Systems and methods for forming a compact gas sensor include using a lithographically fabricated high Q resonator coupled to at least one of a Gunn diode and an IMPATT diode. The resonator may include a plurality of cavities filled with a sample gas. A detector coupled to the resonator may measure the amplitude of the emitted mm wave radiation.

Provided is a multi-negative differential resistance device. The multi-negative differential resistance device includes a first negative differential resistance device and a second negative differential resistance device connected in parallel with the first negative differential resistance device, and a peak and a valley of the first negative differential resistance device and a peak and a valley of the second negative differential resistance device are synthesized, and, thus, the multi-negative differential resistance device has two peaks and two valleys.

A Gunn diode is disclosed which comprises a first contact layer, a second contact layer, and an active layer based on a gallium nitride (GaN) semiconductor material having a base surface and a side surface non-parallel thereto. Optionally, related materials such as aluminum indium gallium nitride (AlInGaN) materials may also be used as the active layer. The first contact layer electrically contacts the side surface to form a side contact. The second contact layer forms an electrical contact for the base surface, so that a maximum of the electric field strength is formed when an electric voltage is applied between the first contact layer and the second contact layer at the side contact.

A rectifier is provided for converting an oscillating electromagnetic field into a direct current and comprises an electrically conductive antenna layer configured to absorb electromagnetic radiation, an electrically conductive mirror layer configured to provide an electromagnetic mirror charge of the antenna layer, an electrically insulating tunnel barrier layer positioned between the antenna layer and the mirror layer, and an electronic circuit electrically connected between the conductive mirror layer and the conductive antenna layer. The rectifier employs a metamaterial configuration for room temperature rectification of radiation in regions of the electromagnetic spectrum comprising the MWIR and LWIR regions. Methods for use of the rectifier in rectifying and detecting radiation are described.

Gunn diodes are formed using a set of layered semiconductor materials, with one or more n-doped upper layers and contacts over the uppermost semiconductor layer. A diode may include alternating layers of indium, gallium, and arsenic (e.g., InGaAs) and indium, aluminum, and arsenic (e.g., InAlAs), where an uppermost layer of the stack includes two regions of highly-doped InGaAs, and a layer of InAlAs is directly below the two regions of highly-doped InGaAs. The InAlAs layer forms the active region and is n-doped to a lower dopant concentration than the two InGaAs regions. Further alternating layers of InGaAs and InAlAs may be below the active region. A gate may be included between the two contacts and over the active region; the gate may apply a bias voltage to the active region. The Gunn diodes may advantageously be used in low-temperature environments, such as cooled IC devices.