Excited states of donor bound excitons and bound multiexciton complexes in silicon

The high resolution photoluminescence spectra reported here show new lines giving the first evidence of excited states of excitons bound to P donors in Si. These excited states are of crucial importance for a recently proposed theory of the bound multiexciton complexes which is based on a shell model. In addition several other new lines associated with the decay of the bound multiexciton complexes, which were predicted by the shell model theory, have been observed and their behaviour is found to be in argeement with the theory.     

Experimental evidence against the shell model of bound multiexciton complexes in silicon

We report time resolved and piezospectroscopic measurements on the bound exciton low energy satellite line series induced by the donor phosphorus in silicon. This line series was recently interpreted in terms of a multiple exciton model arranging electrons and holes in shell states around the neutral impurity. Our experimental data are in significant contradiction to a number of properties predicted by this model. We believe that the shell model has therefore to be discarded as a means of the lines interpretation.     

A new model for bound multiexciton complexes

It is proposed that bound multiexciton complexes (BMEC) in Si may be understood in terms of a shell model analogous to those used to describe many electron atoms and atomic nuclei. A detailed scheme has been developed for the case of donor-BMEC's and applied to phosphorus donors. A number of experimental results are explained including the low energy of some BMEC recombination photons, Zeeman and stress-induced spectra, and newly observed luminescence lines. Some predictions are made.     

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

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.     

Comments on “experimental evidence against the shell model of bound multiexciton complexes in silicon”

The recent claims of the refutation of Kirczenow's shell model of the bound multiexciton complexes are shown to be without foundation. It is shown that the shell model does in fact explain much of the piezo-spectroscopic data upon which those claims were, in part, based. Furthermore, the time-resolved luminescence data which appeared to convincingly rule out the shell model are shown to be in disagreement with the detailed time-resolved studies reported here. The present studies support the shell model, and a possible cause for the discrepancy between the two sets of data is suggested.     

Evidence of multiexciton complexes bound to neutral acceptors in GaAs

The first observation of six sharp photoluminescence lines with energies less than the energies of the lines associated with a radiative recombination of a single exciton bound to a neutral acceptor in high purity epilayers of GaAs at liquid helium temperature is reported. It is proposed that these lines arise as a result of a radiative recombination of an exciton in a multiexciton complex bound to a neutral acceptor.     

Observation of luminescence from bound multiexciton complexes in gallium doped germanium

Spectrally resolved luminescence associated with the decay of bound multiexciton complexes in optically excited Ge:Ga is observed. This is the first reported observation of multiexciton complexes in p-type germanium. The observed spectra are consistent with the shell model for bound multiexciton complexes.No-phonon, TA, LA, and TO phonon assisted luminescence are observed. From these spectra, the energies of the LA, TA, and TO phonons in Ge:Ga are determined.     

Photoluminescence studies of bound multiexciton complexes associated with Li in Si

New details of the photoluminescence spectrum of Si doped with the interetitial donor Li are reported. The spectrum is found to be very different from that of Si doped with substitutional donors, and these differences are interpreted in terms of the shell model of the structure of bound multiexciton complexes.     

Polarizabilities of shallow donors in silicon

Capacitance measurements on N-type As, P, and Sb-doped Si samples have been made between 4.2 and 1.35°K, from 0.3 to 100 kHz as a function of (N_D ? N_A) [high purity to 2.7 × 10¹⁸/cm³]. From the dielectric constant variation with (N_D ? N_A) donor polarizabilities α_AS, α_P, and α_Sb are found respectively to be $\text{1.0±0.1, 2.4±0.4,}\text{and}\text{3.1±0.3 × 10}{}^5\text{A}\text{?}{}^3$.     

Polarizabilities of shallow donors in silicon — A comment

A recent experiment on n-type As, P and Sb-doped Si samples to study the donor polarizabilities by the capacitance measurement should be reinterpreted on the basis of the d.c. resistivity data below 4.2 K together with the concentration vs resistivity relations at room temperature.     

Polarizability of shallow donors in silicon - A reply

A reply to the comment of Yoshihiro and Yamanouchi is made explaining the role of Schottky barriers on the capacitance results determined previously by Bethin, Castner, and Lee. Earlier concentration-dependent dielectric constant measurements for Sb-doped Ge are also noted.     

Photoluminescence lifetimes of the In,Tl and Bi bound excitons in silicon

We report measurements of the photoluminescence decay times of bound excitons associated with the donor Bi and the acceptors In and Tl in silicon. These are the first reported results for Tl and Bi, respectively the deepest simple acceptor and donor in silicon. The Tl bound exciton lifetime is found to be in good agreement with a value extrapolated from the results for shallower acceptors. The Bi bound exciton, on the other hand, has a much shorter lifetine than an extrapolation from the shallower donor results would predict.     

Determination of the deformation potential of shallow donors in silicon

The stress dependence of the energy of the ground state of group V impurities (P, Sb) in silicon was investigated by measurement of the Hall effect in a wide range of pressures. A conclusion was reached that the deformation potential of the lowest impurity state of shallow donors (Ξ¹_u) in silicon differs from the deformation potential of the conduction band (Ξ_u), the value of this difference being dependent on the type of the impurity. According to our data, the most probable values for ($\text{Ξ}{}_{\mathrm{u}}\text{ Ξ}{}^1{}_{\mathrm{u}}$) are 0.12 eV for phosphorous-doped silicon and 0.06 eV for antimony-doped silicon.     

Central cell effects on the polarizabilities of shallow donors in silicon

With the Topp and Hopfield form for the ionic pseudopotentials, the screened impurity pseudopotentials of the shallow donors P, As and Sb in silicon are obtained in closed form in the linearized Thomas-Fermi model. The results are compared with the screening using a k-dependent dielectric function. Using these impurity pseudopotentials in the multivalley effective mass equation, the binding energies of these donors in Si are estimated variationally. Adopting the Hasse variational method, the polarizabilities of the P, As and Sb donors in Si are computed and are found to be in excellent agreement with the polarizability values of isolated P and Sb in Si, deduced from recent piezocapacitance measurements.