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Ti/TiN/Cu is established to be an enabling alternative to the better-known Au-based ohmic contact metals such as Ti/Al/Ni/Au. The Cu-based option delivers lower contact resistance and smoother surface morphology and is proven to be compatible with AlGaN/GaN HEMTs device processing. The TiN layer serves as an effective Cu-diffusion barrier as no detectable Cu-diffusion was observed when subjected to thermal treatment up to 600 ℃. There is a tendency of N-diffusion across the Ti/GaN interface near which N-deficiency in the GaN epitaxial layer and formation of a nano-sheath of TiN was found. This ultrathin layer of TiN works to further improve the ohmic performance of the electric contact, as reflected in lowered contact resistivity ρC. It is possible to manufacture the TiN thin films with low sheet resistance at a high deposition rate by adjusting the ratios between argon and nitrogen gas flows during sputtering deposition. Contact resistivity ρC, tested for the AlGaN/GaN HEMT devices fabricated on Si substrate according to the TLM standard were found to be as low as 3.65×10-6 Ω-cm2 (RC = 0.54 Ω-mm). The outcomes benchmark favourably against many reported metal-stacking structures for ohmic contacts. The robustness of surface morphology and interface sharpness against thermal treatments make the established ohmic stack structures suitable for scalable device fabrications.

In this study, the effect of barrier thickness on the DC and RF performances of AlGaN/GaN high electron mobility transistors (HEMTs) on silicon for millimeter wave applications is experimentally investigated. GaN HEMT devices with different barrier thicknesses were fabricated and characterized. While the device with the thinnest barrier exhibited the highest extrinsic transconductance (gm) resulting from the shortest gate-to-channel distance, such configuration suffered from the lowest unit current-gain cut-off frequency (fT) due to the increase of the total gate capacitance. Moreover, degradation in the output power was observed for devices with thinner barriers. Such degradation was related to the severe knee walkout as evidenced from drain-lag characterization.

A high-performance E-mode hybrid ferroelectric charge storage gate (FEG) GaN HEMT with an innovative source-connected field plate (SCFP) structure is reported for the first time. The optimized E-mode FEG-HEMT implements a novel SCFP structure, which creates a cascode-like configuration with a D-mode GaN MISHEMT. This E-mode SCFP GaN FEG-HEMT has a positive ${V}_{\text {th}}$ of 2.81 V, a high ${I}_{\text {D,max}}$ of 757mA/mm, and a BV of 866 V. Dynamic ${R}_{\text {ON}}$ reduced 25% when operated at ${V}_{\text {DSQ}} =400$ V. ON-state stress tests also show improved current collapse phenomena. Additionally, to address the charge storage abilities of FEG-HEMTs, a multi-cycle OFF-state ( ${V}_{\text {DS}} =300$ V, ${V}_{\text {GS}} =0$ V) retention test was conducted. The SCFP FEG-HEMT showed 58.46% less ${V}_{\text {th}}$ shift percentage than the FEG-HEMT without field plates.

A high-pressure (HP) GaN nucleation layer (NL) was inserted between AlGaN buffer and an unintentionally doped (UID) GaN layer of an AlGaN/GaN HEMT on Si. The XRD and TEM showed that when the V/III ratio was optimized during the HP-GaN NL growth, the edge dislocation density in the HP-GaN NL layer could be reduced significantly. Experimental results exhibited a lower off-state leakage current, higher maximum ID and Gm (corresponding to 22.5% and 21.7% improvement, respectively), and lower on-state resistance. These results demonstrate that the electrical properties of the AlGaN/GaN HEMT can be improved through the insertion of a HP-GaN NL.

In this paper, we demonstrate the AlGaN/GaN high electron mobility transistors (HEMTs) on Si substrate using an AlGaN back-barrier (BB) and super-lattice (SL) buffer to achieve high breakdown and low current collapse (CC) properties for Radio-frequency (RF) applications. The HEMTs also demonstrated low initial vertical leakage current, high thermal stability, and smaller drain-lag with reduced leakage currents as compared to the devices using step-graded (SG) AlGaN buffer. Also, the device showed improved RF performances with higher f T and f max as compared to the devices with SG buffer.

An AlGaN/GaN/Si high electron mobility transistor (HEMT) using a GaN:C buffer with a 2 nm AlGaN electron-blocking layer (EBL) is investigated for the first time for millimeter-wave applications. Compared with the double heterostructure field effect transistor (DHFET), the AlGaN/GaN HEMT with the GaN:C/EBL buffer has a lower vertical leakage, higher thermal stability, and better RF performance. In addition, AlGaN EBL can prevent carbon-related traps from GaN:C and improve electron confinement in 2DEG during high-frequency operation. Finally, a Pout of 31.2 dBm with PAE of 21.7% were measured at 28 GHz at 28 V. These results demonstrated the great potential of HEMTs using GaN:C with AlGaN EBL epitaxy technology for millimeter-wave applications.

using inorganic photo resist material with composition GeSbSnOx to nanolithrography process ,to fabricate nano honeycomb structure .The reflectance of the nanostructure in near visible light is 8~13%

A low-temperature (LT) AlGaN interlayer is inserted in the Al0.1Ga0.9N back barrier layer of an Al0.2Ga0.8N/GaN/Al0.1Ga0.9N double heterostructure grown on a 150 mm Si substrate. It is found that the 21-nm-thick LT-AlGaN interlayer plays an important role in stress relaxation and dislocation reduction of the Al0.1Ga0.9N back barrier layer, especially for screw dislocation reduction. In addition, a buffer breakdown voltage higher than 600 V is achieved, which is much higher than those of conventional heterostructures. These results demonstrate the effectiveness of combining the LT-AlGaN interlayer and the Al0.2Ga0.8N/GaN/Al0.1Ga0.9N double heterostructure on a Si substrate to increase the breakdown voltage for high-power applications.

An Al0.2Ga0.8N/GaN/Al0.1Ga0.9N double-heterostructure field effect transistor (DH-FET) structure was grown on a 150-mm-diameter Si substrate and the crystalline quality of the epitaxial material was found to be comparable to that of an Al0.2Ga0.8N/GaN single-heterostructure field effect transistor (SH-FET) structure. The fabricated DH-FET shows a lower buffer leakage current of 9.2 × 10−5 mA/mm and an improved off-state breakdown voltage of higher than 200 V, whereas the SH-FET shows a much higher buffer leakage current of 6.0 × 10−3 mA/mm and a lower breakdown voltage of 130 V. These significant improvements show that the Al0.2Ga0.8N/GaN/Al0.1Ga0.9N DH-FET is an effective structure for high-power electronic applications.