Relaxation l.s.a. mode in InP

What are believed to be the first convincing observations of relaxation l.s.a.-mode operation in InP are reported. Devices fabricated from vapour-phase epitaxial material have shown the characteristic `signatures¿ of the mode in oscillators operated in S- and X-bands. So far, conversion efficiencies have not exceeded those for comparable samples in GaAs, almost certainly owing to remaining material limitations in the relatively thick active layers. The significance of the results lies, in practical terms, in the promise of high-peak-power sources with acceptable efficiencies, and, in diagnostic terms, in the derived information on the magnitude of the fundamental transferred-electron characteristic peak/valley ratio in InP and in achievable material quality factors for thick epitaxial layers.