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X-ray based techniques were used to characterize AlN single crystal substrates at different stages of production, providing essential information about substrate orientation, surface finish, structural perfection, and heteroepitaxy. X-ray topographs acquired on a commercial diffractometer confirmed that iterative diameter expansion of AlN boules, without the introduction of low angle grain boundaries, was successfully achieved. As a result, high-quality, macrodefect-free, 2-inch AlN substrates were demonstrated.

Compositionally graded AlxGa1-xN epilayers were coherently grown on AlN single crystal substrates by MOCVD, and polarization-induced doping was determined by contactless sheet resistance and capacitance-voltage measurements on unintentionally doped, n-type graded layers; and by temperature-dependent Hall effect measurements on a Mg doped, p-type graded layer. The room-temperature resistivity, hole concentration, and hole mobility of the p-type layer graded from x= 1.0 to x= 0.36 were 1.2 Ocm, 4.5x1018 cm-3, and 1.2 cm2/Vs, respectively, which represents a significant improvement over traditional, thermally-activated Mg doping in AlGaN alloys.

Aluminum nitride (AlN) single crystal boules were grown by physical vapor transport (PVT). Diameter expansion during boule growth, without the introduction of low angle grain boundaries (LAGB) around the boule periphery, was confirmed by crossed polarizer imaging, synchrotron white beam x-ray topography (SWBXT), and synchrotron monochromatic beam x-ray topography (SMBXT). The densities of basal plane dislocations (BPD) and threading edge dislocations (TED) averaged from high-magnification topographs of five regions of a high-quality substrate were 0 cm-2 and 992 cm-2, respectively. Substrates fabricated from AlN boules possessed excellent surface finishes suitable for epitaxy.

Quasi-vertical, high Al composition AlGaN Schottky diodes with breakdown voltages up to 500 V were grown on high quality AlN single crystal substrates. Diodes exhibited a ~106 current rectification ratio, a 7 MV/cm peak field at blocking, and a 1.45 MW/cm2 unipolar figure of merit. Challenges for this emerging technology, including doping limitations and compensation in AlGaN alloys, Ohmic contacts, and device termination are discussed.

Understanding the band bending at the interface of GaN/dielectric under different surface treatment conditions is critically important for device design, device performance, and device reliability. The effects of ultraviolet/ozone (UV/O3) treatment of the GaN surface on the energy band bending of atomic-layer-deposition (ALD) Al2O3coated Ga-polar GaN were studied. The UV/O3treatment and post-ALD anneal can be used to effectively vary the band bending, the valence band offset, conduction band offset, and the interface dipole at the Al2O3/GaN interfaces. The UV/O3treatment increases the surface energy of the Ga-polar GaN, improves the uniformity of Al2O3deposition, and changes the amount of trapped charges in the ALD layer. The positively charged surface states formed by the UV/O3treatment-induced surface factors externally screen the effect of polarization charges in the GaN, in effect, determining the eventual energy band bending at the Al2O3/GaN interfaces. An optimal UV/O3treatment condition also exists for realizing the “best” interface conditions. The study of UV/O3treatment effect on the band alignments at the dielectric/III-nitride interfaces will be valuable for applications of transistors, light-emitting diodes, and photovoltaics.

We report a kV class, low ON-resistance, vertical GaN junction barrier Schottky (JBS) diode with selective-area p-regions formed via Mg implantation followed by high-temperature, ultra-high pressure (UHP) post-implantation activation anneal. The JBS has an ideality factor of 1.03, a turn-on voltage of 0.75 V, and a specific differential ON-resistance of 0.6 mΩ·cm2. The breakdown voltage of the JBS diode is 915 V, corresponding to a maximum electric field of 3.3 MV cm−1. These results underline that high-performance GaN JBS can be realized using Mg implantation and high-temperature UHP post-activation anneal.

A systematic study on the density and distribution of extended defects in a typical single crystal AlN boule grown by the physical vapor transport (PVT) method has been carried out in order to gain a detailed understanding of the formation of defects such as dislocations and low angle grain boundaries (LAGBs). Boule surface studies reveal that LAGBs are nucleated during initial stages of growth and propagate to the end of growth. Basal plane dislocations (BPDs) are generated during growth due to thermal gradient stresses. Higher BPD densities are found near the LAGBs at the boule edges due to additional stresses from constrained growth. Threading edge dislocations (TEDs) are typically replicated from the seed, and LAGBs composed of arrays of threading dislocation walls are formed to accommodate the c-axis rotation between different groups of threading screw dislocation (TSD) mediated growth centers.

Using the physical vapor transport (PVT) method, single crystal boules of AlN have been grown and wafers sliced from them have been characterized by synchrotron white beam X-ray topography (SWBXT) in conjunction with optical microscopy. X-ray topographs reveal that the wafers contain dislocations that are inhomogeneously distributed with densities varying from as low as 0 cm-2 to as high as 104 cm-2. Two types of dislocations have been identified: basal plane dislocations and threading dislocations, both having Burgers vectors of type 1/3<112-0> indicating that their origin is likely due to post-growth deformation. In some cases, the dislocations are arranged in low angle grain boundaries. However, large areas of the wafers are nearly dislocation-free and section X-ray topographs of these regions reveal the high crystalline perfection.

AlN and AlGaN epitaxial films were deposited by metal organic chemical vapor deposition on single crystal AlN substrates processed from AlN boules grown by physical vapor transport. Structural, chemical, and optical characterization demonstrated the high crystalline quality of the films and interfaces.

In recent years, InGaN-based LED's emitting in the blue and green spectral regions have emerged into widespread use. However, due to fundamental material issues, achieving yellow and red emission from InGaN-based structures has presented a unique challenge. We have developed conditions for the MOCVD growth of a series of InGaN-based MQW devices that emit over a wide spectral range (420nm - 600nm). It has been found that the emission properties of these monochromatic devices depend critically on the growth rate, growth temperature, QW width, barrier growth conditions, and p-type capping layer growth conditions. Additionally, we have demonstrated white electroluminescence through the proper mixing of complementary colors.

The density and distribution of extended defects in AlN single crystals grown by physical vapor transport (PVT) was studied by bright field and polarized light microscopy, defect‐selective etching, and high resolution X‐ray diffraction (HRXRD). Etch pits associated with dislocation arrays forming low angle grain boundaries (LAGB) were observed and two types of LAGB were identified. Reduction of LAGB in AlN grown under reduced radial temperature gradients, as estimated by simulation of the growth cell, was demonstrated.

X-ray based techniques were used to characterize AlN single crystal substrates at different stages of production, providing essential information about substrate orientation, surface finish, structural perfection, and heteroepitaxy. X-ray topographs acquired on a commercial diffractometer confirmed that iterative diameter expansion of AlN boules, without the introduction of low angle grain boundaries, was successfully achieved. As a result, high-quality, macrodefect-free, 2-inch AlN substrates were demonstrated.

Compositionally graded AlxGa1-xN epilayers were coherently grown on AlN single crystal substrates by MOCVD, and polarization-induced doping was determined by contactless sheet resistance and capacitance-voltage measurements on unintentionally doped, n-type graded layers; and by temperature-dependent Hall effect measurements on a Mg doped, p-type graded layer. The room-temperature resistivity, hole concentration, and hole mobility of the p-type layer graded from x= 1.0 to x= 0.36 were 1.2 Ωcm, 4.5x1018cm-3, and 1.2 cm2/Vs, respectively, which represents a significant improvement over traditional, thermally-activated Mg doping in AlGaN alloys.

Quasi-vertical, high Al composition AlGaN Schottky diodes with breakdown voltages up to 500 V were grown on high quality AlN single crystal substrates. Diodes exhibited a ~106current rectification ratio, a 7 MV/cm peak field at blocking, and a 1.45 MW/cm2unipolar figure of merit. Challenges for this emerging technology, including doping limitations and compensation in AlGaN alloys, Ohmic contacts, and device termination are discussed.

The reliability and output power of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) fabricated on AlN substrates prepared by hydride vapor phase epitaxy are reported. TEM analysis revealed that dislocation density in LED layers, except the p-GaN layer, was below 106cm-2. DUV-LEDs emitting at 261 nm exhibited an output power of 10.8 mW at 150 mA. The lifetime of these LEDs was estimated to be over 10,000 h for cw operation at 50 mA. No significant acceleration of output power decay at higher operation currents was observed. The estimated lifetime at the operation current of 150 mA was over 5,000 h.

AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) were fabricated on AlN substrates. The AlN substrates were prepared by growing thick hydride vapor phase epitaxy (HVPE)-AlN layers on bulk AlN substrates prepared by physical vapor transport (PVT). After growing an LED structure, the PVT-AlN substrates were removed by mechanical polishing. This process allowed the fabrication of DUV-LEDs on HVPE-AlN substrates with high crystalline quality and DUV optical transparency. The DUV-LEDs exhibited a single emission peaking at 268 nm through the HVPE-AlN substrates. The output power as high as 28 mW was obtained at an injection current of 250 mA.

The structural and optical quality of a freestanding AlN substrate prepared from a thick AlN layer grown by hydride vapor phase epitaxy (HVPE) on a bulk (0001)AlN substrate prepared by physical vapor transport (PVT) were investigated. The prepared HVPE-AlN substrate was crack- and stress-free. High-resolution X-ray diffraction ?-rocking curves of symmetric (0002) and skew-symmetric (1011) reflections had small full widths at half maximum (FWHMs) of 31 and 32 arcsec, respectively. Deep-ultraviolet optical transparency of the HVPE-AlN substrate was higher than that of the PVT-AlN substrate, which was related to lower concentrations of C, O impurities, and Al vacancy.

AlN and AlGaN epitaxial films were deposited by metal organic chemical vapor deposition on single crystal AlN substrates processed from AlN boules grown by physical vapor transport. Structural, chemical, and optical characterization demonstrated the high crystalline quality of the films and interfaces.

In recent years, InGaN-based LED's emitting in the blue and green spectral regions have emerged into widespread use. However, due to fundamental material issues, achieving yellow and red emission from InGaN-based structures has presented a unique challenge. We have developed conditions for the MOCVD growth of a series of InGaN-based MQW devices that emit over a wide spectral range (420nm - 600nm). It has been found that the emission properties of these monochromatic devices depend critically on the growth rate, growth temperature, QW width, barrier growth conditions, and p-type capping layer growth conditions. Additionally, we have demonstrated white electroluminescence through the proper mixing of complementary colors.