This paper reports that Al1 xInxN epilayers were grown on GaN template by metalorganic chemical vapor de-position with an In content of 7%-20%. X-ray diffraction results indicate that all these Al1 xInxN epilayers have a relatively low density of threading dislocations. Rutherford backscattering/channeling measurements provide the exact compositional information and show that a gradual variation in composition of the Al1 xInxN epilayer happens along the growth direction. The experimental results of optical reflection clearly show the bandgap energies of Al1 xInxN epilayers. A bowing parameter of 6.5 eV is obtained from the compositional dependence of the energy gap. The cathodoluminescence peak energy of the Al1 xInxN epilayer is much lower than its bandgap, indicating a relatively large Stokes shift in the Al1 xInxN sample.
We present the growth of GaN epilayer on Si(111) substrate with a single AlGaN interlayer sandwiched between the GaN epilayer and AlN buffer layer by using the metalorganic chemical vapour deposition.The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy,atomic force microscopy,optical microscopy and high-resolution x-ray diffraction.It is found that an AlN buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer,which can introduce a more compressive strain into the subsequent grown GaN layer,and reduce the crack density and threading dislocation density in GaN film.
A violet laser diode (LD) structure is grown on a free-standing c-plane GaN substrate and 4 μm×800 μm ridge waveguide LDs are fabricated.The electrical and the optical characteristics of LDs under different facet-coating and chip-mounting conditions are investigated under pulse mode operation.The active region temperatures of p-side up and p-side down mounted LDs are calculated with different injection currents.The calculated thermal resistances of p-side up and p-side down mounted LDs are 4.6 K/W and 3 K/W,respectively.The threshold current of the p-side down mounted LD is much lower than that of the p-side up mounted LD.The blue shift of the emission wavelength with increasing injection current is observed only for the LD with p-side down mounting configuration,due to the more efficient heat dissipation.
To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au (5 nm/5 nm) film deposition. The surface morphology of wafers and the current-voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.
High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single AlGaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si (111) substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlGaN interlayer on the structural properties of the resulting GaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AlGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated.
