close

Вход

Забыли?

вход по аккаунту

?

el%3A19810120

код для вставкиСкачать
the predominant contribution to the total carrier scattering. At
(ND — NA) = 1015 cm" 3 , the calculated mobility is three times
larger than the measured mobility. While this calculation gives
good agreement for the case of GaAs, it thus appears to fail for
Gao.47Ino.53 As. Since the most obvious difference between
these materials is that Ga 0 .47^053As is an alloy semiconductor, it is reasonable to ask if the discrepancy between
the calculated and measured mobilities at 77 K can be attributed entirely to alloy scattering.
Acknowledgment: The author acknowledges the indispensable
help of N. Visentin of Laboratoire Central de Recherche,
Thomson-CSF, Orsay, France, for his work on this study.
T. P. PEARSALL
Bell Laboratories
600 Mountain Avenue
Murray Hill, NJ 07904, USA
19th January 1981
References
1 WOLFE, c. M., STILLMAN, G. E., and LINDLEY, w. T. : 'Electron mobility
in high-purity GaAs', J. Appl. Phys., 1970, 41, pp. 3088-3091
2 OOSAKA, F., SUGANO, T., OKABE, Y., and OKADA, Y.: 'Scattering of
electrons by potential clusters in ternary alloy semiconductors',
Japan J. Appl. Phys., 1976, 15, pp. 2371-2380
10-
3 WOLFE, c. M., STILLMAN, G. E., and DIMMOCK, j . D.: ionized impurity
density in n-type GaAs', J. Appl. Phys., 1970, 41, pp. 504-507
4 STILLMAN, G. E., and WOLFE, c. M.: 'Electrical characterization of
epitaxial layers', Thin Solid Films, 1976, 31, pp. 69-88
5 BARDEEN, J., and SHOCKLEY, w.: 'Deformation potentials and mobilities for non-polar crystals', Phys. Rev., 1950, 80, pp. 72-80
6 EHRENREICH, H.: 'Band structure and transport properties of some
III-V compounds', J. Appl. Phys., 1961, 32, pp. 2155-2166
7 MEIJER, H. J. G., and POLDER, D.: 'Note on polar scattering of conduction electrons in regular crystals', Physica, 1953,21, pp. 255-264
8 FALICOV, c. M., and CUEVAS, M.: 'Mobility of electrons in com3
10
K)1
K)1
TO1
net carrier c o n c e n t r a t o r !
10 18
ND-NA, c m '
Fig. 1 Calculated
and measured Hall mobilities in n-type
GaQ.41 Ino.53As
with NA/ND = 05. No alloy scattering has been
included in the calculation
(a) T = 11 K
A Present work
(b) T = 295 K
O Present work
A Oliver & Eastman
# Oliver & Eastman
2
Brooks has given an expression for electron scattering from
random spatial variations in the periodic crystal potential because of short range variations in the crystal composition:
HaUoy(X, T) -
-
^
-
-
^
(2)
where x is the mole fraction of one alloy constituent. The
temperature variation of the alloy scattering mobility is simple,
and if the magnitude of this mobility were known at one temperature it could be calculated for others. The alloy scattering
mobility necessary to produce agreement with the measured
77 K Hall mobility would be /ifl/,o>,(77 K) ~ 60000
cm2 V" 1 s~l. The Brooks theory would then require that the
295 K alloy scattering mobility be /ia//OJ,(295 K) ~ 30000
cm2 V~ * s~!. The presence of this additional scattering would
lower the calculated room temperature mobility to 9000
c m ^ - ' s ' 1 at (ND-NA)=
1015 cm" 3 and to 8500
1
c r r ^ V ' s " at {ND - NA) = 1016 cm" 3 . These calculated
values would be more than 30% below measured Hall mobilities. Hence it is concluded that alloy scattering, as it is currently understood, cannot account for the temperature
variation of the electron mobility in Ga o . 47 In o . 53 As. This conclusion is subject to the assumption that Matthiessen's rule can
be used to combine the various contributions to the mobility.
However, these results, calculated by a semianalytic approach,
are in very good agreement with the mobility calculated by the
Monte Carlo method, where it is not necessary to assume
Matthiessen's rule. Because the analytic approach works well
for closely related binary semiconductors, it is reasonable to
believe that it will also work well for the ternary alloy too.
In conclusion, it has been shown that the relaxation time
approximation which works well for GaAs can be used to
calculate the electron mobility in Gao.47Ino.53 As which is in
excellent agreement with calculations made by the Monte
Carlo method. The analysis of the measured Hall mobility in
Gao.47Ino.53 As shows the presence of additional scattering
in the low temperature electron mobility, which is probably the
manifestation of alloy effects. This scattering, however, has a
more complex temperature variation than that given by the
Brooks formulation of alloy scattering.
170
pensated semiconductors: (ii) Theory', Phys. Rev., 1967, 164, pp.
1025-1032
9 RODE, D. L., and KNIGHT, S.: 'Electron transport in GaAs', Phys.
Rev. B., 1971, 3, pp. 2534-2541
10 TAKEDA, Y., and SASAKI, A.: 'Hall mobility and Hall factor of
In o . 5 3 Ga o . 2 7 As', Japan. J. Appl. Phys., 1980, 19, pp. 383-384
1 1 PEARSALL, T. P., BEUCHET, G., HIRTZ, J. P., VISENTIN, N., BONNET, M.,
and ROIZES, A.: 'Electron and hole mobilities in Ga o . 4 7 In O 5 3 As'.
Int. Conf. GaAs and Related Compounds, Vienna 1980, (Bristol,
Institute of Physics, 1981), to be published, 1981
12 OLIVER, j . D., and EASTMAN, L. F. : 'Liquid phase epitaxial growth and
characterization of high purity lattice-matched Ga JC In,_ JC As on
<111>B InP', J. Electron. Mat., 1980, 9, pp. 693-712
13 LEHENY, R. F., POLLACK, M. A., BALLMAN, A. A., DEWINTER, J. C , a n d
NAHORY, R. E.: 'Compositional dependence of electron mobility in
InGaAsP', ibid., 1980, 9, pp. 561-568
0013-5194/81/040169-02$!.50/0
EFFECTIVE CANTING ANGLE OF
DISTORTED RAINDROPS ALONG EARTHSPACE PROPAGATION PATH
Indexing
terms:
precipitation
Radiowave
propagation,
Atmospheric
The effective canting angle of distorted raindrops along an
earth-space propagation path has been obtained from a oneyear phase amplitude measurement of two orthogonal components of satellite signals. It is shown that the distribution of
canting angles is centred around the horizontal orientation,
with the standard deviation of about 11°.
Introduction: A rain depolarisation test in earth-satellite
propagation path was carried out at Ibaraki, Japan, by use of
the Intelsat-IV satellite with an elevation angle of 35°. Measurements were based upon the phase-amplitude detection of two
orthogonal components of the satellite downlink signals at
4 GHz, and the crosspolarisation discrimination (XPD) and
tilt angle of the incident polarisation (usually a fat ellipse)
during rain were calculated from measured values of phase and
amplitude.
Although the major purpose of this experiment was to
obtain the rain depolarisation statistics for satellite links, the
information of the effective canting angle of distorted raindrops along an earth-space propagation path was also
ELECTRONICS LETTERS
19th February 1981
Vol.17
No. 4
deduced by comparing the XPD and tilt angle of incident polarisation during rain with those in fine weather, that is, the
baseline values.
Formulation: Let ep0 and epl denote the ellipticity (in nepers)
in clear weather and rain, respectively, related to XPD by
e P o,i - 1
and 0o, 0i the corresponding tilt angles of the incident elliptical polarisation (in radians). Then the effective canting angle 9
of distorted raindrops averaged over the earth-satellite propagation path and the rain-induced differential phase shift B can
be calculated by
(1)
d sin
| sin 2(0.0-0)
_x itan (2 cot" 1 <
tan
X
— ^ry-,
(2)
:
where
cos (2 cot
cos (2 cot
x
ep0)
Since the differential attenuations of distorted raindrops are
known to be negligibly small at 4 GHz, they are excluded in
the above formulations.
Experimental results: Fig. 1 shows the result of measurement.
In this scattergram, values of 9 are plotted against the simultaneously measured values of XPD. Each data point represents
•
80
an equivalent path-averaged canting angle of all distorted
raindrops and does not imply the canting angle of a specific
single raindrop. In the Figure, it is seen that the canting angles
are centred around zero degrees (horizontal direction) with a
secondary peak around —60 to —90 degrees. When the
amount of rain depolarisation is small enough, a certain portion of the small fluctuations in phase/amplitude measurement,
which may be due to polarisation impurity of the earth-station
antenna and/or the experimental system, could result in errors
in the estimates of canting angles by about 90°. When the XPD
is less than 30 dB, most values of canting angle exist in the
range between — 5° and 20° from the horizontal direction. So
the secondary peak in this figure may primarily be due to this
measurement error, but the effect of hydrometeors other than
raindrops, like ice particles, may possibly play a certain role in
the formation of this anomalous secondary peak.
The exclusion of the collection of data around the secondary
peak provides the mean and the standard deviation of the
residual 'genuine' distribution of canting angles of about 2°
and 11°, respectively.
This result implies that most of the major axis orientations
of the distorted raindrops are in approximately the horizontal
direction. As for the standard deviation, the value obtained in
this experiment seems to be somewhat smaller than the values
previously reported, though such measurements are still
insufficient. This may be because the above-mentioned value is
the standard deviation of the averaged values of all distorted
raindrops along the path, rather than that of the individual
raindrops.
Conclusion: The effective mean-path canting angle of distorted
raindrops along earth-space propagation paths obtained from
a phase-amplitude measurement of a satellite downlink signal
showed a distribution with mean value of about 2° and standard deviation of about 11°. Since existing data of raindrop
canting angles are insufficient, these values will be of help in
the prediction of rain depolarisation and/or in the design of
polarisation compensators.
O. FURUTA
M. YAMADA
15th December 1980
Research & Development Laboratories
Kokusai Denshin Denwa Co. Ltd.
2-1-23 Nakameguro, Meguro-ku, Tokyo 153, Japan
60
•
•
0013-5194/81/040170-02$1.50/0
•
•
»#. •:*• • •• •
£
fc_v__.i-
o
&•
STRAYS-INSENSITIVE SWITCHED
CAPACITOR BIQUADS WITH REDUCED
NUMBER OF CAPACITORS
*
-20 *.*. •
•• •
Indexing terms: Switched-capacitor networks, Filters
-40
•^-
-60
-80
••*••••••••. ••• ••:: •j
w
1 * * •*•
* *• •! "•
-90
40
A new general structure for strays-insensitive switched capacitor biquadratic cells based on an altered set of input/output
conditions is proposed. Several transformations which reduce
the size or number of capacitors or create a filter characteristic independent of capacitor ratios are presented. Finally, a
family of biquads which realise all inverting and noninverting
bilinear transformed functions for leapfrog and follow-theleader feedback filters are derived from the general structure.
1 • ••
•
•
•
30
XPD(4GHz),dB
20
J69A7TI
Fig. 1 Distribution of effective canting angles of distorted raindrops
along earth-space propagation path at Ibaraki, Japan
Elevation angle, 35 degrees; period, Apr 1976-Mar 1977
(Angles are measured counter-clockwise from horizon seen from
earth station). Measurement frequency, 4 GHz
ELECTRONICS LETTERS
19th February 1981
Vol. 17
High order filters can be realised by switched capacitor biquadratic cells connected in various topologies. Such building
blocks, based on a two-integrator two-clock-phase structure,
have been demonstrated previously.1'2 This letter describes a
slightly different biquad structure which offers several advantages with regards to transfer function realisability and number
of capacitors required.
The bilinear transform allows the use of classical synthesis
No. 4
171
Документ
Категория
Без категории
Просмотров
0
Размер файла
367 Кб
Теги
3a19810120
1/--страниц
Пожаловаться на содержимое документа