Broadband low-noise GaN HEMT TWAs using an active distributed drain bias circuit

Modern communication and radar systems show an increasing demand for robust ultra-broadband amplifiers for low-noise applications. A set of three different 0.5 GHz to 20 GHz MMIC LNAs using a GaN HEMT technology with a gate length of 0.25 μm was designed and fabricated, each with a noise figure between 3 dB and 7 dB over frequency. Two designs with four and five FET cells feature approx. 10 dB and 11 dB broadband gain, while a third MMIC with a chain connection of both figures more than 20 dB of gain. A distributed active drain bias circuit substitutes large area or off-chip inductor structures and enables a full-MMIC chain connection of both TWA stages

Electronic and photoconductive properties of ultrathin InGaN photodetectors

We report on the compositional dependencies of electron transport and photoconductive properties for ultrathin metal-semiconductor-metal photodetectors based on In-rich InxGa1-xN alloys. For a In0.64Ga0.36N/GaN structure, the rise time close to the RC constant at low fields has been measured along with a transparency of similar to 77% and an absorbance of similar to 0.2 at a wavelength of 632 nm. The electron density profiles and low-field mobilities for different compositions of InGaN have been calculated by numerically solving the Schrodinger and Poisson equations and applying the ensemble Monte Carlo method, respectively. It was demonstrated that in ultrathin InxGa1-xN/GaN (0.5 < x < 1) heterostructures, in contrast to bulk InN exhibiting a strong surface electron accumulation, free electrons mostly tend to accumulate at the buried InGaN/GaN interface. We have also found that the low-field mobility in the InGaN/GaN heterostructures is strongly limited by the buried interface roughness which causes more than 95% of all scattering events occurred by two-dimensional electron transport under low electric field conditions.Comisión Interministerial de Ciencia y Tecnología (CICYT) MAT2007-60643 Españ

A 183 GHz metamorphic HEMT low-noise amplifier with 3.5 dB noise figure

This paper presents a 183 GHz low-noise amplifier (LNA), designed primarly for water vapor detection in atmosphere. The LNA requirements were defined by MetOp Second Generation (MetOp-SG) Microwave Sounder, Microwave Imager and Ice Cloud Imager instruments. MetOp-SG is the European contribution to operational meteorological observations from polar orbit. This LNA advances the current state-of-the-art for the InGaAs metamorphic high electron mobility transistor (mHEMT) technology. The five-stage common-source MMIC amplifier utilizes transistors with a gate length of 50 nm. On-wafer measurements show a noise figure of 3.5 dB at the operative frequency, about 1 dB lower than previously reported mHEMT LNAs, and a gain of 24±2 dB over the bandwidth 160-200 GHz. The input and output matching are -11 dB and -10 dB, respectively. Moreover, the DC power dissipation at the optimal bias for noise is as low as 24 mW

Effect of dislocations on electrical and electron transport properties of InN thin films. II. Density and mobility of the carriers

The influence of dislocations on electron transport properties of undoped InN thin films grown by molecular-beam epitaxy on AlN 0001 pseudosubstrates is reported. The microstructure and the electron transport in InN 0001 films of varying thickness were analyzed by transmission electron microscopy and variable temperature Hall-effect measurements. It was found that crystal defects have strong effects on the electron concentration and mobility of the carriers in the films. In particular, the combined analysis of microscopy and Hall data showed a direct dependence between free carrier and dislocation densities in InN. It was demonstrated that threading dislocations are active suppliers of the electrons and an exponential decay of their density with the thickness implies the corresponding decay in the carrier density. The analysis of the electron transport yields also a temperature-independent carrier concentration, which indicates degenerate donor levels in the narrow band-gap InN material. The relative insensitivity of the mobility with respect to the temperature suggests that a temperature-independent dislocation strain field scattering dominates over ionized impurity/defect and phonon scattering causing the increase of the mobility with rising layer thickness due to the reducing dislocation density. Room temperature mobilities in excess of 1500 cm2 V−1 s−1 were obtained for 800 nm thick InN layers with the dislocation densities of 3 109 cm−2.Deutsche Forschungsgemeinschaft AM105 ∕ 1-1, AlemaniaComisión Interministerial de Ciencia y Tecnología MAT2004-01234, EspañaUnión Europea NMP4-CT-2003- 505641Unión Europea NMP4-CT-2004-50010