Photonic p-n junction: An ideal near-field heat flux modulator

Using a pair of $p$- and $n$-type semiconductors separated by a nanoscale vacuum gap, we introduce the concept of a prototype optoelectronics element, the ``photonic $p\text{\ensuremath{-}}n$ junction,'' as an analog of the electronic $p\text{\ensuremath{-}}n$ junction, and demonstrate that the cooperation of $p$-type and $n$-type carriers is ideal for tuning of photon tunneling and modulating near-field heat flux electrically. Three fundamental modes of photon-carrier interaction specific in the photonic $p\text{\ensuremath{-}}n$ junction tunable under a bias voltage are revealed, namely, surface plasmon polariton mode, symmetric depleted internal plasmon polariton mode, and symmetric accumulated surface plasmon polariton mode. The switch among these three modes explains the high-modulation performance. The presented concept opens an avenue in the design of smart thermal management devices and tunable or programmable integrated optoelectronic devices.