LONG-WAVELENGTH LOW-THRESHOLD LASERS BASED ON III-V-COMPOUNDS

Low-threshold (J(th) < 100 A/cm2) injection lasers emitting in the wav elength range 3-4 mum and made from InAsSbP/InGaAsSb heterostructures with compositions close to InAs have been studied. The main properties of the laser structures were considered using double heterostructures with an active region of InAs as an example. The value and the temper ature dependence of the threshold current, and the maximum temperature at which lasing was observed were governed by competition between the radiative and nonradiative recombination mechanisms. At low temperatu res (T less-than-or-equal-to 50 K) the radiative recombination mechani sm predominated and the internal quantum efficiency was eta(i) almost- equal-to 100%. The interband Auger recombination, involving the excita tion of a heavy hole to a band split off by the spin-orbit coupling, p redominated at temperatures of 77-150 K and it reduced eta(i) to 2.5% at 150 K. The experimental dependences of the threshold current densit y on the thickness of the active region, on dopant concentration, and on the resonator length were used to find the optimal parameters of th e lasers based on n-type InAs and the free-carrier absorption in the s ame material: when the electron density in this compound was n = 5 X 1 0(16) cm-1, the absorption coefficient was alpha(i) almost-equal-to 5 cm-1 at 77 K. The observed scatter of the laser peak energies exhibite d by InAsSbP/InAs double heterostructures (hv = 393-410 meV at 77 K) w as attributed to possible band-band and band-acceptor transitions, as well as to interface recombination, i.e., the transfer from an energy ''pocket'' in the conduction band to acceptor levels typical of type-I I heterojunctions in a system of this kind.