An investigation is made of the energy spectra of A and B excitons in CdS by measuring the transmission and reflectivity of very thin highly perfect crystals a t 1.8 K. The excited states of both series follow hydrogen-like series in a good approximation yielding different Rydberg's Rf = = (28 & 0.4) and R:3 = (31.3 0.4) meV, whereas the ground states are shifted in opposite direction with respect to the series, 8EB = -2.2, 6EF = t 0 . 5 meV, resulting in exciton binding energies Ell;" = 30.2 and E:kB = 30.8 meV, which are different from the corresponding Rydberg energies. This effect could not be attributed to a single perturbation acting on the gronnd state in different ways. Moreover, oscillator strengths are determined. A discussion is given in terms of the quasi-cubic model. For CdSe, the exciton-LO-phonon interaction is investigated using a line-shape analysis of the absorption lines a t different temperatures. Analogous to other 11-VI compounds, a t higher temperatures (2' > 77 K) this interaction is the dominate one for the exciton absorption spectra. Es werden die Energiespektren von A-und B-Exzitonen in CdS diirch

a), I?. SPIEC:KLRRRG (a), €1. CLEICHMAKN (b), and I). \TRUCK (a)The precipitation of oxygen in bulk dislocation-free Czochralski silicon subjected to isothermal annealing at temperatures b e h e e n 400 and 1100 "C is studied by means of infrared spectroscopy and transmission electron microscopy. From the changes in the infrared spectra observed after heat treatment it is concluded that (i) for low annealing temperatures (400 to 750 "C) the precipitates consist of amorphous SiO, (x < 2) which with rising temperature is transformed into amorphous SiO,, (ii) a t medium annealing temperatures (750 to 950 "C) a-cristobalite precipitat,es are formed, which (iii) at high annealing temperatures (950 to 1100 "C) are converted in amorphous SiO,. I n transmission electron microscopy the temperature range (i) is characterized by the appearance of "rod-like'' defects and its transformation into dislocation loops, and the ranges (ii) and (iii) b y the observation of platelet-shaped precipitates generating dislocation loops and stacking faults, leading to the conversion of the platelet-shapcd precipitates into microprecipitates.Es wird die PrLzipitat.ion von Sauerstoff in versetzungsfreiem Czochralski-Silizi~~m nach isothermaler Warmebehandlung bei Temperaturen zwischen 400 und 1100 "C mit Hilfe der Infrarotspektroskopie und der Transmissions-Elektronenmikroskopie untersncht. Bus den Anderungen im lnfrarotspektruni, die nach der Warmebehandlung beobachtet werden, wird geschlossen, daB fur niedrige Temperungstemperaturen (400 bis 750 "C) die Prazipitate aus aniorphem SiO, (x < 2) bestehen, welches sich mit wachsender Temperatnr in amorphes SiO, umwandelt., daB bei mitbleren Temperungstemperaturen (750 bis 950 "C) a-Cristobalit-Prazipitate gebildet werden, die sich bei hohen Temperungstemperaturen (950 bis 1100 "C) in amorphes SiO, umwandeln. I n der Transmissions-Elektronenmikroskopie wird der erste Temperaturbereich durch das Auftreten von ,,stabchenformigen" Defekten und deren Umwandlung in Versetzungsschleifen charakterisiert und die beiden anderen Temperaturbereiche durch die Beobachtung von plattchenformigen Prazipitaten, die Versetzungsschleifen und Stapelfehler erzeugen, was schlieDlirh z u einer Umwandlung der plattchenformigen Prazipitate in Mikroprazipitate fuhrt.

The excitonic absorption and emission are investigated on the same, extremely thin (d w 3 x cm) CdS single crystals in the range 77 O K to room temperature. It is found that the zero-phonon emission line is strongly influenced by reabsorption. After a reabsorption correction of the emission data the conclusions from the absorption and emission investigations agree with respect to the exciton-phonon interaction. There is a contribution to the halfwidths and energetic positions of the exciton lines which is proportional to a Bose factor of LO phonons with f q = 38 meV. No evidence is found for polariton effects from the reabsorption correction of the emission data. It is concluded, from the temperature dependence of the total emission intensity, that a quasi-equilibrium exists between excitons and electron-hole pairs. The exciton ionization energy is determined to be 31.6 meV. The dependence of the total emission intensity from the excitation intensity shows the occurrence of non-radiative recombination processes. Band shapes and intensity ratios of the one-and two-phonon satellites in the emission are also investigated and discussed.Die Exzitonenabsorption und -emission werden an denselben, sehr diinnen (d m w 3 x cm) CdS-Einkristallen im Temperaturbereich von 77 O K bis Zimmertemperatur untersucht. Es wird gefunden, daB die Null-Phononlinie in der Emission sehr stark durch Reabsorptionsprozesse verfilscht wird. Nach einer Reabsorptionskorrektur der Emissionsdaten stimmen die Aussagen der Absorptions-und Emissionsuntersuchungen hmsichtlich der Exziton-Phonon-Wechselwirkung iiberein. Halbwertsbreite und energetische Lage der Exzitonenlinien enthalten einen Anteil, der einem Bosefaktor fiir LO-Phononen mit h q = = 38 meV proportional ist. Aus der Reabsorptionskorrektur der Emissionsergebnisse ergeben sich keine Hinweise auf Polaritoneffekte. Aus der Temperaturabhiingigkeit der Gesamtemission wird auf ein Quasigleichgewicht zwischen Exzitonen und Elektron-Loch-Paaren geschlossen. Die Ionisierungsenergie der Exzitonen wird zu 31,5 meV bestimmt. Die Intensitiitsabhiingigkeit der Gesamtemission zeigt das Auftreten von strahlungslosen Rekombinationsprozessen. SchlieBlich werden Bandenformen und Intensititsverhiiltnisse der Ein-und Zwei-Phononsatelliten in der Emission untersucht und diskutiert.

In the last years, our knowledge about the electronic structure of oxygenrelated donors formed after heat treatment at temperatures between 300 and 500 OC in oxygen-containing silicon, the so called thermal donors, has been greatly enlarged by a successful use of infrared spectroscopic techniques /1 to 4/.Up to now it has been well established that these thermal donors give rise to a series of double donor species with closely spaced ionization energies. For explaining these properties, new microscopic models have been elaborated /5, 6/, assuming the formation of electrically active clusters with increasing number of oxygen atoms to be responsible for the occurrence of the different donor species. Especially in /5/ it was pointed out that in the "starting" phase metastable oxygen complexes would be stabilized by successively captured oxygen atoms. red absorption spectra of the high-energy s e r i e s (D ) of oxygen-related donors in silicon which gives some evidence for the metastable character of donor species in the initial stage of its formation.by appropriate heat treatment at 450 . ' C, thermal donors have been introduced with concentrations of lX1014 cmm3 (sample l), 1~1 0~~ cm-3 (sample 2), and 1. 3x1015 cm-3 (sample 3). Infrared transmission measurements have been carried out with a commercial infrared grating spectrophotometer allowing the sample to be illuminated with polychromatic light with o r without band gap excitation.In this note we report the observation of some unusual behaviour in the infra- +The samples used were boron-doped Czochralski silicon crystals into which,The full curve of Fig. 1 shows a part of the spectrum of the high-energy (D+) series of oxygen-related donors of sample 3 measured at liquid neon temper-1 ) Hausvogteiplatz 5 -7, DDR-1086 Berlin, GDR.

The absorption coefficient of CdS is measured over the whole region of the fundamental absorption edge, between liquid helium and room temperature. The experimental results are analysed and discussed in the framework of known theoretical work on exciton-phonon interaction, I n this connection the excitonic self-energy in dependence on energy and temperature is derived from the experimental data on the one hand and from theory on the other. It is shown that the absorption behaviour is determined by different mechanisms of interaction, namely i) scattering of excitons optically generated a t k = 0 and ii) manyphonon proceeses and phonon-assisted transitions. Each mechanism is subjected to a special temperature dependence, reflecting the share of the interaction with acoustic and longitudinal optical phonons, respectively.Der Absorptionskoeffizient des CdS wird iiber den gesamten Bereich der Grundgitterabsorptionskante fur Temperaturen zwischen der des flussigen Heliums und Raumtemperatur gemes,sen. Die experimentellen Ergebnisse werden im Rahmen bekannter Theorien zur Exziton-Phonon-Wechselwirkung analysiert und diskutiert. I n diesem Zusamnienhang wird die Exzitonenselbstenergie als Funktion von Energie und Temperatur einmal experimentell, zum anderen t,lieoretisch bestimmt. Es wird gezeigt, dal3 das Absorptionsverhalten von zwei verschiedenen Wechselwirkungsmechanismen gepriigt ist, niimlich 1) der Streuung bei k N 0 optisch erzeugter Exzitonen und 2) Vielphononenprozessen bzw. phononenassistierten obergangen. Jeder dieser Mechanismen unterliegt einer besonderen Temperaturabhangigkeit, welche die anteilmiil3ige Bedeutung der Wechselwirkung mit akustkchen und longitudinalen optischen Phononen widerspiegelt.