Demonstration and modeling of unipolar-carrier-conduction GaN Schottky-pn junction diode with low turn-on voltage

By introducing a thin p-type layer between the Schottky metal and n-GaN layer, this work presents a Schottky-pn junction diode(SPND) configuration for the GaN rectifier fabrication. Specific unipolar carrier conduction characteristic is demonstrated by the verification of temperature-dependent current–voltage(I–V) tests and electroluminescence spectra.Meanwhile, apparently advantageous forward conduction properties as compared to the pn diode fabricated on the same wafer have been achieved, featuring a lower turn-on voltage of 0.82 V. Together with the analysis model established in the GaN SPND for a wide-range designable turn-on voltage, this work provides an alternative method to the GaN rectifier strategies besides the traditional solution.

AlGaN solar‐blind APD with low breakdown voltage

A p-i-i-n type AlG a N heterostructure avalanche photodiodes(APDs)is proposed to decrease the avalanche breakdown voltage and to realize higher gain by using high-Al-content AlG aN layer as multiplication layer and low-Al-content AlG aN layer as absorption layer.The calculated results show that the designed APD can significantly reduce the breakdown voltage by almost 30%,and about sevenfold increase of maximum gain compared to the conventional Al GaN APD.The noise in designed APD is also less than that in conventional APD due to its low dark current at the breakdown voltage point.Moreover,the one-dimensional(1D)dual-periodic photonic crystal(PC)with anti-reflection coating filter is designed to achieve the solar-blind characteristic and cutoff wavelength of 282 nm is obtained.

High-efficiency photon-electron coupling resonant emission in GaN-based microdisks on Si

Resonance effects caused by the photon-electron interaction are a focus of attention in semiconductor optoelectronics,as they are able to increase the efficiency of emission.GaN-on-silicon microdisks can provide a perfect cavity structure for such resonance to occur.Here we report GaN-based microdisks with different diameters,based on a standard blue LED wafer on a Si substrate.A confocal photoluminescence spectroscopy is performed to analyze the properties of all microdisks.Then,we systematically study the effects of radial modes and axial modes of these microdisks on photon-electron coupling efficiency by using three-dimensional finite-difference time-domain simulations.For thick microdisks,photon-electron coupling efficiency is found to greatly depend on the distributions of both the radial modes and the axial modes,and the inclined sidewalls make significant influences on the axial mode distributions.These results are important for realization of high-efficiency resonant emission in GaN-based microcavity devices.

A lateral AlGaN/GaN Schottky barrier diode with 0.36-V turn-on voltage and 10-kV breakdown voltage by using double-barrier anode structure

GaN power electronic devices,such as the lateral AlGaN/GaN Schottky barrier diode(SBD),have received significant attention in recent years.Many studies have focused on optimizing the breakdown voltage(BV)of the device,with a particular emphasis on achieving ultra-high-voltage(UHV,>10 kV)applications.However,another important question arises:can the device maintain a BV of 10 kV while having a low turn-on voltage(V_(on))?In this study,the fabrication of UHV AlGaN/GaN SBDs was demonstrated on sapphire with a BV exceeding 10 kV.Moreover,by utilizing a doublebarrier anode(DBA)structure consisting of platinum(Pt)and tantalum(Ta),a remarkably low Von of 0.36 V was achieved.This achievement highlights the great potential of these devices for UHV applications.

Progress on AlGaN-based solar-blind ultraviolet photodetectors and focal plane arrays

Solar-blind ultraviolet(UV)photodetectors(PDs)have attracted tremendous attention in the environmental,industrial,military,and biological fields.As a representative Ill-nitride material,AlGaN alloys have broad development prospects in the field of solar-blind detection due to their superior properties,such as tunable wide bandgaps for intrinsic UV detection.In recent decades,a variety of AlGaN-based PDs have been developed to achieve high-precision solar-blind UV detection.As integrated optoelectronic technology advances,AlGaN-based focal plane arrays(FPAs)are manufactured and exhibit outsta nding solar-blind imaging capability.Con sidering the rapid development of AlGaN detection techniques,this paper comprehensively reviews the progress on AlGaN-based solar-blind UV PDs and FPAs.First,the basic physical properties of AlGaN are presented.The epitaxy and p-type doping problems of AlGaN alloys are then discussed.Diverse PDs,including photoconductors and Schottky,metal-semiconductor-metal(MSM),p-i-n,and avalanche photodiodes(APDs),are dem on strated,and the physical mechanisms are analyzed to improve device performance.Additionally,this paper summarizes imaging technologies used with AlGaN FPAs in recent years.Benefit!ng from the development of AlGaN materials and optoelectronic devices,solar-blind UV detection technology is greeted with significant revolutions.

High-efficiency green micro-LEDs with GaN tunnel junctions grown hybrid by PA-MBE and MOCVD

We fabricated p-i-n tunnel junction(TJ)contacts for hole injection on c-plane green micro-light-emitting diodes(micro-LEDs)by a hybrid growth approach using plasma-assisted molecular beam epitaxy(PA-MBE)and metal–organic chemical vapor deposition(MOCVD).The TJ was formed by an MBE-grown ultra-thin unintentionally doped In Ga N polarization layer and an n^(++)∕n^(+)-GaN layer on the activated p^(++)-Ga N layer prepared by MOCVD.This hybrid growth approach allowed for the realization of a steep doping interface and ultrathin depletion width for efficient inter-band tunneling.Compared to standard micro-LEDs,the TJ micro-LEDs showed a reduced device resistance,enhanced electroluminescence intensity,and a reduced efficiency droop.The size-independent J-V characteristics indicate that TJ could serve as an excellent current spreading layer.All these results demonstrated that hybrid TJ contacts contributed to the realization of high-performance micro-LEDs with long emission wavelengths.

Reverse leakage current in AlGaN-based ultraviolet light-emitting diodes

The reverse leakage characteristics of AlGaNbased ultraviolet light-emitting diodes fabricated on sapphire substrate are studied by temperature-variable current–voltage(I–V)measurement from 300 to 450 K.At low-reverse bias range(0–0.5 V),the reverse leakage current exhibits tunneling characteristics.Meanwhile,under a more negative reverse bias range([0.5 V),the log(I)–log(V)plots exhibit close-to-linear dependency,which is in good agreement with the transport mechanism of space-charge limited current.A phenomenological leakage current model focusing on electron transmission primarily through continuous defect band formed by linear defects like dislocations is suggested to explain the reverse current–voltage characteristics.

Magnesium ion-implantation-based gallium nitride p-i-n photodiode for visible-blind ultraviolet detection

In this work, a GaN p-i-n diode based on Mg ion implantation for visible-blind UV detection is demonstrated.With an optimized implantation and annealing process, a p-GaN layer and corresponding GaN p-i-n photodiode are achieved via Mg implantation. As revealed in the UV detection characterizations, these diodes exhibit a sharp wavelength cutoff at 365 nm, high UV/visible rejection ratio of 1.2 × 10~4, and high photoresponsivity of 0.35 A/W, and are proved to be comparable with commercially available GaN p-n photodiodes. Additionally, a localized states-related gain mechanism is systematically investigated, and a relevant physics model of electricfield-assisted photocarrier hopping is proposed. The demonstrated Mg ion-implantation-based approach is believed to be an applicable and CMOS-process-compatible technology for GaN-based p-i-n photodiodes.

Avalanche mechanism analysis of 4H-SiC n-i-p and p-i-n avalanche photodiodes working in Geiger mode

Understanding detailed avalanche mechanisms is critical for design optimization of avalanche photodiodes(APDs).In this work,avalanche characteristics and single photon counting performance of 4H-SiC n-i-p and p-i-n APDs are compared.By studying the evolution of breakdown voltage as a function of incident light wavelength,it is confirmed that at the deep ultraviolet(UV)wavelength region the avalanche events in 4H-SiC n-i-p APDs are mainly induced by hole-initiated ionization,while electron-initiated ionization is the main cause of avalanche breakdown in 4H-SiC p-i-n APDs.Meanwhile,at the same dark count rate,the single photon counting efficiency of n-i-p APDs is considerably higher than that of p-i-n APDs.The higher performance of n-i-p APDs can be explained by the larger impact ionization coefficient of holes in 4H-SiC.In addition,this is the first time,to the best of our knowledge,to report single photon detection performance of vertical 4H-SiC n-i-p-n APDs.