We present a detailed investigation of light emission phenomena connec
ted with the presence of hot carriers in AlGaAs/GaAs heterojunction bi
polar transistors. Electrons heated by the strong electric field at th
e base-collector junction lead to both impact ionization and light emi
ssion. A new general-purpose weighted Monte Carlo procedure has been d
eveloped to study such effects. The measured hot electroluminescence i
s attributed to radiative recombinations within the valence and the co
nduction bands. Good agreement is found between theory and experiment.