Abstract

A new complex, two excitons bound to a neutral double acceptor, was first observed in photoluminescence (PL) measurement of Zn doped Ge samples with extremely low concentration of other impurities. The complex, which we call a bound-double exciton complex (BDEC), has a novel feature of the closed hole shell structure and provides an extraordinarily strong PL intensity. Such a complex has been neither proposed nor observed in semiconductors. The PL spectra from our least doped sample (N_A = 1.2 x 10¹⁴ cm⁻³), denoted Ge/Zn-1, are shown in Fig. 1. The peaks α are unambiguously assigned to radiative recombination of BDEC by strong dependence of their PL intensity on excitation intensity. The spectra also contain another kind of luminescence arising from a single exciton bound to the double acceptor, that we will denote (BE)_da. Existence of (BE)_da was originally predicted by Hopfield and first detected for unidentified double acceptor in GaSb.¹ To our knowledge, there are no reports on (BE)_da in Si or Ge. The broad peaks γ were assigned to (BE)_da by their weak dependence on excitation intensity.

© 1984 Optical Society of America