Semiconductor room-temperature maser

We report the first demonstration of a semiconductor maser based on silicon vacancies (V_Si) in 4H-silicon carbide (SiC). Using an active feedback loop, we enhance the resonator's quality factor, enabling continuous-wave maser operation even above room temperature. We analyzed the SiC maser as a high-performance preamplifier, with measured gain exceeding 10 dB at 110 K and simulations suggesting potential amplification beyond 30 dB. Leveraging the small zero-field splitting of V_Si, the device can also function as an optically pumped microwave photon absorber, reducing the resonator's mode temperature by 40 K relative to the environment. Additionally, the maser's ultranarrow linewidth supports highly sensitive magnetometry, achieving a nine-order-of-magnitude improvement in contrast-to-linewidth ratio over electrical and optical detection of magnetic resonance. This results in an estimated magnetic field sensitivity of 20 pT/√Hz at room-temperature based on the relative intensity noise of the excitation laser. These results underscore the potential of SiC to reshape room-temperature maser technologies, and lay the groundwork for future development of compact, electrically driven maser diodes.