Carrier Recombination Dynamics of Surface-Passivated Epitaxial (100)Ge, (110)Ge, and (111)Ge Layers by Atomic Layer Deposited Al₂O₃

Abstract

Germanium (Ge) and its heterostructures with compound semiconductors offer a unique optoelectronic functionality due to its pseudo-bandgap nature, that can be transformed to a direct bandgap material by providing strain and/or mixing with tin. Moreover, two crystal surfaces, (100)­Ge and (110)­Ge, that are technologically important for ultralow power fin or nanosheet transistors, could offer unprecedented properties with reduced surface defects after passivating these surfaces by atomic layer deposited (ALD) dielectrics. In this work, the crystallographically oriented epitaxial Ge/AlAs heterostructures were grown and passivated with ALD Al2O3 dielectrics, and the microwave photoconductive decay (μ-PCD) technique was employed to evaluate carrier lifetimes at room temperature. The X-ray photoelectron spectroscopy analysis reveals no role of orientation effect in the quality of the ALD Al2O3 dielectric on oriented Ge layers. The carrier lifetimes measured using the μ-PCD technique were benchmarked against unpassivated Ge/AlAs heterostructures. Excitation wavelengths of 1500 and 1800 nm with an estimated injection level of ∼1013 cm–3 were selected to measure the orientation-specific carrier lifetimes. The carrier lifetime was increased from 390 ns to 565 ns for (100)Ge and from 260 ns to 440 ns for (110)Ge orientations with passivation, whereas the carrier lifetime is almost unchanged for (111)Ge after passivation. This behavior indicates a strong dependence of the measured lifetime on surface orientation and surface passivation. The observed increase (>1.5×) in lifetime with Al2O3-passivated (100)Ge and (110)Ge surfaces is due to the lower surface recombination velocity compared to unpassivated Ge/AlAs heterostructures. The enhancement of carrier lifetime from passivated Ge/AlAs heterostructures with (100)Ge and (110)Ge surface orientations offers a path for the development of nanoscale transistors due to the reduced interface state density.

GeSn-on-GaAs with photoconductive carrier lifetime >400 ns: role of substrate orientation and atomistic simulation

“…This could be attributed to high electrical conductivity. 19,21 This effect is widely noted for epitaxial Ge on (111)A GaAs with and without surface passivation, 23 possibly ruling out the use of (111)A oriented epitaxial GeSn active layer in optoelectronics.…”

“…There are variations in the semiconductor properties like carrier lifetime ( τ ), mobility ( μ ), conductivity, surface state density ( N ss ), and density of interface states ( D it ), based on crystal orientation. 19–23 For instance, it is noted that among (100), (110), and (111) crystal orientations, the (110) surface is least conductive in Si, Ge, and GaAs wafers, and N ss is least for (100) surfaces in Ge and Si. 19,21 In addition, the epitaxial Ge layers when grown on oriented and misoriented GaAs substrates exhibit different materials properties 24–26 and metal–oxide-semiconductor capacitor properties.…”

“…1,2 In addition, high carrier lifetime signifies low leakage current due to D it and N ss in a transistor. 20,23,27 Moreover, the current Si non-planar devices like fin field effect transistors (FinFETs), gate-all-around FETs, and nanosheet FETs utilize (100) and (110) orientations. 29–36 Furthermore, substrate misorientations (100)/2° towards 〈110〉 direction have an impact on these properties, 37–39 which becomes crucial in heterostructure material systems.…”

Elucidating the Role of InGaAs and InAlAs Buffers on Carrier Dynamics of Tensile-Strained Ge Double Heterostructures

“…Material quality strongly affects the defect-limited carrier lifetime, which follows Shockley–Read–Hall (SRH) carrier dynamics and, as such, can indicate the viability of a material for device-based applications. , The presence of defects and impurities within the bulk of the material can significantly alter the lifetime of carriers, as they act as trapping and recombination centers. Additionally, surface roughness plays a crucial role in adversely affecting the lifetime of carriers, with unpassivated active layers showing degraded carrier lifetime . The most widespread used technique in this regard is the μ-PCD technique, which allows for noncontact and rapid collection and analysis of minority carrier lifetime, − circumventing multiple microfabrication steps that can alter the material quality.…”

Observation of the Transition from Triple Bonds to Single Bonds between Ru–Ge Bonding in RuGeO(CO)n– (n = 3–5)

“…Main group metal element germanium (Ge) and its oxides have important applications in fields like aerospace, solar cells, and biomedicine, in addition to their potential as catalysts in the optical industry. − Moreover, ruthenium (Ru), as a homotope of iron, has similar chemical reactivity. − Investigating the reaction of CO with the Ru–GeO heterodimers would not only help understand the chemical bonding between main group metal and transition metal but also can be used as a model system to study CO/GeO oxidation on metal surface from the molecular level, thereby facilitating the exploration and development of novel catalysts.…”