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The characteristics of an AlGaN/GaN high-electron-mobility transistor buffer structure are studied and optimized by employing an AlN/GaN superlattice (SL) structure. Through vertical leakage analysis and back-gate measurement, combined with Silvaco-TCAD simulation, the influence of buffer trapson the carrier transport behaviors and electrical performance for SL buffer structures under a high electric field is analyzed. The AlN/GaN SL buffer structures are further optimized with various AlN/GaN thickness ratios and their total thickness through both simulation and experimental studies. As a result, a high breakdown voltage of up to 1.3 kV with a maximum breakdown electric field of 2.8 MV cm−1 has been achieved. Moreover, the buffer trapping effect is dramatically suppressed, leading to a minimum drop of channel current for the optimized sample, in which donor traps are found to play a positive role in the device dynamic characteristics.

The paramount issues facing commercialization of GaN-on-Si RF devices include the inevitable wafer bowing and large thermal resistance when incorporating the conventional AlN/AlGaN multilayer or superlattice buffer for stress control. The large thermal resistance due to the strong phonon scattering by the AlGaN alloy and multiple interfaces of the AlN/AlGaN multilayer or superlattice buffer must be carefully addressed, which can significantly affect the performance and reliability of GaN-on-Si RF devices. In this letter, we report a successful growth of crack-free 2 μm-thick GaN film on 6 inch high-resistivity (>10 kΩ cm) Si with a single-layer AlN buffer. By virtue of a quasi-2D GaN nucleation on the AlN buffer layer, the as-grown GaN-on-Si wafer presents a tremendous reduction in warpage from 800 to less than 8 μm, while preserving a high crystalline quality. The full width at half maximum of x-ray diffraction of GaN (0002) and (10 1 ˉ 2) planes are 457 and 509 arcsec, respectively, and the residual stress is as low as 0.2 GPa. The underlying physical mechanisms of the quasi-2D GaN nucleation layer involved in stress engineering and dislocation annihilation have been discussed in detail. This work paves the way for the fabrication of low-cost and high-performance GaN RF devices grown on HR-Si.

This letter has studied the gate reliability of p-GaN high electron mobility transistors (HEMTs) influenced by the Mg doping level at the initial growth stage of p-GaN layer. Normally-off HEMTs with p-GaN gate fabricated with relatively low and high Mg doping concentration have been analyzed and compared based on their performances at various statuses of as-fabricated, forward step-stressed, reverse step-stressed and long-term reverse stressed. It reveals that Mg over-doping has a detrimental effect on the p-GaN gate reliability through degrading the PIN diode formed by p-GaN/AlGaN/GaN structure. Severe drain current reduction, threshold voltage instability and gate leakage increase have been observed after being negatively stressed due to the high-density defects acting as apparent acceptor-like traps induced by Mg over-doping. The detailed studies on the p-GaN gate performance with various Mg concentrations give a greater depth of understanding to realize high gate reliability of p-GaN gate HEMTs.

The increasing demand for complementary metal-oxide-semiconductor integrated GaN-based optoelectronics and power electronics calls for wafer-scale crack-free and high quality GaN thick film grown on Si. However, the huge mismatch in both lattice constant and coefficient of thermal expansion between GaN and Si often causes a high density of threading dislocations (TDD, typically 109–1010 cm−2) and the formation of micro-crack networks, producing a poor-quality GaN film with a limited thickness (

An abnormal aging phenomenon is reported for GaN-based near-ultraviolet laser diodes (LDs). Under an electrical stress for several minutes, the threshold current of the LDs decreased, while the light output power and the operation voltage increased. The amplitude of the abnormal aging phenomena was found to be mainly related to the excess Mg concentration in the p-AlGaN electron blocking layer (EBL). It almost disappeared when the Mg concentration in the AlGaN EBL was reduced to 2??×??1019 cm?3. We propose that this phenomenon was related to the Mg?VN?H complex defects formed in highly doped AlGaN EBL ([Mg]??>??3??×??1019 cm?3).

Thin AlN spacer layer is widely adopted in Al(In)GaN/AlN/GaN heterostructures to improve the mobility of two-dimensional electron gas (2DEG) by increasing the 2DEG confinement and reducing the remote alloy scattering. However, the nominal AlN spacer is found to be an AlGaN spacer mainly due to the unintentional incorporation of Ga from the decomposition of the underlying GaN channel during the growth of AlN spacer and the temperature ramping process from the GaN channel to the Al(In)GaN barrier. The growth conditions of AlN spacer layer were varied systematically to study their influences on the unintentional Ga incorporation and the 2DEG mobility of AlInGaN/AlN/GaN heterostructures. Interestingly, the nominal AlN spacer (or AlGaN spacer in fact) can still effectively reduce the remote alloy scattering and deliver a 2DEG mobility substantially higher than that of AlInGaN/GaN heterostructures with no spacer or an AlGaN spacer uniformly containing a Ga content similar to the average Ga composition of the nominal AlN spacer. A simplified microstructure of the nominal AlN spacer with an inhomogeneous Ga incorporation was proposed to discuss about the influence of the spacer on the 2DEG mobility.