We have used subpicosecond laser pulses to study the generation of nonequilibrium LO phonons in both InP and InAs. These two semiconductors provide a contrast in that the decaying of the Raman signal probes different relaxation mechanisms. In InP, for example, we find that the decay of the Raman signal is dominated by the lifetime of the LO phonons. On the contrary, in InAs, our studies show that the decay of the Raman signal is governed by the time required for electrons to return to the Γ valley from the L valleys of the conduction bands. In addition, nonequilibrium electron distributions were also studied in InP and InAs. We have found that the single-particle-scattering spectrum in InAs can only be observed with the use of a much longer laser pulse width than subpicosecond as a result of electron intervalley scattering and very small electron effective mass. © 1996 The American Physical Society.

• Received 29 November 1995

DOI:https://doi.org/10.1103/PhysRevB.53.9847