Efficient generation of an electron–hole plasma in electronbeam excited GaAs

An investigation was made of the laser energy and spectral characteristics of specially pure epitaxial GaAs films, having a carrier density of 7×10¹³–3×10¹⁵ cm^–3, excited by a pulsed (τ≈100 nsec, f = 50 Hz) 50 keV electron beam at temperatures 92–300°K. It was found that coherent radiation is generated as a result of the recombination of carriers which form a high-density electron-hole plasma. At 92°K, the lasing threshold was fairly low, ~0.4 A/cm², but the differential quantum efficiency was high, ~20–25%. As the temperature increased (up to 300°K), the efficiency decreased negligibly, by a factor of 1.5–2, and j_th varied as ~T^3/2. Waveguide modes, in which the radiation was completely polarized, were observed in the emission spectra of these lasers. The reasons for the formation of a waveguide on excitation of undoped GaAs are discussed.