Using photovoltage (PV) spectroscopy we analyse the electronic structure of a series of GaBi x As x 1− /(Al)GaAs dilute bismide quantum well (QW) laser structures. The use of polarisation-resolved PV measurements allows us to separately identify transitions involving bound light-and heavy-hole states in the QWs, as well as bound-to-continuum transitions from the QWs to the barriers. Analysis of these transitions enables us to probe the GaBi x As x 1− /(Al) GaAs conduction and valence band offsets, thereby quantifying the band offsets. Using a 12band k p• Hamiltonian, we extract the band offsets in the QWs explicitly by constraining the Birelated parameters of the model against the experimentally measured transition energies. The PV measurements and k p• calculations we present provide the first explicit confirmation of a type-I band offset at the GaBi x As x 1− /GaAs heterointerface near x = 2%. This result, combined with the theory we present for calculating the band offsets at GaBi x As x 1− /(Al)GaAs heterointerfaces, can be used to determine the band offsets at arbitrary Bi composition x.

We present a theoretical study of the gain characteristics of GaBixAs1−x/(Al)GaAs dilute bismide quantum well (QW) lasers. After providing a brief overview of the current state of development of dilute bismide alloys for semiconductor laser applications, we introduce the theoretical model we have developed for the description of the electronic and optical properties of dilute bismide QWs. Using a theoretical approach based on a 12-band k·p Hamiltonian we then undertake a detailed analysis of the electronic and optical properties of a series of ideal and real GaBixAs1−x/(Al)GaAs QW laser structures as a function of Bi composition x. We theoretically optimize the gain characteristics of an existing low x device by varying the Al composition in the barrier layers, which governs a trade-off between the electronic and optical confinement. The theoretical results are compared to temperature-dependent spontaneous emission measurements at low x, which reveals the presence of significant Bi-induced inhomogeneous broadening of the optical spectra. We also investigate the gain characteristics of GaBixAs1−x/(Al)GaAs QW lasers at higher values of x, including a QW designed to emit at 1.55 µm. Our theoretical results elucidate the impact of Bi incorporation on the electronic and optical properties of GaAsbased QW lasers, and reveal several general trends in the gain characteristics as a function of x. Overall, our analysis confirms that dilute bismide alloys are a promising candidate material system for the development of highly efficient, uncooled GaAsbased QW lasers operating at telecommunication wavelengths.

The authors observe a bistability of threshold in a quantum dash ridge-waveguide laser diode at temperatures below 230 K. A giant and sometimes negative characteristic temperature, T 0 , is measured at temperatures between 230 K and 320 K. They analyse the temperature dependent light-current characteristics of this device, and a similar device with lower barriers, to gain an insight into the mechanism causing bistable behaviour. A rate equation model shows localisation and passive saturable absorption as the causes of the bistable behaviour in the higher barrier laser at low temperature. They find good qualitative agreement between the experimental and the theoretical results.

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