Oscillator strengths, quantum efficiencies, and laser cross sections of Yb3+ and Er3+ in III-V compounds

An absolute oscillator strength is obtained for the first time for a rare earth in a III-V compound semiconductor. The value for Yb3+ in InP is f=(3±1)×10−6. It is of same order as for insulating ionic hosts, confirming what available theory can predict. From observed emission spectra, laser cross sections of 10−21 cm2 for Yb3+ at 1.0 μm and <1.4×10−20 cm2 for Er3+ at 1.54 μm are obtained. Yb3+, entering III-V compounds more covalently, presents a quantum efficiency for direct photon excitation two orders of magnitude smaller than Er3+. Predicted laser gains are in the range of 10−2 to a few 10−1 cm−1, showing that gains will be marginal in semiconductor devices of usual dimensions.