Conductivity, Hall Effect, Optical Absorption, and Band Gap of Very Pure Boron

Dietz, W. F.; Herrmann, H.

doi:10.1007/978-1-4899-6574-5_11

Cited by 16 publications

(2 citation statements)

References 5 publications

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“…The Eg values extrapolated to 1 atm in Figure 4 (i.e. 1.2-1.3 eV), are in fair agreement with other workers in the field for tetragonal (14,16,18,21,22) and /~-rhombohedral boron (13,17,20,(23)(24)(25)(26)(27)(28)(29)(30). The energy gap values of the above workers range from 1.1 to 1.6 eV, which is a considerable spread of values for the energy gap of one material.…”

Section: Intrinsic Regionsupporting

confidence: 89%

Pressure Effects on the Electrical Properties of Polycrystalline Boron

Andersen

Bezirjian

Eyring

1967

J. Electrochem. Soc.

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The electrical resistances of ~-rhombohedraloand tetragonal polycrystalline boron were measured at temperatures from 25 to 300 Cand pressures from 1 atm to 60 kb (kilobars); the thermoelectric power was measured to 13 kb. Pressures were applied with an anvil press. With increasing temperature the resistance, R, continually decreased and the thermoelectric power, Q, at first increased and then levelled off. The shapes of the log R vs. 1/T and Q. vs. T curves are explained by intrinsic conduction at high temperatures going to extrinsic conduction at the lowest temperatures studied. In the intrinsic region an increase in pressure causes a reduction in the resistance, energy gap, and thermoelectric power of boron. For the low-temperature extrinsic region pressure lowers the resistance and hardly affects the thermoelectric power. These effects are discussed.The effects of pressure on the band gap have been studied for several elements such as the group IV semimetals, phosphorus, selenium, and iodine (1-3). Although quite a number of electrical measurements have been made on boron at atmospheric pressure, work at elevated pressures is sparse. Hamann (4) has reported the electrical resistance of a boron sample at room temperature and pressures up to 40 kb, and Vereshchagin et aI. (5) have measured the resistance of boron at room temperature from 25 to 250 kb. The crystal form of the boron in both of the above studies was unspecified, but both studies revealed a decrease in resistance with increasing pressure, as well as an absence of any phase transitions. Studies of boron are made difficult by the fact that it has several crystal modifications, the structures of which are all quite complex (6), and only one of which appears to be commercially available. Furthermore, the melting point of boron is very high (2300~ which makes purification of it difficult (especially since the forms other than ~-rhombohedral crystallize to fl-rhombohedral upon being melted and recrystallized) (6).In the present work the effects of pressure and temperature on the electrical resistance and thermoelectric power of three polycrystalline boron samples have been studied. The three materials studied were fl-rhombohedral and a tetragonal modification of boron, both prepared in this laboratory, and a commercially available ~-rhombohedral boron. Since the two types of crystals prepared here appeared to have similar impurity content, which was at least an order of magnitude lower than that of the commercial p-rhombohedral boron, the study was intended to serve also as a comparison of the importance of structural vs. purity differences on electrical properties of boron. Preparation and Identification of BoronBeing unable to purchase tetragonal boron, we prepared it, as well as some p-rhombohedral boron, using the hot filament technique (7) in which BBr8 was reduced by H2 on a glowing Ta filament. The conditions of preparation (8) were identical for the two modifications except for the filament temperature which measured 1250~ in the case of the tetra...

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Section: Intrinsic Regionsupporting

confidence: 89%

Pressure Effects on the Electrical Properties of Polycrystalline Boron

Andersen

Bezirjian

Eyring

1967

J. Electrochem. Soc.

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“…The anisotropy of optical absorption and resistivity of boron has been reported in (1,2). The present paper describes the anisotropy in the reflection coefficient observed in monocrystalline p -rhombohedral boron samples.…”

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confidence: 78%

Anisotropy in the Reflection Coefficient of β‐Rhombohedral Boron in the Region 1 to 6 eV

Kierzek‐Pecold

Kołsodziejczak

Pracka

1968

Physica Status Solidi (b)

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On the thermoelectric power of boron

Zareba

Maszkiewicz

1970

Phys. Stat. Sol. (a)

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m the last few years the thermoelectric power OL was measured in boron crystals over a wide temperature range (1 to 7). All results for samples of various purity indicate a p-type conductivity. The most representative data are plotted in Fig. 1. Two types of temperature dependence of Q may be seen. Above 400 to 5OO0K cu; decreases with temperature as 1/T (for samples of high purity). This is the usual behaviour for semiconductors when the carrier concentration depends exponentially on the reciprocal temperature as exp(-e/BkT). The activation energy & obtained from the slope doL/d(l/T) is about 1 . 4 eV, which is close to the activation energy of the electrical conductivity at high .temperatures and to the energy gap found from optical measurements. So it may be concluded that the thermoelectric power in this temperature range is caused by the diffusion of current carriers due to the gradient of their concentration in the sample.In samples of high concentration of impurities and in pure samples at lower temperatures different temperature dependence has been observed: OG increases with increasing temperature. Such a behaviour is observed in metals and in semiconductors in the impurity conduction range at constant carrier concentration. In both cases the carrier concentration is independent of temperature and the thermoelectric power is caused by a kind of thermodiffusion i. e. is due to the gradient of carrier mobility in the sample. The similar interpretation of his data has been presented by Uno (l)*who has found an increase of a with temperature in polycrystalline boron samples with high concentration of impurities. Using a simple theory he deduced that in his case the carrier concentration remained nearly constant and the mobility varied exponentially with the reciprocal temperature. Such temperature dependence of mobility is im good agreement with the idea presented by many authors (8 to 11) that in boron electrical conductivity is due to the thermally activated hopping processes between some local states. It may be supposed that this kind of transport takes place also in

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Conductivity, Hall Effect, Optical Absorption, and Band Gap of Very Pure Boron

Cited by 16 publications

References 5 publications

Pressure Effects on the Electrical Properties of Polycrystalline Boron

Pressure Effects on the Electrical Properties of Polycrystalline Boron

Anisotropy in the Reflection Coefficient of β‐Rhombohedral Boron in the Region 1 to 6 eV

On the thermoelectric power of boron

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