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Defects in GaN grown using metalorganic chemical vapor deposition were studied through the use of monoenergetic positron beams. For Mg-doped GaN, no large change in the diffusion length of positrons was observed before and after activation of Mg. This was attributed to the scattering of positrons by potentials caused by electric dipoles of Mg–hydrogen pairs. For Si-doped GaN, the line-shape parameter S increased as carrier density increased, suggesting an introduction of Ga vacancy due to the Fermi level effect. Based on these results, we discuss the effects of the growth polar direction of GaN on optical properties in this article. Although the optical properties of a GaN film grown toward the Ga face direction exhibited excitonic features, a film grown toward the N face (−c) direction exhibited broadened photoluminescence and transmittance spectra, and a Stokes shift of about 20 meV was observed. This difference was attributed to extended band-tail states introduced by high concentrations of donors and ...

Optical properties of the InGaN single-quantum-well amber light-emitting-diodes were investigated to verify the importance of localized quantum well (QW) excitons in their spontaneous emission mechanisms. The internal piezoelectric field (FPZ) across the QW of the order of 1.4 MV/cm was confirmed to point from the surface to the substrate. Transmittance and photovoltaic spectra exhibited a broad band tail state, and the emission lifetime increased with decreasing detection photon energy. The electroluminescence spectra did not show remarkable energy shift between 10 and 300 K. The spectra exhibited an exponential tail and the higher energy portion increased more rapidly than that of the lower energy one, reflecting a thermal distribution of the localized carriers within the tail states. Since the well thickness is only 2.5 nm and is atomically flat, the device is considered to exhibit reasonably efficient emission with the external quantum efficiency of 5% at 20 mA in spite of the presence of FPZ and larg...

High‐quality In0.22Ga0.78N/In0.06Ga0.94N superlattices were grown on GaN films with periods of 60 and 200 A by the two‐flow metalorganic chemical‐vapor deposition method. The double‐crystal x‐ray rocking curve measurements showed satellite peaks which indicated the existence of the In0.22Ga0.78N/In0.06Ga0.94N superlattices. The quantum effects were observed through room‐temperature photoluminescence (PL) measurements. These PL spectra were compared to theoretical solutions for the In0.22Ga0.78N/In0.06Ga0.94N superlattices.

Strain states in wurtzite III-nitride semiconductor quantum wells (QWs) are investigated. X-ray diffraction (XRD) reciprocal space mapping using semipolar (11math2) and (1math01) InGaN/GaN QWs as test samples demonstrates that the projections of reciprocal lattice vectors of unstrained GaN and pseudomorphically strained InGaN on the interface agrees, indicating continuity of layers across the interface. High resolution transmission electron microscopy supports the XRD analysis. Based on the experimental results, strain tensor elements are extracted for arbitrary crystalline orientation. Furthermore, expansion of the model to arbitrary crystal structures is suggested.

High‐brightness InGaN/AlGaN double‐heterostructure blue‐green‐light‐emitting diodes with a luminous intensity of 2 cd were fabricated by increasing an indium mole fraction of the InGaN active layer up to 0.23. Both Zn and Si were codoped into the InGaN active layer to afford relatively stronger luminescence. The blue‐green emission intensity of room‐temperature photoluminescence became maximum when the electron carrier concentration of the InGaN active layer was around 1×1019 cm−3. Donor‐acceptor pair recombination is a dominant emission mechanism of the InGaN active layer. The external quantum efficiency was as high as 2.4% at a forward current of 20 mA at room temperature. The peak wavelength and the full width at half‐maximum of the electroluminescence were 500 and 80 nm, respectively.