Using experimental measurements of the gain–current characteristic as a function of temperature in InGaAs quantum-dot lasers, we demonstrate that it is the population of wetting-layer states that leads to a saturation of the population inversion in dot states and hence to the saturation of gain in a quantum-dot laser. At 300 K, the maximum modal gain for a three-layer structure is reduced from 53 to 14 cm−1.

We describe a technique for the measurement of optical gain and loss in semiconductor lasers using a single, multisection device. The method provides a complete description of the gain spectrum in absolute units and over a wide current range. Comparison of the transverse electric and transverse magnetic polarized spectra also provides the quasi-Fermi-level energy separation. Measurements on AlGaInP quantum well laser structures with emission wavelengths close to 670 nm show an internal loss of 10 ${\mathrm{cm}}^{\mathrm{-1}}$ and peak gain values up to 4000 ${\mathrm{cm}}^{\mathrm{-1}}$ for current densities up to 4 ${\mathrm{kA cm}}^{\mathrm{-2}}.$

Pulsed light–current characteristics of InGaN/GaN quantum well light-emitting diodes have been measured as a function of temperature, with sublinear behavior observed over the whole temperature range, 130–330 K. A distinctive temperature dependence is also noted where the light output, at a fixed current, initially increases with temperature, before reaching a maximum at 250 K and then decreases with subsequent increases in temperature. On the basis of a drift diffusion model, we can explain the sublinear light–current characteristics and the temperature dependence by the influence of the large acceptor ionization energy in Mg-doped GaN together with a triangular density of states function characteristic of localized states. Without the incorporation of localization effects, we are unable to reproduce the temperature dependence whilst maintaining emission at the observed wavelength. This highlights the importance of localization effects on device performance.

Building optoelectronic devices on a Si platform has been the engine behind the development of Si photonics. In particular, the integration of optical interconnects onto Si substrates allows the fabrication of complex optoelectronic circuits, potentially enabling chip-to-chip and system-to-system optical communications at greatly reduced cost and size relative to hybrid solutions. Although significant effort has been devoted to Si light generation and modulation technologies, efficient and electrically pumped Si light emitters have yet to be demonstrated. In contrast, III–V semiconductor devices offer high efficiency as optical sources. Monolithic integration of III–V on the Si platform would thus be an effective approach for realizing Si-based light sources. Here, we describe the first superluminescent light-emitting diode (SLD) monolithically grown on Si substrates. The fabricated two-section InAs/GaAs quantum-dot (QD) SLD produces a close-to-Gaussian emission spectrum of 114 nm centered at ∼1255 nm wavelength, with a maximum output power of 2.6 mW at room temperature. This work complements our previous demonstration of an InAs/GaAs QD laser directly grown on a Si platform and paves the way for future monolithic integration of III–V light sources required for Si photonics.