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Based on metal organic chemical vapor deposition (MOCVD), growth mechanism and stress modulation of van der Waals (vdW) heteroepitaxial GaN microwave material were studied with few-layer BN as an interlayer on 4-inch sapphire substrates. The influence of AlN nucleate process on growth mechanism of GaN buffer layer and its correlation with crystalline quality, stress, and electrical properties were discussed. A stress modulation scheme based on AlN/ AlGaN composite nucleation process is proposed, achieving stress well in control for large-size vdW heteroepitaxy firstly. The as-grown GaN microwave material possesses a wafer bow of + 20. 4 μm, fullwidth at half maximum of GaN (002) / (102) peaks of 471. 6/933. 5 arcsec, root-mean-square roughness of 0. 52 nm and electron mobility of 2 000 cm² / (V·s). Finally, largesize wafe-scale GaN microwave material was successfully separated from sapphire substrate by a mechanical lift-off process, providing convenience for transfering to high thermal conductivity substrates and creating conditions for fabricating high-power RF devices. [ABSTRACT FROM AUTHOR]

The electrode made of transparent semiconductor indium tin oxide (ITO) can reduce the edge current crowding effect of photoconductive semiconductor switches and improve the utilization of pulse laser. In this paper, 10 nm Ti and TiN layer were inserted into the interface between ITO and GaN, and the influences of Ti and TiN layer on the Ohmic contact performance between ITO and GaN were studied. I-V test results show that with the increase of the annealing temperature, the GaN photoconductive semiconductor switch with Ti insertion layer changes from Ohmic contact to Schottky contact, while the photoconductive semiconductor switch with TiN insertion layer keeps Ohmic contact characteristics. TEM observation shows that when Ti is used as the insertion layer, ITO diffuses through the insertion layer to the interface between the insertion layer and GaN, resulting in the formation of Ti oxide and holes at the interface. The transmission spectra show that the transmittance of samples with Ti insertion layer is less than 38.3% at different annealing temperatures, while the transmittance is 38.8% ~55.0% when TiN is used as the insertion layer. Therefore, the photoconductive semiconductor switch containing TiN insertion layer shows a higher thermal stability and transmittance, which provides reference for the application of GaN photoconductive semiconductor switch in the field of high temperature and high power. [ABSTRACT FROM AUTHOR]

Solid-state power amplifiers using semiconductor technology have the advantages of small size and high stability, and have replaced traditional travelling wave tube amplifiers in many microwave applications. Among all types of semiconductor materials, the third-generation semiconductor material GaN(Gallium Nitride) has been widely used in power amplifiers because of its advantages of wide band gap, high electron mobility, and high breakdown voltage. Based on the development of power amplifiers, this study describes the development history of solid-state power amplifiers, summarizes the performance comparison between GaN technology and other semiconductor technologies, and focuses on power amplifiers using GaN HEMT(GaN High Electron Mobility Transistor) technology. This study discusses various types of GaN HEMT power amplifiers, including class A, B, C, D, and E, etc., introduces the efficiency and linearity improvement techniques applied to GaN power amplifiers, including Doherty power amplifiers and envelopes tracking technology, and digital pre-distortion technology, etc., and makes a summary and comparison of related technologies. [ABSTRACT FROM AUTHOR]

In order to investigate the influence of InxGa1-xN barrier with different indium ( In) composition on photoelectric performance of green laser diode, a series of green laser diode with InxGa1-xN barrier of different In composition were simulated by SiLENSe ( simulator of light emitters based on nitride semiconductors) software. The results show that the InxGa1-xN barrier structure with 3% In composition has the highest slope efficiency and the lowest internal optical loss, and also show the largest optical confinement factor and the optimum performance. Based on the multiple quantum well structure with In0.03Ga0.97N barrier, the composition step-graded (CSG) InGaN barrier model structure was designed, which effectively improves the slope efficiency and electro-optical conversion efficiency. Moreover, the optical field confinement increase. The simulation results show that at the injection current of 120 mA, the efficiency of electro-optical conversion increases from 17.7% to 19. 9% for the multiple quantum well structure with CSG InGaN barrier, the slope efficiency increases from 1. 09 mW/mA to 1. 14 mW/mA, and the optical confinement factor increases from 1. 58% to 1. 62%. The study provides theoretical guidance and data support for the preparation of high-power GaN-based green laser diode. [ABSTRACT FROM AUTHOR]

With the widespread application of gallium nitride (GaN) in the high-power field, the heat dissipation of GaN based devices has become the main factor restricting the power density. Therefore, it is crucial to develop novel thermal management solutions. Diamond substrates with high thermal conductivity can be used to improve the heat dissipation of GaN devices. However, due to the natural lattice mismatch between diamond and GaN, the direct epitaxy of GaN on diamond substrates remains an insurmountable problem. This work achieved van der Waals epitaxy of single crystal GaN films on polycrystalline diamond substrates using a two-dimensional material / Al gradient AlGaN heterostructure as the nucleation layer between the substrate and the epitaxial layer. Among them, two-dimensional materials can effectively shield against the adverse effects caused by lattice mismatch between the substrate and epitaxial layer, while the Al component gradient AlGaN buffer layer can achieve orderly migration of Ga and N atoms, thereby accurately controlling the growth of GaN thin films. This work provides a novel approach for high-quality growth of nitrides on heterogeneous substrates. The experimental results indicate that the introduction of nucleation layers effectively eliminates the impact of lattice mismatch, thereby breaking the bottleneck of the difficulty in directly epitaxial single crystal GaN films on diamond substrates. This work provides a foundation for further improving the power density of GaN based devices. [ABSTRACT FROM AUTHOR]

In this study, a large area laser lift-off (LLO) of GaN-based micro light-emitting diodes (Micro LED) was achieved using an excimer laser at 248 nm. The critical laser energy density required for separation of devices is 800 ~ 835 mJ·cm - 2. The separated device is intact with a residual stress of 0. 071 4 GPa and a mean square roughness of 0. 597 nm, which is much lower than that of the LLO method reported so far. This study provides a promising idea for the fabrication of GaN-based Micro LED chips with high quality and high efficiency, which is of great significance for the fabrication of flexible GaN-based devices. [ABSTRACT FROM AUTHOR]

Epitaxial growth of InN films on GaN ( 0001 ) by metal organic chemical vapor deposition ( MOCVD) was investigated with adding an InGaN bedding layer. It is found that pure InN can be obtained on the InGaN bedding layer with quality higher than on bare GaN surface. By adopting proper In composition (In0. 23Ga0. 77N in this work) in the InGaN bedding layer, indium droplet formation can be totally suppressed during the growth of InN. The structure and optical properties of InN were investigated by using optical microscopy, high-resolution X-ray diffraction (HR-XRD), transmission electron microscopy (TEM), photoabsorption and photoluminescence at room temperature. From the HR-XRD measurements, the ω and ω-2θ scans show the elimination of In diffraction signal by using the InGaN bedding layer and the ω scan gives a linewidth of 0. 23° for 150 nm InN film. From the selective area electron diffraction pattern in the TEM, the InN is found to be almost strain free. Both photoabsorption and strong photoluminescence of InN film at room temperature indicate that the energy band gap of the InN is about 0. 74 eV. Abnormal excitation-dependent photoluminescence behavior of the InN was preliminarily investigated too. It is proved that the surface effect of InN materials has a strong effect on the radiation recombination. [ABSTRACT FROM AUTHOR]

A novel coupled barrier heterojunction structure ( i. e. Al 0. 26 Ga0. 74 N/ GaN/ Al 0. 20 Ga0. 80 N/ GaN) was proposed and prepared in this paper to improve transconductance linearity of GaN high electron mobility transistor. A double two-dimensional electron gas (2DEG) channel in the coupled barrier heterojunction structure is demonstrated by theoretically calculation and capacitance-voltage (C-V) measurement. 2DEG mobility of 1 510 cm 2·V - 1·s - 1 and sheet density of 9. 7 × 10 12 cm - 2 are obtained. Benefiting from the double channels, the transconductance profile of the device with coupled heterojunction barrier structure shows two peaks, and the voltage swing is 3. 0 V, which is 1. 5 times larger than that of normal structure. First-order and second-order derivative characteristics of transconductance indicate that the device of the coupled barrier structure has higher harmonic suppression capability. This study demonstrates a superiority of coupled barrier heterojunction in the area of high linearity application. [ABSTRACT FROM AUTHOR]

Due to the advantages of both large size, low cost, and compatibility with existing CMOS processes, GaN based ratio frequency (RF) electronic materials and devices on Si substrates have become the next focus of attention in this field after power electronic devices. Due to the different mechanical properties of high-resistivity Si substrates, it is still difficult to control stress and suppress dislocations in the growth of GaN based epitaxial materials on high-resistivity Si substrates, as well as address serious RF loss issues that limit their applications in the field of RF electronics. This work briefly introduces the research status and challenges of GaN based RF electronic materials on Si substrates, focusing on the main research progress of the Peking University research team in the formation mechanism of RF loss, epitaxial growth of GaN on high-resistivity Si substrates with low dislocation density and low RF loss. Finally, the future development of GaN based RF electronic materials and devices on Si substrates is prospected. [ABSTRACT FROM AUTHOR]

After adjusting the component parameters of the designed AlGaInN/InGaN DBR structure with a central wavelength of 520 nm, strain compensation was realized and the overall strain of DBR turned to 0. The transmission matrix method was used to calculate the reflectance spectra of Al0.7 Ga0.3 - x Inx N/InGaN DBR, Al0.8 Ga0.2 - x Inx N/InGaN DBR, and Al0.9 Ga0.1 - x Inx N/InGaN DBR. By comparing the structure parameters of DBR, the structure and reflection performance of DBR are optimized. First, high and low refractive index layer growth sequence was compared for Al0. 8 Ga0. 14 In0. 06 N/In0. 123 Ga0. 877 N DBR. For DBR with first grown high refractive index layer, the reflectance is as high as 99. 61%, while for DBR first grown low refractive index layer, the reflectance is only 97. 73%. Then, by comparing the odd-layer DBR and even-layer DBR, it is found that the reflection spectra of the two layers are almost identical, and there is no significant difference. By comparing the periods of DBR, it is found that the reflectance increases obviously with the increase of period number between 20 and 30 pairs, while the reflectance increases slowly with the increase of period number between 30 and 40 pairs. At last, the influence of the material components on the reflection spectrum is studied. It is found that the DBR with high Al component has a large refractive index difference and better reflection performance, while the lower content of In in the same Al component AlGaInN, the higher the reflectivity. Due to the possible deviation of thickness and component in the preparation of DBR, the changes of reflection spectra resulted from the deviation of thickness and components were simulated. It is found that the reflection spectrum is red-shifted or blue-shifted by 4 nm to 5 nm when the layer thickness of high or low refractive index is increased or decreased by 1 nm. While the component deviations caused significant changes in high anti-band bandwidth and reflectivity at central wavelength. The study in this paper provides some theoretical reference for the design and preparation of AlGaInN/InGaN DBR. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) material has become a research hotspot at home and abroad because of its unique properties and application prospects. High quality GaN single crystals are the prerequisite for obtaining optoelectronic devices and power devices with excellent performance. Because of its mild growth conditions, the sodium flux method is easy to obtain high quality and large size GaN single crystals, and it is a promising method for the growth of GaN single crystals. Since the sodium flux method was invented in the late 1990s, the crystals grown by the sodium flux method have made considerable progress in size and quality after more than 20 years of development. Recent research progress of GaN single crystals grown by the sodium flux method from the aspects of crystal growth principle, seed crystal selection, temperature gradient and additives are summarized in this paper, and the challenges and future development trend are also prospected. [ABSTRACT FROM AUTHOR]

In this paper, a double-barrier structure AlGaN-InGaN/ GaN MQWs-AlGaN solar cell materials containing high indium components was grown on (001)-oriented patterned sapphire substrate (PSS) by metal organic chemical vapor deposition (MOCVD) technology. Compared with the MQWs solar cell material containing AlGaN electron barrier structure with low indium, it is found that the material of this structure has a smaller full width at half maximum (FWHM) by high-resolution X-ray diffraction (HRXRD) and photoluminescence (PL) spectroscopy analysis, and the dislocation density of this structural material is also reduced by an order of magnitude to 107 cm-2 by the dislocation density formula; at the same time, the strain relaxation in the active region decreases by 51%. In addition, luminous intensity of this structural material is enhanced by 35%. The results show that the epitaxial material containing AlGaN double barrier structure can reduce the dislocation density in the active region, decrease the number of non-radiative recombination centers, and increase the number of effective photo-generated carriers in the active region, which provides experimental basis for the preparation of high efficiency solar cells. [ABSTRACT FROM AUTHOR]

The substitution position of indium (In) atoms is significant for developing novel orthorhombic GaN hydrogen storage materials. Currently, research on the influence of In atom substitution position on the orthorhombic GaN is still relatively limited. In this paper, based on the first-principles, formation energy, electronic structure, elastic properties, and mechanical stability of InGaN materials with different In atom substitution positions were studied. The results show that the formation energy of In atom substitution position separated by three atoms is the smallest, and the structure is most easily formed. Under the same doping conditions, the InGaN materials with this structure also have larger band gap and smaller elastic modulus, bulk modulus, shear modulus, and elasticity modulus, which means that its compressive strength and shear stress are slightly weaker, and its toughness and hardness are lower. In addition, the calculation results of phonon spectrum show that the InGaN material with three atoms interval also has good mechanical stability under ambient pressure. This study provides a theoretical basis for studying new hydrogen storage metamaterials with orthorhombic GaN. [ABSTRACT FROM AUTHOR]

In this paper, the polarization luminescence characteristics of the near-band-edge peak and Fe3 + related emission peaks(4T1 (G)-6A1 (S)) of the non-polar surfaces including a-plane {11 20} and m-plane {1 100} of Fe-doped GaN crystal were studied by low-temperature photoluminescence(PL) measurement. The results show that the optical anisotropy of a-plane and m-plane are similar. When the linearly polarized electric-field vector E is parallel to the c-direction [0001] (E//c), the intensity of GaN near-band-edge peak is the lowest, and the intensity of Fe3+ zero-phonon line (1.299 eV) is the strongest. The degree of polarization of Fe3+ zero-phonon line is greater than that of near-band-edge peak. The degree of polarization of near-band-edge peak of a-plane is 26%, while the degree of polarization of Fe3+ zero-phonon line reaches up to 55% and 58% of a-plane and m-plane GaN, respectively. The polarization characteristics of Fe3+ fine peak and the additional lines are further measured at 5 K. The results show that, except for one weak peak, other peaks are consistent with the polarization characteristics of Fe3+ zero-phonon line. This study is helpful to expand the application of Fe-doped GaN crystal in the field of novel optical and electrical devices. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) high electron mobility transistor (HEMT) has attracted much attention due to its high breakdown field strength, low on-resistance and high conversion efficiency, and it is expected to be applied in power electronics systems. However, its high power density and high frequency characteristics bring great challenges to packaging technology. The parasitic inductance parameters in the package of traditional silicon power electronic devices is large, which will cause switch oscillation and other problems, so that the excellent performance of GaN cannot be fully utilized. In addition, the thermal management ability of the package determines the reliability of the power device. If the self-heating effect of the device cannot be well solved, its performance will be reduced, and even the chip will be burned. On the basis of explaining the switching oscillation and thermal management problems caused by traditional packaging technology applied to gallium nitride power electronic devices, the research progress of GaN packaging technology aiming at the above problems are reviewed in detail in this paper, including by optimizing the control circuit, reducing Lg inductancing, improving Rg inhibition of dv/dt, increasing ferrite beads on the gate electrode, PCB layout optimization and increasing magnetic flux offset method to solve the problem of switch oscillation caused by the parasitic inductance, the application of high thermal conductivity material of diamond in devices thermal management, improvement of device package structure and other heat dissipation technologies. [ABSTRACT FROM AUTHOR]