Stimulated emission from bulk field-ionized GaAs

High-field domains passing through
n
-type gallium arsenide pulsed above a critical field produce electron-hole pairs by impact ionization, resulting in emission of recombination radiation of band gap energy. Specimens have been made in a configuration that allows intense ionization to be produced at 78°K in material having initial electron densities of the order of
5 \times 10^{17}
cm
^-3
Above a certain threshold ionization density, stimulated emission occurs; the linewidth is of the order of 30 Å and emission is mainly within an angle of 7 degrees to the normal to the plane parallel polished faces of the specimen. The threshold current varies little with temperature up to 170°K and above this increases linearly. At currents above the threshold, the spectrum broadens somewhat; the output power is measured to be about 3 watts. The near-field pattern shows that lasing occurs over small separated areas that vary in location from pulse to pulse. Overall power efficiency of the device is low; if, however, only the lasing areas are considered, the efficiency comes much nearer to the theoretical maximum which, it is argued, is about 5 percent. Time dependence of the spectral distribution is complicated and evidence is given to show that carrier heating is an important phenomenon. The lasing process is similar to that occurring in a junction diode laser; some points of difference are discussed. The output frequently shows an unexplained strong polarization.