Abstract
For the past two decades, repeatable resonant tunneling transport of electrons in III-nitride double barrier heterostructures has remained elusive at room temperature. In this work we theoretically and experimentally study III-nitride double-barrier resonant tunneling diodes (RTDs), the quantum transport characteristics of which exhibit new features that are unexplainable using existing semiconductor theory. The repeatable and robust resonant transport in our devices enables us to track the origin of these features to the broken inversion symmetry in the uniaxial crystal structure, which generates built-in spontaneous and piezoelectric polarization fields. Resonant tunneling transport enabled by the ground state as well as by the first excited state is demonstrated for the first time over a wide temperature window in planar III-nitride RTDs. An analytical transport model for polar resonant tunneling heterostructures is introduced for the first time, showing a good quantitative agreement with experimental data. From this model we realize that tunneling transport is an extremely sensitive measure of the built-in polarization fields. Since such electric fields play a crucial role in the design of electronic and photonic devices, but are difficult to measure, our work provides a completely new method to accurately determine their magnitude for the entire class of polar heterostructures.
- Received 7 February 2017
DOI:https://doi.org/10.1103/PhysRevX.7.041017
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
The wave nature of electrons manifests dramatically in resonant tunneling diodes (RTDs), electronic devices where two barriers actually create less resistance to electron flow than one barrier. These diodes rely on quantum-mechanical tunneling, where particles surmount hurdles that they could not penetrate classically. Quantum tunneling of electron waves helps reveal fundamental properties of semiconductor quantum heterostructures. Because this process is robust at room temperature, RTDs are used in ultrafast oscillators to generate signals at terahertz frequencies for communications and in quantum cascade lasers for environmental monitoring and sensing. Such physics remained masked in the revolutionary gallium nitride (GaN) semiconductor family, however, because of high defect densities and poor interface control in crystal growth. By using precision-controlled growth on single-crystal substrates, we report a breakthrough, bringing new understanding of resonant tunneling physics to the GaN family of semiconductors.
Because of the advances in materials, we observe several unexpected features, such as asymmetric tunneling thresholds, which are found to be signatures of the built-in spontaneous and piezoelectric fields originating from the geometric quantum phase induced by the broken crystal symmetry. These features offer a fundamentally new metrology tool to measure internal polarization fields, and they pave the way for applications in high-speed oscillators and quantum cascade lasers, which can reach wavelengths that have remained unachievable in other semiconductors.