An AlxGa1−xN/GaN two-dimensional electron gas structure with x = 0.13 deposited by molecular beam epitaxy on a GaN layer grown by organometallic vapor phase epitaxy on a sapphire substrate was characterized. Hall effect measurements gave a sheet electron concentration of 5.1×1012 cm−2 and a mobility of 1.9 × 104 cm2/Vs at 10 K. Mobility spectrum analysis showed single-carrier transport and negligible parallel conduction at low temperatures. The sheet carrier concentrations determined from Shubnikov-de Haas magnetoresistance oscillations were in good agreement with the Hall data. The electron effective mass was determined to be 0.215±0.006 m0 based on the temperature dependence of the amplitude of Shubnikov-de Haas oscillations. The quantum lifetime was about one-fifth of the transport lifetime of 2.3 × 10−12 s.

Good ohmic contacts with both low contact resistance and smooth surface morphology are required for the development of a robust manufacturing process of AlGaN/GaN based high power, high frequency MMICs. This extended abstract provides an optimization of the Ti/Al/Ni/Au ohmic metal stacks on AlGaN/GaN HEMT structures with a focus on the thickness of Ni and Au layer. It is found that the Ni thickness is the dominant factor to affect the contact resistance, while the Au thickness affects the surface morphology significantly. An optimal metal stack including a thick Ni and thin Au layer is found, which produces a low contact resistance around 0.26 ohm mm and a smooth surface morphology with a surface roughness of 22nm. An excellent edge acuity is observed. Initial device results from optimized ohmic metal stack are also discussed.

This paper presents two ultra wide bandwidth low noise amplifiers utilizing 0.18-um AlGaN/GaN HEMT technology. The single-stage, resistive feedback microstrip amplifiers target two different frequency bands, 0.3 - 4 GHz and 1.2 - 18 GHz, capable of better than 13:1 bandwidth. Both amplifiers use dual-gate HEMT devices with an on-chip drain bias network. The low frequency amplifier achieves 17.7 dB flat gain between 300 MHz - 3 GHz, and 1.2 dB minimum noise figure around 1.3 GHz. The high frequency LNA shows an average of 13 dB gain and between 2 to 3 dB noise figure across the band. The robust LNAs can be operated under various bias voltages while similar gain and noise figure performance are maintained.

Field effect transistor device (10) comprising: - a substrate (12); - more to the substrate applied (12) semiconductor device layers (14); - a plurality of the semiconductor device layers (14) deposited dielectric passivation layers (16, 18, 20); - a to the semiconductor device layers (14) applied source terminal (24); - a to the semiconductor device layers (14) applied drain terminal (26); - an at least one of the passivation layers (16, 18, 20) applied gate terminal (38), wherein at least two of the passivation layers of different dielectric material, and wherein the thickness of the passivation layers between the source terminal (24) and the gate connection (38) and the drain (26) and the gate terminal (38) is greater than the thickness of the one or more passivation layers between the gate terminal (38) and the semiconductor device layers (14), so that on the sides of the gate terminal (38) are passivation layers, - wherein a plurality of passivation layers three passivation layers (16, 18, 20), and wherein the thickness of the combination of the two closest to the device layers ...

A V-band push-push GaN monolithic microwave integrated circuit voltage controlled oscillator (VCO) has been realized based on a 0.2 mu m T-gate AlGaN/GaN high electron mobility transistor technology with an f(T) similar to 65 GHz. The GaN VCO delivered an output power of + 11. dBm at 53 GHz with an estimated phase noise of -97 dBc/Hz at 1 MHz offset based on on-wafer measurement. To the best of our knowledge, this is the highest frequency VCO ever reported for GaN technology with a high output power at V-band, without using any buffer amplifier. This work demonstrates the potential of applying GaN technology to millimeter wave band, high power, and low phase noise frequency sources applications.

Using harmonic balance simulations, we have examined the survivability limiting mechanisms of a 0.2 mum T-gate AlGaN/GaN HEMT device under RF overdrive. Simulations are performed using a 4-finger 200 mum AlGaN/GaN HEMT device model. Two catastrophic failure mechanisms are identified. At low quiescent drain-source voltages (<10 V), the forward turn-on of the gate diode may exceed the burnout limit, resulting in a sudden failure. Increasing the quiescent drain-source voltage increases the peak drain-gate voltage and changes the failure mechanism to gate-drain reverse breakdown. The model is consistent with experimental measurements.

The reaction-diffusion limited trap generation model used to explain MOSFET degradation has been applied to GaN HEMT degradation. An analytical expression to describe the time dependence of RF output power has been derived based on this model. In addition, the voltage and temperature dependence of the fitting parameters have been determined.

To improve the passivation process of AlGaN/GaN HEMTs, a unique passivation process has been developed in which an SiN passivation layer is deposited by MBE immediately following epitaxial growth of the HEMT structure. The effectiveness of this in situ passivation process is evaluated by comparing devices fabricated with this process to the conventional PECVD passivation process in which the SiN is deposited after gate metallisation. The improved material quality and the protection offered by the MBE-grown SiN may contribute to the significantly reduced dispersion and improved power performance measured for the wafer fabricated with the in situ passivation process.

This paper presents a broadband low noise amplifier MMIC utilizing 0.2 urn AlGaN/GaN HEMT technology. The single-stage, resistive feedback amplifier is designed in co-planar waveguide (CPW) topology. It uses dual-gate devices with on-chip drain bias network to achieve 18 dB flat gain between 300 MHz -4 GHz. Measured noise figure is around 1.5 dB between 2 and 5 GHz, and better than 2 dB between 1 and 2 GHz. The amplifier is capable of 25 dBm saturated output power with 1 dB compression point around 20 dBm across the band. Due to high breakdown voltage of GaN devices, the LNA can withstand high input power and shows no sign of degradation.

Abstract not Available.

A Q-band 40-GHz GaN monolithic microwave integrated circuit voltage controlled oscillator (VCO) based on AlGaN/GaN high electron mobility transistor technology has been demonstrated. The GaN VCO delivered an output power of +25dBm with phase noise of -92dBc/Hz at 100-KHz offset, and -120dBc/Hz at 1-MHz offset. To the best of our knowledge, this represents the state-of-the-art for GaN VCOs in terms of frequency, output power, and phase noise performance. This work demonstrates the potential for the use of GaN technology for high frequency, high power, and low phase noise frequency sources for military and commercial applications

RF stability measurements have been performed on over 300 MBE and MOCVD grown devices with and without a thin (~10 Aring) AlN interlayer located between the AlGaN barrier and GaN channel. 70 % of devices with the AlN interlayer showed an increase in gate leakage during RF stress, while only 28 % of the devices without the AlN interlayer showed an increase in gate leakage during RF stress. An increase in gate leakage is inconsistent with increased trapping as the degradation mechanism for decreased output power. The unusual increase of gate leakage in devices with AlN interlayers was further explored. The results suggest one mechanism for the increase of gate leakage seen during RF stability measurements in devices with an AlN interlayer is due to localized breakdown along the gate finger caused by the inability to control the AlN interlayer thickness to within a monolayer along the entire gate width. Devices without an AlN interlayer typically exhibit a decrease in gate leakage with stress time, consistent with increased trapping at the gate edge

Equations governing scans along arbitrary directions in reciprocal space were developed and used to map reciprocal lattice points (RLPs) with radial raster patterns to study mosaic structure in GaN thin films deposited on semi-insulating 4H-SiC substrates using AlN nucleation layers (NLs). The films were grown by molecular beam epitaxy, keeping the GaN growth conditions the same, but using different AlN NL growth conditions. Mosaic tilt angles determined from symmetric RLP breadth measurements were similar for all samples measured, consistent with screw and mixed dislocation densities determined from transmission electron microscopy (TEM) measurements. Mosaic twist was determined using off-axis skew-symmetric high resolution x-ray diffraction measurements of asymmetric RLP breadths, yielding results consistent with grazing incidence in-plane x-ray diffraction twist measurements. A clear correlation between the twist angle and the edge and mixed dislocation densities determined by TEM was not observed, warranting careful consideration of dislocation structure.

The effect of the AlN nucleation layer growth conditions on buffer leakage in unintentionally doped AlGaN∕GaN high electron mobility transistors was investigated. The samples were grown by rf-plasma assisted molecular beam epitaxy on 4H–SiC (0001). Drain-source leakage currents were found to be markedly different for samples grown with different Al∕N flux ratios during the AlN nucleation layer. Growth of N-rich nucleation layers (Al∕N<1) resulted in a significant reduction in buffer leakage. Secondary ion mass spectroscopy results showed that Si incorporation into Al-rich AlN layers (Al∕N>1) grown on SiC was as high as ∼1–2×1018atoms∕cm3. In contrast, Si incorporation into N-rich AlN layers was two orders of magnitude lower, ∼2×1016atoms∕cm3. Initial devices grown on low-leakage material realized via N-rich nucleation yielded output power densities at 4GHz of 4.8W∕mm with a power added efficiency (PAE) of 62% at a drain bias of 30V, and 8.1W∕mm with a PAE of 38% at a drain bias of 50V.