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Register a new userDetermination of carrier density and dynamics via magneto-electroluminescence spectroscopy in resonant tunneling diodes
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Edson Rafael Cardozo de Oliveira
Publication date
2020
fields
Physics
and research's language is
English
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We study the magneto-transport and magneto-electroluminescence properties of purely n-doped GaAs/Al$_{0.6}$Ga$_{0.4}$As resonant tunneling diodes with an In$_{0.15}$Ga$_{0.85}$As quantum well and emitter prewell. Before the resonant current condition, magneto-transport measurements reveal charge carrier densities comparable for diodes with and without the emitter prewell. The Landau level splitting is observed in the electroluminescence emission from the emitter prewell, enabling the determination of the charge carrier build-up. Our findings show that magneto-electroluminescence spectroscopy techniques provide useful insights on the charge carrier dynamics in resonant tunneling diodes and is a versatile tool to complement magneto-transport techniques. This approach will drive the way for developing potentially more efficient opto-electronic resonant tunneling devices, by e.g., monitoring voltage dependent charge accumulation for improving built-in fields and hence to maximize photodetector efficiency and/or minimize optical losses.
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N-polar GaN/AlN resonant tunneling diodes are realized on single-crystal N-polar GaN bulk substrate by plasma-assisted molecular beam epitaxy growth. The room-temperature current-voltage characteristics reveal a negative differential conductance (NDC) region with a peak tunneling current of 6.8$pm$ 0.8 kA/cm$^2$ at a forward bias of ~8 V. Under reverse bias, the polarization-induced threshold voltage is measured at ~$-$4 V. These resonant and threshold voltages are well explained with the polarization field which is opposite to that of the metal-polar counterpart, confirming the N-polarity of the RTDs. When the device is biased in the NDC-region, electronic oscillations are generated in the external circuit, attesting to the robustness of the resonant tunneling phenomenon. In contrast to metal-polar RTDs, N-polar structures have the emitter on the top of the resonant tunneling cavity. As a consequence, this device architecture opens up the possibility of seamlessly interfacing$-$via resonant tunneling injection$-$a wide range of exotic materials with III-nitride semiconductors, providing a route to explore new device physics.
We explore the nature of the electroluminescence (EL) emission of purely n-doped GaAs/AlGaAs resonant tunneling diodes (RTDs) and the EL evolution with voltage. A singular feature of such a device is unveiled when the electrical output current changes from high to low and the EL on-off ratio is enhanced by 2 orders of magnitude compared to the current on-off ratio. By combining the EL and current properties, we are able to identify two independent impact ionization channels associated with the coherent resonant tunneling current and the incoherent valley current. We also perform the same investigation with an associated series resistance, which induces a bistable electrical output in the system. By simulating a resistance variation for the current-voltage and the EL, we are able to tune the EL on-off ratio by up to 6 orders of magnitude. We further observe that the EL on and off states can be either direct or inverted compared to the tunneling current on and off states. This electroluminescence, combined with the unique RTD properties such as the negative differential resistance (NDR) and high frequency operation, enables the development of high speed functional opto-electronic devices and optical switches.
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The authors combine acousto-optoelectric and multi-channel photon correlation spectroscopy to probe spatio-temporal carrier dynamics induced by a piezoelectric surface acoustic wave (SAW). The technique is implemented by combining phase-locked optical micro-photoluminescence spectroscopy and simultaneous three-channel time resolved detection. From the recorded time correlated single photon counting data the time transients of individual channels and the second and third order correlation functions are obtained with sub-nanosecond resolution. The method is validated by probing the correlations SAW-driven carrier dynamics between three decay channels of a single polytypic semiconductor nanowire on a conventional LiNbO$_mathrm{3}$ SAW delay line chip. The method can be readily applied to other types of nanosystems and probe SAW-regulated charge state preparation in quantum dots, charge transfer processes in van der Waals heterostructures or other types of hybrid nanoarchitectures.
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