Donors In CdS Research Articles

Spin-Flip Raman Echo inn-Type CdS

We report on the first observation of a Raman echo, using spin-flip Raman scattering at 4905 \AA{} of bound donors in CdS to create a coherent spin state. The free-induction decays associated with each pulse in the sequence of two $\frac{\ensuremath{\pi}}{2}$ pulses as well as the echo are probed by spin-flip Raman scattering at 4880 \AA{}.

Measurement of Spin-Flip-Raman-Scattering Cross Section and Exchange Effects for Donors in CdS by Faraday Rotation

The simple connection between spin Faraday rotation and spin-flip-Raman-scattering (SFRS) cross section is used to deduce the SFRS cross section for donors in CdS from Faraday-rotation measurements. The Faraday rotation also reveals an antiferromagnetic exchange interaction between donors.

The identity of the native donor in CdS at high Cd pressures

The identity of the native donor in CdS at high Cd pressures

Iodine as a donor in CdS

Iodine doped single crystals of CdS were grown from the vapor phase. High temperature Hall effect measurements for the crystals equilibrated with Cd and S 2 vapors at temperatures between 700 and 1000°C gave the free electron concentration as a function of p Cd or p S2 and temperature. The results can be explained on the basis of a model in which the CdS is saturated with iodine at low p Cd (=high p S2) but unsaturated at high p Cd. The solubility of iodine in CdS is given by c t =1·73×10 22 p S2 −1/8 exp (−1·045 eV/ kT) cm −3 atm −1/8=4·62×10 19 p Cd 1/4 exp (−0·195 eV/ kT) cm −3 atm 1/4 The formation of pairs ( I S V Cd)′ from I S · and V Cd″ is governed by the equilibrium constant K P(I, V) =4 exp (≤1·1 eV/ kT) If Cd diffusion occurs primarily by free vacancies, the Cd * tracer self diffusion leads to a vacancy mobility of (1·2±0·5)×10 −5 cm 2 sec −1 at 900°C, in agreement with results reported by Woodbury [12], but (7±3) times larger than reported by Kumar and Kroger [10].

Iodine as a donor in CdS

Iodine as a donor in CdS

Resonant Interactions between Localized LO Phonons and Continuum States of Donors in CdS and CdSe

Resonant Interactions between Localized LO Phonons and Continuum States of Donors in CdS and CdSe

Optical Studies of Shallow Acceptors in CdS and CdSe

We show that Li and Na are the only soluble substitutional acceptors in CdS and CdSe with relatively small binding energies. A shallow acceptor is observed for P doping, but it arises from a complex. These results, and also the fact that the substitutional P is a deep acceptor in the sulfides and selenides, but not in the tellurides, are consistent with the trends in acceptor binding energy observed in other semiconductors. We present evidence that a native double donor exists in CdS, but that Li and Na acceptors are compensated by ordinary donors and not by isolated double donors. Analysis of thermodynamic data shows that isolated native donors should not be effective in compensating acceptors in ZnSe, CdSe, or CdTe. The compensating donors in CdS are found to be unusually shallow, indicating that they may be Li or Na interstitials. An attempt to drift out the Li-interstitial donors with an applied electric field is discussed.

Excited States of Bound Excitons and Neutral Donors in CdS

A technique employing a monochromator to select the incident photon energy and a spectrometer to analyze the low temperature photoluminescence of CdS crystals has proven to be valuable, both in analyzing the usual photoluminescent spectra and in obtaining new information on excited states of bound excitons and excited states of neutral donors in the crystal. An accurate measurement of the donor energy levels and the donor binding energy gave a binding energy for the Cl donor in CdS of 33.0 ± 0.2 meV. Energies of excited states of the bound exciton complexes were also measured and for the bound exciton – neutral donor complex (I2 complex) some seven excited state levels were found. One type of radiative decay observed for this I2 complex is a radiative Auger process. This has important consequences in interpreting photoconductivity spectra.

Self-diffusion and the defect structure of cadmium sulfide

Cd and S tracer diffusivities were measured in undoped and In-doped CdS crystals as a function of temperature, the partial pressure of Cd or S 2, and In concentration. Above 700°C and under high Cd pressures, sulfur diffuses by a vacancy mechanism involving the doubly ionized vacancy V ·· s; this vacancy is also the major electrically active point defect and is the commonly reported double donor in CdS. Under these conditions, Cd diffusion occurs by singly ionized Cd interstitials, these interstitials being the fastest moving point defects, but only a minority as donors compared to S vacancies. Under high S 2 pressures, sulfur diffuses by the interstitial mechanism involving the neutral S i × interstitials. Cd diffusion under these conditions is controlled by doubly ionized Cd vacancies. Experiments on indium-doped samples show that at moderate-to-high Cd pressures In is incorporated with the release of an equal number of electrons into the conduction band, whereas at low Cd pressures, the incorporation occurs with the creation of doubly ionized native acceptors. These acceptors are most probably the Cd vacancies responsible for Cd diffusion in this range of Cd pressures. The absolute mobilities of V ·· s, V″ Cd and (In Cd V Cd)′ have been determined, assuming [ V″ Cd] > [ S″ i ]. For Cd · i and S i × a separation of diffusivities into mobilities and concentrations was not possible. Estimates for the position of the acceptor levels of V Cd are obtained.

Electron Spin Resonance Studies of Shallow Donors in CdS

The electric spin resonance of donor electrons was investigated in the temperature range from 1.4 K to 4.2 K in several types of CdS, i.e. the undoped crystals grown from the vapour phase and grown by the melt, the crystals doped with chlorine, iodine, oxygen, and both chlorine and neodymium. In Cl-doped CdS and also I-doped CdS, the also I-doped CdS, the variation of the line width with the excess donor concentration and the temperature indicated that the motional narrowing effect due to the hopping motion of the donor electron occurred on the line width in a certain donor concentration range. In Cl-doped CdS the additional line broadening due to the shortening of the relaxation time occurred at the concentrations above 7×16 16 cm -3 . The hyperfine splitting of the donors Cl and I was estimated by the line width extraporated to the lower limit of their concentration. In other crystals, the nature of the donor is discussed on the basis of the results of ESR measurements and optical emission ones. The electric field effect on the donor resonance was examined at 1.4 K, but no change in the resonance line was observed in the static electric field up to 3.29 kV/cm.

Magneto-Optical Studies of Excited States of the Cl Donor in CdS

We have studied the $2s$ and $2p$ levels of the Cl donor in CdS by two methods: first, by observing "two-electron transitions" in which an exciton bound to the neutral donor Cl decays, leaving the donor in its $n=2$ excited states; second, by observing Raman-scattering transitions between the $n=1$ and $n=2$ donor levels. We have accurately measured the positions of the $2{p}_{x}$, $2{p}_{z}$, and $2s$ levels relative to the $1s$ state to be 24.36 \ifmmode\pm\else\textpm\fi{} 0.02, 24.19 \ifmmode\pm\else\textpm\fi{} 0.02, and 23.88 \ifmmode\pm\else\textpm\fi{} 0.02 meV; the anisotropy factor $\ensuremath{\alpha}=0.054\ifmmode\pm\else\textpm\fi{}0.005$; and the electron mass ${m}_{\ensuremath{\perp}}=0.190\ifmmode\pm\else\textpm\fi{}0.002$. With less precision, we have measured ${m}_{\ensuremath{\parallel}}=0.180\ifmmode\pm\else\textpm\fi{}0.010$ and estimated the donor binding energy to be 32.7 \ifmmode\pm\else\textpm\fi{} 0.4 meV.

Note on Spin-Lattice Relaxation of Shallow Donors in Wurtzite-Type Semiconductors

The spin-lattice relaxation rates of shallow donors in wurtzite-type semiconductors are calculated. The admixture of the excited p -states with the ground 1 s -state through the k -linear term in the conduction band and the trigonal component of the impurity potential plays an important role in the present relaxation mechanism in contrast with the case of the many valley semiconductors. In particular, it is shown that the k linear term in the \(\varGamma_{7}\) conduction band may contribute to the spin-lattice relaxation rate of shallow donors in CdS at liquid helium temperatures, taking into account the concentration dependent relaxation process, This relaxation process occurs through the hopping motion of donor electrons accompanied by reversal of spin orientation.

Spin resonance of donors in CdS

R.3 Hyperfine structure due to interaction with Ni6’ has been detected”’ in samples doped with nickel enriched to contain 83 per cent of that isotope. The principal axes of the hyperfine interaction are the same as those of the g-tensor, and one finds the principal values A, = 10.3, A, 6 16, A, = 12.2 (in units of 1O-a cm-l) in the directions corresponding to g, = 2.1128, g, = 2.0294, and g, = 2.0176.