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We report on the electrical characterization of V-defects in GaN-based heterostructures via Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM). The KPFM measurements show for n- and p-doped GaN top layers an increase in the work function within the V-defects. Surprisingly, an increase in the current flow within the V-defects is found by C-AFM in case of the n-doped structure, while current flow into the V-defect is suppressed for the p-doped structure. For a consistent explanation of these results we suggest a model, which is based on an increase in the electron affinity of the {10-11}-surfaces within the V-defects as compared to the planar (0001)-surface. [ABSTRACT FROM AUTHOR]

Infrared spectroscopic ellipsometry is used to study the influence of strain and composition on the transverse-optical phonon mode of E[sub 1] symmetry in hexagonal Al[sub 1-x]In[sub x]N films for 0.12≤x≤0.21. The 0.1-0.2-μm thick films were grown on slightly compressively strained hexagonal GaN buffer layers, or directly on [0001] sapphire by metalorganic vapor phase epitaxy. The Al[sub 1-x]In[sub x]N E[sub 1](TO) phonon shows a one-mode behavior in contrast to recent theoretical predictions [H. Grille, C. Schnittler, and F. Bechstedt, Phys. Rev. B 61, 6091 (2000)]. Films grown on GaN reveal the influence of strain on the phonon mode frequencies due to pseudomorphic film growth. Al[sub 1-x]In[sub x]N deposited directly on sapphire possesses phonon modes which indicate fully relaxed film growth. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Wurtzite InGaN thin films grown by metalorganic chemical vapor deposition on sapphire substrates with and without GaN buffer layers are investigated by high-resolution x-ray diffraction measurements. The structural quality, lattice constants, strain, and indium composition of 100 nm thick films with In concentrations up to 33% are evaluated by measuring symmetric (00.2) and asymmetric (20.5) reflexes. The quality of the InGaN layers with widely different biaxial stress is measured and compared. An analytical solution for the determination of the In content of strained epitaxial layers is introduced. The results show that neglecting the strain can result in a severe miscalculation of the In concentration. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied the electrical and optical characteristics of (AlGaIn)N multiple quantum well light-emitting diodes. Minimizing contact effects by utilizing platinum as p-contact metal, ideality factors as low as 1.1 have been achieved. In agreement with basic semiconductor theory, a correlation between ideality factor and small-current efficiency was found. We were able to emulate the experimental current-voltage characteristic over seven orders of magnitude utilizing a two diode model. This model enables a very good prediction of internal quantum efficiency at moderate current densities out of purely electrically derived parameters. [ABSTRACT FROM AUTHOR]

In GaN layers grown by molecular beam epitaxy and metalorganic vapor phase epitaxy on c-axis oriented sapphire, a defect-to-band transition at a photon energy of 0.44 eV was found by optical admittance spectroscopy. This transition was investigated as a function of temperature and modulation frequency. The height of the corresponding optical admittance peak shows a thermally activated quenching with an activation energy of 0.4±0.1 eV caused by a thermal carrier emission from the same defect state to the conduction band at higher temperatures. Based on this thermal quenching, the 0.44 eV level is assigned to an electron trap located in the upper half of the gap. The spectral photoionization cross section was determined, resulting in a photoionization energy at 80 K estimated to be below 0.425 eV. The omnipresence of the 0.44 eV electron trap in GaN layers grown by various epitaxial techniques and in different reactors implicates its intrinsic nature. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]