Double Channel High Electron Mobility Research Articles

Studies on the coupling correlation and strain state of AlGaN/GaN double channel heterostructures grown by metal organic chemical vapor deposition

In this work, high quality AlGaN/GaN double channel heterostructures were grown by metal organic chemical vapor deposition and the coupling correlation between the two channels, as well as the strain state of this multilayer structure are investigated in detail. It was revealed that the stronger coupling correlation affect the 2DEG distribution and leads to the lower channel is similar to the upper channel with the thinner thickness of the upper channel. In addition, the impact of the multilayer strain state on the characteristics of double channel heterostructures was discussed. Moreover, the effects of coupling correlation and strain state on the performance of double channel high electron mobility transistor (HEMT) was shown by 2-D simulation. This work is not only beneficial for the further study of the double (multiple) channel heterostructures and devices, but also instructive to the design and realization of the future atomic hyperfine structures of nitride semiconductors.

Numerical investigation of the performance of AlGaN/GaN/BGaN double-gate double-channel high electron mobility transistor

<p><span>In this work, we examine the direct-current (DC) behavior and the radio-frequency (RF) performance of both single-gate simple-channel (SGSC), single-gate double-channel (SGDC) and double-gate double-channel (DGDC) AlGaN/GaN/BGaN high electron mobility transistor (HEMT) with BGaN back-barriers consist of 250 nm gate length. Using Technologie Computer Aided Design (TCAD) Silvaco, our isothermal simulation results reveal that the proposed structure of double-gate double-channel HEMT with BGaN back-barriers (DGDCBB HEMT) increases electron concentration and consequently the saturation drain current, breakdown voltage, the transconductance. On the other hand, decreases the gate leakage current compared to a conventional HEMT and to a double-channel HEMT back-barriers. Furthermore, the proposed double-gate double-channel back-barrier HEMT device shows good cutoff frequency (94 GHz) and a maximum oscillation frequency (170 GHz). These results suggest that double-gate double channel HEMT back-barriers could be useful for high-frequency and high-power microwave applications.</span></p>

High performance InGaN double channel high electron mobility transistors with strong coupling effect between the channels

In this paper, high performance InGaN double channel (DC) high electron mobility transistors (HEMTs) are proposed and systematically investigated. Due to the coordination of double InGaN channels, a large maximum drain current density and a distinct double-hump feature of the transconductance and frequency performance are achieved. More importantly, it is revealed that the coupling effect between the two InGaN channels is much stronger than that of the conventional GaN DC HEMTs. This characteristic leads to a remarkable enhancement in the gate voltage swing, indicating the excellent linearity of the InGaN DC HEMTs at both dc and rf conditions. Benefiting from the enhanced electron confinement in InGaN channels, the fabricated HEMTs show a low off state drain leakage current of 0.26 μA/mm and a high on/off current ratio (Ion/Ioff) of 5.1 × 106. In addition, the desirable current collapse and breakdown characteristics are also obtained. This work convincingly demonstrates the great potential and practicality of the InGaN DC HEMTs for high power and high bandwidth applications.

Analysis of plasma-modes of a gated bilayer system in high electron mobility transistors

We present rigorous analytical and computational models to study the plasma-waves in a gated-bilayer system present in a double-channel high electron mobility transistor. By analytically deriving the dispersion relations, we have identified the optical and acoustic modes in such systems. We find that the presence of the metal gate selectively modifies the optical plasmons of an ungated-bilayer, while the acoustic plasmons remain largely unchanged. Analysis shows that these modified optical plasmons could be advantageous for resonant and non-resonant plasma-wave devices. The paper further serves to verify our analytical formulae using a full-wave hydrodynamic numerical solver, based on finite difference time domain algorithm. Using the solver, we examine these modes in the gated/ungated bilayers under a plane wave excitation. We observe that, most incident power couples to the optical mode for such an excitation. Nevertheless, acoustic modes can also be excited, if the discontinuity dimensions are optimized accordingly. These observations are also explained using 2D field-plots for the first time, thus providing intuitive understanding of the plasmon excitation in the bilayers.

Trap states in InAlN/AlN/GaN-based double-channel high electron mobility transistors

We present a detailed analysis of trap states in InAlN/AlN/GaN double-channel high electron mobility transistors grown by pulsed metal organic chemical vapor deposition. By frequency dependent conductance measurements, trap densities and time constants at both InAlN/AlN/GaN interfaces were determined. Two types of traps, with a high density of up to ∼1014 cm−2 eV−1, were observed existing at the higher InAlN/AlN/GaN interface. On the other hand, the density dramatically decreased to ∼1012 cm−2 eV−1 for traps located at lower InAlN/AlN/GaN interface on which a low-temperature grown GaN (LT-GaN) layer was deposited. Additionally, photo-assisted capacitance-voltage measurements were performed to estimate deep-level defects, yielding a low density of 1.79 × 1011 cm−2 acting as negative fixed charges at the LT-GaN and lower InAlN interface.

Double-Channel AlGaN/GaN High Electron Mobility Transistor With Back Barriers

We have developed a double-channel high electron mobility transistor with back barriers for carrier confinement. We have observed that the double-channel devices may suffer from the lack of gate control particularly for the lower channel. However, the problem can be contained by using a suitable back barrier for the lower channel. The double-channel back-barrier devices show good current gain and power gain cutoff frequencies. These devices can be operated with excellent gain linearity up to a larger value for input power and frequency.

Fabrication and characterization of InAlN/GaN-based double-channel high electron mobility transistors for electronic applications

In our previous work [J. S. Xue et al., Appl. Phys. Lett. 100, 013507 (2012)], superior electron-transport properties are obtained in InAlN/GaN/InAlN/GaN double-channel (DC) heterostructures grown by pulsed metal organic chemical vapor deposition (PMOCVD). In this paper, we present a detailed fabrication and systematic characterization of high electron mobility transistors (HEMTs) fabricated on these heterostructures. The device exhibits distinct DC behavior concerning with both static-output and small-signal performance, demonstrating an improved maximum drain current density of 1059 mA/mm and an enhanced transconductance of 223 mS/mm. Such enhancement of device performance is attributed to the achieved low Ohmic contact resistance as low as 0.33 ± 0.05 Ω·mm. Moreover, very low gate diode reverse leakage current is observed due to the high quality of InAlN barrier layer deposited by PMOCVD. A current gain frequency of 10 GHz and a maximum oscillation frequency 21 GHz are also observed, which are comparable to the state-of-the-art AlGaN/GaN-based DC HEMT found in the literature. The results demonstrate the great potential of PMOCVD for application in InAlN-related device’s epitaxy.

2DEG properties in InGaN/InN/InGaN‐based double channel HEMTs

AbstractThis paper describes the 2DEG properties of InGaN/InN/InGaN double channel high electron mobility transistor (DHEMT). These include an in‐depth theoretical investigation of 2DEG sheet carrier concentration and mobility. The 2DEG mobility is calculated using ensemble Monte Carlo taking into account all relevant scatterings. The calculated sheet carrier concentration reaches as high as 1.77×1014 cm‐2 for DHEMT. While for single channel high electron mobility transistor (SHEMT) the calculated sheet carrier concentration was found to be 7.06×1013 cm‐2. The maximum total 2DEG mobility is found to be around 12×104 and 8×104 cm2V‐1s‐1, respectively, for DHEMT and SHEMT for a sheet carrier concentration of ns = 5×1012 cm‐2 at 77 K. Thus, the 2DEG sheet carrier concentration and mobility for dual channel is higher than conventional single channel HEMTs. The high values of 2DEG sheet carrier concentration and mobility strongly suggest that the InGaN/InN/InGaN based double channel HEMT is very promising for the fabrication of high performance high speed device (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

AlGaN/GaN double-channel HEMT

The fabrication of AlGaN/GaN double-channel high electron mobility transistors on sapphire substrates is reported. Two carrier channels are formed in an AlGaN/GaN/AlGaN/GaN multilayer structure. The DC performance of the resulting double-channel HEMT shows a wider high transconductance region compared with single-channel HEMT. Simulations provide an explanation for the influence of the double-channel on the high transconductance region. The buffer trap is suggested to be related to the wide region of high transconductance. The RF characteristics are also studied.

A comparative study on single and double channel AlGaN/GaN high electron mobility transistor

AbstractWe present a numerical investigation on the DC and AC characteristics of AlGaN/GaN single (SCHEMT) and double channel high electron mobility transistors (DCHEMT) using the APSYS simulation program. The simulation results indicate that the DCHEMT has a slightly wider range of transconductance and cut‐off frequency for device operation at high current levels than SCHEMT. Besides, we also examine the effect of barrier layer thickness between the two channels in DCHEMT on the transconductance profile. It is found that the operation range of transconductance can be tailored by adjusting the barrier layer thickness. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Low-frequency noise properties of double channel AlGaN/GaN HEMTs

Low-frequency noise in MOCVD-grown AlGaN/GaN/AlGaN/GaN double channel high electron mobility transistors (HEMTs) on sapphire substrate was investigated over a wide range of temperatures from 80 K to 300 K. Generation–recombination (g–r) noise was observed arising from the traps with activation energies 140 meV, 188 meV and 201 meV. Hooge parameter was estimated to be 1.6 × 10 −3 at room temperature. Our work demonstrates good dc and low-frequency noise properties for the device.

AlGaN-GaN Double-Channel HEMTs

We present the design, fabrication, and characterization of AlGaN-GaN double-channel HEMTs. Two carrier channels are formed in an AlGaN-GaN-AlGaN-GaN multilayer structure grown on a sapphire substrate. Polarization field in the lower AlGaN layer fosters formation of a second carrier channel at the lower AlGaN-GaN interface, without creating any parasitic conduction path in the AlGaN barrier layer. Unambiguous double-channel behaviors are observed at both dc and RF. Bias dependent RF small-signal characterization and parameter extraction were performed. Gain compression at a high current level was attributed to electron velocity degradation induced by interface scattering. Dynamic IV measurement was carried out to analyze large-signal behaviors of the double-channel high-electron mobility transistors. It was found that current collapse mainly occurs in the channel closer to device surface, while the lower channel suffers minimal current collapse, suggesting that trapping/detrapping of surface states is mainly responsible for current collapse. This argument is supported by RF large-signal measurement results.