitherto been possible.
Acknowledgments: This work wasfinanciallysupported by the
Natural Sciences and Engineering Research Council of
Canada, and via a Killam Memorial Scholarship to M. K. N.
Rao.
J. W. HASLETT
M. K. N. RAO
L. T. BRUTON
Department of Electrical Engineering
The University of Calgary
Alberta, Canada
BIALKO, M., and NEWCOMB, R. w.: 'Generation of all finite linear
circuits using the integrated DVCCS', IEEE Trans., 1971, CT-18,
pp. 733-736
2
SEDRA, A., and SMITH, K. C : 'A second-generation current conveyor
and its applications', ibid., 1970, CT-17, pp. 132-134
3
HUUSING, J. H., and DEKORTE, J.: 'Monolithic nullor—a universal
active network element', IEEE J. Solid-State Circuits, 1977, SC-12,
pp. 59-64
4 RAO, M. K. N., and HASLETT, J. W.: 'A modified current mirror with
level shifting capability and low input impedance', ibid., 1979,
SC-14, pp. 762-764
5 Inferdesign Inc., Sunnyvale, California, 1979
6 HASLETT, j . w., and RAO, M. K. N.: 'A high quality controlled current
source', IEEE Trans., 1979, IM-28, pp. 132-140
7
RAO, M. K. N., HASLETT, J. w., and BRUTON, L. T.: 'Novel g.i.c. suitable
for RC active filter applications', Electron. Lett., 1979, 15, pp.
462-464
0013-5194/80/050175-03$!. 50/0
ELECTRONICS LETTERS
Indexing terms: Semiconductors, Simulation, Transistors
It is suggested that electronic devices made from quaternary
alloys in which' the carrier velocity is strongly influenced by
alloy scattering will have an intrinsically higher temperature
stability. This is illustrated by Monte Carlo computer simulations of the steady-state velocity-field characteristic of
n-type Ga o . 2 4 In o . 7 6 As o .jP o . 5 around the velocity peak.
23rd January 1980
References
1
CALCULATIONS OF THE INTRINSICALLY
HIGHER TEMPERATURE STABILITY OF
ELECTRONIC DEVICES MADE FROM
QUATERNARY ALLOYS
Considerable attention is at present being given to quaternary
alloys such as GaxIn1_xAsyP1_y because of their considerable
potential for optoelectronic devices. It was also pointed out1
that theoretically these materials might be attractive for a
range of other applications, since they had a potentially high
peak electron velocity of interest for f.e.t.s and a large
peak/valley ratio suitable for efficient transferred-electron
devices. Recently,23 however, experimental investigations of
n-type GalnAsP grown lattice-matched in InP by liquid epitaxy have shown that alloy scattering of electrons in this material is much more severe than had been predicted. This has led
to a theoretical re-evaluation of the material which indicates
that the peak electron velocity is considerably reduced by the
alloy scattering.4 The work presented here supports this conclusion but points out that the presence of strong alloy scattering also leads to the possibility of producing electronic devices
with a higher intrinsic temperature stability.
The argument can be simply stated. Because the electron
velocity is strongly influenced by alloy scattering which arises
from the atomic distribution built into the lattice, it is not so
dependent on temperature as it would be if controlled by
28th February 1980 Vol. 16 No. 5
177
phonons alone. This is particularly true at high electric fields,
where the electron temperature also becomes relatively
independent of the lattice temperature. To illustrate the point,
results are presented of Monte Carlo computer calculations of
the velocity field curve around the velocity peak in
Ga o . 2 4Ino76As o .5Pos- Similar calculations for GaAs are also
presented, and comparison indicates that the electron velocity
variation with temperature in the alloy is only a third that in
GaAs.
The Monte Carlo computer program used is based on that
first described by Fawcett, Boardman and Swain5 bat impurity
and alloy scattering have been added. Calculations including
impurity scattering in the related ternary compound InAsP
have already been discussed 6 and measurements of alloy scatr
tering at low electric fields on G a o ^ J n o ^ A s o - s P o - s have been
presented. 2 Briefly, analysis of the temperature dependence of
the Hall mobility indicated that, in addition to polar optical
and impurity scattering, there exists a further component with
a temperature dependence T~1/2. Assuming a totally random
distribution, as one would expect from thermodynamic considerations of the alloy, and taking m* = 0059, based on the
magnetophonon measurements of Nicholas et al., 1 we obtained an alloy scattering potential A(/ = 0-62 eV following the
approach of Littlejohn et al} This combination of effective
mass and At/ has been taken in these calculations together
with the other most important parameters listed in Table 1.
about 0-27% K 1 is in good agreement with the experimental
value. 8 As can be seen, however, the temperature variation of
the electron velocity in the alloy is close to only one-third
of this value.
It should be pointed out that G a O 2 4 l n o 7 6 A s o . s P o 5 was not
chosen as the alloy or composition in which the greatest temperature stability is to be expected but rather as one which has
been relatively well investigated experimentally. Indeed, preliminary calculations indicate that certain other alloys such as
GajIni-jASySb x -,, may be more favourable, although this
still-awaits experimental investigafion. "Clearly it lias always
been possible to so degrade a material with imperfections that
they dominate the transport properties and make them temperature insensitive. Work on the GaxIni_xAsyPi_ y quaternary, however, indicates that alloy scattering is intrinsic and
reproducible and that properties such as the peak electron
velocity remain comparable with GaAs and related compounds. It would therefore appear that quaternary alloys are of
interest for the construction of electronic devices in which
good thermal stability is required.
Table 1 PHYSICAL PROPERTIES ASSUMED
FOR G a o . 2 4 l n o . 7 6 A s . P o . 5
A. R. ADAMS
Physics Department, University of Surrey
Guildford, Surrey, England
51 gem"3
13028
10-31
4-7x10scms"1
435 K
0-62 eV
5-869 A
0059
0-72 eV
108 eV
Density
£o
«00
Sound velocity
Polar phonon temperature
At/
Lattice constant
Effective mass ratio
Sub-band gap F-L
Sub-band gap F-X
Acknowledgments: The author wishes to thank W. Fawcett for
providing the original computer program and Mrs. J. Hilton
and J. R. Hayes for help with the computing presented here. He
is also grateful to P. D. Greene for interesting discussions about
the thermodynamic properties
17th December 1979
References
1
LITTLEJOHN, M. A., HAUSER, J. R., and GLISSON, T. H.: 'Velocity field
characteristics of Gaj.^n^Pj.yAs,, quaternary alloys', Appl. Phys.
Lett., 1977, 30, pp. 242-244
2
GREENE, P. D., WHEELER, S. A., ADAMS, A. R., EL-SABBAHY, A. N., a n d
AHMAD, c. N.: 'Background carrier concentration and electron
mobility in L P E I n t _xGaJCAsJ,P1 _ y layers', ibid., 1979,35, pp. 78-80
3
LITTLEJOHN, M. A., SADLER, R. A., GLISSON, T. H., a n d HAUSER, J. R.:
'Carrier compensation and alloy scattering in G a j . ^ I n ^ . ^ A S j ,
grown by liquid phase epitaxy'. Inst. Phys. Conf. Ser., 1979, 45, pp.
239-247
The results of the calculations are shown in Fig. 1. An
ionised impurity density of 1017 cm" 3 was assumed as appropriate forfield-effecttransistors. As can be seen, at 300 K the
peak velocity is 1-6 x 107 cm s" 1 and occurs at 10 kV cm" 1 .
For comparison curves have been calculated including an impurity density of 1017 cm" 3 for GaAs and for the same quaternary without alloy scattering. Fig. 1 shows there is a
considerable decrease in electron velocity due to alloy scattering in the quaternary, in agreement with the results of Littlejohn et al.* When compared with GaAs, however, we see that
the peak velocities are similar although the peak field in the
quaternary is more than twice that of GaAs. Of particular
interest here is the variation of velocity when the temperature
is increased to 350 K. Again, for comparison, calculations have
been on GaAs and where the variation with temperature of
4
LITTLEJOHN, M. A., ARLEOGE, L. A., GLISSON, T. H., a n d HAUSER, J. R.\
influence of central valley effective mass and alloy scattering on
transient drift velocity in G a ^ J n ^ ^ y A s ^ ' , Electron. Lett., 1979,
15, pp. 586-588
5
FAWCETT, w., BOARDMAN, A. D., and SWAIN, s.: 'Monte Carlo deter-
mination of electron transport properties in gallium arsenide', J.
Phys. Chem. Sols., 1970, 31, pp. 1963-1990
6
EL-SABBAHY, A., ADAMSY A: R., and YOUNG, M. L.: 'Pressure and com-
position dependence of high field instabilities in I n A s j . j P , alloys',
Solid-State Electron, 1978, 21, pp. 83-90
7
NICHOLAS, R. J., PORTAL, J. C , HOULBERT, C , PERRIER, P., a n d PEAR-
SALL, T. p.: 'An experimental determination of the effective masses
for Ga,_ J n ^ S y P , _,, alloys grown on InP', Appl. Phys. Lett., 1979,
34, pp. 492-494
8
ADAMS, A. R., and TATHAM, H. L.: 'Temperature dependence of the
Gunn threshold in GaAs' (to be published)
0013-5194/80/050177-02S1.50/0
2-5r
300K
c
r
5! 1-0
300 K / "
\
\
300K
\
HARD RADIATION EFFECTS IN X-RAY
LITHOGRAPHY
//35OK
/
o
Indexing terms: Radiation, X-rays
b
electric10field.kV cm"1
Results- of X-ray exposure of polymethyl methacrylate
through various materials are described. These indicate that
the hard radiation effect on exposed resist may be quite large.
10
Fig. 1 Calculated velocity field characteristics including 1011 cm 3
ionised impurities for (a) GaAs, (b) Gao. 24In0.T6Aso.5Po.s and
(c) Ga0.2*Ino.16Aso.5Po.5 imagined without alloy scattering
178
The soft part of the X-ray spectrum is mainly responsible for
exposure effects in X-ray-sensitive polymers. The hard part of
the radiation is usually considered as having negligible influence on the polymer layer;, the only effect of such radiation
ELECTRONICS LETTERS 28th February 1980
Vol. 16 No. 5
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