Cyclotron emission from quantized Hall devices: Injection of nonequilibrium electrons from contacts

Emissions of cyclotron radiation associated with the inter-Landau-level transition of nonequilibrium electrons are experimentally studied in quantum-Hall-effect devices. It is confirmed that both the longitudinal resistance and the contact resistance are vanishing when the cyclotron emission (CE) is being observed. For the CE, a critical source-drain voltage $V_{\mathrm{SD}}$ is found to exist at $V_{\mathrm{SD}}=ħ{\omega }_c/2e,$ where $ħ{\omega }_c$ is the inter-Landau-level energy spacing. Spatially resolved measurements reveal that the CE takes place at both of the current entry and exit corners (“hot spots”) of the Hall bars. A model of ideal current contacts is discussed. The CE on the source side is interpreted as being due to injection of nonequilibrium electrons from the source contact, and the CE on the drain side as due to an inter-Landau-level electron tunneling caused by a steep potential wall formed at the drain contact.