Arrays of Si0.80Ge0.20/Si(001) square mesas were epitaxially grown by low pressure chemical vapor deposition to optimize the light emission in the near infrared range. To study the influence of mesa size on light emission the current–voltage characteristics, the spectral photocurrent, and the electroluminescence of p-i-n structures were measured. While the plastic relaxation has a strong influence on the electroluminescence spectra, the current–voltage characteristics are only slightly changed. At low temperatures, a tunneling current was observed and its possible location is discussed. Due to the high SiGe thickness, both the contributions of the no-phonon and transversal optical phonon-assisted transitions to the photocurrent spectra could be observed. Direct evidence of the higher band gap of relaxed SiGe was obtained from electroluminescence studies. © 2003 American Institute of Physics.