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Surface conductivity of germanium doped with gold
Solid State Communications Vol. 3, pp. ]xix-bxlv, 1965. Pergamon Press Ltd. Printed in Great Britain.
Abstracts of Important Papers Published in Soviet Physics-Solid State (Fizika Tverdogo Tela) A complete cover-to-cover translation of the Russian journal is published by the American Institute of Physics approximately six months after the date of original publication. for p 3: (5-10) x 10~cm~,when the carrier concentration is sufficient for degeneracy of the Intrinsic band, the intrinsic band and the Impurity band overlap.
FORMATION AND PROPERTff~SOF fl~iPURITY BAND IN n-TYPE GaAs. 0. V. Emellanenko, T. S. Lagunova, D. N. Nasledov, G. N. T~1~ihkin,(Vol. 7, No. 5, p. 1315). The study of kinetic effects in GaAs at low temperatures allows to examine the properties of the Impurity band: The electrical conductivIty and the Hall effect were studied at low temperatures (2-300°K) in crystals of n-type GaAs having electron concentrations of 3 x 1O’~-2x1O’~ cm The experiments were performed on Undoped single crystals where the main Impurity was singly charged Si shallow donors. Some crystals were doped with sulfur or selenium which also formed shallow levels. The following results were obtained. For electron concentra1~,the donors form a highly contions n~5x1O ducting narrow impurity band separated from the conduction band by a ~ E of about 2 x iO~eV, which is much lower than the activation energy of localized impurities calculated on the basis of a hydrogenoid model. As the carrier concentration increases~ t~Edecreases and becomes zero when n>4x10~cm~.The linear temperature dependence of the Fermi level in crystals with ND = (1.5 5) x 10~cm3 can be followed up to 10-20°K. It is on this basis that it is concluded that the thickness of the impurity band does not exceed (1-2) x 10~eV. A broader band, according to calculations, would have led to a deviation of ~ (T) from linearity. The same de fects which limit the mobility of electrons in the intrinsic band limit it also in the impurity band. The negative resistance in a magnetic field at low temperatures is explained by a scattering of electrons on the localized spins of impurity band atoms. Measurements of Hall effect In p-type GaAs show that when the hole concentration is p = 2 x 10’-~cm~and the acceptor concentration Na = 5 x 10” cm3, the separation between the
SURFACE CONDUCTWITY OF GERMANIUM DOPED WiTH GOLD. E. A. Katrich, 0. G. Sabrei, D.T. Tarashchenko (Vol. 7, No. 5, p.1352).
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impurity band and the intrinsic band is 2x 10~ lxix
This paper elucidates the results of a study of the temperature dependence of surface conductivity, the Hall effect, and the Influence of crystallographic orientation on the conduction of a germanium by cleavage of the crystal in surface vacuum.prepared Conductivity vs. ternperature measurements were made In a special vacuum apparatus for the range of temperatures 60-190°K. The Au-doped germanium studied had a donor concentration Nd = 2. 35x10~cm~ and an acceptor concentration Na = 3. 26x 10~ cm~. The samples were paralleleplpeds 0. 5 x 3 x 5 mm3, and theIr resistance at liquid nitrogen temperature was about I x 10? ohms. It should be noted that after cleaving In good vacuum and regardless of the temperature at which the samples were cleaved, resistance at low temperatures dropped due to surface conductivity along the newly formed, clean germanium surface. It has been established that exposure of the clean germanium surface, doped with gold and well compensated, leads to the appearance of a large p-type surface conductivity, which considerably exceed bulk conductivity at low temperatures. The temperature dependence of the surface conductivity, a, was obtained, and the carrier mobility In the region of the space charge was measured. From the sign of the Hall emf, V 0, it was found that the conductivity is p-type. The surface carrier mobility
lxx
ABSTRACTS OF PAPERS IN SOVIET PHYSICS-SOLD) STATE
is considerably lower than the bulk conductivity and iqpreases with temperature. The relationship ~, proportional to the effective concentratio~i~f the carriers, does not vary with temperature. Comparison of the obtained conductIvity data with the theoretically calculated conductivity indicates that there is considerable degeneracy at the surface (5 10 larger than the Fermi level). Therefore, to confirm the observed temperature dependence of a, the theory of Shriffer is generalized for the case of degeneracy. -
ANISOTROPIC ABSORPTION OF ELECTROMAGNETIC WAVES BY HOT CARRIERS IN SEMICONDUCTORS. E. M. Gershenzon, Yu. A. Gurvitch, L. V. Lltvak-Gorskaya (Vol. 7, No. 5 p. 1378). In a strong electric field, the absorption of electromagnetic power depends on the polarization of radiation with respect to the applied field. This dependence has been evaluated; experimental results confirming this evaluation are reported. The experiment consists essentiaUy of a simultaneous illumination of the specimen by two electromagnetic waves polarized along the applied field and transversely to it. For each polarization, the transmitted power was measured assumii g that the losses which are not due to free carrier absorption do not depend on the intensity of the electric field. The field dependence of the absorption shows that for E ~4kV/cm the drift velocity saturates and the absorption of parallel polarization becomes very low. The dependence of absorption on direction of polarization in p-type Ge is well-described by a formula derived on the assumption of isotropic affective mass. Experimental results are reported; the theoretical derivations show that in the absorption of millimeter waves by hot carriers one needs not take into account the additional heating of carriers by the electric field of the wave. The data show: dependence of absorption on intensity of the applied field, field dependence of ~, dependence of ~ for p-type Ge.
ANOMALIES OF THE COERCiVE FORCE AND THE RESIDUAL MAGNETIZATION ~ SUBSTITUTED RARE EARTH- FERRITE GARNETS. I. S. Liubutin (Vol. 7, No. 5 p. 1397). The temperature dependence of the coercive
Vol. 3, No.8
force, Hc, and the residual magnetization, ~r has been Investigated in substituted ferrite-gad-’ 012 0~ X ~ 1. 2) ollnlum garnets, C~Gd~ ~ X and ferrite-yttrium garnets, aXY3 SnXFe~X0l3 (0 ~ x ~ 1.2) (Fe~ions were substl~tutedby Sn~ions, and ~ or Y’~ions by Ca~2: the stoichiometric formula is ~ where R = Gd, Y; 0 x 1.2 Measurements of the temperature dependence of the coercive force In the neighborhood of 8k in the substituted ferrite-gadolinium game ts were made the ballistic method, utilizing mm3 by samples. An anomalous rise of He50x4x4 in the compensation point region ek was observed for all gadolinium compounds; doubling of the maxIma of He at 8k has been observed in the majority of samples. It has also been found that the curves ar(T) have a maximum at temperatures below 8k• The magnitude of the maxima was found to be closely dependent on the ferrite composition; I. e., It decreases with an increase in x. The drop in the He maximum occurs regardless of the increase in structural inhomogenieties in these ferrites with the rise in x. The measurements of the temperature dependence of Hc and ar for the substituted ferrite-yttrium garnets showed that, unlike the gadolthium compounds, the sharp anomaly in the change of H~ and 0r with temperature is absent. Small anomalous effects in H~are observed in the 80-90°K temperature region; their appearance is due to the presence of rare earth impurities, or divalent ferrite Ions, which affect the anomaly of the magnetic anisotropy and the ferromagnetic resonance absorption line width. It is presumed that the anomalous behavior of the coercive force and the residual magnetization in the substituted ferrite-gadolinium garnets, the strong dependence of the anomaly on the ferrite composition, and also the absence of sharp anomalous effects in the substituted yttrium garnets, is due to the rare earth sublattice. Several experimental dependences are given. ~.
~
.
P-N JUNCTION IN VERY DEGENERATE SEMICONDUCTOR VERY M. HIGH DENSiTIES. A. I. AT Imenkov, M. CURRENT Koslov, D. N. Nasledov, B. V. Tsarenkov (Vol. 7, No. 5, p. 1480). Formulae are derived for the V-I characteristic and the width of the recombthation region in a p-n structure in which degeneracy of excess carriers Is achieved. The experimental verification of the formulae is perf ormed on tunnel diodes since in tunnel pn junctions it is easy to
Abstracts of Important Papers Published in Soviet Physics-Solid State (Fizika Tverdogo Tela) A complete cover-to-cover translation of the Russian journal is published by the American Institute of Physics approximately six months after the date of original publication. for p 3: (5-10) x 10~cm~,when the carrier concentration is sufficient for degeneracy of the Intrinsic band, the intrinsic band and the Impurity band overlap.
FORMATION AND PROPERTff~SOF fl~iPURITY BAND IN n-TYPE GaAs. 0. V. Emellanenko, T. S. Lagunova, D. N. Nasledov, G. N. T~1~ihkin,(Vol. 7, No. 5, p. 1315). The study of kinetic effects in GaAs at low temperatures allows to examine the properties of the Impurity band: The electrical conductivIty and the Hall effect were studied at low temperatures (2-300°K) in crystals of n-type GaAs having electron concentrations of 3 x 1O’~-2x1O’~ cm The experiments were performed on Undoped single crystals where the main Impurity was singly charged Si shallow donors. Some crystals were doped with sulfur or selenium which also formed shallow levels. The following results were obtained. For electron concentra1~,the donors form a highly contions n~5x1O ducting narrow impurity band separated from the conduction band by a ~ E of about 2 x iO~eV, which is much lower than the activation energy of localized impurities calculated on the basis of a hydrogenoid model. As the carrier concentration increases~ t~Edecreases and becomes zero when n>4x10~cm~.The linear temperature dependence of the Fermi level in crystals with ND = (1.5 5) x 10~cm3 can be followed up to 10-20°K. It is on this basis that it is concluded that the thickness of the impurity band does not exceed (1-2) x 10~eV. A broader band, according to calculations, would have led to a deviation of ~ (T) from linearity. The same de fects which limit the mobility of electrons in the intrinsic band limit it also in the impurity band. The negative resistance in a magnetic field at low temperatures is explained by a scattering of electrons on the localized spins of impurity band atoms. Measurements of Hall effect In p-type GaAs show that when the hole concentration is p = 2 x 10’-~cm~and the acceptor concentration Na = 5 x 10” cm3, the separation between the
SURFACE CONDUCTWITY OF GERMANIUM DOPED WiTH GOLD. E. A. Katrich, 0. G. Sabrei, D.T. Tarashchenko (Vol. 7, No. 5, p.1352).
~.
-
-
impurity band and the intrinsic band is 2x 10~ lxix
This paper elucidates the results of a study of the temperature dependence of surface conductivity, the Hall effect, and the Influence of crystallographic orientation on the conduction of a germanium by cleavage of the crystal in surface vacuum.prepared Conductivity vs. ternperature measurements were made In a special vacuum apparatus for the range of temperatures 60-190°K. The Au-doped germanium studied had a donor concentration Nd = 2. 35x10~cm~ and an acceptor concentration Na = 3. 26x 10~ cm~. The samples were paralleleplpeds 0. 5 x 3 x 5 mm3, and theIr resistance at liquid nitrogen temperature was about I x 10? ohms. It should be noted that after cleaving In good vacuum and regardless of the temperature at which the samples were cleaved, resistance at low temperatures dropped due to surface conductivity along the newly formed, clean germanium surface. It has been established that exposure of the clean germanium surface, doped with gold and well compensated, leads to the appearance of a large p-type surface conductivity, which considerably exceed bulk conductivity at low temperatures. The temperature dependence of the surface conductivity, a, was obtained, and the carrier mobility In the region of the space charge was measured. From the sign of the Hall emf, V 0, it was found that the conductivity is p-type. The surface carrier mobility
lxx
ABSTRACTS OF PAPERS IN SOVIET PHYSICS-SOLD) STATE
is considerably lower than the bulk conductivity and iqpreases with temperature. The relationship ~, proportional to the effective concentratio~i~f the carriers, does not vary with temperature. Comparison of the obtained conductIvity data with the theoretically calculated conductivity indicates that there is considerable degeneracy at the surface (5 10 larger than the Fermi level). Therefore, to confirm the observed temperature dependence of a, the theory of Shriffer is generalized for the case of degeneracy. -
ANISOTROPIC ABSORPTION OF ELECTROMAGNETIC WAVES BY HOT CARRIERS IN SEMICONDUCTORS. E. M. Gershenzon, Yu. A. Gurvitch, L. V. Lltvak-Gorskaya (Vol. 7, No. 5 p. 1378). In a strong electric field, the absorption of electromagnetic power depends on the polarization of radiation with respect to the applied field. This dependence has been evaluated; experimental results confirming this evaluation are reported. The experiment consists essentiaUy of a simultaneous illumination of the specimen by two electromagnetic waves polarized along the applied field and transversely to it. For each polarization, the transmitted power was measured assumii g that the losses which are not due to free carrier absorption do not depend on the intensity of the electric field. The field dependence of the absorption shows that for E ~4kV/cm the drift velocity saturates and the absorption of parallel polarization becomes very low. The dependence of absorption on direction of polarization in p-type Ge is well-described by a formula derived on the assumption of isotropic affective mass. Experimental results are reported; the theoretical derivations show that in the absorption of millimeter waves by hot carriers one needs not take into account the additional heating of carriers by the electric field of the wave. The data show: dependence of absorption on intensity of the applied field, field dependence of ~, dependence of ~ for p-type Ge.
ANOMALIES OF THE COERCiVE FORCE AND THE RESIDUAL MAGNETIZATION ~ SUBSTITUTED RARE EARTH- FERRITE GARNETS. I. S. Liubutin (Vol. 7, No. 5 p. 1397). The temperature dependence of the coercive
Vol. 3, No.8
force, Hc, and the residual magnetization, ~r has been Investigated in substituted ferrite-gad-’ 012 0~ X ~ 1. 2) ollnlum garnets, C~Gd~ ~ X and ferrite-yttrium garnets, aXY3 SnXFe~X0l3 (0 ~ x ~ 1.2) (Fe~ions were substl~tutedby Sn~ions, and ~ or Y’~ions by Ca~2: the stoichiometric formula is ~ where R = Gd, Y; 0 x 1.2 Measurements of the temperature dependence of the coercive force In the neighborhood of 8k in the substituted ferrite-gadolinium game ts were made the ballistic method, utilizing mm3 by samples. An anomalous rise of He50x4x4 in the compensation point region ek was observed for all gadolinium compounds; doubling of the maxIma of He at 8k has been observed in the majority of samples. It has also been found that the curves ar(T) have a maximum at temperatures below 8k• The magnitude of the maxima was found to be closely dependent on the ferrite composition; I. e., It decreases with an increase in x. The drop in the He maximum occurs regardless of the increase in structural inhomogenieties in these ferrites with the rise in x. The measurements of the temperature dependence of Hc and ar for the substituted ferrite-yttrium garnets showed that, unlike the gadolthium compounds, the sharp anomaly in the change of H~ and 0r with temperature is absent. Small anomalous effects in H~are observed in the 80-90°K temperature region; their appearance is due to the presence of rare earth impurities, or divalent ferrite Ions, which affect the anomaly of the magnetic anisotropy and the ferromagnetic resonance absorption line width. It is presumed that the anomalous behavior of the coercive force and the residual magnetization in the substituted ferrite-gadolinium garnets, the strong dependence of the anomaly on the ferrite composition, and also the absence of sharp anomalous effects in the substituted yttrium garnets, is due to the rare earth sublattice. Several experimental dependences are given. ~.
~
.
P-N JUNCTION IN VERY DEGENERATE SEMICONDUCTOR VERY M. HIGH DENSiTIES. A. I. AT Imenkov, M. CURRENT Koslov, D. N. Nasledov, B. V. Tsarenkov (Vol. 7, No. 5, p. 1480). Formulae are derived for the V-I characteristic and the width of the recombthation region in a p-n structure in which degeneracy of excess carriers Is achieved. The experimental verification of the formulae is perf ormed on tunnel diodes since in tunnel pn junctions it is easy to