Ⅲnitride wide bandgap semiconductors, such as gallium nitride (GaN) and aluminum nitride (AlN), are the key materials for the development of shortwavelength optoelectronic devices, as well as highfrequency and highpower electronic devices. Due to the lack of highquality and lowcost homogeneous GaN and AlN substrates, nitride semiconductors are mainly realized by means of heteroepitaxy, especially the large latticemismatched heteroepitaxy, resulting in high defect density and huge residual stress in the epilayers, which have become the key bottlenecks in the development of deep ultraviolet light emitting devices and power electronic devices, and other nitride semiconductor ones. In this paper, the research history of the large latticemismatched heteroepitaxy of nitride semiconductors by means of metal organic chemical vapor deposition (MOCVD) is first briefly introduced. Then, the research progress on the MOCVD epitaxial growth and ptype doping of AlN and high Al composition AlGaN on sapphire substrate, as well as the MOCVD epitaxial growth and defect control of GaN and its heterostructures on Si substrate in Peking University are demenstrated. Finally, the current challenges and developing trends on the large latticemismatched heteroepitaxy for Ⅲnitride wide bandgap semiconductors are reviewed and expected.

Bulk GaN is an ideal substrate for the fabrication of blue and green laser diodes (LDs), RF devices, and power electronic devices, which has broad prospects in the application of laser display, 5G mobile communication, and smart grid. The commercial bulk GaN substrates are mainly produced by hydride vapor phase epitaxy (HVPE) at present. Driven by the market demand, HVPE technology has developed rapidly in recent years. In this paper, recent progress in HVPE growth of bulk GaN substrate were reviewed, including the growth mechanisms of HVPE, doping in bulk GaN and the controlling of optical and electrical properties, the main defects in bulk GaN and their evolution, and the application of bulk GaN substrates in related devices. At last, the development trend of HVPE technology is previewed.

At present, cplane GaNbased lightemitting diodes(LED) have already been mature and commercialized, but they still suffer from the issues of efficiency droop at high injection and low efficiency in the yellowgreen wavelength caused by polarization electric fields. In order to eliminate the influence of polarization electric field, nonpolar/semipolar GaN has attracted people’s research interest. The growth of threedimensional GaN structures based on traditional cplane substrates to obtain nonpolar/semipolar facets has recently been intensively studied due to its simple process and low cost. In this paper, three kinds of growth methods of GaN threedimensional structures are summarized with the analysis of mechanisms at first. And then, the epitaxy and luminescence characteristics of InGaN quantum wells with different crystal planes based on these structures are introduced. Finally, the applications of GaNbased threedimensional structure in semipolar LEDs, colortunable LEDs and phosphorfree white LEDs are shown.

GaNbased blue and green laser diodes have important applications and large market demands in projection display, laser processing, laser lighting, storage and other fields. This paper focuses on the technical difficulties of GaNbased blue and green edge emitting laser diodes and our corresponding solutions.Optimization methods of layer structures and technology for GaNbased blue and green laser diodes are introduced including fabricating high quality InGaN/GaN multiple quantum wells(MQWs), reducing internal optical loss and increasing hole injection efficiency. The research status of vertical cavity surface emitting laser (VCSEL) and distributed feedback laser (DFB) are briefly introduced.

Modern society has realized informationization and is developing towards intelligentization. The technology of display is the key tache to achieve the information intercharge and intelligence. Among the many display technologies, the MicroLED display has emerged as the nextgeneration displays due to the excellent properties, such as high contrast, fast response, wide color gamut, low power consumption and long lifetime which could be used in the application with advanced display needs. However, in the commercialization of MicroLED display technology, there are still some technical bottlenecks that have not been solved. For epitaxial technology, the substrate selection, wavelength uniformity and defect management need to be considered for the application of MicroLED display. For the MicroLED devices, there is still no effective solution to solve the efficiency attenuation. Furthermore, by using the color conversion media, the monolithic fullcolor display technology is not yet mature which need further investigation. Starting from the above three issues, this article reviews the development and the current technical issues of MicroLED displays.

Gallium nitride (GaN) has excellent properties such as high breakdown field strength, high saturation electron drift rate, strong radiation resistance and good chemical stability. It is an ideal substrate material for the fabrication of wide spectrum, high power, high efficiency photoelectron, power electronics and microelectronics. In addition to vapor phase method (including HVPE (hydride vapor phase epitaxy), MOCVD (metalorganic chemical vapor deposition), MBE (molecular beam epitaxy)) of GaN single crystal growth, liquid phase method (including ammonothermal method and flux method) has made great progress in recent years. In this paper, the growth principle, equipment characteristics and growth habit of ammonothermal method and flux method are introduced. The research process of two liquid phase growth methods are reviewed. The development trend and main challenges of liquid phase growth of GaN single crystal are prospected.

Gallium nitride (GaN) is a typical material of the third generation of semiconductor materials. It is an ideal material for application in optoelectronic devices and power electronic devices, due to its good physical and chemical properties and thermal stability. Fabrication of GaNbased devices on GaN single crystal substrates by using homoepitaxial technique is the fundamental way to obtain devices with high performances. This article reviews the research progress of method for grown of GaN single crystal substrate, such as hydride vapor phase epitaxy technology, trihalide vapor phase epitaxy technology, ammonothermal method and Naflux method. The future development of technology for mass production of freestanding GaN substrate is also discussed.

AlGaN based materials are promising to fabricate UV photoelectric devices due to the direct, wide and adjustable bandgap. With decades of research efforts, great progress has been made in improving the quality of AlGaN based materials on heterogeneous substrates, and the doping efficiency has been greatly improved. As a result, great progress has been made on the fabrication of UV photoelectric devices. In this review, the growth methods to obtain high quality AlGaN based materials by metalorganic chemical vapor deposition(MOCVD) and the methods to achieve high doping efficiency are summarized. Moreover, the recent progress of UV LED and UV photodetectors are also introduced.

AlGaN quantum structure is the core of realizing high light efficiency and high stability ultraviolet(UV) solidstate light source. In recent years, great progress has been made in AlGaN based semiconductor materials and UV emission devices. However, AlGaN materials can only be grown under nonequilibrium conditions. The growth kinetics involved is very complex, which restricts the improvement of the quality of quantum wells and other structures. Because of the wide band gap, the difficulty of ptype doping and the low activation efficiency, the carrier injection is limited. The optical anisotropy is obvious, which is not conducive to light emission from the front of the device. Therefore, the performance of AlGaN based UV devices, especially in deep UV band, needs to be improved. In this paper, the relationship between AlGaN quantum structures and the efficiency of UV emission devices are summarized, and the key scientific problems and research progress in active region quantum structures, ptype doping issue of AlGaN quantum structures and optical polarization control are reviewed.

Deep ultraviolet (DUV) light has a large potential application in sterilization, biochemical detection, UV curving, UV communication, and so on. AlGaN based DUV light emitting diodes (LEDs) have attracted tremendous attention and research because of their unique advantages such as nontoxicity, small size, low power consumption, long service life and wavelength tunability. After nearly 20 years research and development, the emission efficiency and device lifetime of AlGaN DUV LEDs have been promoted significantly, and some products have been commercialized. However, compared with the GaN based blue LEDs, the efficiency of current AlGaN DUV LEDs is still very low, which means the promotion room is very large for the research community. This paper first introduces the research status of the stateofart AlGaN DUV LEDs, and analyses the reasons for the low emission efficiency. Then, the recent progresses of the AlGaN DUV LEDs, from the internal quantum efficiency (IQE), light extraction efficiency (LEE), and wallplug efficiency (WPE), respectively, have been systematically reviewed. The various solutions that improve the efficiencies have been summarized. Finally, the future development directions and possible solutions for the efficiency have been provided.

Aluminum nitride (AlN) nanostructures possess the excellent intrinsic physical properties of AlN, such as wide band gap, high thermal conductivity, high breakdown field strength and excellent thermal stability, as well as the unique physical and chemical properties due to the surface effect and small size effect, gaining widespread attention. After years of hard work and studies, the high quality AlN nanostructures have been prepared, which play the important role in optical, electronic and magnetic fields. Here, the research progresses of the methods for preparing AlN nanostructures are discussed at first, including chemical vapor deposition method, physical vapor transport method, arc discharge method, hydride vapor phase epitaxy method, molecular beam epitaxy method and so on. Then, the effects of temperature, source, atmosphere, growth time and catalysts on the morphology and crystal quality of AlN nanostructures have been summarized and analyzed systematically, as well as the growth mechanism. Finally, the physical properties of AlN nanostructures are presented and discussed in detail.

Since the technical progress of SiC power metal oxide semiconductor field effect transistor(MOSFET) were published in 2017, the device structure design were optimized in view of the high specific onresistance (RON,SP). Our research group has improved the key processing technology to reduce the RON,SP of 1 200 V SiC MOSFET from 8 mΩ·cm2 to 4.8 mΩ·cm2. Using the new design methods and fabrication processes, high performance SiC MOSFET for voltage ratings from 6.5 kV up to 15 kV were achieved. The RON,SP is 144 mΩ·cm2 for the 10 kV devices and 204 mΩ·cm2 for the 15 kV devices which is close to the SiC theoretical limit.

4HSiC semiconductor is an ideal electronic material for high temperature, high frequency, and high power electronic devices. In recent 20 years, the material growth technology has been developed, and the quality of 4HSiC materials has been gradually improved. In this paper, the necessity of homoepitaxial growth of 4HSiC is briefly described. Then, several important aspects of the material science of 4HSiC, such as impurity doping, extended and point defects, and highspeed growth process are reviewed. At last, the current status of domestic 4HSiC epitaxy industrialization is introduced.

In this review, the microwave plasma chemical vapor deposition (MPCVD) single crystal diamond growth and diamond electronic devices in recent years are reviewed, and diamond prospects are also discussed. The characteristics, principle, equipment and substrate treatment during diamond growth are introduced in detail. In order to obtain the optimal growth conditions, the key factors affecting the MPCVD diamond growth are discussed. Key growth technologies such as lateral overgrowth, mosaic growth and threedimensional growth techniques are analyzed to gradually improve the quality and size. In the research progress of diamond doping, the research progress of ntype and ptype doping is introduced detailly. Through the research on diamond Schottky diodes, hydrogen terminated diamond field effect transistors and diamond ultraviolet detectors, the achievements and progress of diamond in the field of electronic devices have been demonstrated. Finally, the challenges of diamond growth and application in electronic devices are summarized. We believe that diamond has great potentials in application of electronic field in the future.

SnSe crystal is a new type of lowcost and environmentfriendly thermoelectric semiconductor material, which has become a hot spot around the world in recent years. In order to obtain SnSe crystal, vertical Bridgman method and vertical gradient frozen method are the two main techniques that are usually used at home and abroad. However, the unique layered structure and complex thermal expansion characteristics of SnSe crystal make it easy to cleave and crack in the process of crystal growth, therefore, the preparation of large size SnSe crystal has become a big matter up to today. In order to solve this problem, many novel crystal growth techniques were developed in our group under the guidance of phase diagram of material system and thermogravimetric analysis, such as gas phase method, horizontal Bridgman method and horizontal encapsulate method. Finally, large size SnSe single crystals were all successfully obtained by each method. In this paper, the process principle, technical points, crystal growth results of these technique innovations are introduced in detail, and their advantages and disadvantages are compared. It is considered that the horizontal encapsulate method has significant advantages for obtaining high integrity SnSe crystal and properties adjustment, and will gradually become a popular approach in the future.

Within visible lightemitting diode (LED) range, because of the the world problem of “yellow gap”, the white LED is based on yellow phosphor conversion of blue LED. However, the lighttolight conversion efficiency of the phosphor is prone to decline in the high temperature environment generated by selfheating, which leads to the problems of luminous decay and color temperature drift. Based on the breakthrough of high luminous efficiency InGaN yellow LED, our group has develop a new type of low color temperature LED light source by using high luminous efficiency red and yellow LED, which has the technical characteristics of no phosphor and no blue light. In this paper, we named it the siliconbased golden light LED. When the current density of LED is 20 A/cm2, the color temperature of 2 170 K, luminous efficiency of 156 lm/W, and color rendering index Ra of 77 is obtaiend for this siliconbased golden light LED device. When the current density of LED is 1 A/cm2, the luminous efficiency can reach 217 lm/W. This paper reports the variation of luminous efficiency and color temperature of this new type LED device with changes of input current and ambient temperature. At the same time, the spatial spectrum distribution of the device has been optimized. In addition, the hightemperature, hightemperature & highhumidity, and thermal shock reliability tests of the device have been carried out, which verified the high reliability of the siliconbased golden light LED device. Finally, this paper introduces the applications of siliconbased golden light LED devices in road lighting, tunnel lighting and other fields, as well as the promotion and application in home lighting fields such as maternal and child lighting.

Vertical GaNonGaN devices with high power rating and high frequency has been developed rapidly thanks to the emergence of highquality freestanding GaN substrate. This work discusses the fabrication, mechanisms and characterization of the vertical GaN power rectifiers. The vertical GaN Schottky barrier diode (SBD) can exhibit low turnON voltage of 0.55 V(at 0.1 A/cm2) and high breakdown voltage of ~800 V, thanks to the highquality Schottky interface as well as highefficient fluorine ion implantation termination. With the ultrathin AlGaN tunneling enhancement layer, further enhanced turnON voltage (0.43 V) and breakdown voltage (~1 020 V) can be realized. In addition, the vertical GaN power rectifier can exhibit nearzero reverse recovery performance as well as currentcollapsefree performance by using highspeed boardlevel test.

High quality heteroepitaxy is the key to realize high performance microelectronic devices. In this work, Si1-xGex (0<x≤1) films with a full spectrum of the Ge content x on Si substrates were successfully grown by low temperature molecular beam epitaxy, and the relaxation of the Si1-xGex/Si heterostructures and thermal transport properties were studied in detail. In addition, both low temperature epitaxy and high temperature annealing to modulate the misfit dislocations at the Ge/Si interface were utilized, and ultra high mobilities in the Ge films grown on Si were obtained. The growth and manipulation of the Ge quantum dots are also introduced in this work. All of the abovementioned work can provide new ideas and pathways for both theoretical studies and device applications on heteroepitaxy with a large lattice mismatch.

The high quality βGa2O3 single crystal doped with Si was grown by edgedefined filmfed grown (EFG) method with the doping concentration of 2×1018 cm-3. The crystal is light blue and the basic properties of the crystal were characterized by Laue diffraction, cathodoluminescence (CL) and Raman test. These characterisations show that the quality of the asgrown crystal is high. The bandgap is about 4.71 eV obtained by ultraviolet transmittance spectrum. In addition, vertical Schottky diode was fabricated on the crystal by electron beam evaporation, lithography and development techniques. The average breakdown field strength EAva of the Schottky diode is 2.1 MV/cm and the on resistance is 3 mΩ·cm2. Therefore, the simple βGa2O3 device shows excellent performance.

In this paper, the morphologies of AlN crystals prepared by the physical vapor transport method under different substrate temperatures and temperature differences were studied. The results show that the growth of AlN crystal is affected by the surface energy of AlN, the average kinetic energy of Al element and the polarity of AlN surface. When the temperature difference is 60 ℃, the growth rate of the (0001) plane of AlN crystal is lower than that of the (10-10) crystal plane, and the AlN belts are observed. Applying the processes to bulk AlN crystal growth, the (0001) surface of AlN crystal exhibites a domain growth mode as the temperature difference at 60 ℃, and the crystal quality is the worst; the (0001) surface of AlN crystal presentes a step flow growth mode as the temperature difference at 35 ℃, and the crystal quality is the best; the (0001) surface of AlN crystal shows a step cluster growth mode as the temperature difference at 20 ℃, and the crystal is easy to crack. AlN substrate with a diameter of 40 mm was finally obtained by process optimization which meets the requirements of device preparation.

In this work, 4HSiC epilayers were performed on 4°offaxis Siface substrates by horizontal hot wall chemical vapor deposition (CVD) with a standard chemistry of silanepropanehydrogen. A new type of triangular defect with inverted pyramid located at its apex(IPRTD) was observed. The morphology, microstructure and formation mechanism of the triangular defect were investigated by Nomarski optical microscope, laser scanning confocal microscope and microRaman spectroscopy. Characterization results indicates that the triangular defect observed has a 3CSiC nature. Based on these observations and analysis, a model of the formation mechanism of the triangular defect was proposed. In this model, the origination of IPRTD is attributed to 2D nucleation caused by dislocation located on the upstream of the growth direction. The difference in the growth rates between the stepflow growth direction of ［112-0］ and lateral growth along with the directions of ［11-00］/［1-100］ as well as the etching of the epitaxial layer by hydrogen are the main reasons for the formation of the inverted pyramid structure at the top of the defect.