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The strain dependence of the free-exciton resonance energies in AlN epilayers and the values are analyzed by using an appropriated Hamiltonian assuming equibiaxial stress for the wurtzite crystal structure in order to obtain valence band parameters. The strain dependence of the valence band ordering, optical transition probability and free-exciton binding energy are analyzed.

The electrical and structural characterization of Mg-doped Al-rich p-type [Al.sub.0.69][Ga.sub.0.31]N alloys on SiC substrate grown by metal organic chemical vapor deposition is presented. Transmission electron microscopy has shown the generation of vertical spike-like defects with increasing Mg doping and the increase in resistivity with the increase in Mg doping.

The adsorption and subsequent desorption of Ga on (0001) GaN using simultaneous line-of-sight quadrapole mass spectroscopy (QMS) and reflection high-energy electron diffraction (RHEED) is investigated. It is concluded that the experimental results show the complementary nature of the information provided by the RHEED oscillations and the Ga-adlayer coverage measured by QMS.

Laser assisted atom probe tomography is used to characterize the alloy distribution in BGaN. The effect of the evaporation conditions applied on the atom probe specimens on the mass spectrum and the quantification of the III site atoms is first evaluated. The evolution of the Ga++/Ga+ charge state ratio is used to monitor the strength of the applied field. Experiments revealed that applying high electric fields on the specimen results in the loss of gallium atoms, leading to the overestimation of boron concentration. Moreover, spatial analysis of the surface field revealed a significant loss of atoms at the center of the specimen where high fields are applied. A good agreement between X-ray diffraction and atom probe tomography concentration measurements is obtained when low fields are applied on the tip. A random distribution of boron in the BGaN layer grown by molecular beam epitaxy is obtained by performing accurate and site specific statistical distribution analysis. [ABSTRACT FROM AUTHOR]

InAlN dipole diodes were developed and fabricated on both (0001) Ga-Face and (000...) N-face oriented GaN on sapphire templates by molecular beam epitaxy. The orientation and direction of the InAlN polarization dipole are functions of the substrate orientation and composition, respectively. Special consideration was taken to minimize growth differences and impurity uptake during growth on these orientations of opposite polarity. Comparison of devices on similarly grown structures with In compositions in excess of 50% reveals that dipole diodes shows poorer forward bias performance and exhibited an increase in reverse bias leakage, regardless of orientation. Similarly, (0001) Ga-face oriented InAlN at a lowered 40% In composition had poor device characteristics, namely, the absence of expected exponential turn on in forward bias. By contrast, at In compositions close to 40%, (000...) N-face oriented InAlN devices had excellent performance, with over five orders of magnitude of rectification and extracted barrier heights of 0.53- 0.62 eV; these values are in close agreement with simulation. Extracted ideality factors ranging from 1.08 to 1.38 on these devices are further evidence of their optimal performance. Further discussion focuses on the growth and orientation conditions that may lead to this discrepancy yet emphasizes that with proper design and growth strategy, the rectifying dipole diodes can be achieved with InAlN nitride dipole layers. [ABSTRACT FROM AUTHOR]

Red micro-size light-emitting diodes (μLEDs) less than 10 × 10 μm2 are crucial for augmented reality (AR) and virtual reality (VR) applications. However, they remain very challenging since the common AlInGaP red μLEDs with such small size suffer from a dramatic reduction in the external quantum efficiency. In this work, we demonstrate ultra-small 5 × 5 μm2 607 nm amber μLEDs using InGaN materials, which show an EQE over 2% and an ultra-low reverse current of 10−9 A at −5 V. This demonstration suggests promising results of ultra-small InGaN μLEDs for AR and VR displays. [ABSTRACT FROM AUTHOR]

An orientational dependence on the interfacial reaction between aluminum and (010), (001), and ( 2 ̄ 01) β-Ga2O3 substrates is addressed. Electron microscopy and x-ray diffraction were used to assess the interface crystallinity, thickness, and chemical composition of the interfacial layers. At the interface, amorphous aluminum oxide is observed in all three samples with a thicknesses of 3.5 nm for (010) β-Ga2O3 and 2 nm for (001) β-Ga2O3 and ( 2 ̄ 01) β-Ga2O3. Aluminum oxide is formed at the interface as a result of a chemical reaction that reduces the Ga2O3 surface when aluminum is deposited. We propose that in Al on (010) β-Ga2O3, in which the thickest interfacial oxide layer is observed, diffusional pathways of consecutive octahedral Ga sites perpendicular to the interface promote increased interdiffusion in the out-of-plane direction. In contrast, the (001) β-Ga2O3 and ( 2 ̄ 01) β-Ga2O3 substrates exhibit alternating rows of tetrahedral and octahedral Ga sites parallel to the interface, where the rows of tetrahedral Ga sites act as increased energy barriers that impede interdiffusion of Al and β-Ga2O3. The orientational dependence of metal-oxide interlayers in β-Ga2O3 can impact electronic and thermal transport, pointing to the importance of understanding the impact of β-Ga2O3 orientation on interfacial properties. [ABSTRACT FROM AUTHOR]

We study the high-temperature electroluminescence properties of 600 nm InGaN red 40 × 40 μm2 micro-light-emitting diodes (μLEDs) with a peak external quantum efficiency (EQE) of 3.2%. Temperature-dependent peak wavelength measurements show a low redshift of 0.05 nm/K. The injection efficiency improves with increasing temperature. The hot/cold (HC) factor is used to quantify the thermal droop: at 400 K, the EQE and wall-plug efficiency HC factors at 50 A/cm2 reach high values of 0.72 and 0.85, respectively. This demonstrates the robustness of InGaN red μLEDs up to high temperature, with a much-improved stability over conventional AlInGaP red μLEDs. [ABSTRACT FROM AUTHOR]

A new study seeks to advance growth and fabrication technology for GaN HBTs.