GaN for THz sources

Abstract

In this work we investigate two different approaches to generate THz radiation by the use of the unique electrical and thermal properties of GaN. One method is heterodyne photomixing, a compact and inexpensive approach to generate continuous electromagnetic radiation in the terahertz range, with tuneable frequency. It uses two lasers with slightly different wavelengths that illuminate an ultrafast photoconductor. The interference of both laser beams generates a beat frequency of the illumination intensity in the terahertz range. One drawback of the conventionally used LT GaAs as ultrafast photoconductor material is the relatively low THz power in the nW to µW range. The aim of our work is to increase the output power by replacing the LT GaAs with GaN. This semiconductor is rather known as basic material for blue LEDs and lasers, but it has also remarkable electrical and thermal properties that allow higher laser power and bias voltage.A more conventional, electronic approach to generate THz radiation consists in the fabrication of an oscillator circuit based on ultrafast transistors, e.g. Hetero Field Effect Transistors based on InGaAs. These circuits can be designed up to about 100 GHz oscillation frequency. The THz region is achieved by frequency multipliers, e.g. realized by very smallsized Schottky diodes. However, each multiplier stage considerable reduces the output power. In this field we investigate GaN based transistor devices to profit from the much better power performance of this material, compared to classical semiconductors. Devices in this material system are usually used for high power applications at moderate frequencies, but the very high electron saturation velocity of GaN allows the application above 100 GHz as well.

Terahertz technologies: present and future

“…The output power of 20∼40 μW is achieved at 1.7∼1.9 THz [15]. Use of high-power amplifiers with GaN-related materials will increase the THz power up to a milliwatt level [16].…”

Trap-assisted enhancement of the responsivity in asymmetric planar GaN-based nanodiodes at low temperature

“…Moreover, even if the mobility of GaN is not especially high, it has high saturation velocity and low permittivity, and its wide bandgap provides robustness and high thermal stability. On the other hand the AlGaN/GaN heterostructure, due to the piezoelectric effect, produces a 2DEG without the need of any doping, with the result that it has become one of the preferred choices for high frequency and high power applications [9][10][11][12]. Moreover, excellent RF detection performance have been achieved with several AlGaN/GaN based FETs: HEMTs providing responsivities of 15.5 kV W -1 at 0.14 THz [13], gated nanowire field-effect rectifiers (NW-FERs) exhibiting an excellent value of 3 kV W -1 @10 GHz [14], or gated-asymmetric diodes showing values of 600 V W -1 @0.3 THz [15], respectively.…”

Review of GaN-based devices for terahertz operation

“…As a result, GaN devices offer higher output power and operation frequency compared with other conventional III to V devices. [88][89][90][91] The mentioned characteristics of GaN together with its capabilities of providing high two-dimensional (2-D) election densities and high LO phonon of ∼90 meV make it one of the most promising semiconductors for the future of the generation, detection, mixing, and frequency multiplication of the electromagnetic waves in THz frequency regime. As Fig.…”