Performance optimization of GaAs-based photomixers as sources of THz radiation

The performance optimization of GaAs-based photomixers using novel device structures is reported. Lowtemperature grown (LT) GaAs devices with recessed interdigitated finger contacts, which improve the electric field distribution in the active region, were investigated. Further, the devices with an enhancedmixing area using finger contacts integrated into the coplanar stripline were experimentally verified. The output power of such photomixers was twice of that with conventional surface contacts. High-energy nitrogen implanted GaAs was used as an alternative to LT GaAs, and a further increase of the output power was observed.Measured power level of 2.6 μW at 850 GHz was higher than that reported before for any photomixer in the THz region

Conduction in nonstoichiometric molecular-beam epitaxial GaAs grown above the critical thickness

Different conduction behavior is observed in nonstoichiometric ~NS! molecular-beam epitaxial GaAs grown at 200 °C below and above the critical thickness. In the low-field Ohmic region only the monocrystalline part of the layer contributes to the room-temperature resistivity, but at higher temperatures the resistivity scales with the total layer thickness. In NS GaAs grown above the critical thickness, a superlinear J –V^n (n=2 – 3) dependence is found at intermediate fields. The prebreakdown voltage is proportional to the total thickness. This indicates that different defects control the electrical properties of the polycrystalline and monocrystalline parts of the NS GaAs. These results can be useful in the design of NS GaAs based devices, which operate at higher temperature and/or higher electric fields

A novel two-color photodetector based on an InAlAs-InGaAs HEMT layer structure

The spectral responsivity of an InAlAs–InGaAs metal–semiconductor–metal diode above a two-dimensional electron gas (2DEG) is investigated as a function of the applied bias. At low voltages, only the InAlAs layer above the 2DEG contributes to the photocurrent, while the InGaAs channel layer is activated at higher bias. This results in a voltage-dependent spectral response of the photodetector. The ratio of the responsivities at 1300 and 850 nm changes from 0.03- at 1-V to 0.44- at 1.6-V bias. This property makes the device a candidate suitable to detect and to separate optical information originated both from the GaAs (850 nm) and in the InGaAs (1300, 1550 nm)-based optoelectronic technology