IMPACT IONIZATION AND LIGHT-EMISSION IN GAAS METAL-SEMICONDUCTOR FIELD-EFFECT TRANSISTORS

A study of light emission from GaAs metal-semiconductor field effect t ransistors and its connection with impact ionization phenomena is pres ented. First, the electrical behavior of the device in the preavalanch e regime is characterized by measuring the excess gate current. Numeri cal simulations are performed, showing that the excess gate current is due to the collection of impact-ionization-generated holes at the gat e electrode. Then, the energy distribution of the emitted photons in t he range 1.5-3.1 eV is analyzed. The integrated intensity of photons e mitted with energy above 1.5 eV is shown to be proportional, for large negative gate biases, to the product of gate and drain currents, sugg esting direct recombination of channel hot electrons with impact-ioniz ation-generated holes as the dominant emission mechanism. The deviatio n from simple proportionality at gate voltages around 0 V indicates th at in implanted devices in open channel conditions other mechanisms, s uch as bremsstrahlung, may significantly contribute to the intensity o f the emitted light.