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In this paper, an inverted scanning microwave microscope (iSMM) is used to characterize the channel of a gateless GaN/AlN high-electron-mobility transistor (HEMT). Unlike conventional SMM, iSMM allows for 2-port measurements. Unlike conventional iSMM, the present iSMM probe is connected to Port 1 of a vector network analyzer with the HEMT drain and source remain on Port 2. Under different DC biases VGS (applied through the iSMM probe) and VDS (kept constant at 1 V), changes in both reflection coefficient S11 and transmission coefficient S21 are monitored as the iSMM probe scans along the width of the channel, revealing significant nonuniformity. Additionally, changes in S11 and S21 are significant when VGS ≥ −4 V, but insignificant when VGS = −8 V, consistent with the measured threshold voltage at −6 V for a gated HEMT. These results confirm that iSMM can be used to locally modulate the channel conduction of a HEMT while monitoring its RF response, before the actual gate is added. In turn, the nonuniformity measured by the iSMM can be used to diagnose and improve HEMT materials and processes. 

Defect-based single photon emitters play an important role in quantum information technologies. Quantum emitters in technologically mature direct wide bandgap semiconductors, such as nitrides, are attractive for on-chip photonic integration. GaN has recently been reported to host bright and photostable defect single photon emitters in the 600–700 nm wavelength range. Spectral diffusion caused by local electric field fluctuation around the emitter limits the photon indistinguishability, which is a key requirement for quantum applications. In this work, we investigate the spectral diffusion properties of GaN defect emitters integrated with a solid immersion lens, employing both spectral domain and time domain techniques through spectroscopy and photon autocorrelation measurements at cryogenic temperature. Our results show that the GaN defect emitter at 10 K exhibits a Gaussian line shape with a linewidth of ∼1 meV while the spectral diffusion characteristic time falls within the range of a few hundred nanoseconds to a few microseconds. We study the dependency of the spectral diffusion rate and Gaussian linewidth on the excitation laser power. Our work provides insight into the ultrafast spectral diffusion in GaN defect-based single photon emitter systems and contributes toward harnessing the potential of these emitters for applications, especially for indistinguishable single photon generation.

 

Abstract High-quality N-polar GaN p-n diodes are realized on single-crystal N-polar GaN bulk substrate by plasma-assisted molecular beam epitaxy. The room-temperature current–voltage characteristics reveal a high on/off current ratio of >10 11 at ±4 V and an ideality factor of 1.6. As the temperature increases to 200 °C, the apparent ideality factor gradually approaches 2. At such high temperatures, Shockley–Read–Hall recombination times of 0.32–0.46 ns are estimated. The measured electroluminescence spectrum is dominated by a strong near-band edge emission, while deep level and acceptor-related luminescence is greatly suppressed. 

While the properties of β-Ga2O3 continue to be extensively studied for high-power applications, the effects of strong electric fields on the Ga2O3 microstructure and, in particular, the impact of electrically active native point defects have been relatively unexplored. We used cathodoluminescence point spectra and hyperspectral imaging to explore possible nanoscale movements of electrically charged defects in Ga2O3 vertical trench power diodes and observed the spatial rearrangement of optically active defects under strong reverse bias. These observations suggest an unequal migration of donor-related defects in β-Ga2O3 due to the applied electric field. The atomic rearrangement and possible local doping changes under extreme electric fields in β-Ga2O3 demonstrate the potential impact of nanoscale device geometry in other high-power semiconductor devices.

 

Multimode lasing at sub-300 nm wavelengths is demonstrated by optical pumping in AlGaN heterostructures grown on single-crystal AlN substrates by plasma-assisted molecular beam epitaxy. Edge-emitting ridge-based Fabry–Pérot cavities are fabricated with the epitaxial AlN/AlGaN double heterostructure by a combined inductively coupled plasma reactive ion etch and tetramethylammonium hydroxide etch. The emitters exhibit peak gain at 284 nm and modal linewidths on the order of 0.1 nm at room temperature. The applied growth technique and its chemical and heterostructural design characteristics offer certain unique capabilities toward further development of electrically injected AlGaN laser diodes. 

The polarization difference and band offset between Al(Ga)N and GaN induce two-dimensional (2D) free carriers in Al(Ga)N/GaN heterojunctions without any chemical doping. A high-density 2D electron gas (2DEG), analogous to the recently discovered 2D hole gas in a metal-polar structure, is predicted in a N-polar pseudomorphic GaN/Al(Ga)N heterostructure on unstrained AlN. We report the observation of such 2DEGs in N-polar undoped pseudomorphic GaN/AlGaN heterostructures on single-crystal AlN substrates by molecular beam epitaxy. With a high electron density of ∼4.3 ×1013/cm2 that maintains down to cryogenic temperatures and a room temperature electron mobility of ∼450 cm2/V s, a sheet resistance as low as ∼320 Ω/◻ is achieved in a structure with an 8 nm GaN layer. These results indicate significant potential of AlN platform for future high-power RF electronics based on N-polar III-nitride high electron mobility transistors.