Infrared Optical Absorption in Semiconducting Cd<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">F</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>:Y Crystals

The dielectric response of semiconducting CdF 2 crystals with bistable In centers in the range of 10 1 Ϫ10 6 Hz reveals a quasi-Debye relaxation due to Schottky barriers at the Au/Ag contacts. These spectra can be modeled with a two-or tri-layer capacitor, the characteristics of which are determined by the conductivity and capacity of the crystal volume and the depletion layers at the contacts ͑the Maxwell-Wagner capacitance͒. Analyses of the temperature dependence of these parameters show that the volume conductivity is due to free-electron motion, whereas the depletion-layer conductivity probably is caused by electron jumps over the deep In centers. Illumination of the crystals in the photoionization absorption band of the deep centers has the same effect upon the dielectric response as an increase of the temperature since both factors increase the free-electron concentration.

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“…The effective mass m* of electrons in CdF 2 is 0.45 of the free-electron mass 26 and the binding energies of the centers…”

Section: ͑14͒mentioning

confidence: 99%

Radio-frequency response of semiconductingCdF2:Incrystals with Schottky barriers

et al. 2001

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“…1, curve 1 shows tlhe absorpt,ion spectrum measured a t room temperature on a CdF, crystal doped with 100 ppm I n after annealing in Cd vapour for 5 h. It consists of a broad asymmetric band in the near ultraviolet with a peak at 3.15 eV and the high-energy tail of the well-known I R absorption due to Me3+ : edonors in the near infrared [5]. By cooling to 20 K the I R absorption vanishes (cf.…”

Section: Optical Absorptionmentioning

confidence: 99%

Electrical and Optical Studies of Semiconducting CdF₂:In Crystals

Kunze¹,

Ulrici

1973

Physica Status Solidi (b)

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Optical absorption and electrical conductivity of In-doped CdF, crystals have been measured at various temperatures. The results confirm the assumption of Trautweiler e t al.[12] that the In3+ centers offer two localization possibilities t o the electrons introduced by annealing the crystals in Cd vapour: an atomic ground state (In2+) and a hydrogenic ground state (In3+ :e-). From an analysis of the results 0.055 eV is obtained for the energy distance between the two ground states and approximate values for their positions below the bottom of the conduction band. The latter depend on the degree of conversion. At temperatures below 50 K the occupation ratio between the two ground states can be strongly altered permanently in favour of the In3+ : e-donor states by irradiation with visible or UV light producing a photo-induced conductivity and absorption. From measurements of the dependence of the photo-induced conductivity below 50 K on temperature, irradiation time, and intensity, some properties of the In3+:e-donors are deduced.Die optische Absorption und die elektrische Leitfahigkeit von In-dotierten CdF,-Kristallen wurde bei verschiedenen Temperaturen gemessen. Die Ergebnisse bestiitigen die Annahme von Trautweiler e t al.[12], daB die In3*-Zentren zwei Lokalisierungsmoglichkeiten fur die durch Temperung der Kristalle im Cd-Dampf eingefuhrten Elektronen besitzen: einen ,,Atom"-Grundzustand ( In2+) und einen wasserstoffahnlichen Zustand (In3+ :e-). Aus der Analyse der MeBergebnisse werden fur den Abstand der beiden Grundzustande voneinander 0,055 eV und Naherungswerte fur ihren Abstand vom unteren Rand des Leitungsbandes erhalten. Letztere hangen vom Konversionsgrad ab. Bei Temperaturen unterhalb 50 K kann das Besetzungsverhaltnis zwischen den beiden Grundzustanden zugunsten des In3+ : e-Zustandes durch Bestrahlung mit sichtbarem oder UV Licht dauerhaft stark verandert werden, so daB eine photoinduzierte Leitfahigkeit und Absorption erzeugt wird. -411s Messungen der Abhangigkeit der photoinduzierten Leitfahigkeit unterhalb 50 K von Temperatur, Bestrahlungszeit und -intensitat konnten einige Eigenschaften der In3+ : e--Donatoren ermittelt werden.

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“…2 Various authors estimate the Bohr radius of this orbital as 4 -16 Å. [3][4][5][6][7][8] The donor state in CdF 2 has a binding energy of ϳ100 meV. This is well above the corresponding energy in conventional semiconductors ͑for comparison, in most of the III-V crystals, this energy is about several meV and in II-VI crystals it amounts to 10-30 meV͒.…”

Section: Introductionmentioning

confidence: 99%

Ionized donor pairs and microwave and far-infrared absorption in semiconductingCdF2

2002

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The dielectric permittivity ϭ 1 Ϫi 2 of semiconducting CdF 2 :In, CdF 2 :Ga, and CdF 2 :Y crystals was studied over the frequency range from 34.0 to 37.5 GHz at temperatures from 1.8 to 100 K. The photoinduced transition from a semi-insulating to a conducting state in photochromic CdF 2 :In and CdF 2 :Ga crystals results in a significant increase of both the dielectric constant ͑by ⌬ 1 ϭ0.5 to 1.4͒ and the dielectric-loss factor ͑by about an order of magnitude͒. The low-field dielectric-loss factor in these photodecolored crystals and in CdF 2 :Y ͑ 2 ϭ0.1 to 0.3͒ may be decreased by approximately an order of magnitude with an increase in the microwave-field power at 1.8 K. However, 2 ceases to depend on the field at TϾ4 K. These features are explained by the theory of Tanaka et al. for resonant-saturated absorption of ionized donor pairs. We have modified this theory to cover the far-IR range of the absorption spectrum of semiconductors with various degree of compensation. Results following from the modified theory were compared with those obtained by three other groups, namely, Blinowski and Mycielski, Efros and Shklovskii, and Baranovskii and Uzakov. We have shown that the ionized donor pairs are responsible for the far-IR absorption in semiconducting CdF 2 studied experimentally by Eisenberger, Pershan, and Bosomworth. The role of impurity clusters in storage of an ''excess'' impurity and as a source of interstitial F Ϫ ions during thermochemical treatment of as-grown crystals ͑which determines the ultimate semiconductive properties of CdF 2 ͒ is also discussed.

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Infrared Optical Absorption in Semiconducting CdF2:Y Crystals

Cited by 55 publications

References 13 publications

Radio-frequency response of semiconductingCdF2:Incrystals with Schottky barriers

Radio-frequency response of semiconductingCdF2:Incrystals with Schottky barriers

Electrical and Optical Studies of Semiconducting CdF₂:In Crystals

Ionized donor pairs and microwave and far-infrared absorption in semiconductingCdF2

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Infrared Optical Absorption in Semiconducting CdF2:Y Crystals

Cited by 55 publications

References 13 publications

Radio-frequency response of semiconductingCdF2:Incrystals with Schottky barriers

Radio-frequency response of semiconductingCdF2:Incrystals with Schottky barriers

Electrical and Optical Studies of Semiconducting CdF2:In Crystals

Ionized donor pairs and microwave and far-infrared absorption in semiconductingCdF2

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Electrical and Optical Studies of Semiconducting CdF₂:In Crystals