D.L. Smith

Binding of an exciton to a neutral acceptor

Abstract The dissociation energy, ED, of an exciton bound to a neutral acceptor is calculated as a function of the electron to hole mass ratio. For a variation of the electron to hole mass ratio of between 0.1 and 1.0, the calculated ratio of ED to the acceptor ionization energy, Ei, is found to vary between 0.075 and 0.13. This variation is in agreement with the experimental values of the ratio found for a number of different acceptors in Si, Ge, GaAs and various II-VI compounds.

Bound exciton lifetimes for acceptors in Si

Abstract We present measurements of the bound exciton lifetimes for the four common acceptors in Si and for the first two bound multiple exciton complexes in Si:Ga and Si:Al. We present a calculation of the Auger transition rate for the acceptor bound excitons in Si which accounts for the observed lifetimes and their dependence on the acceptor type.

Impurity effects in electron hole droplets

Abstract We use a simple model to describe the effects of impurities on the electron hole droplet emission spectrum. In this model, an attractive interaction between the droplet and impurities causes a decrease in droplet density and an increase in the droplet work function. The predictions of the model are in good agreement with experiment.

Capture cross section of excitons on neutral indium impurities in silicon

Abstract Studied of the photoluminescent decay of Si:In bound excitons in the temperature range 10 to 30°K show that the decay is limited by the capture of the exciton on the neutral In site. Measurements of the decay time give values for the capture cross section which change rapidly with temperature ranging between greater than 10 -13 cm 2 at 10°K to about 10 -15 cm 2 at 30°K.

Dependence of the saturation intensity of p-type germanium on impurity concentration and residual absorption at 10.59 μm

Abstract We present a calculation of the saturation intensity Is of p-Ge at 10.59 μm as a function of the impurity concentration. The effect of residual absorption is calculated and found to be important in the interpretation of experiments for intensities much greater than Is.

Absorption and luminescence of the bound exciton in thallium doped silicon

Abstract We report the photoluminescence and absorption spectra of the bound exciton in Si:Tl. Four lines are observed in both spectra in contrast to three lines observed in the Al, Ga, In doped Si. The total oscillator strength is approximately 4x10-4 continuing a trend of increasing oscillator strength with binding energy.

Luminescence of bound exciton and bound multiexciton complexes in Si:Li

Abstract We report on the observation of a number of new lines in the photo- luminescence spectrum of Si:Li. Some of these lines are interpreted as luminescence from excited initial states of the bound exciton and bound multiexciton complexes. Thermodynamic measurements of the binding energy for one and two exciton complexes are reported. One of the bound exciton excited states is correctly positioned to be the final state for the observed decay of the two exciton complex.

Ratio of TO- to LA-phonon assisted luminescence intensities from the exciton and electron-hole condensate in Ge

Abstract The ratio of TO- to LA-phonon assisted luminescence intensities from the exciton and electron-hole condensate is measured as a function of temperature in Ge. A temperature dependence in the exciton ratio, due to a splitting of the exciton ground state, is observed. The condensate ratio is independent of temperature and is equal to the high temperature limit of the exciton ratio.

Auger and radiative recombination of acceptor bound excitons in semiconductors

Abstract We report on a theoretical and experimental study of acceptor bound exciton recombination. We present calculations of phononless Auger and radiative recombination in direct and indirect band gap materials. We consider hydrogenic acceptors in the direct band gap material Hg 1− x Cd x Te in which the band gap can be varied by changing alloy composition. We present calculations of the Auger transition rate and no-phonon oscillator strengths for the common acceptors in Si and Ge. We have measured the bound exciton lifetimes and no-phonon oscillator strengths for the acceptors in Si and find reasonable agreement with the calculated values.

Phonon damping of the electron-hole droplet motion

Abstract We report on a study of phenomena limiting the motion of electron-hole droplets in Ge. The role of screening of the carrier-phonon interaction in the droplet by the carriers making up the droplet is examined using a Hartree approximation. We consider damping of the droplet motion for droplet velocities both greater and less than the sound velocity.