Luminescence spectra of InGaN/AlGaN/GaN p-n-heterostructures were studied at reverse bias sufficient for impact ionization. There is a high electric field in the active InGaN-layer, and the tunnel component of the current dominates at the low reverse bias. Avalanche breakdown begins at |Vth|> 8⋄10 V, i.e. ≈3 Eg/e. Radiation spectra have a short wavelength edge 3.40 eV, and maxima in the range 2.60⋄2.80 eV corresponding to the injection spectra. Mechanisms of the hot plasma recombination in p-n-heterojunctions are discussed.