We report the successful integration of low-temperature polycrystalline all-around diamond as heat spreaders with 150 nm gate length N-polar GaN MISHEMT platform to improve power efficiencies for X-band applications. With an all-around integration scheme, the CVD-grown diamond reduces channel’s peak temperature, improving device performance and reliability. A combination of optimized low-temperature diamond growth at 500 °C with the thermally stable molybdenum gate metal and MOCVD-grown SiN_x gate-dielectric was utilized for the successful integration. The fabricated device exhibited a I_DSS of 0.96 A mm⁻¹ and an ON-to-OFF ratio of 10⁵. This marks the first post-process diamond integration on a RF GaN HEMT device.

We report thin, high quality n ⁺ type doped N-polar GaN contact layers grown using metal-organic chemical vapor deposition with carrier concentration as high as 3.5 × 10 ²⁰ cm ⁻³ and an electron mobility of 80 cm ² V ⁻¹ s ⁻¹ at room temperature resulting in a low sheet resistance of 57.3 Ω/□ and specific contact resistance of 1.7 × 10 ⁻⁷ Ω.cm ² . These results were obtained via silicon doping of ( 000 1 ‾ ) N-polar GaN grown on 4° miscut sapphire substrates using a flow modulation growth scheme at a deposition temperature of 850 °C.

Integration of nitrides with other material systems has recently become of interest due to the high performance of GaN-based high-electron mobility transistors. However, the elevated growth temperatures often used to grow high quality AlN pose challenges toward metalorganic chemical vapor deposition (MOCVD) on temperature sensitive substrates such as processed wafers. In this work, the growth of AlN was conducted at temperatures below 550 °C via MOCVD using a flow-modulated epitaxy scheme, and their morphological, compositional, and electronic properties of these films were investigated. Sheet charges up to 2.1 × 10¹³ cm⁻² and mobilities on the order of 400 cm²/V s were measured for two dimensional electron gases, which formed at the interface between the low temperature grown AlN layers and the semi-insulating GaN base layers deposited at high temperatures. Despite their low growth temperatures, nominally pure AlN barrier layers exhibited measurable unintentional gallium incorporation adjacent to the GaN interface. The result sets the stage for the integration of nitride-based electronics via epitaxy-based schemes on temperature sensitive substrates.

Achieving high-quality, relaxed InGaN substrates for longer-wavelength light emitting diodes (LEDs) is of great interest for the development of micro-LED based display technology. This work demonstrates molecular beam epitaxy (MBE)-grown In_0.2Ga_0.8N with a strain relaxation of 60% corresponding to an equivalently fully relaxed In composition of 12%. This was done by growing on a GaN-on-porous GaN pseudo-substrate (PS). The surface morphology of this film was found to be free of V-defects on the surface and with a threading dislocation density comparable to that of the GaN layers beneath. While InGaN grown on planar GaN-on-sapphire substrates remained nearly strained to the GaN underlayer, InGaN grown under identical conditions on PS displayed elastic-like relaxation. Furthermore, an increase in indium (In) composition was observed for the InGaN grown on PS. Where past work of InGaN grown on porous GaN PS by metalorganic chemical vapor deposition also resulted in relaxed InGaN templates suitable for device application, the surfaces of these relaxed films exhibited V-defects for thicker layers. Employing MBE, thicker films with higher In composition can be achieved with smooth surface morphology, thus enabling pseudo-substrates with a wide range of lattice constants. These pseudo-substrates of varying in-plane lattice constant are attractive for III-nitride based optoelectronics, particularly for green, amber, and red micro-LEDs.

In this paper, we demonstrate the first GaN/InGaN high electron mobility transistor with a partially relaxed InGaN channel, realized by utilizing a porous GaN buffer obtained by the selective and controlled electrochemical etch of GaN. According to reciprocal space map analysis, ∼70% of InGaN relaxation relative to GaN was achieved by this process. With the transfer length method and extracted charge profile, the relaxed InGaN channel demonstrates ∼9.6% two-dimensional electron gas mobility enhancement with respect to the strained InGaN channel which is consistent with a reduced effective mass predicted by theoretical analysis based on Vegard’s law. On comparing the output characteristics of devices with relaxed and strained InGaN channel, the relaxed channel devices show a 10% improvement of on-resistance while maintaining similar saturation current. A non-uniform charge distribution was found in the relaxed InGaN channel, which can be attributed to the strain relaxation fabrication process.

A wet-etching technique based on a mixture of hydrochloric (HCl) and nitric (HNO₃) acids is introduced, demonstrating exceptional 42:1 selectivity for etching N-polar GaN over Al_0.24Ga_0.76N. In the absence of an AlGaN etch stop layer, the etchant primarily targets N-polar unintentionally doped (UID) GaN, indicating its potential as a suitable replacement for selective dry etches in the fabrication of GaN high-electron-mobility transistors (HEMTs). The efficacy and selectivity of this etchant were confirmed through its application to a gate recess module of a deep-recess HEMT, where, despite a 228% over-etch, the 2.6 nm AlGaN etch stop layer remained intact. We also evaluated the proposed method for the selective etching of the GaN cap in the n+ regrowth process, achieving a contact resistance matching that of a BCl₃/SF₆ ICP process. These findings underscore the applicability and versatility of the etchant in both the electronic and photonic domains and are particularly applicable to the development of N-polar deep-recess HEMTs.