Infrared radiation from breakdown plasmas in Si, GaSb, and Ge: Evidence for direct free hole radiation

The luminescence during avalanche breakdown of Si, GaSb, and Ge p–n-junctions is measured in the energy range 0.5Eg < hv ≦ Eg. As has been shown in most other group IV and III–V semiconductors, these spectra exhibit bands which extend to energies far below and above Eg with a maximum near 0.8Eg, and which are essentially independent of the lattice temperature. These spectra can be explained by direct radiative transitions between different valence bands. This is shown explicitly for Si and GaP. The theory of Baraff is used for the calculation of hot carriers distribution functions. The parameters of this function are derived from photo-current multiplication data. Theoretical expressions for indirect intraband transitions of hot carriers (i.e. “bremsstrahlung”) yield emission bands, which do not contain the experimentally observed low energy decrease of the spectra. In highly efficient direct gap materials and in efficient GaP, additional lines caused by usual minority carrier recombination are observed at low temperatures.