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Strain-Compensated Type-II “W” Quantum Wells for GaAs-Based Telecom Lasers
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The realization of efficient semiconductor lasers on GaAs substrates operating at 1.55 μm and beyond remains a technological challenge. As a potential solution, epitaxial heterostructures with type-II band alignment are currently discussed as an active region. Each individual layer in such heterostructures features a comparably large bandgap energy; therefore, spurious effects in laser operation such as reabsorption, multi-photon absorption, or Auger scattering are expected to be suppressed. The actual laser operation occurs across the internal interfaces as the electron and hole wave functions have their extrema in adjacent layers. Hence, a large wave-function overlap is key for efficient recombination. A direct comparison of symmetric and asymmetric Ga(N,As)/Ga(As,Bi) type-II quantum well heterostructures reveals that the symmetry of the layer arrangement drastically influences the charge-carrier recombination: disorder in the Ga(As,Bi) layer has more prominent effects for the asymmetric configuration compared to the symmetric one. The temperature dependence of the emission energy is mainly influenced by the Ga(N,As)-electron layers, while the temperature dependence of the full width at half maximum and the excitation dependence of the emission energy are dominated by the Ga(As,Bi)-hole layers. Photoluminescence excitation spectroscopy reveals the corresponding carrier-relaxation paths to the type-II transition.
The potential to extend the emission wavelength of photonic devices further into the near-and mid-infrared via pseudomorphic growth on conventional GaAs substrates is appealing for a number of communications and sensing applications. We present a new class of GaAs-based quantum well (QW) heterostructure that exploits the unusual impact of Bi and N on the GaAs band structure to produce type-II QWs having long emission wavelengths with little or no net strain relative to GaAs, while also providing control over important laser loss processes. We theoretically and experimentally demonstrate the potential of GaAsBi/GaNAs type-II QWs on GaAs and show that this approach offers optical emission and absorption at wavelengths up to ~3 µm utilising strain-balanced structures, a first for GaAs-based QWs. Experimental measurements on a prototype GaAs(0.967)Bi(0.033)/GaN(0.062)As(0.938) structure, grown via metal-organic vapour phase epitaxy, indicate good structural quality and exhibit both photoluminescence and absorption at room temperature. The measured photoluminescence peak wavelength of 1.72 µm is in good agreement with theoretical calculations and is one of the longest emission wavelengths achieved on GaAs to date using a pseudomorphically grown heterostructure. These results demonstrate the significant potential of this new class of III-V heterostructure for long-wavelength applications.
The mechanism of Auger recombination in type‐II heterostructures is studied theoretically. It is shown that the Auger recombination rate is a power function of temperature rather than an exponential function as in bulk materials. The feasibility of suppression of the Auger recombination process in the type‐II heterostructures is demonstrated. The possibility of controlling the Auger recombination rate is shown to be very important for development of optoelectronic devices with improved characteristics. © 1995 American Institute of Physics.