Electrical and Optical Studies of Semiconducting CdF₂:In Crystals

Abstract

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.

Determination of the parameters of semiconductingCdF2:Inwith Schottky barriers from radio-frequency measurements

“…This behavior has been indeed observed in Ref. [15] at temperatures 40 K to 80 K. Since the electron mobility µ in CdF 2 depends only weakly on temperature (at the temperatures 70 ÷ 300 K,…”

“…16 [15]. For increasing temperature, the higher levels of this band become populated, leading to an effective decrease of E cap .…”

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

“…Along with the ''shallow'' hydrogenic state, they also have a ''deep'' strongly localized state featuring a large lattice relaxation, i.e., a large shift in the corresponding configuration coordinate. [20][21][22] As is shown in Refs. 23-26, the deep state is a two-electron state.…”

CdF2 crystals with bistable impurity centers as media of the real-time holography

“…The large lattice relaxation accompanying the deep state formation creates the barrier that separates shallow state from deep state and makes the shallow state a metastable one (Fig. 2) [17,18]. This relaxation is a consequence of the electron-lattice interaction that compensates the Coulomb repulsion of two electrons, which occupy the same orbital; such relaxation is typical for centers with the negative correlation energy (negative-U centers).…”