Theory of the Electronic and Optical Properties of Dilute Bismide Quantum Well Lasers

Abstract

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.

GaAs-based dilute bismide semiconductor lasers: Theory vs. experiment

“…For the experimental analysis, multi-section devices were fabricated and measurements of the SE and optical gain spectra were undertaken using the segmented contact method. By comparing the measured and calculated SE spectra, we have determined that (i) the spectral broadening is best described using a hyperbolic secant lineshape, and (ii) the large spectral linewidth, δ = 25 meV, is relatively independent of temperature, indicating strong inhomogeneous broadening associated with Bi-related alloy disorder [7], [8]. Fig.…”

“…Our calculations indicate that Al incorporation in the barrier layers is required for Bi compositions < 6% in order to mitigate the low GaBi x As 1−x /GaAs conduction band offset and bring about appreciable material gain. This leads to a trade-off between the carrier and optical confinement, which can be engineered to minimise the threshold current density [8]. As x is increased, the beneficial effects of compressive strain on the band structure dominate.…”

“…(See Ref. [8] for details.) Secondly, we have performed a detailed comparison between theory and experiment for GaBi x As 1−x /(Al)GaAs QW lasers at low x.…”

“…[5]. The theoretical gain spectra were computed as Γg − α i where the material gain g and optical confinement factor Γ were calculated directly for the laser structure [8], and the internal (cavity) losses α i = 15 cm −1 were extracted from optical absorption measurements [9]. In order to compare the measured and calculated spectra, analysis of the measured gain spectrum at each J was undertaken in order to extract a corresponding carrier density n to be used in the theoretical calculations [9].…”

“…In our model, the material gain spectrum at fixed carrier density is computed by transforming the SE spectrum. The resulting thermodynamic consistency means that each current density (J) in experiment can be associated directly with a carrier density (n) in the theoretical calculations, thereby facilitating direct comparison between theory and experiment [8], [9]. Key to our computation of the optical spectra is the direct use of the QW eigenstates, so that the crucial effects of Bi-induced hybridisation and epitaxial strain are accounted for explicitly.…”