Microscopic analysis of interface composition dynamics in m-plane AlInN

We present first microscopic evidence on approximately two monolayers of interfacial indium depletion in one-directionally lattice-matched AlInN grown on m-plane GaN as measured by energy dispersive X-ray spectroscopy. Contrary to other reports, we find no significant incorporation of parasitic gallium into the volume material, but only some spreading of gallium across the GaN/AlInN heterointerface. Using a quantitative description of this behaviour, we conclude that the observed effects are not depending on the crystal orientation, nominal stoichiometry and strain state of the AlInN, but rather represent an inherent characteristic of its growth dynamics, related to the differences in metal-nitrogen binding energies of AlN and InN

Plasma Profiling Time-of-Flight Mass Spectrometry for Fast Elemental Analysis of Semiconductor Structures with Depth Resolution in the Nanometer Range

Plasma profiling time of flight mass spectrometry (PP-TOFMS) has recently gained interest, as it enables the elemental profiling of semiconductor structures with high depth resolution in short acquisition times. As recently shown by Tempez et al., PP-TOFMS can be used to obtain the composition in the structures for modern field effect transistors [1]. There, the results were compared to conventional SIMS measurements. In the present study, we compare PP-TOFMS measurements of an Al-/In-/GaN quantum well multi stack to established micro- and nano-analysis techniques like cathodoluminescence (CL), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). We show that PP-TOFMS is able to resolve the layer structure of the sample even more than 500 nm deep into the sample and allows the determination of a relative elemental composition with an accuracy of about 10 rel. %. Therefore, it is an extremely rapid alternative method to obtain semiconductor elemental depth profiles without expensive and time consuming sample preparation as it is needed for TEM. Besides, PP-TOFMS offers better depth resolution and more elemental information than for example electrochemical capacitance-voltage (ECV), as the acquisition of all elements occurs in parallel and not only electrically (ECV) or optically (CL) active elements are observed

Semiconductor membranes for electrostatic exciton trapping in optically addressable quantum transport devices

Combining the capabilities of gate defined quantum transport devices in GaAs-based heterostructures and of optically addressed self-assembled quantum dots could open broad perspectives for new devices and functionalities. For example, interfacing stationary solid-state qubits with photonic quantum states would open a new pathway towards the realization of a quantum network with extended quantum processing capacity in each node. While gated devices allow very flexible confinement of electrons or holes, the confinement of excitons without some element of self-assembly is much harder. To address this limitation, we introduce a technique to realize exciton traps in quantum wells via local electric fields by thinning a heterostructure down to a 220 nm thick membrane. We show that mobilities over $1 \times 10^{6}$ cm$^{2}$V$^{-1}$s$^{-1}$ can be retained and that quantum point contacts and Coulomb oscillations can be observed on this structure, which implies that the thinning does not compromise the heterostructure quality. Furthermore, the local lowering of the exciton energy via the quantum-confined Stark effect is confirmed, thus forming exciton traps. These results lay the technological foundations for devices like single photon sources, spin photon interfaces and eventually quantum network nodes in GaAs quantum wells, realized entirely with a top-down fabrication process.Comment: v2: added missing acknowledgement. v3: fixed typos in acknolwedgemen

Two-color picosecond and continuous-wave experiments on anti-Stokes and Stokes carrier-transfer phenomena in GaAslAl(x)Ga(1-x)As and InGaP2/AlxGa1-xAs heterostructures

We present direct evidence of the two-step absorption process in anti-Stokes photoluminescence in both GaAs/AlxGa1-xAs and InGaP2/AlxGa1-xAs heterostructures using two-color picosecond and continuous-wave photoluminescence experiments. We show information about the lifetime of the defect states that participate in the two-step absorption process. As a result, we conclude that the long-lived states rather than excitons play the dominant role in the two-step absorption process. We also study the possible contribution of the two-step absorption process to Stokes carrier transfer in GaAs/AlxGa1-xAs asymmetric double quantum well structuresclos

Strong evidence for diffusion of point defects in GaInN/GaN quantum well structures

The reduction of the defect density in quantum wells (QWs) is important to maximize the internal quantum efficiency. We investigate non-radiative recombination in GaInN/GaN single QWs (SQWs) grown on In-free and In-containing so-called underlayers (ULs). The non-radiative lifetime of SQWs increases with increasing UL thickness and decreases exponentially with increasing UL growth temperature. Moreover, the presence of low-temperature UL strongly increases the non-radiative lifetime of SQWs. As non-radiative recombination at threading dislocations is efficiently suppressed by means of V-pits, our results suggest that point defects diffuse from the high temperature buffer layer through the UL into the QW. The resulting point defect density in the QW is strongly influenced by the UL growth conditions

Ultrafast Terahertz Nanoseismology of GaInN/GaN Multiple Quantum Wells

Mannan A, Bagsican FRG, Yamahara K, et al. Ultrafast Terahertz Nanoseismology of GaInN/GaN Multiple Quantum Wells. Advanced Optical Materials. 2021;9(15): 2100258.Terahertz (THz) emission spectroscopy and microscopy are applied to investigate the electron and lattice dynamics of Ga0.8In0.2N/GaN multiple quantum wells (MQWs). The THz emission consists of three distinct, differently timed signals, whose physical mechanisms are attributed to i) laser-induced ultrafast dynamical screening of built-in bias electric field in MQWs followed by ii) capacitive charge oscillation of the excited carriers and iii) the coherent acoustic phonon (CAP)-driven polarization surge at the discontinuity between the GaN capping layer and air. These multifunctional optical responses show strong dependence on the quantum well width and photon energies. The temporal separation between the first and third THz pulses corresponds to the propagation of the CAP across the GaN capping layer of the MQW structure, whose thickness can thus be determined with 10 nm precision