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To improve the threshold voltage and gate reliability of conventional enhancement-mode p-GaN-gated AlGaN/GaN high electron mobility transistors while maintaining a low on-resistance, an improved design solution for p-GaN HEMTs with P-I-N junction gate (PIN-HEMTs) has been proposed. Simulation results show that energy band modulation is achieved by adjusting the doping concentration and thickness of each layer of the PIN junction, and high-performance p-GaN gate HEMTs with adjustable threshold voltages ranging from 0.56 V to 4.75 V and gate breakdown voltages ranging from 19.8 V to 30.3 V would be prepared. The PIN-HEMT has a quasi-self-alignment property, which means that good gate control is independent of gate metal alignment. This not only improves the production efficiency but also solves the problems of weak gate control and electric field aggregation at the gate edge caused by the gate misalignment in conventional p-GaN gate HEMTs, thus realizing lower on-resistance and higher gate breakdown voltage, which demonstrates this proposed structure has excellent potentials for realizing effective and reliable high-power transistors. [ABSTRACT FROM AUTHOR]

In this paper, the ohmic contact mechanism and gate electrostatic control of a deep-recessed ohmic contact structure for multi-channel Al0.3Ga0.7N/GaN high electron mobility transistors (HEMTs) is investigated. A transmission electron microscope and an energy dispersive spectrum are utilized to investigate the ohmic contact interface mechanism. Due to a reduction of source/drain parasitic resistances and simultaneous connection of five channels by using deep-recessed ohmic contact, a large maximum drain current density and a distinct five hump feature of ultra-wider trans-conductance are achieved. More importantly, it is revealed that the downward expansion of the gate potential for the deep-recessed ohmic contact structure is much deeper than that for conventional devices. This characteristic leads to a remarkable reduction in subthreshold swing (SS) and off-state leakage, indicating an ultra-wide and high trans-conductance profile. The fabricated devices show a lower off-state drain leakage, a lower SS, and a wider gate voltage swing (40 V). Due to an enhancement of gate electrostatic control, the current collapse and electrical reliability characteristics of multi-channel Al0.3Ga0.7N/GaN HEMTs with deep-recessed ohmic contact also improve. The results presented here indicate that the multi-channel device has great potential for high current and wide bandwidth applications. [ABSTRACT FROM AUTHOR]

Passivation is commonly used to suppress current collapse in AlGaN/GaN HEMTs. However, the conventional PECV-fabricated SiNx passivation layer is incompatible with the latest process, like the "passivation-prior-to-ohmic" method. Research attention has therefore turned to high-temperature passivation schemes. In this paper, we systematically investigated the differences between the SiNx/GaN interface of two high-temperature passivation schemes, MOCVD-SiNx and LPCVD-SiNx, and investigated their effects on the ohmic contact mechanism. By characterizing the device interface using TEM, we reveal that during the process of MOCVD-SiNx, etching damage and Si diffuses into the semiconductor to form a leakage path and reduce the breakdown voltage of the AlGaN/GaN HEMTs. Moreover, N enrichment at the edge of the ohmic region of the LPCVD-SiNx device indicates that the device is more favorable for TiN formation, thus reducing the ohmic contact resistance, which is beneficial to improving the PAE of the device. Through the CW load-pull test with drain voltage VDS = 20V, LPCVD-SiNx devices obtain a high PAE of 66.35%, which is about 6% higher than MOCVD-SiNx devices. This excellent result indicates that the prospect of LPCVD-SiNx passivation devices used in 5G small terminals will be attractive. [ABSTRACT FROM AUTHOR]

In this study, AlGaN/GaN nanochannel high-electron-mobility transistors (HEMTs) with tri-gate (TGN-devices) and dual-gate (DGN-devices) structures were fabricated and investigated. It was found that the peak value of the transconductance (Gm), current gain cut-off frequency (fT) and power gain cut-off frequency (fmax) of the TGN-devices were larger than that of the DGN-devices because of the enhanced gate control from the top gate. Although the TGN-devices and DGN-devices demonstrated flattened transconductance, fT and fmax profiles, the first and second transconductance derivatives of the DGN-devices were lower than those of the TGN-devices, implying an improvement in linearity. With the nanochannel width decreased, the peak value of the transconductance and the first and second transconductance derivatives increased, implying the predominant influence of sidewall gate capacitance on the transconductance and linearity. The comparison of gate capacitance for the TGN-devices and DGN-devices revealed that the gate capacitance of the tri-gate structure was not simply a linear superposition of the top planar gate capacitance and sidewall gate capacitance of the dual-gate structure, which could be attributed to the difference in the depletion region shape for tri-gate and dual-gate structures. [ABSTRACT FROM AUTHOR]

To resolve the parasitic problems and to fully leverage the superiority of GaN‐based high electron mobility transistors, monolithic integration of different function blocks is a promising solution. The enhancement mode (E‐mode) GaN‐based p‐channel heterostructure field‐effect transistor (p‐HFET) is one of the key components. Herein, the threshold voltage (VTH) is modeled, and the influence of the Mg out‐diffusion effect on VTH is investigated. The impact of the diffusion coefficient of Mg, the Mg concentration in the p‐GaN layer, the thicknesses of the AlGaN layer (tb), p‐GaN channel layer (tch), and an oxide layer (tox) on VTH are all taken into consideration for systematic exploration. The analysis illustrates that lower Mg concentration, smaller diffusion coefficient, and thinner p‐GaN channel and AlGaN layers facilitate the realization of E‐mode p‐HFETs. Furthermore, it can be observed that lower Mg concentration in the p‐GaN layer diminishes the VTH sensitivity to the thickness of the p‐GaN channel layer. Hence, a heterostructure with two p‐GaN layers of different concentrations is suggested to reduce the complexity of the etching technique while improving the ohmic contacts. As a result, the model can effectively guide the design of GaN‐based E‐mode p‐HFETs. [ABSTRACT FROM AUTHOR]

In this paper, AlN films grown by magnetron sputtering method have been proposed as the gate insulator layer of AlGaN/GaN high electron mobility transistors (HEMTs) to decrease gate leakage current and suppress the interface trap. The effect of the temperature of substrate on the quality of AlN films have been investigated. By inserting the thin AlN film (35 nm) as a gate insulator layer, the on-state resistance of AlGaN/GaN HEMTs decrease from 11.1 Ω mm to 10.3 Ω mm @ V g = 0 V, the current collapse decreases from 16.6% to 3.2%, the gate leakage can be reduced from 1.2 Ă— 10âˆ'1A mmâˆ'1 to 4.4 Ă— 10âˆ'6A mmâˆ'1 @ V g = 2 V by five orders of magnitude, and the fast interface states disappear and the normal trap density decreases from 0.96â€"1.3 Ă— 1013 cmâˆ'2eVâˆ'1 to 1.3â€"3.4 Ă— 1012 cmâˆ'2 eVâˆ'1, proving that magnetron-sputtered AlN is an effective way to improve the performance of GaN HEMTs. [ABSTRACT FROM AUTHOR]

A hybrid Schottky–ohmic drain technology for millimeter-wave (mmW) AlGaN/GaN high-electron-mobility transistors (HEMTs) is proposed. The Schottky metal extension in the ohmic region of drain reduces the actual source–drain spacing, resulting in a smaller ON-resistance and a higher maximum current. Extended Schottky metal in the drain region modulates the electric-field distribution, thereby leading to an improved breakdown voltage, suppressed current collapse, and high reliability. Compared with the ohmic drain, the current gain cutoff frequency (${f}_{T}$) was improved from 64 to 76 GHz, and the maximum oscillation frequency (${f}_{\text {max}}$) was improved from 125 to 157 GHz, resulting from the decreased parasitic drain resistance (${R}_{d}$). Moreover, large-signal measurements in continuous wave (CW) at 30 GHz demonstrated a peak power-added efficiency (PAE) of 45.5% and a saturated output power density (${P}_{\text {sat}}$) of 8.5 W/mm at ${V}_{\text {ds}}= {30}$ V. In addition, the direct current (DC) and radio frequency (RF) characteristics showed a negligible degradation after large-signal measurements at 30 GHz. [ABSTRACT FROM AUTHOR]

This work reports an AlN/GaN/InGaN high electron mobility transistor (HEMT) with a steep subthreshold swing (SS) of sub-60 mV/dec utilizing a coupling-channel architecture. The fabricated transistors show a negligible hysteresis, a SS of 39 mV/dec, a large gate voltage swing of >4.2 V, and achieving an excellent quality factor Q = gm/SS of 6.3 μS-dec/μm-mV. The negative differential resistance effect was found in the subthreshold region in the gate current–voltage (Ig–VGS) curve. The hot carrier transfer mechanism that occurred in the turn-on/pinch-off progress of the CC-HEMT under the dual-directional sweep, proved by the VDS- and Lg-dependent bi-directional transfer I–V characteristics, can be responsible for these excellent device performances. This work is believed to encourage further study of the AlN/GaN platform to power the future group III-nitrides CMOS technology. [ABSTRACT FROM AUTHOR]

In this work, ultrathin barrier (∼6 nm) AlGaN/GaN high-electron-mobility transistors (HEMTs) with in situ SiN gate dielectric and slant-field plate (SFP) T-gates were fabricated and analyzed. Since the proposed scheme of gate dielectric and SFP effectively suppresses the gate leakage and alleviates the peak electric field (E-field) around gate region, the maximum breakdown voltage (VBK) was improved to 92 V, which is 54 V higher than that of the conventional device. The fabricated ultrathin AlGaN/GaN HEMT with 60-nm SFP-T-gate exhibited the peak fT of 177 GHz and peak fmax of 393 GHz, yielding high figure-of-merits of fT · VBK = 16 THz V and fmax·VBK = 36 THz V. Moreover, load-pull measurements at 30 GHz reveal that these devices deliver output power density (Pout) of 4.6 W/mm at Vds = 20 V and high power-added efficiency up to 52.5% at Vds = 10 V. Essentially, the experimental results indicate that the employment of SFP and in situ SiN gate dielectric is an attractive approach to balance the breakdown and speed for millimeter wave devices. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high-electron-mobility transistors (HEMTs) with Si-rich SiN/Si3N4 bilayer passivation were studied in this article. The use of a Si-rich SiN interlayer leads to improved channel transport property, current collapse, power performance, and temperature-dependent stability. Devices without Si-rich SiN interlayer passivation exhibit an increase in the gate leakage current by over three orders of magnitudes with temperature increasing from 300 to 420 K, leading to an increase in a current collapse from 9.7% to 24.7%, while the devices with Si-rich SiN passivation exhibit a weak temperature dependence of leakage current and a constant current collapse about 5%. Small signal characterization shows that Si-rich SiN passivation results in a remarkable decrease in the effective gate length by ~15% with temperature up to 420 K. At 17 GHz, devices with Si-rich SiN interlayer passivation exhibit an output power density of 7 W/mm and a peak power-added efficiency (PAE) of 56%. The improved power performance of devices using Si-rich SiN interlayer passivation is attributed to the suppressed current collapse and superior device stability under high channel temperature. [ABSTRACT FROM AUTHOR]

In this work, high-performance millimeter-wave AlGaN/GaN structures for high-electron-mobility transistors (HEMTs) are presented using a Si-rich SiN passivation layer. The analysis of transient and x-ray photoelectron spectroscopy measurements revealed that the presence of the Si-rich SiN layer leads to a decrease in the deep-level surface traps by mitigating the formation of Ga–O bonds. This results in a suppressed current collapse from 11% to 5% as well as a decreased knee voltage (Vknee). The current gain cutoff frequency and the maximum oscillation frequency of the devices with the Si-rich SiN layer exhibit the values of 74 and 140 GHz, respectively. Moreover, load-pull measurements at 30 GHz show that the devices containing the Si-rich SiN deliver excellent output power density of 8.7 W/mm at Vds = 28 V and high power-added efficiency up to 48% at Vds = 10 V. The enhanced power performance of HEMTs using Si-rich SiN interlayer passivation is attributed to the reduced Vknee, the suppressed current collapse, and the improved drain current. [ABSTRACT FROM AUTHOR]

In this work, the performance of AlGaN/ gallium nitride (GaN) high-electron mobility transistors (HEMTs) with different Fe doping tails was systematically investigated and compared. It is illustrated that the combination of the unintentionally doped (UID) GaN layer and a thinner Fe doping buffer layer would result in a faster slope rate of Fe concentration in the UID GaN layer. The devices with the fastest slope rate of Fe concentration in the UID GaN layer exhibited excellent large signal performance, including the saturated power density (${P}_{sat}$) of 9 W/mm and the power-added efficiency (PAE) of 65.6%. In addition, the ${P}_{sat}$ and the PAE of the device with the fastest slope rate of Fe concentration in UID GaN layer are 27.7% and 14.7%, which are higher than that of the device with the slowest slope rate of Fe concentration under the class AB operation conditions. Pulse ${I}$ ,– ${V}$ measurement results demonstrated that the buffer-related current collapse was more effectively suppressed in the 0.5- $\mu \text{m}$ Fe doping buffer layer because of faster slope rate of Fe concentration in UID GaN layer. Moreover, the frequency-dependent capacitance and conductance measurement results indicated that the current collapse was relevant to deep traps in the UID GaN layer introduced by Fe doping. By reducing the concentration of the deep traps caused by Fe doping, the device showed excellent characteristics of dc and RF. Furthermore, controlling the Fe doping tail was important for designing the GaN-based power amplifier with high ${P}_{sat}$ and PAE. [ABSTRACT FROM AUTHOR]

In this article, we report on the high dc and RF performance of AlGaN/GaN high electron mobility transistors that employ Ti/Au/Al/Ni/Au metallization stack with shallow trench etching ohmic contact (STEOC). An excellent ohmic contact performance including low contact resistance (${R}_{C}$) of $0.28~\Omega \cdot $ mm and smooth surface morphology have been achieved simultaneously. Atomic force microscope (AFM) reveals a highly smooth surface morphology with a root mean square (rms) roughness of 6.3 nm even after 810 °C high-temperature annealing (HTA), achieving an improvement of 79% as compared to the conventional Ti/Al/Ni/Au ohmic contact (COC). A high-resolution transmission electron microscope (HRTEM) showed a glossy morphology with a continuous and uniform TiN layer formed in the interface for the STEOC sample, while a bumpy morphology caused from the Ni-Al complexes balling up and TiN island penetrating into the AlGaN/GaN heterostructure were observed for the conventional sample. Consequently, the fabricated transistors with the STEOC process show a high output current of 1.52 A/mm and low ON-resistance (${R}_{ \mathrm{ ON}}$) of $2.09~\Omega $ mm. In addition, a high current cutoff frequency (${f}_{T}$) of 60 GHz and maximum oscillation frequency (${f}_{\text {max}}$) of 150 GHz were obtained for the STEOC HEMT with a gate length (${L}_{\text {g}}$) of 150 nm. Sub-6 GHz continuous-wave mode power sweep measurements deliver a high power-added-efficiency (PAE) of 67%. These results show the significant potential of the STEOC process to facilitate the development of GaN-based power amplifier (PA) applied for 5G. [ABSTRACT FROM AUTHOR]

The gate and drain bias dependence of hot electron-induced degradation in GaN-based metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) was investigated in this work. Devices exhibit an abnormal increase in peak transconductance (${G}_{m}$ ,max) during hot carrier stress (HCS) and a partially quick recovery of that after removing the electrical stress. A physical model is proposed to explain the abnormal electrical characteristics caused by HCS. By using density functional theory (DFT), we calculated the energy for electrons to dehydrogenate preexisting [NGaH3]−1 complexes in GaN layer during stress. The dehydrogenation of defects affects the Gm,max of devices. Meanwhile, the neutralization of donor traps in AlGaN barrier layer also plays a significant role in the increase of Gm,max and the detrapping effect of electrons from these traps after removing the electrical stress accounts for the partially quick recovery of ${G}_{m, \text{max}}$. [ABSTRACT FROM AUTHOR]

Ultra-thin barrier (UTB) 4-nm-AlGaN/GaN normally-off high electron mobility transistors (HEMTs) having a high current gain cut-off frequency (fT) are demonstrated by the stress-engineered compressive SiN trench technology. The compressive in-situ SiN guarantees the UTB-AlGaN/GaN heterostructure can operate a high electron density of 1.27 × 1013 cm−2, a high uniform sheet resistance of 312.8 Ω/□, but a negative threshold for the short-gate devices fabricated on it. With the lateral stress-engineering by full removing in-situ SiN in the 600-nm SiN trench, the short-gated (70 nm) devices obtain a threshold of 0.2 V, achieving the devices operating at enhancement-mode (E-mode). Meanwhile, the novel device also can operate a large current of 610 mA/mm and a high transconductance of 394 mS/mm for the E-mode devices. Most of all, a high fT/fmax of 128 GHz/255 GHz is obtained, which is the highest value among the reported E-mode AlGaN/GaN HEMTs. Besides, being together with the 211 GHz/346 GHz of fT/fmax for the D-mode HEMTs fabricated on the same materials, this design of E/D-mode with the realization of fmax over 200 GHz in this work is the first one that can be used in Q-band mixed-signal application with further optimization. And the minimized processing difference between the E- and D-mode designs the addition of the SiN trench, will promise an enormous competitive advantage in the fabricating costs. [ABSTRACT FROM AUTHOR]

In this article, we report on the effective transconductance (gm) and gain linearity improvement of submicrometer gate AlN-barrier-based transistors using GaN/InGaN coupling-channel structures. The fabricated AlN/GaN/InGaN coupling-channel high electron mobility transistor (CC-HEMT) showed flat gm profile, greatly reduced gm derivatives, and constant dynamic source resistance compared with an AlN/GaN HEMT using the same fabrication process. The highest extrinsic current gain cutoff frequency (ƒT) of 55 GHz and the maximum oscillation frequency (ƒmax) of 80 GHz were obtained for 0.15- μm gate-length transistors, both of which remain constant values across wide input voltage (VGS) of 4 V. Moreover, a significant theoretical OIP3 value boost by 7.1 dB has been observed using the CC-HEMT as compared to the AlN/GaN HEMT. The superior linearity performance of the CC-HEMT can be attributed to the strong channel-to-channel coupling effect. The drain bias-dependence of gm, ƒT, and ƒmax versus VGS profiles illustrate that the linearity characteristics of the CC-HEMT greatly improve with an increase in VDS. These results demonstrate the AlN/GaN/InGaN material system as a viable platform for high frequency requiring high-linearity applications. [ABSTRACT FROM AUTHOR]

In this letter, we explore the impact of configuration parameters for Fin-like high-electron-mobility transistors (HEMTs) formed by partially etching barrier under the gate on improving transconductance (Gm) and cutoff frequency (ƒT) linearity. It is found that the Gm profile for Fin-like HEMTs can be optimized by choosing appropriate device parameters, including the etching depth (HR) and width (WR) of recess region, as well as the duty ratio (α) of the planar elements in a periodic unit along the gate width. In general, not only does WR affect the gate voltage swing (GVS) but also HR and α have an important role in Gm profile flatness. In addition, the fabricated Fin-like HEMTs shows a GVS of the transconductance plateau larger than 5.6 V and a constant ƒT/ƒmax of 45 GHz/65 GHz over a wide gate voltage range. Furthermore, the proposed architecture also features an exceptional linearity performance at 8 GHz with an output third-order intercept point (OIP3) of 38.5 dBm, whereas that of the planar HEMT is 31 dBm. The device demonstrated in this article has great potential to be a new paradigm for future wireless communication systems where high linearity is essential. [ABSTRACT FROM AUTHOR]

In order to further improve the electrical characteristics of AlGaN-buffer devices, we propose a new in situ SiN/AlGaN-sandwich-barrier (SWB)/GaN/Al0.05GaN high-electron mobility transistors (HEMTs). The dc, channel temperature, and RF temperature of the proposed AlGaN-buffer devices have been systematically studied and analyzed. The SWB structure can effectively reduce the peak value of the electric field, thus effectively reducing the self-heating effect and improving the breakdown characteristics. Through the channel temperature extraction method of pulsed IV and TCAD thermal simulation, the channel temperature of devices with different barrier structures is compared and analyzed, which proves that SWB structure can effectively reduce the channel temperature of devices. Due to the more obvious potential modulation effect between gate and drain, the ƒmax of device can improve more effectively with the increase of drain voltage. In addition, load-pull measurement at 10 GHz revealed that a saturated power density increased from 7.3 to 8.4 W/mm and an associated PAE increased from 24.9% to 29.4%. [ABSTRACT FROM AUTHOR]

In this paper, AlGaN/GaN Fin-HEMTs with different fin configurations are theoretically and experimentally investigated. A simple physical-based threshold voltage model for AlGaN/GaN Fin-HEMTs is built for qualitative analysis. It is shown that the threshold voltage of AlGaN/GaN Fin-HEMTs depends on the width and height of the fin structure. The peak value and linearity of transconductance and current gain cutoff frequency are improved by reducing the fin length. It is also found that the linearity of transconductance is sensitive to the fin height, which can be attributed to the capacitance control from sidewalls. [ABSTRACT FROM AUTHOR]

This letter reports on a novel enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMT) that combines nanowire channel and fluorine plasma treatment using inductively coupled plasma (ICP). Compared with the conventional HEMTs, the threshold voltage of E-mode HEMT shifts from −2.8 to +0.7 V, and the Schottky reverse leakage current is reduced by one order of magnitude. The device exhibits a superior performance with a drain current of 460 mA/mm at V {{\text {GS}}} - V {{\text {TH}}} = 2 V. High \textI{ \mathrm{\scriptscriptstyle ON}}/\textI{ \mathrm{OFF}} ratio of approximately $10^{{\mathbf {9}}} and high breakdown voltage of 138 V with \textL{{\text {DS}}}=4~\mu \text{m} are obtained, i.e., the breakdown voltage of E-mode HEMT is improved by 25% than that in conventional HEMTs. The drain induced barrier lowering (DIBL) is as low as 4 mV/V, and the subthreshold swing (SS) of 70 mV/decade is achieved. The device exhibits an intrinsic current gain cutoff frequency f{\text T} of 22 GHz and a maximum oscillation frequency f {\text {max}} of 60 GHz. [ABSTRACT FROM AUTHOR]

A new simple model of threshold voltage for AlGaN/GaN nanowire channel high electron mobility transistors (NC-HEMTs) is built in this work. Firstly, four NC-HEMTs with different nanowire channel width are fabricated, and the conventional HEMT is produced for comparison. With the nanowire channel width decreasing, the threshold voltage of NC-HEMTs moves positively. Then, the dependence of electron concentration on the nanowire channel width is studied by Silvaco simulation software. With the nanowire channel width decreasing, the electron concentration reduces. Finally, we recognize the threshold voltage model of conventional HEMT for NC-HEMT modeling, and the new model of threshold voltage of NC-HEMT is obtained. This model can explain the dependence of electron concentration on nanowire channel width. The depletion region width formed by side gate is about 37 nm which is obtained by the equation of the new model. [ABSTRACT FROM AUTHOR]

Gate-recessed AlGaN/AlN/GaN metal–oxide–semiconductor heterostructure high-mobility transistors (MOS-HEMTs) on SiC substrate are fabricated. The device with a gate length of 0.6 \mu\m and a gate periphery of 100 \mu\m exhibits a maximum dc drain current density of 1.59 A/mm at VGS = \3\ \V with an extrinsic transconductance (gm) of 374 mS/mm. An extrinsic current gain cutoff frequency (fT) of 19 GHz and a maximum oscillation frequency (f\max) of 50 GHz are deduced from S-parameter measurements. The output power density is 13 W/mm, and the associated power-added efficiency is 73% at 4-GHz frequency and 45-V drain bias. The power performance is comparable to state-of-the art AlGaN/GaN HEMTs, which demonstrates the great potential of gate-recessed MOS-HEMTs as a very promising alternative to GaN HEMTs. [ABSTRACT FROM AUTHOR]

In this paper, in order to solve the interface-trap issue and enhance the transconductance induced by high-k dielectric in metal--insulator--semiconductor (MIS) high electron mobility transistors (HEMTs), we demonstrate better performances of recessed-gate Al2O3 MIS-HEMTs which are fabricated by Fluorine-based Si3N4 etching and chlorine-based AlGaN etching with three etching times (15 s, 17 s and 19 s). The gate leakage current of MIS-HEMT is about three orders of magnitude lower than that of AlGaN/GaN HEMT. Through the recessed-gate etching, the transconductance increases effectively. When the recessed-gate depth is 1.02 nm, the best interface performance with tit = (0.20[?]1.59) us and Dit = (0.55[?]1.08) x 1012 cm[?]2 * eV[?]1 can be obtained. After chlorine-based etching, the interface trap density reduces considerably without generating any new type of trap. The accumulated chlorine ions and the N vacancies in the AlGaN surface caused by the plasma etching can degrade the breakdown and the high frequency performances of devices. By comparing the characteristics of recessed-gate MIS-HEMTs with different etching times, it is found that a low power chlorine-based plasma etching for a short time (15 s in this paper) can enhance the performances of MIS-HEMTs effectively. [ABSTRACT FROM AUTHOR]

An enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMTs) was fabricated with 15-nm AlGaN barrier layer. E-mode operation was achieved by using fluorine plasma treatment and post-gate rapid thermal annealing. The thin barrier depletion-HEMTs with a threshold voltage typically around [?]1.7 V, which is higher than that of the 22-nm barrier depletion-mode HEMTs ([?]3.5 V). Therefore, the thin barrier is emerging as an excellent candidate to realize the enhancement-mode operation. With 0.6-um gate length, the devices treated by fluorine plasma for 150-W RF power at 150 s exhibited a threshold voltage of 1.3 V. The maximum drain current and maximum transconductance are 300 mA/mm, and 177 mS/mm, respectively. Compared with the 22-nm barrier E-mode devices, VT of the thin barrier HEMTs is much more stable under the gate step-stress. [ABSTRACT FROM AUTHOR]

A 1.5-μm polycrystalline diamond was deposited on the AlGaN/GaN heterojunction on SiC substrate with a 20-nm SiN dielectric layer. A (5.8 ± 0.1)% increase in 2DEG density after the diamond growth due to the increase in tensile strain of GaN layer was confirmed by micro-Raman measurements. Top-side integration of polycrystalline diamond heat spreader with AlGaN/GaN high electron mobility transistors was demonstrated. Using a dry/wet combined etching process for the removal of the diamond and SiN interlayer, the integration fabrication of diamond heat spreader and GaN HEMTs with low surface damage was achieved. After the diamond growth, Off-state drain current shows no degradation. Besides, both the drain current and peak transconductance of the GaN HEMTs were enhanced. Temperature reduction of 25 °C at power density of 20 W/mm was achieved by electro-thermal simulation using the thermal properties determined by TDTR measurements. [Display omitted] • Diamond was deposited on the AlGaN/GaN heterojunction with a 20-nm SiN layer. • A dry/wet combined etching was used for the removal of diamond and SiN interlayer. • No degradation of the off-state drain current was achieved after device fabrication. • Drain current and peak transconductance of the GaN HEMTs were enhanced. [ABSTRACT FROM AUTHOR]