Charge-Carrier Recombination in Dilute Bismuthide Semiconductors
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The rapidly increasing use of the internet through cloud services or streaming-based applications creates a steadily growing demand for faster and more stable data transmission. Semiconductor lasers are a key component of the current data communication infrastructure. The aim of current research is to investigate new material systems or concepts to improve the efficiency and reliability of these lasers. In recent years, bismuth containing semiconductors have come into focus. In addition to higher energy efficiency, they also promise to extend the range of addressable emission wavelengths beyond the data-communication band into the mid-infrared spectral range. In this thesis, two concepts of bismuth containing semiconductors are analyzed using spectroscopic methods. On the one hand, Ga(N,As)/ Ga(As,Bi) heterostructures are investigated. Here, the spatially indirect transition (type-II transition) between electrons from the Ga(N,As) layers and holes in the Ga(As,Bi) layers is analyzed. The aim is to understand, how the respective layers affect the emission properties of the spatially indirect transition. The disorder effects of the Ga(N,As) layers significantly influence the disorder characteristics of the emission energy, whereas the Ga(As,Bi) layer clearly dominates the line width. Localized states in the Ga(As,Bi) layer are identified as the cause. Furthermore, the difference between symmetric (W) and asymmetric type-II structures is investigated. The symmetric structure consists of two Ga(N,As) layers, which are arranged around the Ga(As,Bi) layer. Fewer disorder effects in the recombination via the type-II transition are observed for the symmetric arrangement. Finally, additional experiments provide information about the recombination channels in such type-II andW-type semiconductor heterostructures. Electrons that are excited in the GaAs and Ga(N,As) layers contribute signi cantly to the recombination via the spatially indirect transition. The results obtained here provide direct information about the dominant optical loss channels within the structures and, thus, point to potentials for optimization. This enables targeted improvements that allowthe optical properties to be tailored as precisely as possible to a requirement profile. Secondly, the quaternary material system (Ga,In)(As,Bi) is investigated. For optoelectronics on the InP platform, this material system has very promising properties for addressing the mid-infrared spectral range. The epitaxial growth of such quaternary system is challenging. In particular, as bismuth has a strong influence on the incorporation of the Group-III elements. This makes it difficult to deposit layers with a specific desired elemental composition. Using input from photoluminescence and Xray photoelectron spectroscopy, establishes a relation between disorder properties and growth parameters. Gallium and bismuth precursor partial-pressures during growth are correlated with bismuth segregation. This enables improved growth control. The investigation of the charge-carrier temperatures by means of photoluminescence spectroscopy shows that they are influenced by the precursor partial-pressures, too. For lower gallium partial pressures, lower charge-carrier temperatures and, thus, lower disorder effects are observed.